Martinelli, Michael A. (Winchester, MA, US)
Haase, Wayne C. (Sterling, MA, US)

09/494213

07/14/2009

01/24/2000

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Medtronic Navigation, Inc. (Louisville, CO, US)

128/899

600/424

A61B5/05

600/508, 128/899, 324/260, 600/117, 600/424, 324/207.22, 324/207.13, 600/373, 600/408

3016899	Surgical instrument	January, 1962	Stenvall
3017887	Stereotaxy device	January, 1962	Heyer
3061936	Stereotaxical methods and apparatus	November, 1962	Dobbeleer
3073310	Surgical instrument positioning device	January, 1963	Mocarski
3294083	Dosimetry system for penetrating radiation	December, 1966	Alderson
3367326	Intra spinal fixation rod	February, 1968	Frazier
3439256	INDUCTIVE ANGULAR POSITION TRANSMITTER	April, 1969	Kahne et al.	323/51
3577160	X-RAY GAUGING APPARATUS WITH X-RAY OPAQUE MARKERS IN THE X-RAY PATH TO INDICATE ALIGNMENT OF X-RAY TUBE, SUBJECT AND FILM	May, 1971	White
3674014	MAGNETICALLY GUIDABLE CATHETER-TIP AND METHOD	July, 1972	Tillander	128/2.05
3702935	MOBILE FLUOROSCOPIC UNIT FOR BEDSIDE CATHETER PLACEMENT	November, 1972	Carey et al.
3704707	ORTHOPEDIC DRILL GUIDE APPARATUS	December, 1972	Halloran
3868565	OBJECT TRACKING AND ORIENTATION DETERMINATION MEANS, SYSTEM AND PROCESS	February, 1975	Kuipers	324/34
3941127	Apparatus and method for stereotaxic lateral extradural disc puncture	March, 1976	Froning
4037592	Guide pin locating tool and method	July, 1977	Kronner
4052620	Method and apparatus for improved radiation detection in radiation scanning systems	October, 1977	Brunnett
4054881	Remote object position locater	October, 1977	Raab	343/112
4117337	Patient positioning indication arrangement for a computed tomography system	September, 1978	Staats
4173228	Catheter locating device	November, 1979	Van Steenwyk et al.	128/653
4202349	Radiopaque vessel markers	May, 1980	Jones
4262306	Method and apparatus for monitoring of positions of patients and/or radiation units	April, 1981	Renner	358/93
4287809	Helmet-mounted sighting system	September, 1981	Egli et al.	89/41
4314251	Remote object position and orientation locater	February, 1982	Raab	343/112
4317078	Remote position and orientation detection employing magnetic flux linkage	February, 1982	Weed et al.	324/208
4328813	Brain lead anchoring system	May, 1982	Ray
4339953	Position sensor	July, 1982	Iwasaki	73/654
4358856	Multiaxial x-ray apparatus	November, 1982	Stivender et al.
4368536	Diagnostic radiology apparatus for producing layer images	January, 1983	Pfeiler
4396885	Device applicable to direction finding for measuring the relative orientation of two bodies	August, 1983	Constant	324/208
4403321	Switching network	September, 1983	Kruger
4418422	Aiming device for setting nails in bones	November, 1983	Richter et al.
4422041	Magnet position sensing system	December, 1983	Lienau	324/207
4431005	Method of and apparatus for determining very accurately the position of a device inside biological tissue	February, 1984	McCormick	128/656
4485815	Device and method for fluoroscope-monitored percutaneous puncture treatment	December, 1984	Amplatz
4543959	Diagnosis apparatus and the determination of tissue structure and quality	October, 1985	Sepponen
4548208	Automatic adjusting induction coil treatment device	October, 1985	Niemi
4572198	Catheter for use with NMR imaging systems	February, 1986	Codrington	128/653
4584577	Angular position sensor	April, 1986	Temple	340/870.32
4613866	Three dimensional digitizer with electromagnetic coupling	September, 1986	Blood	343/448
4618978	Means for localizing target coordinates in a body relative to a guidance system reference frame in any arbitrary plane as viewed by a tomographic image through the body	October, 1986	Cosman	378/164
4621628	Apparatus for locating transverse holes of intramedullary implantates	November, 1986	Bludermann
4625718	Aiming apparatus	December, 1986	Olerud et al.
4642786	Method and apparatus for position and orientation measurement using a magnetic field and retransmission	February, 1987	Hansen	364/559
4645343	Atomic resonance line source lamps and spectrophotometers for use with such lamps	February, 1987	Stockdale et al.
4649504	Optical position and orientation measurement techniques	March, 1987	Krouglicof et al.	364/559
4651732	Three-dimensional light guidance system for invasive procedures	March, 1987	Frederick
4653509	Guided trephine samples for skeletal bone studies	March, 1987	Oloff et al.
4673352	Device for measuring relative jaw positions and movements	June, 1987	Hansen
4706665	Frame for stereotactic surgery	November, 1987	Gouda
4719419	Apparatus for detecting a rotary position of a shaft	January, 1988	Dawley	324/208
4722056	Reference display systems for superimposing a tomagraphic image onto the focal plane of an operating microscope	January, 1988	Roberts et al.
4722336	Placement guide	February, 1988	Kim et al.
4727565	Method of localization	February, 1988	Ericson
4737794	Method and apparatus for determining remote object orientation and position	April, 1988	Jones	342/448
4737921	Three dimensional medical image display system	April, 1988	Goldwasser et al.
4750487	Stereotactic frame	June, 1988	Zanetti
4771787	Ultrasonic scanner and shock wave generator	September, 1988	Wurster et al.
4791934	Computer tomography assisted stereotactic surgery system and method	December, 1988	Brunnett
4793355	Apparatus for process for making biomagnetic measurements	December, 1988	Crum et al.
4797907	Battery enhanced power generation for mobile X-ray machine	January, 1989	Anderton
4803976	Sighting instrument	February, 1989	Frigg et al.
4821206	Ultrasonic apparatus for positioning a robot hand	April, 1989	Arora
4821731	Acoustic image system and method	April, 1989	Martinelli et al.	128/662.06
4836778	Mandibular motion monitoring system	June, 1989	Baumrind et al.	433/69
4845771	Exposure monitoring in radiation imaging	July, 1989	Wislocki et al.
4849692	Device for quantitatively measuring the relative position and orientation of two bodies in the presence of metals utilizing direct current magnetic fields	July, 1989	Blood	324/207
4862893	Ultrasonic transducer	September, 1989	Martinelli	128/662.03
4889526	Non-invasive method and apparatus for modulating brain signals through an external magnetic or electric field to reduce pain	December, 1989	Rauscher et al.
4905698	Method and apparatus for catheter location determination	March, 1990	Strohl, Jr. et al.	128/653
4923459	Stereotactics apparatus	May, 1990	Nambu
4931056	Catheter guide apparatus for perpendicular insertion into a cranium orifice	June, 1990	Ghajar et al.
4945305	Device for quantitatively measuring the relative position and orientation of two bodies in the presence of metals utilizing direct current magnetic fields	July, 1990	Blood	324/207.17
4945914	Method and apparatus for providing related images over time of a portion of the anatomy using at least four fiducial implants	August, 1990	Allen
4951653	Ultrasound brain lesioning system	August, 1990	Fry et al.
4977655	Method of making a transducer	December, 1990	Martinelli	29/25.35
4989608	Device construction and method facilitating magnetic resonance imaging of foreign objects in a body	February, 1991	Ratner	128/653
4991579	Method and apparatus for providing related images over time of a portion of the anatomy using fiducial implants	February, 1991	Allen	128/653
5002058	Ultrasonic transducer	March, 1991	Martinelli	128/662
5005592	Method and apparatus for tracking catheters	April, 1991	Cartmell	128/899
5013317	Medical drill assembly transparent to X-rays and targeting drill bit	May, 1991	Cole et al.
5016639	Method and apparatus for imaging the anatomy	May, 1991	Allen	128/653
5027818	Dosimetric technique for stereotactic radiosurgery same	July, 1991	Bova et al.
5030196	Magnetic treatment device	July, 1991	Inoue
5030222	Radiolucent orthopedic chuck	July, 1991	Calandruccio et al.
5031203	Coaxial laser targeting device for use with x-ray equipment and surgical drill equipment during surgical procedures	July, 1991	Trecha
5042486	Catheter locatable with non-ionizing field and method for locating same	August, 1991	Pfeiler et al.	128/653
5050608	System for indicating a position to be operated in a patient's body	September, 1991	Watanabe et al.	128/653
5054492	Ultrasonic imaging catheter having rotational image correlation	October, 1991	Scribner et al.	128/662.06
5057095	Surgical implement detector utilizing a resonant marker	October, 1991	Fabian
5059789	Optical position and orientation sensor	October, 1991	Salcudean	250/206.1
5079699	Quick three-dimensional display	January, 1992	Tuy et al.
5086401	Image-directed robotic system for precise robotic surgery including redundant consistency checking	February, 1992	Glassman et al.	395/94
5094241	Apparatus for imaging the anatomy	March, 1992	Allen
5097839	Apparatus for imaging the anatomy	March, 1992	Allen
5099845	Medical instrument location means	March, 1992	Besz et al.	128/653.1
5105829	Surgical implement detector utilizing capacitive coupling	April, 1992	Fabian et al.	128/899
5107839	Computer controlled stereotaxic radiotherapy system and method	April, 1992	Houdek et al.
5107843	Method and apparatus for thin needle biopsy in connection with mammography	April, 1992	Aarnio et al.
5107862	Surgical implement detector utilizing a powered marker	April, 1992	Fabian et al.
5109194	Electromagnetic position and orientation detector for a pilot's helmet	April, 1992	Cantaloube	324/207.17
5119817	Apparatus for imaging the anatomy	June, 1992	Allen
5142930	Interactive image-guided surgical system	September, 1992	Allen et al.
5152288	Apparatus and method for measuring weak, location-dependent and time-dependent magnetic fields	October, 1992	Hoenig et al.	128/653.1
5160337	Curved-shaped floor stand for use with a linear accelerator in radiosurgery	November, 1992	Cosman
5161536	Ultrasonic position indicating apparatus and methods	November, 1992	Vilkomerson et al.	128/660.07
5178164	Method for implanting a fiducial implant into a patient	January, 1993	Allen
