Title:
Electronic surgical metal body locator
United States Patent 2393717


Abstract:
This application relates to a device for locating foreign metal bodies in living tissue. More specifically it relates to a surgical metal body locator adapted to serve, alone, or as an adjunct to known X-ray and fluoroscope means, for locating metal bodies in living tissue. An object of the...



Inventors:
Speaker, David M.
Application Number:
US54073344A
Publication Date:
01/29/1946
Filing Date:
06/16/1944
Assignee:
Speaker, David M.
Primary Class:
Other Classes:
324/236, 324/328, 324/655, 331/37, 331/134, 600/11, 600/12, 600/13, 600/550
International Classes:
G01V3/10
View Patent Images:



Description:

This application relates to a device for locating foreign metal bodies in living tissue. More specifically it relates to a surgical metal body locator adapted to serve, alone, or as an adjunct to known X-ray and fluoroscope means, for locating metal bodies in living tissue.

An object of the invention is to provide a simple, practical and efficient locator of the above mentioned kind.

Another object of the invention is to provide a metal body locator for surgical use, which will have high sensitivity to non-ferromagnetic as well as to ferromagnetic metal.

Another object of the invention is to provide such a device which will have high accuracy of localization.

Another object -of the invention is to provide a device of the kind described which is adapted to indicate to the operator in a clear and definite manner the position of a foreign metal body with respect to a probe forming part of the device.

Another object of the invention is to provide a metal body locator wherein small changes in the fundamental frequency will produce relatively great changes in the frequency of a harmonic thereof.

Other objects of the invention will be in part obvious or in part pointed out hereinafter.

The invention accordingly consists in the features of construction, combinations of elements, arrangements of parts, and in the several steps and relation and order of each of said steps to one or more of the others thereof, all as will be pointed out in the following description, and the scope of the application of which will be indicated in the following claims.

The invention will best be understood if the following description is read in connection with the drawings, in which: Figure 1 is a view of a circuit representing one embodiment of my device; Figure 2 shows the circuit of Figure 1 modified by the insertion of a harmonic amplifier between B and C; Figure 3 shows another modification of the circuit of Figure 1 in which a multi-vibrator is inserted between B and C; Figure 4 is a fully schematic representation of a circuit similar to that shown in Figure 1 but showing an amplifier tube added to the circuit of Figure 1 between B and E; Figure 5 is a view similar to Figure 4 but showing amplifying means inserted between E and C; and Figure 6 is a view of a modification of circuits I to 5 inclusive wherein a single tube combining the functions of the separate crystal oscillator and mixer shown in the previous figures is substituted for the said separate crystal oscillator and mixer.

In the embodiment of the invention indicated in Figure 1 a source of stable high frequency oscillations such for example as crystal oscillator A, which may be a tube of the 6V6 type, and a negative transconductance type of oscillator, such for example as transitron oscillator B (see "The Radio Engineering Handbook," McGraw Hill Book Co., Inc. 1941, 3rd Edition, page 302, and "Ultra-High-Frequency Techniques," D. Van Nostrand Co., Inc., 1942, pages 192, 193, and 194), which may be a tube of the 6A8 type, are shown connected to a mixer tube C, which may be of the 6SA7 type. As will be explained, the transitron oscillator B includes a parallel tuned circuit 10 the coil II of which is contained within a tubular envelope or probe 12, which is moved over the patient's body, and into any incision made to locate the exact position of a foreign metal body, such as a bullet, piece of shrapnel, or a fragment of a needle, or the like. The mixer tube C is in turn connected to a frequency indicating device adapted to inform the operator of changes in beat frequency which occur in the output of the mixer tube due to changes in the harmonic frequency of the transitron oscillator B resulting from changes in the inductance of the tuned circuit 10 depending on the proximity of the said probe to the metal foreign body. 'The frequency indicating device may be adapted to give auditory or visual signals to the operator as desired, and may be for example a set of ear-phones 13a, a loud speaker 13, or a visual signal device 13b.

Preferably the frequency indicating device is connected to the mixer tube C through an amplifier 14. As oscillators and mixing tubes of the type referred to are well known and no claim is made to them per se they are not individually described in detail herein but only as parts of the circuits disclosed and claimed herein.

The frequency of oscillator A may desirably be in the three to four megacycle range. The alternating voltage generated at this frequency in the secondary winding of the tank coil 15 is supplied to the grid 16 of the mixer tube C. The high frequency signals of oscillator A are mixed in the mixer tube C with the frequency of the negative transconductance type oscillator B which is supplied to grid 17 of the mixer tube C. The fundamental frequency of oscillator B is determined by the parallel tuned circuit 10, and is somewhat above the audio range, being of the order of 25 kc. to 40 kc. The wave shape in the plate circuit of oscillator B (across 18) is distorted intentionally (through choice of component values). The harmonic component selected is mixed, as previously described, with the reference high frequency signal from oscillator A.

