Electronic anatomical probe

A wire sensing coil is sealed in the tip of an elongate, rigid, plastic probe, and is connected by a coaxial cable releasably to a housing containing a fixed frequency, crystal-controlled oscillator, the output of which is applied through a high impedance resistor and the cable to the coil. The number of turns in the coil and the cable length are carefully selected so that the coil remains tuned to the frequency of the oscillator, except when the tip of the probe approaches a metal object, at which time the voltage drop across the coil decreases. The housing also contains an audible alarm, and a sensing circuit which detects the voltage drop across the coil, and which energizes the alarm when the voltage across the coil drops below a preset or predetermined level. The housing also contains a rechargable battery for supplying power to the oscillator and alarm circuits, and a recharging circuit for recharging the battery. A manually operable switch on the housing connects the battery to the oscillator when the switch is in its ON position, and connects the recharging circuit to the battery when in its OFF position.

BACKGROUND OF THE INVENTION 
This invention relates to an electronic detector for locating metallic 
objects in a human or animal body, and more particularly to a hand 
manipulated probe for use by surgeons and the like for locating metal 
objects hidden from view within a wound or surgical opening. 
One of the major difficulties encountered by surgeons, medical examiners, 
veterinarians, and the like, is the location of foreign objects which have 
entered a body or carcass as a result of a wound or surgical procedure. 
More often than not such objects are metallic (bullets, broken scalpel 
blades, surgical needles, metallic fragments, etc.), and because of the 
particular manner in which they entered the body their exact locations 
cannot be determined simply by observation. In many instances, even when 
multiple X-Ray studies can demonstrate the location of metallic foreign 
objects, physically locating, grasping, and removing these foreign objects 
can be extremely difficult because of limited visibility, limited 
usability of tactile sensations, and limited range of motion of surgical 
instruments within certain areas of the body. Moreover, in many cases the 
urgency of the situation rules out the use of any time-consuming 
procedures for locating the foreign objects. Consequently there is a 
critical need for an instrument which can be used quickly and relatively 
simply to locate foreign metal particles in a wound, surgical opening, or 
the like. 
For example, when a bullet enters a person's body at high speed, it may be 
deflected several times along different paths once it has entered the 
body, thus making it extremely difficult to determine where it finally 
came to rest. For that matter fragments of such an object might be located 
in different parts of the body, and if not completely removed during a 
surgical procedure could result in malpractice litigation against the 
surgeon who was responsible for removing the bullet. Surgeons also face 
the threat of litigation resulting from the accidental loss of surgical 
needles in a patient's body or accidental breakage and loss of metal 
instruments (e.g., the tip of a scalpel blade) during a surgical 
procedure. It is therefore of primary importance that an instrument be 
provided which will enable a surgeon rapidly and accurately to detect 
small metal objects in wounds or surgical openings. 
Heretofore efforts have been made to provide metal detecting instruments of 
the type described and typically such instruments have included an 
electric coil wound within a probe which can be inserted into an incision 
or wound. For example, U.S. Pat. Nos. 2,393,717 and 2,442,805 disclose 
instruments of the type in which the tank coil of one of two oscillators 
is located in the probe. The outputs of the two oscillators are mixed, 
amplified, and applied to a speaker, or the like, which under normal 
conditions produces a low frequency beat note. However, when the probe 
coil approaches a metallic object in a wound or the like, its inductance 
is changed and causes an audible and unmistakable change in the normal 
beat frequency to occur, thereby to denote the presence of the metal 
object. 
In the case of U.S. Pat. Nos. 2,321,355 and 2,321,356, one or more probe 
coils are connected remote from the probe to corresponding balancing 
coils. When the circuit is energized, the probe coils create around the 
outside of the probe a field which, when placed in the vicinity of a metal 
object in a wound, creates an imbalance in the circuit, and thereby 
triggers an indicator to denote the presence of the object. 
Although not concerned with surgical probes, U.S. Pat. No. 3,546,628 
discloses a metal detector of the eddy current killed oscillator variety. 
In this device the detecting coil is the tank coil of an oscillating tank 
circuit. The oscillator circuit normally is tuned at a high frequency 
above the audible range, but when the tank coil is detuned by placing the 
probe near a metal object, the frequency of the output signal drops to an 
audible range. U.S. Pat. No. 3,381,217 discloses a device for detecting 
metal particles in fruit, tobacco, and the like, by using the tank coil of 
an oscillator to detect metal particles in a manner similar to that 
described above. However, the device is designed to be fixed in a 
stationary position adjacent a moving conveyor which advances the fruit or 
tobacco past the detector. 