5178621	Two-piece radio-transparent proximal targeting device for a locking intramedullary nail	January, 1993	Cook et al.
5186174	Process and device for the reproducible optical representation of a surgical operation	February, 1993	Schlondorff et al.
5187475	Apparatus for determining the position of an object	February, 1993	Wagener et al.	340/870.31
5188126	Surgical implement detector utilizing capacitive coupling	February, 1993	Fabian et al.
5190059	Surgical implement detector utilizing a powered marker	March, 1993	Fabian et al.
5197476	Locating target in human body	March, 1993	Nowacki et al.	128/660.03
5197965	Skull clamp pin assembly	March, 1993	Cherry et al.
5198768	Quadrature surface coil array	March, 1993	Keren	324/318
5198877	Method and apparatus for three-dimensional non-contact shape sensing	March, 1993	Schulz	356/375
5211164	Method of locating a target on a portion of anatomy	May, 1993	Allen	128/653.1
5211165	Tracking system to follow the position and orientation of a device with radiofrequency field gradients	May, 1993	Dumoulin et al.	128/653.1
5211176	Ultrasound examination system	May, 1993	Ishiguro et al.
5212720	Dual radiation targeting system	May, 1993	Landi et al.
5214615	Three-dimensional displacement of a body with computer interface	May, 1993	Bauer	367/128
5219351	Mammograph provided with an improved needle carrier	June, 1993	Teubner et al.
5222499	Method and apparatus for imaging the anatomy	June, 1993	Allen et al.	128/653.1
5228442	Method for mapping, ablation, and stimulation using an endocardial catheter	July, 1993	Imran	128/642
5233990	Method and apparatus for diagnostic imaging in radiation therapy	August, 1993	Barnea
5237996	Endocardial electrical mapping catheter	August, 1993	Waldman et al.	128/642
5249581	Precision bone alignment	October, 1993	Horbal et al.	128/664
5251127	Computer-aided surgery apparatus	October, 1993	Raab
5251635	Stereoscopic X-ray fluoroscopy system using radiofrequency fields	October, 1993	Dumoulin et al.	128/653.2
5253647	Insertion position and orientation state pickup for endoscope	October, 1993	Takahashi et al.	128/653.1
5255680	Automatic gantry positioning for imaging systems	October, 1993	Darrow et al.	128/653.1
5257636	Apparatus for determining position of an endothracheal tube	November, 1993	White	128/897
5265610	Multi-planar X-ray fluoroscopy system using radiofrequency fields	November, 1993	Darrow et al.	128/653.1
5265611	Apparatus for measuring weak, location-dependent and time-dependent magnetic field	November, 1993	Hoenig et al.	128/653.1
5269759	Magnetic guidewire coupling for vascular dilatation apparatus	December, 1993	Hernandez et al.	604/96
5271400	Tracking system to monitor the position and orientation of a device using magnetic resonance detection of a sample contained within the device	December, 1993	Dumoulin et al.	128/653.2
5273025	Apparatus for detecting insertion condition of endoscope	December, 1993	Sakiyama et al.	128/6
5274551	Method and apparatus for real-time navigation assist in interventional radiological procedures	December, 1993	Corby, Jr.	364/413.13
5279309	Signaling device and method for monitoring positions in a surgical operation	January, 1994	Taylor et al.	128/782
5291199	Threat signal detection system	March, 1994	Overman et al.
5295483	Locating target in human body	March, 1994	Nowacki et al.	128/660.03
5297549	Endocardial mapping system	March, 1994	Beatty et al.	128/642
5299254	Method and apparatus for determining the position of a target relative to a reference of known co-ordinates and without a priori knowledge of the position of a source of radiation	March, 1994	Dancer et al.	378/163
5299288	Image-directed robotic system for precise robotic surgery including redundant consistency checking	March, 1994	Glassman et al.	395/80
5305091	Optical coordinate measuring system for large objects	April, 1994	Gelbart et al.
5305203	Computer-aided surgery apparatus	April, 1994	Raab
5309913	Frameless stereotaxy system	May, 1994	Kormos et al.	128/653.1
5315630	Positioning device in medical apparatus	May, 1994	Sturm et al.	378/64
5316024	Tube placement verifier system	May, 1994	Hirschi et al.	128/899
5318025	Tracking system to monitor the position and orientation of a device using multiplexed magnetic resonance detection	June, 1994	Dumoulin et al.	128/653.2
5320111	Light beam locator and guide for a biopsy needle	June, 1994	Livingston
5325728	Electromagnetic flow meter	July, 1994	Zimmerman et al.
5325873	Tube placement verifier system	July, 1994	Hirschi et al.	128/899
5329944	Surgical implement detector utilizing an acoustic marker	July, 1994	Fabian et al.
5333168	Time-based attenuation compensation	July, 1994	Fernandes et al.
5353795	Tracking system to monitor the position of a device using multiplexed magnetic resonance detection	October, 1994	Souza et al.	128/653.2
5353800	Implantable pressure sensor lead	October, 1994	Pohndorf et al.
5353807	Magnetically guidable intubation device	October, 1994	DeMarco
5368030	Non-invasive multi-modality radiographic surface markers	November, 1994	Zinreich et al.	128/653.1
5375596	Method and apparatus for determining the position of catheters, tubes, placement guidewires and implantable ports within biological tissue	December, 1994	Twiss et al.	128/653.1
5377678	Tracking system to follow the position and orientation of a device with radiofrequency fields	January, 1995	Dumoulin et al.	128/653.1
5383454	System for indicating the position of a surgical probe within a head on an image of the head	January, 1995	Bucholz	128/653.1
5385146	Orthogonal sensing for use in clinical electrophysiology	January, 1995	Goldreyer	128/642
5385148	Cardiac imaging and ablation catheter	January, 1995	Lesh et al.	128/662.06
5386828	Guide wire apparatus with location sensing member	February, 1995	Owens et al.	128/653.1
5389101	Apparatus and method for photogrammetric surgical localization	February, 1995	Heilbrun et al.	606/130
5391199	Apparatus and method for treating cardiac arrhythmias	February, 1995	Ben-Haim	607/122
5394457	Device for marking body sites for medical examinations	February, 1995	Leibinger et al.
5397329	Fiducial implant and system of such implants	March, 1995	Allen
5399146	Isocentric lithotripter	March, 1995	Nowacki et al.
5400384	Time-based attenuation compensation	March, 1995	Fernandes et al.
5402801	System and method for augmentation of surgery	April, 1995	Taylor	128/898
5408409	Image-directed robotic system for precise robotic surgery including redundant consistency checking	April, 1995	Glassman et al.	364/413.13
5417210	System and method for augmentation of endoscopic surgery	May, 1995	Funda et al.	128/653.1
5419325	Magnetic resonance (MR) angiography using a faraday catheter	May, 1995	Dumoulin et al.	128/653.2
5423334	Implantable medical device characterization system	June, 1995	Jordan
5425367	Catheter depth, position and orientation location system	June, 1995	Shapiro et al.	128/653.1
5425382	Apparatus and method for locating a medical tube in the body of a patient	June, 1995	Golden et al.	128/899
5426683	One piece C-arm for X-ray diagnostic equipment	June, 1995	O'Farrell, Jr. et al.
5426687	Laser targeting device for use with image intensifiers in surgery	June, 1995	Goodall et al.
5427097	Apparatus for and method of carrying out stereotaxic radiosurgery and radiotherapy	June, 1995	Depp
5429132	Probe system	July, 1995	Guy et al.	128/653.1
5433198	Apparatus and method for cardiac ablation	July, 1995	Desai	128/642
RE35025	Battery enhanced power generation for mobile X-ray machine	August, 1995	Anderton
5437277	Inductively coupled RF tracking system for use in invasive imaging of a living body	August, 1995	Dumoulin et al.	128/653.1
5443066	Invasive system employing a radiofrequency tracking system	August, 1995	Dumoulin et al.	128/653.1
5443489	Apparatus and method for ablation	August, 1995	Ben-Haim	607/115
5444756	X-ray machine, solid state radiation detector and method for reading radiation detection information	August, 1995	Pai et al.
5445144	Apparatus and method for acoustically guiding, positioning, and monitoring a tube within a body	August, 1995	Wodicka et al.	128/207.14
5445150	Invasive system employing a radiofrequency tracking system	August, 1995	Dumoulin et al.	128/653.1
5445166	System for advising a surgeon	August, 1995	Taylor	128/897
5446548	Patient positioning and monitoring system	August, 1995	Gerig et al.
5447154	Method for determining the position of an organ	September, 1995	Cinquin et al.
5448610	Digital X-ray photography device	September, 1995	Yamamoto et al.
5453686	Pulsed-DC position and orientation measurement system	September, 1995	Anderson	324/207.17
5456718	Apparatus for detecting surgical objects within the human body	October, 1995	Szymaitis	623/11
5458718	Heat sealing method for making a luggage case	October, 1995	Venkitachalam
5464446	Brain lead anchoring system	November, 1995	Dreessen et al.
5478341	Ratchet lock for an intramedullary nail locking bolt	December, 1995	Cook et al.
5478343	Targeting device for bone nails	December, 1995	Ritter
5480422	Apparatus for treating cardiac arrhythmias	January, 1996	Ben-Haim	607/122
5483961	Magnetic field digitizer for stereotactic surgery	January, 1996	Kelly et al.	128/653.1
5485849	System and methods for matching electrical characteristics and propagation velocities in cardiac tissue	January, 1996	Panescu et al.	128/699
5487391	Systems and methods for deriving and displaying the propagation velocities of electrical events in the heart	January, 1996	Panescu	128/699
5487729	Magnetic guidewire coupling for catheter exchange	January, 1996	Avellanet et al.	604/96
5487757	Multicurve deflectable catheter	January, 1996	Truckai et al.	607/122
5490196	Multi energy system for x-ray imaging applications	February, 1996	Rudich et al.
5494034	Process and device for the reproducible optical representation of a surgical operation	February, 1996	Schlondorff et al.
5503416	Undercarriage for X-ray diagnostic equipment	April, 1996	Aoki et al.
5513637	Method and apparatus for determining the position of catheters, tubes, placement guidewires and implantable ports within biological tissue	May, 1996	Twiss et al.	128/653.1