A small change in the fundamental frequency of oscillator B will produce a relatively great change in the harmonic, and this change will be equal to the change produced in the fundamental multiplied by the ratio of the frequency of the harmonic to that of the fundamental. In this way the apparatus is made sensitive to small changes in the fundamental frequency of oscillator B. In practice, before the probe 12 is brought close to the site of exploration, tuning condenser 14a of tuned circuit 10 is adjusted to produce a low frequency beat note. If the probe coil II is now brought near metal a perceptible and unmistakable variation in the beat note will occur. If the metal is ferromagnetic its proximity will increase the inductance of coil II and hence raise the fundamental frequency of oscillator B. If the metal is not ferromagnetic the eddy current losses induced in it will behave as a reflected resistance in the tuned circuit 10 and thus vary the fundamental frequency. This variation of the fundamental due to a small metallic object is small in magnitude, but the frequency shift is magnified through utilization of the harmonic as explained above.

The ratio of capacity to inductance in the tuned circuit 90 is rather high. The tuning capacity is made relatively large so that the effects of the capacity between the tissues being explored with the probe and the probe coil II will not in themselves seriously affect the fundamental frequency of oscillator B. Tuning condenser 14a may include a small air trimmer (not shown) condenser with which these effects may be balanced if desired.

Preferably the coil II is so wound, that the ground end represents the end of the winding (outside). A certain amount of shielding is automatically achieved in this way.

Between the mixer tube C and the amplifier 14 a low pass filter comprising resistance 19 and condenser 20, is preferably provided to remove from the mixer output frequency components other than the audio beat note.

The frequency indicator serves to give the operator an indication of the direction and distance of the metal body from the probe. As the probe approaches the metal body the rate at which the frequency changes increases. As the probe is moved away from the metal body the rate of change in frequency decreases. After relatively little experience with the device the operator is able to estimate very accurately the distance between the probe and the metal body, particularly if the approximate size of the metal body is known through prior X-ray studies, the sensitivity of the circuit being somewhat higher for large than for small particles. If desired the tuned circuit 10 may contain a plurality of coils II, which may be of different size and may be individually enclosed in probes of different size so that a larger probe may first be used to locate the general position of the foreign metal body, after which a smaller probe may be employed to locate the metal body with greater precision. A probe 12 may conveniently be made of Lucite or a like material adapted to conduct light from a source provided In the handie or body of the probe to the point of the probe to facilitate explorations with the probe, as for example in an incision.

If a loud speaker 13 or head receiver set 13a are used as the frequency indicating device, the change in the frequency of the audible tone is easily detected, and similarly if a visual indicator 13b is employed the movements thereof are ample to be easily read and noted by the operator.

In Figure 2 a harmonic amplifier D is shown inserted between transitron oscillator B and the mixer tube C, by which the harmonic of the output of oscillator B may be amplified before it is supplied to the mixer tube C thereby decreasing the amount to which the output of the mixer tube need be amplified. The harmonic amplifier may be a tube of the 6SJ7 type and is not described in detail herein since it is well known.

In Figure 3 a further modification is shown in which a multi-vibrator E is connected between the transitron oscillator B and the mixer tube C.

In the circuit of Figure 2 the harmonic amplifier D serves to amplify the harmonic of the transitron oscillator which is directly mixed with the high frequency signal supplied by the crystal oscillator A. In the circuit of Figure 3, however, the harmonic frequency which is mixed with the high frequency signal of oscillator A is supplied by the multi-vibrator E, and the transitron oscillator B, instead of providing the harmonic frequency, is utilized to stabilize the frequency of the multi-vibrator E. The multi-vibrator E is so designed as to oscillate at a frequency corresponding to a multiple of the oscillator B, and may be a tube of the 6SN7 GT type. The harmonic of the multi-vibrator E is mixed with the signal from oscillator A. Without the multi-vibrator a very high order of harmonic of oscillator B would be required. By operating the multivibrator so that its fundamental frequency is a multiple of the fundamental frequency of oscillator B a multi-vibrator harmonic, of considerably lower order than the harmonic which would be necessary without the multi-vibrator, may be used for mixing with oscillator A, and hence less amplification is required in the circuit of Figure 3 following the mixer tube C, than is required in the circuit of Figure 1.

