US2393717A - Electronic surgical metal body locator - Google Patents

Description

C 4 Sheets-Sheet l Jan. 29, 1946. D. M. SPEAKER ELECTRONIC SURGICAL lMETAL BODY LOCATOR Filed June 16, 1944 H. y QM A BY Q f l ATTORNY? Jan. 29, 1946. D. M. SPEAKER ELECTRONIC SURGICAL METAL, BODY LOCATOR i.

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UNITED STATES PATENT OFFICE ELECTRONIC SURGICAL METAL BODY LGCATOR David M. Speaker, East Orange, N. J.

Application June 16, 1944, Serial No. 540,733

(Cl. 128-L5) 12 Claims.

This application relates to a device for locating foreign metal bodies in living tissue. More specifically it relates to a surgical metal body lo'- cator adapted to serve, alone, or as an adjunct and mixer shown in the previous figures is substituted for the said separate crystal oscillator to known X-ray and uoroscope means, for loand mixer. V cating metal bodies in living tissue'.A In the embodiment of the invention indicated An object of the invention is to provide-av in Figure 1 a source of stable high frequency simple, practical and eiiicient locator of the above oscillations such for example as crystal oscillator mentioned kind. A, which may be a tube of the 6V6 type, and a 4Another object of the invention is to provide l0 negative transconductance type of oscillator, such a metal body locator for surgical use, which will for example as transitron oscillator B (see The have high sensitivity to non-ferromagnetic as Radio Engineering Handbook, McGraw Hill well as to ferromagnetic metal. Book Co., Inc. 1941, 3rd Edition, page 302, andl Another object of the invention is to provide Ultra-High-Frequency Techniques, D. Van

such a. device which will have high accuracy of l5 Nostrand Co., Inc., 1942, pages 192, 193,-and 194), localization. which may be a tube of the 6A8 type, are shown Another objectof 'the invention is to provide connected to a mixer tube C, which may be of a device of the kind described which is adapted the 6SA7 type. As will be explained, the transito indicate to the operator in a clear and definite tronv oscillator B includes a parallel tuned circuit -manner the position of a foreign metal body with I0 -the coil II of which is contained within a turespect to a probe forming part of the device. bular envelope /or'probe I2, which is moved over- Another object of the invention is to provide the patients body, and into any incision made a metal body locator wherein small changes in to locate the exact positionof a foreign metal the fundamental frequency will produce relatively body, such as a. bullet, piece of shrapnel, or a, fraggreat changes in the frequency of a harmonic ment of a needle, or the like. The mixer tube thereof. l C is in turn connected to a frequency indicating Other objects of the invention will be in part device adapted to inform the operator of changes obvious or in part pointed out hereinafter. in beat frequency which occur in the output of The invention accordingly consists in the feathe mixer tube due to changes in the harmonic 'tures of construction, combinations of elements, 30 frequency of the transitron oscillator B resulting arrangements of parts, and in the several steps from changes in the inductance of the tuned cirand relation andorder of each of said steps to cuit I0 depending on the proximity of the said one or more of the others thereof, all as will be probe to the metal foreign body. The frequency pointed out in the following description, and the indicating device may be adapted to give audiy scope of the application of which will be inditory or visual signals to the operator as desired, cated in the following claims. and may be for example a set of ear-phones I3a,

'I'he invention will best be understood if the a loud speaker I3, or a visual signal device |3b. following description is read in connection with Preferably the frequency indicating device is conthe drawings, in which: nected to the mixer tube C through an amplifier Figure 1 is a view of a circuit representing one 40 Il. As oscillators and mixing tubes of the type embodiment of my device; referred to are ywell known and no claim is made Figure 2 shows the circuit of Figure 1 modified to them per se they are not individually described by the insertion of a harmonic amplifier between in detail herein but, only as parts of the circuits B and C; y disclosed and claimed herein.