5515160	Method and apparatus for representing a work area in a three-dimensional structure	May, 1996	Schulz et al.
5517990	Stereotaxy wand and tool guide	May, 1996	Kalfas et al.	128/653.1
5531227	Imaging device and method	July, 1996	Schneider
5531520	System and method of registration of three-dimensional data sets including anatomical body data	July, 1996	Grimson et al.
5542938	Magnetic guidewire coupling for catheter exchange	August, 1996	Avellanet et al.	604/280
5543951	Method for receive-side clock supply for video signals digitally transmitted with ATM in fiber/coaxial subscriber line networks	August, 1996	Moehrmann
5546940	System and method for matching electrical characteristics and propagation velocities in cardiac tissue to locate potential ablation sites	August, 1996	Panescu et al.	128/642
5546949	Method and apparatus of logicalizing and determining orientation of an insertion end of a probe within a biotic structure	August, 1996	Frazin et al.	128/662.06
5546951	Method and apparatus for studying cardiac arrhythmias	August, 1996	Ben-Haim	128/702
5551429	Method for relating the data of an image space to physical space	September, 1996	Fitzpatrick et al.
5558091	Magnetic determination of position and orientation	September, 1996	Acker et al.	128/653.1
5568809	Apparatus and method for intrabody mapping	October, 1996	Ben-Haim	128/656
5572999	Robotic system for positioning a surgical instrument relative to a patient's body	November, 1996	Funda et al.	128/653.1
5573533	Method and system for radiofrequency ablation of cardiac tissue	November, 1996	Strul	606/34
5575794	Tool for implanting a fiducial marker	November, 1996	Walus et al.
5583909	C-arm mounting structure for mobile X-ray imaging system	December, 1996	Hanover
5588430	Repeat fixation for frameless stereotactic procedure	December, 1996	Bova et al.	128/653.1
5592939	Method and system for navigating a catheter probe	January, 1997	Martinelli	128/653.1
5595193	Tool for implanting a fiducial marker	January, 1997	Walus et al.
5596228	Apparatus for cooling charge coupled device imaging systems	January, 1997	Anderton et al.
5600330	Device for measuring position and orientation using non-dipole magnet IC fields	February, 1997	Blood	342/463
5603318	Apparatus and method for photogrammetric surgical localization	February, 1997	Heilbrun et al.	128/630
5617462	Automatic X-ray exposure control system and method of use	April, 1997	Spratt
5617857	Imaging system having interactive medical instruments and methods	April, 1997	Chader et al.	128/653.1
5619261	Pixel artifact/blemish filter for use in CCD video camera	April, 1997	Anderton
5622169	Apparatus and method for locating a medical tube in the body of a patient	April, 1997	Golden et al.	128/653.1
5622170	Apparatus for determining the position and orientation of an invasive portion of a probe inside a three-dimensional body	April, 1997	Schulz	128/653.1
5627873	Mini C-arm assembly for mobile X-ray imaging system	May, 1997	Hanover et al.
5628315	Device for detecting the position of radiation target points	May, 1997	Vilsmeier et al.
5630431	System and method for augmentation of surgery	May, 1997	Taylor	128/897
5636644	Method and apparatus for endoconduit targeting	June, 1997	Hart et al.
5638819	Method and apparatus for guiding an instrument to a target	June, 1997	Manwaring et al.
5640170	Position and orientation measuring system having anti-distortion source configuration	June, 1997	Anderson	343/895
5642395	Imaging chain with miniaturized C-arm assembly for mobile X-ray imaging system	June, 1997	Anderton et al.
5643268	Fixation pin for fixing a reference system to bony structures	July, 1997	Vilsmeier et al.
5645065	Catheter depth, position and orientation location system	July, 1997	Shapiro et al.	128/653.1
5647361	Magnetic resonance imaging method and apparatus for guiding invasive therapy	July, 1997	Damadian	128/683.2
5662111	Process of stereotactic optical navigation	September, 1997	Cosman	128/653.1
5664001	Medical X-ray imaging apparatus	September, 1997	Tachibana et al.
5674296	Human spinal disc prosthesis	October, 1997	Bryan et al.
5676673	Position tracking and imaging system with error detection for use in medical applications	October, 1997	Ferre et al.	606/130
5681260	Guiding apparatus for guiding an insertable body within an inspected object	October, 1997	Ueda et al.
5682886	Computer-assisted surgical system	November, 1997	Delp et al.
5690108	Interventional medicine apparatus	November, 1997	Chakeres
5694945	Apparatus and method for intrabody mapping	December, 1997	Ben-Haim	128/736
5695500	System for manipulating movement of a surgical instrument with computer controlled brake	December, 1997	Taylor et al.	606/130
5695501	Apparatus for neurosurgical stereotactic procedures	December, 1997	Carol et al.
5697377	Catheter mapping system and method	December, 1997	Wittkampf
5702406	Device for noninvasive stereotactic immobilization in reproducible position	December, 1997	Vilsmeier et al.
5711299	Surgical guidance method and system for approaching a target within a body	January, 1998	Manwaring et al.
5713946	Apparatus and method for intrabody mapping	February, 1998	Ben-Haim	607/122
5715822	Magnetic resonance devices suitable for both tracking and imaging	February, 1998	Watkins
5715836	Method and apparatus for planning and monitoring a surgical operation	February, 1998	Kliegis et al.
5718241	Apparatus and method for treating cardiac arrhythmias with no discrete target	February, 1998	Ben-Haim et al.	128/702
5727552	Catheter and electrical lead location system	March, 1998	Ryan
5727553	Catheter with integral electromagnetic location identification device	March, 1998	Saad
5729129	Magnetic location system with feedback adjustment of magnetic field generator	March, 1998	Acker	324/207.12
5730129	Imaging of interventional devices in a non-stationary subject	March, 1998	Darrow et al.	128/653.1
5730130	Localization cap for fiducial markers	March, 1998	Fitzpatrick et al.
5732703	Stereotaxy wand and tool guide	March, 1998	Kalfas et al.	128/653.1
5735278	Surgical procedure with magnetic resonance imaging	April, 1998	Hoult et al.
5738096	Cardiac electromechanics	April, 1998	Ben-Haim	128/653.1
5741214	Accessory pathway detecting/cauterizing apparatus	April, 1998	Ouchi et al.	600/374
5742394	Optical 6D measurement system with two fan shaped beams rotating around one axis	April, 1998	Hansen
5744953	Magnetic motion tracker with transmitter placed on tracked object	April, 1998	Hansen
5748767	Computer-aided surgery apparatus	May, 1998	Raab
5749362	Method of creating an image of an anatomical feature where the feature is within a patient's body	May, 1998	Funda et al.	128/653.1
5749835	Method and apparatus for location of a catheter tip	May, 1998	Glantz
5752513	Method and apparatus for determining position of object	May, 1998	Acker et al.	128/653.1
5755725	Computer-assisted microsurgery methods and equipment	May, 1998	Druais
RE35816	Method and apparatus for three-dimensional non-contact shape sensing	June, 1998	Schulz
5758667	Device for locating a port on a medical implant	June, 1998	Slettenmark	128/899
5762064	Medical magnetic positioning system and method for determining the position of a magnetic probe	June, 1998	Polvani	128/653.1
5767669	Magnetic field position and orientation measurement system with dynamic eddy current rejection	June, 1998	Hansen et al.
5769789	Automatic technique for localizing externally attached fiducial markers in volume images of the head	June, 1998	Wang et al.
5769861	Method and devices for localizing an instrument	June, 1998	Vilsmeier
5772594	Fluoroscopic image guided orthopaedic surgery system with intraoperative registration	June, 1998	Barrick
5775322	Tracheal tube and methods related thereto	July, 1998	Silverstein et al.
5776064	Frameless stereotaxy system for indicating the position and axis of a surgical probe	July, 1998	Kalfas et al.	600/414
5782765	Medical positioning system	July, 1998	Jonkman
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5792055	Guidewire antenna	August, 1998	McKinnon
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5831260	Hybrid motion tracker	November, 1998	Hansen	250/221
5833608	Magnetic determination of position and orientation	November, 1998	Acker	600/409
5834759	Tracking device having emitter groups with different emitting directions	November, 1998	Glossop
5836954	Apparatus and method for photogrammetric surgical localization	November, 1998	Heilbrun et al.	600/130
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5840025	Apparatus and method for treating cardiac arrhythmias	November, 1998	Ben-Haim	600/424
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5868674	MRI-system and catheter for interventional procedures	February, 1999	Glowinski et al.	600/410
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5884410	Sensing system for coordinate measuring equipment	March, 1999	Prinz
5891034	System for indicating the position of a surgical probe within a head on an image of the head	April, 1999	Bucholz	600/426
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5968047	Fixation devices	October, 1999	Reed
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5983126	Catheter location system and method	November, 1999	Wittkampf
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6019725	Three-dimensional tracking and imaging system	February, 2000	Vesely et al.	600/447
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6156067	Human spinal disc prosthesis	December, 2000	Bryan et al.
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6341231	Position tracking and imaging system for use in medical applications	January, 2002	Ferre et al.
6351659	Neuro-navigation system	February, 2002	Vilsmeier
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6445943	Position tracking and imaging system for use in medical applications	September, 2002	Ferre et al.
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Smith, Ruth S.