If desired an amplifier tube 21 may be employed between oscillator B and the multi-vibrator E (so-called buffer stage) in the circuit of Figure 3 (see Figure 4) to isolate B from E and thereby prevent undesired interaction. Similarly a harmonic amplifier 22 may be employed if desired between the multi-vibrator E and the mixer tube C (see Figure 5), to both increase the amplitude of the desired harmonic and to tend to suppress undesired frequency components otherwise transmitted to mixer tube C.

In Figure 6 I have shown another embodiment of my invention in which the functions of the crystal oscillator A and the mixer C are consolidated in the single tube F. This substitution may be made in the circuit of any of the circuits of Figures 1 to 5 inclusive. For combining the functions of a crystal oscillator and a mixer in a single tube I employ any known type of tube, such for example as a 6K8 type, which is known as a frequency converter or conventionally a "converter." Since tubes of the 6K8 type are well known I will not describe it in detail herein, as no claim is made to such tube per se. The frequency converter tube F illustrated herein consists of two parts having the common cathode 23. One part is a triode section comprising the grid 24 and plate 25 In addition to the cathode 23. The other part includes, in addition to cathode 23, the plate 28 and four grids 27, 28, 29, and 30. The grid 27, which is nearest cathode 23 is connected to grid 24 of the triode section. Grids 28 and 38 serve to shield grids 27 and 29 from each other and thus prevent interaction between the circuits associated with grids 27 and 29 respectively. Interconnected grids 24 and 21 are connected with crystal oscillator 31 which is connected with plate 25 through the tuned circuit 32. Grid 29 is supplied by the source of harmonic frequency which is employed. It may thus be supplied by a negative transconductance type of oscillator such for example as a transitron oscillator shown in Figure 1, or by a harmonic amplifier coupled with a negative transconductance type of oscillator, as shown in Figure 2. Or it may be connected with a multi-vibrator which in turn may be connected with a negative transconductance type of oscillator as shown in any one of Figures 3, 4, and 5 inclusive. If the source of harmonic frequency is supplied through a harmonic amplifier, as shown in Figure 2, the circuit will include a tuned circuit. If the connection from the source of harmonic frequency does not include a harmonic amplifier the tuned circuit may be provided intermediate the source of harmonic frequency and grid 28 to select the particular harmonic desired and to reject unwanted frequencies.

The output beat frequency signal from plate 26 of combined crystal oscillator and mixer F is coupled, through plate resistor 33 and plate coupling condenser 34, with amplifier 14 which is in turn connected with a frequency indicating device 13.

It will be understood that by my invention, various modifications of which are described above, a surgical metal body locator is provided which has high sensitivity to non-magnetic as well as to magnetic metals; which has high accuracy of localization and is characterized by the fact that as the probe is moved so that its longitudinal axis is placed in line with the objects to be detected, a very perceptable change in audio tone (or visual signal) is noted; and which is adapted to give the operator'a dependable indication of the distance of the metal body from the probe.

It will thus be seen that there has been provided by this invention a method, apparatus, and an article in which the various objects hereinabove set forth together with many thoroughly practical advantages are successfully achieved.

As various possible embodiments might be made of the mechanical features of the above invention and as the art herein described might be varied in various parts, all without departing from the scope of the invention, it is to be understood that all matter hereinbefore set forth or shown in the accompanying drawings is to be interpreted as illustrative and not in a limiting sense.

What I claim is: 1. The method of locating an invivo foreign metal body which comprises mixing a high harmonic of a stable source of electrical oscillations with a high frequency signal from another source of electrical oscillations so as to produce a beat note in the audio range, connecting to said first mentioned source of oscillations a tuned circuit including a coil located in a movable probe, connecting said mixing means to a frequency indicating device, and moving said coil in a direction to obtain increased beat frequency variation of the indicator response.

2. The method of locating a foreign metallic body in living tissue which comprises mixing a harmonic produced by a stable source of electrical oscillations somewhat above the audio range with a high frequency signal from another source of electrical oscillations well beyond the audio range, and thereby producing a beat note in the audio range, controlling the fundamental frequency of said first mentioned source of oscillations by means of a tuned circuit connected in parallel therewith and including a movable coil, in rerposing a harmonic amplifier between said first source of oscillations and the said mixing step thereby amplifying the harmonic of the output of the said first source of oscillations, and utilizing the said beat note resulting from said mixing step to actuate a frequency indicator, and moving said coil in a direction to obtain increased beat frequency variation of the indicator response.