Figure 3 shows another modification of the cir- *45 The frequency of oscillator A may desirably be cuit of Figure 1 in which a multi-vibrator is inn the three to four megacycle range. vThe alterserted between B and C; nating voltage generated at this frequency in the Figure 4 is a fully schematic representation of secondary winding of the tank coil I5 is supplied a circuit similar to that shown in Figure 1 .but to the grid I6 of the mixer tube C. The high showing an amplifier tube added to-the circuit of frequency signals of oscillator A are mixed in Figure 1 between B and E; the mixer tube C with the frequency of the nega- Figure 5 is a view similar to Figure 4 but showtive transconductance type oscillator B which is ing amplifying means insertedbetween E and C; supplied to grid II of the mixer tube C. v'The and fundamental frequency of oscillator B is deter- Figure 6 is a .view of a modification of circuits 55 mined by the parallel tuned kcircuit I0, 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 I8) 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 t 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 Abrought near metala perceptible and unmistak-v able variation in the beat note will occur. If the If a loud speaker I 3 or head receiver set Ia are used as the frequency indicating device, the

' change in the frequency of the audible tone is metal is ferromagneticits 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 i0 and thus Vary the.fund a mental 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 I0 is rather high. The tuning capacity is made relativelylarge so that the effects of the capacity between the tissues being explored with the probe and the probe coil i I will not in themselves seriously affect the fundamental frequency of oscillator B. Tuning condenser Ila may include a small air trimmer (not shown) condenser with which these effects may be balanced if desired.,

Preferably the coil II is so woundthat the ground end represents the Aend of the winding (outside) A certain amount of shielding is auto-V matically achieved in this way.

Between the mixer tube C and the amplifier I4 a low pass filter comprising resistance I9 and condenser 20, is preferably provided to remove 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 I0 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 I2 may conveniently be made of Lucite or a like material adapted to conduct light from a source provided in the han- As the probe is moved away from the metal body the solidated in the single tube F.

easily detected. and similarly 1r a visual indicator I3b is employed the movements thereof are amput of oscillator B may be amplified before it isy 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 modication 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 ampliner 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 correspending 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 fundamentalfrequency isa multiple of the fundamental frequency of oscillator B a multi-vibrator harmonic, of consider-l If desired an amplifier tube 2I 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 thereblr preventundesired interaction. Similarly a har monic amplier 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 undesiredfrequency 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 con- 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 converten 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 circuits `associated with grids 21 and 29 respectively. Interconnected grids 2| and 21 are connected with crystal oscillator 3| which is conaaosm'r f netted with plate z5 through the tuned circuit connected with a multi-vibrator which in turn may be connected with a negative transconductance type of oscillator as shown in any one of Figu'es 3, 4, and 5 inclusive. If the'. source of harmonic frequency is supplied through a har-l monic 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 o f harmonic frequency and grid 28 to select the particular harmonic desired and to reject unwanted frequencies. Y

The output .beat frequency signal from plate 2B of combined crystal oscillator and mixerF is -coupled,qthrough plate resistor 33 and plate coupling condenser 34, with amplifier I4 which is in turn connected with a frequency indicating device i3.

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 accuracyof localization and is characterized by the fact that as the probe is moved so thatits 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 lfrom the probe.

It will thus be seen that there has been provided by this invention a method, apparatus, andan article in which the various objects hereinabove set forth together with many thoroughly practical advantages are successfullyv achieved. As various possible embodiments might be made of the mechanical features of the above invention and asthe 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. f v

What I claim is: I

1. The method of locatingan invivo foreign vmetal body which comprises mixing a high har-l monic 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 to obtain increased beat frequency variatlonof the indicator response. Y

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 tunedcircuit connected in parallel therewith and including a movable coil, in .zerposing a harmonic amplier 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 indicatonand 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, controllingthe frequency of the multi-vibrator by connecting it 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, andoscillator means adapted to produce a high fre.- quency 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 vharmonic 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 vin a tubular envelope permitting it to be movedv and to vthereby modify the. frequency of said transitron oscillator according to changes in impedance of said tuned circuit depending on the position of said tubular enveloperelative to said metal body.

comprising an electrical circuit including, a. mixer tube having a grid connected to a crystal oscilmentioned source of oscillations a tuned circuit including a coil located in a movable probe, connecting said mixing means to a. frequency indilator, and having another grid connected to -a multi-vibrator 'which is in turn connected to a `transitron oscillator, said multi-vibrator being so designed las to oscillate at a frequency corresponding to a multiple of the Afundamental of said transitron oscillator, a tuned circuit conlnectedto said transitron oscillator including a coil contained in a tubular envelope, a device 6. An electronic surgical metal body locator 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 correspondingto a multiple of ythe fundamental of said transitron oscillator,v a tuned circuit, connected to s aid 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 locatoi` comprising an electrical circuit including, a mixer tube connected between a crystal oscillator, and

a'multi-vibrator which is in tum 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 saidtransitron oscillator, a tuned circuit connected to said transitron oscillator including a coil contained in atubular 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 sourceof 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 metalbodies 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. 'v

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 yoscillator 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 plateA 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.

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