Harness Dickey

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a reissue of U.S. Pat. No. 5,592,939 issued on Jan. 14, 1997 and also claims benefit under 35 U.S.C. § 120 as a continuation of U.S. patent application Ser. No. 09/231,854 filed on Jan. 14, 1999 which also is a reissue of U.S. Pat. No. 5,592,939 issued on Jan. 14, 1997. The disclosures of the above applications are incorporated herein by reference.

What is claimed is:

1. A method of determining the location of a magnetically-sensitive, electrically conductive sensing coil affixed to a distal end of a catheter probe partially inserted into a body cavity within a navigational domain, comprising the steps of: inducing within said sensing coil a set of orientation signal values each representative of an orientation of said sensing coil and independent of a position of said sensing coil; determining the orientation of said sensing coil using said induced orientation signal values; inducing within said sensing coil a set of positional signal values each representative of the position of said sensing coil; and determining the position of said sensing coil using said positional signal values and said determined orientation.

2. The method as recited in claim 1, wherein the step of inducing said set of orientation signal values comprises the steps of: generating from outside said body a series of magnetic fields each penetrating at least said navigational domain and characterized substantially by a principal magnetic component in one axial dimension and relatively smaller magnetic components in two other axial dimensions.

3. The method as recited in claim 1, wherein the step of inducing said set of positional signal values comprises the steps of: generating from outside said body a series of magnetic fields each penetrating at least said navigational domain and characterized substantially by two principal gradient magnetic components in respective axial dimensions and a relatively smaller magnetic components in a third axial dimension.

4. The method as recited in claim 3, wherein said generating step further includes the steps of: generating said fields to provide a plurality of constant signal surfaces for the sensing coil such that an intersection between two such surfaces with components in the same axial dimensions produces a line along which said sensing coil is located; wherein said two such surfaces are identified from among said plurality of constant signal surfaces by their ability to induce one of said positional signal values.

5. The method as recited in claim 4, further comprises the steps of: weighting each line in accordance with a signal strength of said corresponding constant signal surface; and determining an intersection of said weighted lines.

6. The method as recited in claim 5, wherein six constant signal surfaces are generated to produce three intersection lines.

7. A system for determining the location of a magnetically-sensitive, electrically conductive sensing coil affixed to a distal end of a catheter probe partially inserted into a body cavity within a navigational domain, comprising: first transmit means for projecting into said navigational domain magnetic energy that is sufficient to induce signal values within said sensing coil representative of an orientation of said sensing coil and independent of the position of said sensing coil; second transmit means for projecting into said navigational domain magnetic energy that is sufficient to induce signal values within said sensing coil representative of the position of said sensing coil; and analysis means, coupled to said first transmit means and said second transmit means, for determining the position and orientation of said sensing coil from said induced signal values.

8. A system for determining the location of a magnetically-sensitive, electrically conductive sensing coil affixed to a distal end of a catheter probe partially inserted into a body cavity within a navigational domain, comprising: first signal-inducing means for inducing within said sensing coil orientation signals that are representative of the orientation of said sensing coil; analysis means, coupled to said first signal-inducing means, for determining the orientation of said sensing coil using said induced orientation signals and independent from a position of said sensing coil; second signal-inducing means for inducing within said sensing coil position signals that are representative of the position of said sensing coil; and analysis means, coupled to said second signal-inducing means, for determining the position of said sensing coil using said determined orientation and said induced position signals.

9. The system as recited in claim 8, wherein the first signal-inducing means comprises: field generation means for successively generating magnetic field patterns projected into said navigational domain, each characterized substantially by a principal magnetic field component in one direction and relatively smaller magnetic components in two other directions.

10. The system as recited in claim 9, wherein said field generation means comprises a set of magnetic coils.

11. The system as recited in claim 10, wherein said magnetic coils are disposed in a planar top of an examination deck upon which a patient is disposed during a surgical procedure.

12. The system as recited in claim 10, wherein said magnetic coils are disposed in a planar top and in rail members edge supported by said planar top for an examination deck upon which a patient is disposed during a surgical procedure.

13. The system as recited in claim 8, wherein the second signal-inducing means comprises: field generation means for successively generating magnetic field patterns each characterized by a first and second gradient field component in respective directions and a relatively smaller third component in another direction.

14. The system as recited in claim 13, wherein the field generation means comprises a magnetic coil assembly.

15. A method of determining the location of a magnetically-sensitive, electrically conductive sensing coil affixed to a distal end of a catheter probe partially inserted into a body cavity within a navigational domain, comprising the steps of: defining the location of said sensing coil with a set of independent location parameters; and sequentially generating within said navigational domain a sequence of magnetic fields for inducing within said sensing coil a corresponding sequence of induced signals each defined by an induced signal expression that functionally relates said induced signal to certain ones of said location parameters, such that said set of location parameters is determinable by sequentially solving individual signal expression groups each including certain ones of said induced signal expressions and sufficient to represent a subset of said location parameters.

16. The method as recited in claim 15, wherein said sequence of magnetic fields comprises: a series of unidirectional magnetic fields each characterized substantially by a principal magnetic field component in one direction and relatively smaller magnetic components in two other directions; and a series of gradient magnetic fields each characterized by a first and second gradient field component in respective directions and a relatively smaller third component in another direction.

17. The method as recited in claim 16, wherein said signal expression groups include: an orientation group including induced signal expressions each functionally related to a respective one of said unidirectional magnetic fields and an orientation of said sensing coil, and independent of a position of said sensing coil; and a position group including induced signal expressions each functionally related to a respective one of said gradient magnetic fields, the orientation of said sensing coil, and the position of said sensing coil.

18. The method as recited in claim 17, wherein the step of sequentially solving said individual signal expression groups includes the steps of: initially solving the induced signal expressions of said orientation group; and next solving the induced signal expressions of said position group.

19. A system for determining the location of a magnetically-sensitive, electrically conductive sensing coil affixed to a distal end of a catheter probe partially inserted into a body cavity within a navigational domain, comprising: means for defining the location of said sensing coil with a set of independent location parameters; and field generation means for sequentially generating within said navigational domain a sequence of magnetic fields for inducing within said sensing coil a corresponding sequence of induced signals each defined by an induced signal expression that functionally relates said induced signal to certain ones of said location parameters, such that said set of location parameters is determinable by sequentially solving individual signal expression groups each including certain ones of said induced signal expressions and sufficient to represent a subset of said location parameters.

20. The system as recited in claim 19, wherein said sequence of magnetic fields comprises: a series of unidirectional magnetic fields each characterized substantially by a principal magnetic field component in one direction and relatively smaller magnetic components in two other directions; and a series of gradient magnetic fields each characterized by a first and second gradient field component in respective directions and a relatively smaller third component in another direction.

21. The system as recited in claim 20, wherein said signal expression groups include: an orientation group including induced signal expressions each functionally related to a respective one of said unidirectional magnetic fields and an orientation of said sensing coil, and independent of a position of said sensing coil; and a position group including induced signal expressions each functionally related to a respective one of said gradient magnetic fields, the orientation of said sensing coil, and the position of said sensing coil.

22. The system as recited in claim 21, wherein said field generation means comprises: analysis means for solving the induced signal expressions of said orientation group; and analysis means for solving the induced signal expressions of said position group.

23. A method of determining the location of a magnetically-sensitive, electrically conductive sensing coil in a navigational domain within a body, comprising the steps of: inducing within said sensing coil a set of orientation signal values each representative of an orientation of said sensing coil and independent of a position of said sensing coil; determining the orientation of said sensing coil using said induced orientation signal values; inducing within said sensing coil a set of positional signal values each representative of the position of said sensing coil by generating from outside said body a series of magnetic fields each penetrating at least said navigational domain and characterized substantially by two principal gradient magnetic components in respective axial dimensions and a relatively smaller magnetic component in a third axial dimension; generating said fields to provide a plurality of constant signal surfaces for the sensing coil such that an intersection between two such surfaces with components in the same axial dimensions produces a line along which said sensing coil is located; wherein said two such surfaces are identified from among said plurality of constant signal surfaces by their ability to induce one of said positional signal values; and, determining the position of said sensing coil using said positional signal values and said determined orientation.

24. The method as recited in claim 23, wherein the step of inducing said set of orientation signal values comprises the steps of: generating from outside said body a series of magnetic fields each penetrating at least said navigational domain and characterized substantially by a principal magnetic component in one axial dimension and relatively smaller magnetic components in two other axial dimensions.

25. The method as recited in claim 23, further comprises the steps of: weighting each line in accordance with a signal strength of said corresponding constant signal surface; and determining an intersection of said weighted lines.

26. The method as recited in claim 25, wherein six constant signal surfaces are generated to produce three intersection lines.

27. A system for determining the location of a magnetically-sensitive, electrically conductive sensing coil in a navigational domain within a body, comprising: first signal-inducing means for inducing within said sensing coil orientation signals that are representative of the orientation of said sensing coil, including field generation means for successively generating magnetic field patterns projected into said navigational domain, wherein said field generation means comprises a set of magnetic coils and said magnetic coils are disposed in a planar top of an examination deck upon which a patient is disposed during a surgical procedure; analysis means, coupled to said first signal-inducing means, for determining the orientation of said sensing coil using said induced orientation signals and independent from a position of said sensing coil; second signal-inducing means for inducing within said sensing coil position signals that are representative of the position of said sensing coil; and, analysis means, coupled to said second signal-inducing means, for determining the position of said sensing coil using said determined orientation and said induced position signals.

28. The system as recited in claim 27, wherein each of the magnetic field patterns projected into said navigational domain is characterized substantially by a principal magnetic field component in one direction and relatively smaller magnetic components in two other directions.

29. The system as recited in claim 27, wherein the second signal-inducing means comprises: field generation means for successively generating magnetic field patterns each characterized by a first and second gradient field component in respective directions and a relatively smaller third component in another direction.

30. The system as recited in claim 29, wherein the field generation means comprises a magnetic coil assembly.

31. A system for determining the location of a magnetically-sensitive, electrically conductive sensing coil in a navigational domain within a body, comprising: first signal-inducing means for inducing within said sensing coil orientation signals that are representative of the orientation of said sensing coil, including field generation means for successively generating magnetic field patterns projected into said navigational domain, wherein said field generation means comprises a set of magnetic coils and said magnetic coils are disposed in a planar top and in rail members edge supported by said planar top for an examination deck upon which a patient is disposed during a surgical procedure; analysis means, coupled to said first signal-inducing means, for determining the orientation of said sensing coil using said induced orientation signals and independent from a position of said sensing coil; second signal-inducing means for inducing within said sensing coil position signals that are representative of the position of said sensing coil; and, analysis means, coupled to said second signal-inducing means, for determining the position of said sensing coil using said determined orientation and said induced position signals.