Other types of detectors are disclosed in U.S. Pat. Nos. 3,460,528, 
3,209,245 and 4,068,189, but appear to be less pertinent to this invention 
than those discussed above. 
One of the major disadvantages of prior such probes is that their 
respective balancing circuits require very careful adjustment each time 
that the associated instrument is to be employed. In an operating room, 
for example, if the device is powered by a conventional AC power supply, 
it must be frequently adjusted to compensate for fluctuations in the 
voltage supply. In those cases where the detection device utilizes a pair 
of oscillators to develop a beat frequency, ambient temperature changes 
also affect the tuning of the reference oscillator and therefore require 
its adjustment prior to using the instrument. Moreover, since the search 
coils employed in such prior devices are frequently subjected to shock 
loading during handling, the tuning of the associated detector circuit 
frequently must be adjusted to compensate for such disturbances. 
The very size of such prior detectors has also been a disadvantage, 
particularly in those cases where time is of the essence, as for example 
in the emergency room of a hospital where the need for handling bulk 
equipment could interfere with proper care of a patient. For the same 
reasons, the patient's care would be neglected if it were necessary to 
take the time to calibrate or properly adjust a detector of the type 
described, prior to being able to use it on a patient. 
It is therefore an object of this invention to provide an improved 
anatomical probe or detector of the type described which is substantially 
more compact and reliable than prior such probes. 
A more specific object of this invention is to provide an improved 
anatomical probe of the type described which does not have to be tuned or 
adjusted each time prior to its use on a patient or the like. 
A further object of this invention is to provide a small, portable, 
battery-operated anatomical probe or detector which ideally is tuned only 
once during its manufacture, and thereafter need not to be readjusted 
prior to its use, during use, or even after repeated use. 
Other objects of the invention will be apparent hereinafter from the 
specification and from the recital of the appended claims, particularly 
when read in conjunction with the accompanying drawings. 
SUMMARY OF THE INVENTION 
A wire sensing coil is wound about a small, cylindrical ferrite core, which 
is sealed by a non-toxic, completely polymerized polymeric substance, such 
as an epoxy resin, in the outer end or tip of a tubular probe, which is 
about the size of a conventional pencil. The coil ends are attached in the 
probe to one end of an elongate (e.g. six feet) coaxial cable, which is 
releasably attached at its opposite end to a housing containing a crystal 
controlled, solid state oscillator. The output of the oscillator is 
connected through a high impedance element, such as a resistor, to one 
side of the coil, the opposite side of which is grounded. 
The oscillator is powered by a rechargable battery, such as a 
nickel-cadmium battery, and when energized rings or shock excites the 
sensing coil at a high frequency in a manner similar to the tank coil of 
an oscillator. At time of manufacture the probe, coil and coaxial cable 
are carefully tuned to the resonant frequency of the oscillator so that 
the voltage drop across the coil remains constant until such time that the 
coil is placed in the proximity of a metal object. When this occurs, the 
resultant change in the coil inductance lowers the voltage drop across the 
coil. This voltage drop is sensed by a comparator circuit in the housing, 
the output of which then energizes both an indicator lamp on the housing 
and an audible warning device located in the housing. 
Also mounted on the housing is a manually-operable ON-OFF switch for 
selectively connecting the battery to the oscillator and detecting 
circuit. The housing contains a recharging circuit and sockets for 
releasably connecting the recharging circuit to an A.C. power supply.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Referring now to the drawings by numerals of reference, and first to FIG. 
1, 10 denotes generally an elongate, rigid probe, which at one end is 
connected by a coaxial cable 12 and conventional connector 13 with the 
upper end of a rectangularly shaped housing 14, which contains the 
hereinafter described battery operated circuit that powers the probe. 
Projecting form the upper end of housing 14 is a manually operable ON-OFF 
switch 15, which controls the supply of power to the probe 10. In one 
sidewall thereof housing 14 contains a screened opening 16, which is 
disposed to register with an audible alarm device that is mounted in 
housing 14 as noted hereinafter. 