3. The method of locating a metal foreign body in living tissue which comprises mixing a harmonic of a frequency produced by a multi-vibrator with a high frequency signal, controlling the frequency of the multi-vibrator by connecting it to an oscillator of the negative transconductance type, connecting the latter with a tuned circuit the coil portion of which is contained in a tubular envelope or probe, moving the probe and thereby modifying the frequency of said negative transconductance type of oscillator according to changes in the inductance of the coil of said probe, amplifying the beat note produced by mixing the harmonic frequency of the multi-vibrator with said high frequency signal, and utilizing the said amplified impulse to operate a frequency indicator or meter.

4. An electronic surgical metal body locator comprising a tuned circuit, means for probing having therein a coil connected in said tuned circuit, an oscillator of the negative transconductance type connected to said tuned circuit, and oscillator means adapted to produce a high frequency signal, means for mixing the frequencies of said oscillations to produce an output beat frequency signal, a frequency indicating device, and an amplifier between said mixing means and said signalling device.

5. An electronic surgical metal body locator comprising, a mixer tube having a grid connected to a crystal oscillator, and having another grid connected to a transitron oscillator through a harmonic amplifier, a frequency indicating device connected to said mixer tube through an amplifier, and a tuned circuit connected to said transitron oscillator and including a coil enclosed in a tubular envelope permitting it to be moved c0 and to thereby modify the frequency of said transitron oscillator according to changes in impedance of said tuned circuit depending on the position of said tubular envelope relative to said metal body.

6. An electronic surgical metal body locator comprising an electrical circuit including, a mixer tube having a grid connected to a crystal oscillator, and having another grid connected to a multi-vibrator which is in turn connected to a transitron oscillator, said multi-vibrator being so designed as to oscillate at a frequency corresponding to a multiple of the fundamental of said transitron oscillator, a tuned circuit connected to said transitron oscillator including a 76 coil contained in a tubular envelope, a device for indicating changes in frequency, and amplifier means intermediate said mixer tube and said indicating device.

7. An electronic surgical metal body locator comprising an electrical circuit including, a mixer tube, connected between a crystal oscillator, and, a multi-vibrator which is in turn connected to a transitron oscillator, said multi-vibrator being so designed as to oscillate at a frequency corresponding to a multiple of the fundamental of said transitron oscillator, a tuned circuit connected to said transitron oscillator and including a coil contained in a tubular envelope, a device for indicating changes in frequency, and amplifier means between said transitron oscillator and said multi-vibrator.

8. An electronic surgical metal body locator comprising an electrical circuit including, a mixer tube connected between a crystal oscillator, and a multi-vibrator which is in turn connected, to a transitron oscillator, said multi-vibrator being so designed as to oscillate at a frequency corresponding to a multiple of the fundamental of said transitron oscillator, a tuned circuit connected to said transitron oscillator including a coil contained in a tubular envelope, a device for indicating changes in frequency, connected to said mixer tube and a harmonic amplifier between said multi-vibrator and said mixer tube.

9. An electronic surgical metal body locator comprising a tuned circuit including a coil, at least the said coil of said tuned circuit being enclosed in a tubular envelope, said tuned circuit being connected in parallel, by a flexible conductor, with a stable source of oscillations the fundamental frequency of which is determined by said parallel tuned circuit, a constant high frequency source, means for mixing the output of the harmonic of said fundamental frequency source with the output of said constant high frequency source, and means for indicating changes in the frequency of the output of said mixing means.

10. In combination with an electrical circuit for locating foreign metal- bodies in living tissue which includes a multi-vibrator and a crystal oscillator connected through the medium of a mixer tube, the use of a negative transconductance type of oscillator to provide a stable reference frequency for the output of said multivibrator.

11. In combination in an electrical circuit for locating foreign metal bodies in living tissue Which includes a plurality of sources of oscillations and means for mixing the frequencies of said oscillations to produce an audible beat note, the use of a negative transconductance type of oscillator to provide a harmonic component to be mixed with the frequency of said other oscillator, whereby a small change in the fundamental frequency of said negative transconductance type oscillator will produce a relatively great change in the frequency of the harmonic mixed with the frequency of said other oscillator. 12. An electronic surgical metal body locator comprising, a crystal oscillator, and a negative transconductance oscillator, both feeding into a mixer stage, and a high frequency indicator, the electronic tube elements of the crystal oscillator and the electronic tube elements of the mixer being enclosed in a single envelope, said high frequency indicator being connected to the plate included in the said electronic tube elements of the mixer to indicate the' frequency of the output beat signal resulting from the mixing of the frequency of said crystal oscillator with the harmonic of said negative transconductance oscillator.

DAVID M. SPEAKER.