32. A system for determining the location of a magnetically-sensitive, electrically conductive sensing coil affixed to a distal end of a catheter probe partially inserted into a body cavity within a navigational domain, comprising: first signal-inducing means for inducing within said sensing coil orientation signals that are representative of the orientation of said sensing coil, including field generation means for successively generating magnetic field patterns projected into said navigational domain, wherein said field generation means comprises a set of magnetic coils disposed in a planar top of an examination deck upon which a patient is disposed during a surgical procedure; analysis means, coupled to said first signal-inducing means, for determining the orientation of said sensing coil using said induced orientation signals and independent from a position of said sensing coil; second signal-inducing means for inducing within said sensing coil position signals that are representative of the position of said sensing coil; and analysis means, coupled to said second signal-inducing means, for determining the position of said sensing coil using said determined orientation and said induced position signals.

33. The system as recited in claim 32, wherein the second signal-inducing means comprises: field generation means for successively generating magnetic field patterns each characterized by a first and second gradient field component in respective directions and a relatively smaller third component in another direction.

34. The system as recited in claim 33, wherein the field generation means comprises a magnetic coil assembly.

35. A system for determining the location of a magnetically-sensitive, electrically conductive sensing coil affixed to a distal end of a catheter probe partially inserted into a body cavity within a navigational domain, comprising: first signal-inducing means for inducing within said sensing coil orientation signals that are representative of the orientation of said sensing coil, including field generation means for successively generating magnetic field patterns projected into said navigational domain, wherein said field generation means comprises a set of magnetic coils disposed in a planar top and in rail members edge supported by said planar top for an examination deck upon which a patient is disposed during a surgical procedure; analysis means, coupled to said first signal-inducing means, for determining the orientation of said sensing coil using said induced orientation signals and independent from a position of said sensing coil; second signal-inducing means for inducing within said sensing coil position signals that are representative of the position of said sensing coil; and analysis means, coupled to said second signal-inducing means, for determining the position of said sensing coil using said determined orientation and said induced position signals.

FIELD OF THE INVENTION

The present invention relates to catheter navigation systems and, more particularly, to a method and system for determining the position and orientation of a catheter probe being used during a surgical procedure.

BACKGROUND OF THE INVENTION

Various configurations have been proposed to guide and detect a catheter probe through the internal spaces of a patient undergoing a surgical procedure. These proposed configurations are characterized by several alternative approaches including, inter alia, procedures for solving equations to determine unknown location parameters, the generation and detection of magnetic fields, and the use of sensing devices affixed to the catheter probe.

U.S. Pat. No. 4,905,698 to Strohl, Jr. et al. discloses a locator device external to a subject for generating an electromagnetic field that projects into the subject. A catheter inserted into the subject is fitted with a sensing coil at its distal end. The phase of the voltage that is induced in the coil in response to the field is compared to the phase of the generated field. When an in-phase condition occurs, this is an indication that the locator is behind the coil; alternatively, an out-of-phase condition indicates that the locator is beyond the coil. Positions intermediate these two rough approximations of the coil position are not determined other than by a beeping indicator that signifies that this intermediate positioning has been reached.

U.S. Pat. No. 4,821,731 to Martinelli et al. discloses an electroacoustical transducer means secured to the distal end of a catheter that is inserted into a subject for generating acoustical pulses that propagate along an imaging axis and reflect from an anatomical area of interest. The acoustic echoes are converted by the transducer means into electrical signals representative of an image of the anatomical area under reflection and the relative position of the transducer means and angular orientation of the sensing/imaging axis.

U.S. Pat. No. 4,642,786 to Hansen discloses a magnetic position and orientation measurement system that determines the location of an object in space with various configurations, each characterized by the attachment of a retransmitter to the object consisting of passive resonant circuits. The retransmitter is in a predetermined position and orientation with respect to the object. A magnetic field is generated at a resonant frequency of the retransmitter which then retransmits a magnetic field for subsequent reception. The position and orientation of the object may be calculated based upon the induced signals as developed by the reception of the retransmitted magnetic field. The original transmission and reception may be implemented with an integrated transceiver, separate transmitter and receiver elements, or a single transmitter and an array of receiver coils.

U.S. Pat. No. 4,317,078 to Weed et al. discloses how the location of a magnetically sensitive element may be determined by moving a magnetic field source along specified reference axes to induce signals in the sensor so as to identify a set of null points representative of certain flux linkage values. The null point locations are used to calculate the sensor position.

U.S. Pat. No. 3,868,565 describes a system where a magnetic field is generated which rotates about a known pointing vector. The generated field is sensed along at least two axes by a sensor attached to the object to be located or tracked. Based upon the relationship between the sensed magnetic field components, the position of the object relative to the pointing vector can be computed.

U.S. Pat. No. 4,173,228 to Van Steenwyk et al. discloses a catheter locating system that includes a sensor attached to the distal end of the catheter. An electromagnetic field is projected into the body cavity with magnetic probe coils. The field is detected by the sensor, which generates an induced signal whose magnitude and phase are representative of field strength, separation of sensor and probe coils, and relative orientation of sensor and probe coils. The probe coil undergoes linear and rotational movement to identify orientations and locations of the probe coil where minima and maxima occur in the measured signal induced in the sensor. This information is representative of the position and orientation of the sensor.

U.S. Pat. No. 5,211,165 to Dumoulin et al. discloses a modified catheter device that includes a small RF transmit coil attached to its distal end. The transmit coil is driven by an RF source to create an electromagnetic field that induces electrical signals in an array of receive coils distributed around a region of interest. Alternatively, the receive coils can be placed on the invasive device and the transmit coils are distributed outside the patient. A minimum of one transmit coil and three receive coils is necessary to precisely determine the location of the invasive device. A series of equations is developed to solve for the unknowns x-y-z-φ-θ.

PCT Application No. WO94/04938 to Bladen et al. describes how the location and orientation of a single sensing coil may be determined from induced signals developed in response to a sequence of applied magnetic fields emanating from three groups of field generators each including three mutually orthogonal coils.

The positioning methodology developed by Bladen et al. involves calculating the distance from the sensing coil to each group of field generators as a function of the induced voltage developed in the sensing coil by the field generator. The distance calculation is used to define the radius of a sphere centered on the respective field generator. The intersection (i.e., overlap) of the spheres is used to calculate an estimate of the sensor position, using the spherical radius extending from the known location of the field generators as the estimate for each generator.

The orientation algorithm of Bladen et al. develops general equations for induced voltage including the entire set of unknown variables (x-y-z location and φ-θ orientation). The algorithm specifically solves for the orientation parameters by substituting the measured induced voltage and the computed x-y-z coordinates into the general induced voltage equation, and then reduces the equations to the unknown variables φ-θ.

In an alternative orientation algorithm described by Bladen et al., the induced voltage is treated as a vector quantity, allowing the angle between the magnetic field at the generator and the radial vector joining the sensor to the generator to be calculated with a dot product computation. The angle between the radial vector and the sensor axis can be determined from the computed field angle using the dipole equations that define the generator fields. This sensor angle and the radial position as determined by the position algorithm together define the sensor position for use in the alternative orientation algorithm. These values are used to compute the angular orientation φ and θ.

OBJECTS OF THE INVENTION

It is a general object of the present invention to obviate the above-noted and other disadvantages of the prior art.

It is a more specific object of the present invention to provide a catheter navigation system capable of determining the location of a catheter probe.

It is a further object of the present invention to develop a catheter navigation system employing a sensing coil affixed to the end of a catheter probe for generating induced voltage signals that are sufficient to describe the position and orientation of the sensing coil.

It is a further object of the present invention to develop a methodology for generating magnetic fields that are sufficient to create a series of soluble mathematical expressions describing the position and orientation of the sensing coil.

SUMMARY OF THE INVENTION

In one aspect of the present invention, an improved method of determining the location of a magnetically-sensitive, electrically conductive sensing coil affixed to a distal end of a catheter probe partially inserted into a body cavity within a navigational domain comprises the steps of:

• • inducing within said sensing coil a set of orientation signal values each representative of an orientation of said sensing coil and independent of a position of said sensing coil;
  • determining the orientation of said sensing coil using said induced orientation signal values;
  • inducing within said sensing coil a set of positional signal values each representative of the position of said sensing coil; and
  • determining the position of said sensing coil using said positional signal values and said determined orientation.

In another aspect of the present invention, an improved system for determining the location of a magnetically-sensitive, electrically conductive sensing coil affixed to a distal end of a catheter probe partially inserted into a body cavity within a navigational domain comprises:

• • first transmit means for projecting into said navigational domain magnetic energy that is sufficient to induce signal values within said sensing coil representative of an orientation of said sensing coil and independent of the position of said sensing coil;
  • second transmit means for projecting into said navigational domain magnetic energy that is sufficient to induce signal values within said sensing coil representative of the position of said sensing coil; and
  • analysis means, coupled to said first transmit means and said second transmit means, for determining the position and orientation of said sensing coil from said induced signal values.

In another aspect of the present invention, an improved method of determining the location of a magnetically-sensitive, electrically conductive sensing coil affixed to a distal end of a catheter probe partially inserted into a body cavity within a navigational domain comprises the steps of:

• • defining the location of said sensing coil with a set of independent location parameters; and
  • sequentially generating within said navigational domain a sequence of magnetic fields for inducing within said sensing coil a corresponding sequence of induced signals each defined by an induced signal expression that functionally relates said induced signal to certain ones of said location parameters, such that said set of location parameters is determinable by sequentially solving individual signal expression groups each including certain ones of said induced signal expressions and sufficient to represent a subset of said location parameters.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 schematically illustrates a perspective view of a patient-supporting examination deck in accordance with a preferred embodiment of the present invention;

FIGS. 2A-C schematically illustrate a series of magnetic coil sets for generating uniform fields in the x-, y-, and z-directions, respectively, in accordance with a preferred embodiment of the present invention, and which are configured within the deck of FIG. 1;

FIGS. 3 schematically illustrates a magnetic coil assembly for determining the positional coordinates of the sensing coil in accordance with a preferred embodiment of the present invention, and which is configured within the deck of FIG. 1;

FIG. 4 is a flow diagram describing the location algorithm in accordance with the present invention;

FIG. 5 schematically depicts the magnetic coil assembly of FIG. 3 to illustrate representative field patterns generated during an excitation period;

FIG. 6 is a trace representatively illustrating surfaces of constant signal from the sensing coil, as generated by the magnetic assembly of FIG. 3;

FIG. 7 shows an upper plan schematic view of the magnetic assembly of FIG. 3;

FIG. 8 schematically illustrates a perspective view of a patient-supporting examination deck in accordance with another embodiment of the present invention; and

FIGS. 9A-D schematically illustrate a series of magnetic coil assemblies configured in the deck and rails of FIG. 8 for determining the orientation and position of the sensing coil in accordance with another embodiment of the present invention.

Throughout the drawings the same or similar elements are identified by the same reference numeral.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention is directed to a method and system for determining the location of a catheter or endoscopic probe inserted into a selected body cavity of a patient undergoing a surgical procedure. The location data is obtained from electrical measurements of voltage signals that are induced within a sensing coil affixed to the distal end of the catheter probe. These induced voltage signals are generated by the sensing coil in response to prespecified electromagnetic fields that project into the anatomical region of interest which contains all prospective locations of the catheters probe. The electrical measurements of the induced signals provide sufficient information to compute the angular orientation and the positional coordinates of the sensing coil, and hence the catheter probe, which collectively define the location of the sensing coil. The present invention is operative as the patient is disposed on a patient-supporting examination deck.

As used herein, “sensing coil” refers to an electrically conductive, magnetically sensitive element that is responsive to time-dependent magnetic fields for generating induced voltage signals as a function of and representative of the applied time-dependent magnetic field. The sensing coil is adaptable for secure engagement to the distal end of a catheter probe.

As used herein, “navigational domain” refers to a fully enclosed spatial region whose internal volume substantially encloses the complete prospective range of movement of the sensing coil. The navigational domain may be defined by any geometrical space but preferably takes the form of a spherical volume. Under surgical operating conditions, the navigational domain will correspond to an anatomical region of the recumbent patient where surgical viewing or investigation is desired (e.g., a diseased area of tissue or an organ).

As used herein, “last navigational point” (hereinafter “the LNP”) refers to the most recently determined location of the sensing coil before another iteration of the location algorithm is performed.

As used herein, “uniform field” refers to a magnetic field having a large magnetic field component in a specified axial dimension and relatively smaller magnetic field components in the other axial dimensions, and characterized by substantially uniform field values throughout the navigational domain. In the x-y-z coordinate system used herein, where the uniform fields of interest are the x-directed, y-directed, and z-directed fields, the induced voltage signals developed by such fields in the sensing coil are designated V _x , V _y and V _z , respectively. The term “unidirectional field” is used interchangeably with “uniform field” when appropriate.

As used herein, “unidirectional coils” refer to a magnetic assembly that is operative to generate a uniform field (as defined above) within the navigational domain. A distinct magnetic assembly is employed for each uniform field. Although the unidirectional coils described herein are preferably implemented with a collection of appropriately designed magnetic coils, this implementation should not be construed as a limitation of the present invention. Rather, the unidirectional coils may be constructed from any magnetic configuration that is sufficient to generate the uniform fields.

As used herein, “gradient field” refers to a time-dependent magnetic field having non-zero field components (i.e., components with a high spatial gradient) in two of the three axial dimensions for the coordinate system of interest (e.g., x-y-z system), and a substantially zero component in the remaining axial dimension. For mathematical purposes, a substantially zero component is generated when its value is small compared to the net vector resulting from the other two field components.

As used herein, “constant signal surface” or “constant voltage surface” refers to a surface contour along which at every possible point of location for the sensing coil the same induced voltage is developed in the sensing coil.

As used herein, “delta coils” refer to a magnetic assembly for generating a gradient field (as defined above) within the navigational domain. As will become more apparent hereinafter, the delta coils will typically be described in the context of delta coil pairs including a long coil set and a short coil set each generating gradient fields with components in the same axial dimensions but whose magnetic field patterns are different. Each of the long and short coil sets may be considered to generate a family of constant signal or constant voltage surfaces from the sensing coil within the navigational domain. Although the delta coils are preferably implemented with an array of appropriately designed magnetic coils (discussed below), this preferred implementation should not serve as a limitation of the present invention as it should be apparent to those skilled in the art that other magnetic configurations may be used to adequately generate the gradient fields.

As used herein, “magnetic look-up-table” (alternatively referenced as “the LUT”) refers to a database including the magnetic field values at every x-y-z coordinate position within the navigational domain for the unidirectional coils and delta coils used by the present invention. Accordingly, input data consisting of an x-y-z coordinate and a magnetic field identifier, which designates a selected magnetic coil assembly, is indexed within the database to a corresponding set of magnetic field values constituting the output data. For the x-y-z coordinate system, the output data is represented by the magnetic field variables H _x H _y H _z where the subscript indicates the axial dimension along which the magnetic field value is being reported. The database is created through a computational analysis of the magnetic field patterns generated by the magnetic coil configurations used herein. The mathematical model to develop the necessary formulae defining the field patterns may be developed, for example, from near field electromagnetic theory. An instructive text for facilitating such an analysis is “Field and Wave Electromagnetics” 2nd edition Addison Wesley (1989) by D. K. Cheng, herein incorporated by reference. The database may be stored in any type of facility including, inter alia, read-only memory, firmware, optical storage, or other types of computer storage. Additionally, the database information may be organized into any type of format such as a spreadsheet. It should be apparent to those skilled in the art that any suitable technique may be used to ascertain or record the magnetic field values for the magnetic coil assemblies used herein.

Separation of Variables Methodology

The mathematical construct underlying the present invention is a methodology termed separation of variables. In accordance with this methodology, appropriate equations are developed to isolate unknown variables in such a manner that renders the equations uniquely soluble. There are five unknown variables (φ-θ-x-y-z) that define the location and orientation of the sensing coil. A typical approach to solving for these variables would be to develop a series of coupled non-linear equations expressing the relationship among the variables. However, these equations are generally not uniquely soluble, i.e., multiple solutions are possible.

The mathematical approach used herein and predicated on the separation of variables concept is directed to the development of a series of signal expression statements functionally relating induced voltage values to certain ones of the unknown location parameters. The relationships defined by these expression statements (i.e., induced voltage equations) are such that the unknown variables are determinable by sequentially solving the expression statements. In accordance with one aspect of the present invention, a class of special magnetic fields is generated with characteristic spatial structuring and shaping that is sufficient to cause the variables (i.e., the location parameters) to separate within these induced voltage equations so as to permit resolution of the parameters x-y-z-φ-θ when the equations are sequentially solved.

In particular, a series of substantially uniform fields is successively generated in the x-, y-, and z-directions with the group of unidirectional coils, thereby developing induced voltage expressions (discussed below) involving only the variables φ and θ independent of the unknown positional variables x-y-z. This uncoupling of the variables φ-θ from the variables x-y-z as accomplished by the substantially uniform fields is specifically evident in the three induced voltage equations expressed in two unknowns (i.e., φ and θ), which are easily soluble.

The separation of variables methodology as applied to the determination of the unknown positional coordinates x-y-z is implemented with a sequence of gradient fields as generated by an appropriate group of delta coils. Since the gradient fields have components in only two of the axial dimensions, these fields induce voltages in the sensing coil that are dependent upon the magnetic field values in only these two dimensions at the sensing coil position. As a result, each gradient field generates a family of constant signal surfaces from the sensing coil, from which a constant signal surface is identified for each gradient field that produces the measured induced voltage in the sensing coil. The intersection of two such constant signal surfaces is a line along which the catheter is located. This intersection line is defined by an expression in two of the unknown positional coordinates, wherein the other equation parameters are known, i.e., the measured induced voltage values, the magnetic field values at every x-y-z coordinate for the coil groups (as supplied by the LUT), and the as-computed φ-θ orientation. If an appropriate delta coil configuration is used (e.g., three delta coil pairs), an appropriate number of such intersection lines (e.g., three) may be produced to sufficiently and uniquely resolve the x-y-z coordinates (e.g., by calculating the intersection of such three intersection lines).

Since there are five unknown variables to completely define the catheter probe location, an equal number of independent equations are needed to sufficiently describe its location. These unknowns may be determined using one coil and five magnetic fields (as described herein), two coils and three magnetic fields, or three coils and two magnetic fields.

Overview of Location Algorithm

In accordance with the present invention, a location algorithm was developed for determining the location of a sensing coil affixed to the distal end of a catheter probe that is navigated through an anatomical region of interest within a recumbent patient. The location of the sensing coil is defined by an angular orientation and positional coordinates. The angular orientation is represented by an angle φ corresponding to the angle of departure from the z-axis and an angle θ corresponding to the angle between the x-axis and the projection onto the x-y plane of the vector coincident with the longitudinal axis of the coil. In the coordinate system for describing the present invention, the z-axis coincides with the longitudinal dimension extending from the patient's head to foot. The x-axis coincides with a lateral dimension across the patient's body, and the y-axis is perpendicular to the planar top of the pallet or examination deck. These dimensions are identified as the patient is disposed in the recumbent position on the pallet. As discussed below, the angular orientation is determined from signals induced in the sensing coil in response to a sequence of substantially uniform, unidirectional fields generated successively within the navigational domain. The positional coordinates are determined from signals induced in the sensing coil in response to the gradient magnetic fields.

By way of background, the time-dependent magnetic fields projected into the navigational domain induce voltages in the coil that are representative of the orientation of the coil axis relative to the lines of magnetic flux. The development of an induced voltage in an electrical conductor in response to a changing magnetic field is defined by Faraday's law. If one considers any closed stationary path in space which is linked by a changing magnetic field, it is found that the induced voltage V _ind around this path is equal to the negative time rate of change of the total magnetic flux through the closed path. Denoting a closed path with the variable C, the magnetic flux through C is given by, $\Psi ={\int }_{s}B·dS$
where S is any surface bounded by the closed path C. Thus, the mathematical statement of Faraday's law is $V_{\mathrm{ind}}=-\frac{\delta }{\delta t}{\int }_{s}B·dS$
Basically, the law states that a changing magnetic field will induce an electric field which exists in space regardless of whether a conducting wire is present. If a conducting wire is present in the electric field, an induced voltage will develop in the conductor. For a single-turn coil of wire of radius d located in a uniform magnetic field B=B _o sinωt, where the axis of the sensing coil is displaced at an angle θ with respect to the lines of magnetic flux, the induced voltage measured between the two open ends of the coil is expressed as: $V_{\mathrm{ind}}=-\frac{\partial }{\partial t}{\int }_{s}B·dS=-\frac{\partial }{\partial t}\left({\mathrm{\pi d}}^2{B}_o\cos \theta \sin \omega t\right)$ $V_{\mathrm{ind}}=-{\mathrm{\omega \pi d}}^2{B}_o\cos \theta \cos \omega t$ V _ind =−ωπd ² B _o cosθcosωt
This relationship for a single coil may be used to determine the induced voltage within a coil of N turns. Assuming that each turn of the coil is separately and equally linked by the magnetic flux (e.g., in tightly wound coils), the induced voltage within the entire coil assembly may be approximated as the summation of the induced voltages developed in each turn. Accordingly, the total voltage across the entire coil assembly is N times the induced voltage for a single turn; hence, the induced voltage V _ind is equivalent to
V _ind =−Nωπd ² B _o cosθcosωt
Clearly, the induced voltage in the sensing coil will vary with changes in the angular orientation between the coil axis and the direction of the magnetic field lines.

A useful reference frame for spatially conceptualizing the interaction between the sensing coil and the magnetic fields is the Cartesian coordinate system defined by mutually perpendicular axes x-y-z. For purposes of illustration, a nonzero vector â is selected to coincide with the axis through the sensing coil of the present invention (hereinafter “coil axis”).

The angles α, β, and γ that the vector â makes with the unit coordinate vectors î, ĵ, and {circumflex over (k)}, respectively, are called the direction angles of â; the trigonometric terms cosα, cosβ, and cosγ represent direction cosine values. Employing vector product notation, the following expressions are developed: â·î=∥â∥cosα; â·ĵ=∥â∥cosβ; and â·{circumflex over (k)}=∥â∥cosγ. Referencing the induced voltage equations set forth above, these angles α, β and γ correspond to the angular displacement of the coil axis with respect to uniform fields generated along the x-axis, y-axis, and z-axis directions, respectively. Thus, the correspondence between direction cosine expressions is as follows:

• • cosα corresponds to sinφcosθ;
  • cosβ corresponds to sinθsinφ; and
  • cosγ corresponds to cosφ.
    Accordingly, the following relationships illustrate the dependence of induced voltage on the orientation parameters φ and θ:
• V _x =sinφcosθ;
  • V _y =sinθsinφ; and
  • V _z =cosφ,
    where the subscript indicates the direction of the magnetic field that produced the measured induced voltage.

FIG. 4 is a flowchart detailing the location algorithm according to the present invention and should be referenced in connection with the discussion below.

As noted above, the last navigation point (LNP) refers to the x-y-z positional coordinates of the sensing coil as determined by the immediately previous computation cycle of the algorithm. For the first cycle, the LNP is the center of the viewing field.

In accordance with a preferred embodiment of the present invention for implementing the location algorithm, a magnetic assembly of nine individual coil sets are used to generate the magnetic fields sufficient to develop a corresponding set of nine induced voltage signals that are fully representative of the location of the sensing coil. The nine coil sets correspond to a group of three unidirectional coil sets for generating uniform fields in the x, y, and z-directions; a first delta coil group including a short coil set at 0° and a long coil set at 0°; a second delta coil group including a short coil set at 120° and a long coil set at 120°; and a third delta coil group including a short coil set at 240° and a long coil set at 240°. The angular designations associated with the delta coil groups indicate the angle with respect to the z-axis of the coil dimension that is perpendicular to the direction of elongation of the delta coils. Accordingly, the three delta coil groups are arranged pair-wise in a circular orientation about the y-axis at angles of 0°, 120°, and 240°.

The look-up-table (LUT) consists of a database containing the magnetic field values (H _x H _y H _z ) at every x-y-z coordinate location within the navigational domain for five coil sets: the unidirectional coil sets for generating the uniform fields in the x, y, and z-directions; the short coil (SC) set at 0°; and the long coil (LC) set at 0°. The magnetic field value data for the short and long coil sets at 120° and 240° may be obtained from the LUT by rotating the field vectors for the long and short coil sets at 0° by the angle (i.e., ±120°) appropriate for the given coil set. The input data for the LUT consists of the x-y-z coordinates and a designation of which coil set is being used to generate the magnetic fields. In response to this input data, the LUT supplies the magnetic field values H _x H _y H _z at the selected x-y-z coordinates for the designated coil set.

The LUT is present to speed up the operational sequence of the location algorithm. Otherwise, an undesirable computational delay exists if the required magnetic fields from the nine coil sets must be individually calculated during each iteration of the algorithm. By predetermining the magnetic field values and storing them in LUT, the location algorithm need only access the LUT to retrieve the appropriate field value without endeavoring into any complex field analysis. At x-y-z coordinates other than those for which magnetic field values are determined in the LUT, an interpolation procedure is employed to calculate the field value.

Determining Angular Orientation of the Sensing Coil

The location algorithm of the present invention initially undertakes a procedure to determine the angular orientation of the sensing coil. An assumption is first made that the coil orientation does not appreciably change during the period between cycle computations. Accordingly, the magnetic field values corresponding to the uniform field pattern at the LNP are used as an approximation for the magnetic field values at the current but as yet undetermined location.

The unidirectional coils are activated in succession, each generating a substantially uniform field that projects into the navigational domain and induces a corresponding voltage signal in the sensing coil. The induced voltage signals are measured by an appropriate detection unit coupled to a proximal end of the catheter device where an electrical connection to the sensing coil is established via suitable connection means extending along the body of the catheter device.

The LUT is then accessed three times to acquire the magnetic field values at the LNP for each of the three unidirectional coils. These values and the measured voltage signals are then substituted into the appropriate equations set forth below to solve for the unknown variables φ and θ that define the coil orientation.

As a general principle, the voltage induced within the sensing coil may be resolved into components along each of the axial dimensions as determined by the extent to which the magnetic flux density is developed along these axial dimensions. For example, a general formula for the induced voltage produced by the unidirectional coil which generates a substantially uniform field in the x-direction is as follows:
V _x =H _xx K sinφcosθ+H _yx K sinφsinθ+H _zx K cosφ
where magnetic field intensity H is related to magnetic flux density by B=μH and K=μ _o ω Nπd ² . The first subscript in the field intensity term indicates the axial dimension along which the magnetic field value was determined by accessing the LUT for the given coil set at the LNP, while the second subscript indicates the field-generating coil set. For an x-directed substantially uniform field, the terms H _yz and H _zx are small compared to H _xx . Similar equations are developed below for the induced voltages produced by the unidirectional coils successively generating a y-directed and z-directed substantially uniform field:
V _y =H _xy K sinφcosθ+H _yy K sinφsinθ+H _zy K cosφ,
and
V _z =H _xz K sinφcosθ+H _yz K sinφsinθ+H _zz K cosφ.
The terms H _xy and H _zy in the equation for V _y and the terms H _xz and H _yz in the equation for V _z are small compared to H _yy and H _zz , respectively. After substituting the measured values for the induced voltage signals, the equations are simultaneously solved to determine the unknown variables φ and θ defining the orientation of the sensing coil.

Determining Positional Coordinates of the Sensing Coil

By way of summary, the procedure for determining the positional coordinates of the sensing coil in accordance with the present invention first involves activating each delta coil in succession and measuring the induced voltage thereby developed in the sensing coil. Next, the LUT is accessed to obtain the magnetic field values at the LNP for each specified delta coil. These magnetic field values and the as-computed values for the orientation angles φ and θ are then substituted into the appropriate induced voltage equations to calculate for each delta coil the expected value of the voltage signal induced in the sensing coil. This expected value of the induced signal corresponds to a specific and unique member of the family of constant signal surfaces of the delta coils.

Based on the difference between the measured and expected values for the induced voltage signals, a gradient is calculated (representative of the rate of change of the induced signal) that permits identification of the specific constant signal surface that is responsible for generating the measured value of the induced signal. This procedure is repeated for each delta coil.

For the activation of each delta coil group (comprised of one long coil set and one short coil set), there is an intersection line defined by the intersection of the two constant signal surfaces (which were identified as developing the measured induced signal) on which the sensing coil is located. The intersection of the three such lines from the three delta coil groups uniquely provides the x-y-z coordinates of the sensing coil. Although two such lines are sufficient to describe the position of the sensing coil, greater accuracy and more reliable performance in determining the catheter position is achieved with three lines.

The following is a more detailed discussion of the procedure summarized above for determining the positional coordinates.

The magnetic field pattern generated by the entire assembly of short coil and long coil sets is characterized by a family of surfaces of constant signal or constant voltage developed by the sensing coil, each having non-zero components in two of the axis directions and a small component in the remaining axis direction. For example, the magnetic field surfaces generated by the short and long coil sets oriented at 0° relative to the x-axis have a small value in the x-direction. The short coil positioned at 0° (i.e., SC(0°)) and long coil positioned at 0° (i.e., LC (0°)) are each independently activated. The induced voltage in the sensing coil is measured for each coil set. The LUT is then accessed to determine the magnetic field values for the SC(0°) and LC(0°) coil set at the LNP.

These magnetic field values (i.e., H _x =small and non-zero H _y H _z components) are used in conjunction with the as-computed orientation angles φ and θ to calculate the values of the induced catheter signals that would be expected from such magnetic field values. The expected and measured induced voltage values are compared, and the difference is used to identify the constant signal surface from each of the SC(0°) and LC(0°) coil sets that would have produced the measured induced signals. The intersection of these identified magnetic constant signal surfaces is a line parallel to the x-axis (thereby resolving the y-z coordinates).

The aforementioned procedure involving the long and short coils oriented at 0° is iteratively repeated for a long and short coil set oriented at 120° (i.e., SC(120°) and LC(120°)) and 240° (i.e., SC(240°) and LC(240°)).

More specifically, the coil sets SC(120°) and LC(120°) are sequentially activated to induce corresponding catheter signals in the sensing coil. In order to utilize the LUT data on the coil sets oriented at 0° for determining the magnetic field components at the LNP generated by the coil sets SC(120°) and LC(120°), a modified LNP is calculated that is equivalent to the original LNP rotationally displaced by 120°. The LUT is then accessed with the modified LNP to determine the magnetic field values generated by the SC(120°) and LC(120°) coil sets at the modified LNP. The field vectors produced by the LUT for both the long coil and short coil are then rotated (−120°) to go from the modified LNP to the actual LNP. Based upon these field values, a pair of induced catheter signals are calculated that correspond to the expected signal values arising from the magnetic field values for the SC(120°) and LC(120°) coil sets. The difference between the measured and expected induced catheter signals is used to identify the magnetic constant signal surface for each of the SC(120°) and LC(120°) coil sets that could produce the measured catheter signal. The intersection of these identified magnetic constant signal surfaces is a line oriented at 120° to the x-axis.

A similar procedure is used involving a modified LNP that is rotationally displaced 240° to simulate the magnetic field patterns for the SC(240°) and LC(240°) coil sets using the SC(0°) and LC(0°) field data. A line oriented at 240° to the x-axis is then identified along which the catheter is located.

Each of the field lines oriented at 0°, 120° and 240° to the x-axis is weighted according to the strength of the measured catheter signals. For example, a weak measurement indicates a relatively imprecise identification of the intersection line, resulting in a weaker weighting. This weighting reflects the accuracy of the estimation used to determine the location of the catheter with the specified coil set. An averaging technique is used to compute a weighted estimate of the intersection of the lines L(0°), L(120°) and L(240°). The intersection is the new value for x-y-z and will replace the x-y-z of the old LNP to become the next LNP. The algorithm iteratively repeats the aforementioned operations using the updated LNP to arrive at the location of the sensing coil after each computation cycle (e.g., every 0.1 s).

Magnetic Assembly for Determining Angular Orientation of Sensing Coil

FIG. 1 schematically illustrates a perspective view of an examination deck that facilitates implementation of the location algorithm in accordance with a preferred embodiment of the present invention, and which employs a magnetic coil assembly arranged in a flat configuration. The examination deck includes a planar top platform 10 suitable for accommodating a recumbent patient disposed lengthwise on the planar top. The navigational domain is illustratively depicted as the spherical volume 12 enclosing a sensing coil 14 attached via suitable connection means 16 to an external signal detection apparatus (not shown). The coil sets embedded in platform 10 (and described in connection with FIGS. 2A-C and 3 ) are activated by a signal drive unit (not shown) connected via line 18 . The examination deck is preferably constructed from a suitable magnetically-permeable material to facilitate magnetic coupling between the embedded coil sets and the overlying sensing coil.

Coil Set for Generating X-Directed Field

FIG. 2A schematically illustrates the unidirectional coil set for generating a substantially uniform x-directed field throughout the navigational domain 12 . The coil set includes a first coil pair with elements 20 and 24 and a second coil pair with elements 22 and 26 , where the current flow as supplied by drive unit 28 is indicated by the arrow symbol. Coil elements 20 and 22 are disposed in the major surface of platform 10 , while elements 24 and 26 are disposed in the lateral walls of platform 10 . Elements 24 and 26 are preferably used as compensation coils to substantially cancel undesirable field components generated by elements 20 and 22 in the y- and z-directions. The coils cumulatively generate a substantially uniform x-directed field as indicated by representative field line 27 .

Coil Set for Generating Y-Directed Field

FIG. 2B schematically illustrates the unidirectional coil set for generating a substantially uniform y-directed field throughout the navigational domain 12 . The coil set includes a coil pair with elements 20 and 32 disposed in spaced-apart and parallel relationship within platform 10 , with the indicated current flow as supplied by drive unit 34 . The coils generate a substantially uniform y-directed field as indicated by representative field line 33 .

Coil Set for Generating Z-Directed Field

FIG. 2C schematically illustrates the unidirectional coil set for generating a substantially uniform z-directed field throughout the navigational domain 12 . The coil set includes a first coil pair with elements 36 and 40 and a second coil pair with elements 38 and 42 , with the indicated current flow as supplied by drive unit 44 . Coil elements 36 and 38 are disposed in the major surface of platform 10 , while elements 40 and 42 are disposed in the lateral walls of platform 10 . Elements 40 and 42 are preferably used as compensation coils (e.g., Cunard coils) to substantially cancel undesirable field components generated by elements 36 and 38 in the x- and y-directions. The coils cumulatively generate a substantially uniform z-directed field as indicated by representative field line 43 .

The coil configurations shown in the Figures are only illustrative and should not be construed as a limitation of the present invention, as it should be apparent to those skilled in the art that other coil configurations are possible within the scope of the present invention provided such other configurations produce the desired magnetic field patterns. A suitable connection means (not shown) couples the sensing coil 14 to a signal measuring device.

Magnetic Assembly for Determining Positional Coordinates of Sensing Coil

FIGS. 3 and 5 show the coil configuration used to determine the positional coordinates of the sensing coil in accordance with a preferred embodiment of the present invention. The configuration includes six coils grouped into three pairs of long and short delta coils ( 50 - 52 , 54 - 56 , 58 - 60 ). The delta coils are mutually coplanar and are disposed in the planar top of the examination deck immediately beneath the recumbent patient. Interconnection means between a signal drive unit (not shown) and the delta coil groups is shown representatively for only coils 50 - 52 .

The coils are preferably arranged in a circular orientation about the y-axis such that there is an axis perpendicular to the direction of elongation of the coils at 0°, 120° and 240° relative to the z-axis. The magnetic field generated by the first group of long ( 50 ) and short delta coils ( 52 ) is shown representatively by the field lines extending from the upper region of the coils. The field lines from this delta coil group form the family of constant signal surfaces shown within the navigational domain 12 . Superposition of the constant signal surfaces generated by the long and short coils of a delta coil group produces a fishnet pattern as shown in FIG. 6 . The intersection of two such constant signal surfaces generated by a short and long coil pair is a single line represented by the dotted line 70 .

A constant signal surface ( 72 and 74 ) is identified for each short coil and long coil activation of a delta coil pair by determining the surface that matches the induced signals developed in the sensing coil. This procedure is repeated for the other two delta coil pairs to produce two other lines comparable to line 70 . The intersection of these three lines determines the position of the catheter.

FIG. 7 shows an upper plan schematic view of the entire delta coil arrangement relative to an inner circular space representing the projection of the navigational domain into the plane of the delta coils. It is an object of the present invention to design coils having high spatial gradience in two of the axis dimensions and a substantially zero field value in the remaining axial dimension. This particular design is accomplished by modifying the termination points of the coils with compensation coils such that the modified coil is effectively operative as an infinitely long coil. The long coil sets are further compensated by a central “sucker” coil 88 . Accordingly, each of the long coils and short coils is modified by representative compensation coils 80 - 82 , 84 - 86 , 88 and 90 - 94 , 92 - 96 respectively, disposed at the indicated endpoints and center of the corresponding delta coil. The long coil and short coil configurations are shown schematically for only sets 50 - 52 , but similar configurations likewise exist for the coil sets 54 - 56 and 58 - 60 shown representatively as the indicated lines.

The quality of the coils, as measured by the degree of uniformly of the uniform field coils or how close to zero is the field in the non-gradient direction for the delta coils, determines the size of the navigational domain over which the variable separation technique for navigating the catheter will converge and therefore be capable of initially finding the catheter, and hence be of functional utility.

FIG. 8 schematically depicts an examination deck in accordance with another embodiment of the present invention. The deck includes a first rail member 100 and a second rail member 102 in opposed spaced-apart relationship and attached to the platform along respective supporting edges. The navigational domain is illustratively depicted as the spherical volume 12 . The deck includes an apertured opening 104 . Each rail member has an inner wall and an outer wall. The railed configuration is characterized by the embedding of coil sets in both the planar top and in the rail members. The examination deck is preferably constructed from a magnetically permeable material.

FIGS. 9A-C schematically illustrate the unidirectional coils for implementing the railed configuration used in conjunction with the examination deck of FIG. 8 . The magnet assembly for the x-directed unidirectional coil set is shown in FIG. 9 A and includes two coil elements 110 and 112 each embedded in a respective rail member. Each coil pair is designed to project a substantially uniform field in the x-direction throughout the navigational domain. FIG. 9B schematically depicts the y-directed unidirected coils including coil elements 114 and 116 each embedded in respective rail members, and further including coil elements 118 and 120 embedded in the planar top of the examination deck. FIG. 9C schematically depicts the z-directed unidirected coils including coil elements 122 - 124 in one rail member and elements 126 - 128 in the other rail member. The current flow through each coil configuration is indicated by the arrows. FIG. 9D shows the delta coil arrangement used in the railed configuration. This arrangement is the same as used in the flat configuration described above.

In accordance with another embodiment of the present invention, a second sensing coil is used for stabilization purposes. Inaccurate readings of the catheter probe location may occur from motion artifacts due to breathing action, heart motion, or patient movement. The stabilized location coordinates may be determined by placing a second sensing coil on the sternum of the patient at a known location within the navigational domain. The incremental movement experienced by the second sensing coil due to motion artifacts is detected and subtracted from the measured location value of the probe to arrive at the actual location coordinates of the probe. Further extensions of the present invention are possible to facilitate multi-catheter applications by attaching an additional sensing coil to the distal end of each additional catheter.

Since certain changes may be made in the above apparatus and method without departing from the scope of the invention herein described, it is intended that all matter contained in the above description or shown in the accompanying drawings shall be interpreted in an illustrative and not in a limiting sense.