Housing 14 has in its lower end a pair of spaced socket elements 17 of 
conventional design, which are employed for releasably mounting the 
housing on the upper end of a battery charging stand 18. This stand, as 
noted in greater detail hereinafter, contains a transformer for use in 
recharging the battery in housing 14. Also projecting from the upper 
surface of housing 14 adjacent the switch 15 are red and green lamp 
elements 19 and 20, respectively, one of which (element 19) is adapted to 
be illuminated when the switch 15 is in its ON position, and the other of 
which (20) is adapted to be illuminated when the probe detects the 
presence of a metallic object. 
The probe 10 comprises an elongate, rigid tube 22 made from a plastic 
material such as a phenolic resin or the like, and which may be coated 
with a fluid impervious plastic that is acceptable for use within the 
human body. Cable 12 extends into one end of tube 22 (the right end 
thereof as shown in FIG. 1) to a point adjacent a counterbore which is 
formed in the opposite end or tip of the tube. Mounted in the counterbore 
end of tube 22 is a cylindrical, ferrite core 23. Wound around the outside 
of core 23 within tube 22 is a wire coil 24, one end of which is connected 
to the central conductor or core wire 25 in cable 12, and the other end of 
which is connected to the shield 26 of the cable to be grounded thereby. 
As noted in greater detail hereinafter, cable 12 is glued or otherwise 
secured against movement in tube 22; and the tip end of the tube is filled 
and sealed with a non-toxic, completely polymerized polymeric substance, 
such as an epoxy resin or the like, which forms a cap or plug 28 that 
secures the core 23 and its winding against movement in the tube 22. 
As shown more clearly in FIG. 2, housing 14 contains a DC power supply 31 
comprising, for example, a ninevolt nickel-cadium battery 32 the positive 
terminal of which is connected by the switch 15 selectively to an ON or an 
OFF terminal. When switch 15 is engaged with the ON terminal the output of 
battery 32 is applied to a voltage regulator 34, the output of which is 
connected through a capacitor C1 to ground, and to a power supply terminal 
36 to maintain the terminal at approximately five volts. Also at this time 
the output of battery 32 is applied through a diode D1, a resistor R1 and 
a light-emitting diode D2 to ground. As shown by broken lines in FIG. 2, 
diode D2 registers with the lamp element 19 in the top of housing 14 to 
illuminate the latter whenever the output of battery 32 is connected to 
terminal 36. 
Terminal 36 supplies the voltage for powering a fixed frequency oscillator 
41, which includes in its circuit a piezoelectric crystal 42 for 
stablizing its output frequency as described in more detail hereinafter. 
The output of oscillator 41 is connected through a high impedance resistor 
R2 (for example one megohm) to the core conductor 25 of the coaxial cable 
12. The result is that a high frequency signal or pulse is applied by the 
oscillator 41 intermittently to the probe coil 24, thereby causing the 
probe to ring at the driving frequency of the oscillator. Moreover, as 
noted in greater detail hereinafter, the probe 10, the cable 12 and its 
connector 13 are carefully selected and assembled so that they are tuned 
to resonate at the oscillator frequency, and therefore do not require any 
further adjustment in the field. As a consequence, when the probe is 
operating and its sensing coil 24 is not near a metallic object, the 
voltage drop across coil 24 remains a constant, predetermined value. 
However, if during use the tip of the probe approaches a metallic object, 
the field generated by coil 24 around the tip of the probe will create 
eddy currents in the object which in turn will alter the inductance of 
coil 24 in such manner that the voltage across the coil will drop. As 
shown in FIG. 2, this voltage drop is sensed by a conductor 44, which is 
connected at one end between the resistor R2 and the wire 25, and at its 
opposite end to one side of a capacitor C2, which forms the input to an RF 
amplifier noted in FIG. 2 by the numeral 45. At its opposite side C2 is 
connected through another high impedance resistor R3 to ground, and to the 
gate terminal of a field effect transistor Q1, which also forms part of 
the amplifier 45. The source terminal of this transistor is connected to 
ground, while its drain terminal is connected through a resistor R4 to the 
five volt power supply, and also to one side of a capacitor C3, which 
forms the input to a detector stage 46. At its opposite side capacitor C3 
is connected to ground through a diode D3 and a resistor R5, which is in 
parallel in diode D3. 
This opposite side of capacitor C3 is also connected to one side of the 
resistor R6, the opposite side of which is connected through a capacitor 
C4 to ground, and to the gate terminal of another field effect transistor 
Q2, which forms part of a direct current amplifier 47. The souce terminal 
of transistor Q2 is connected to ground, and its drain terminal is 
connected through a resistor R7 to the five volt power supply, and to one 
side of a resistor R8. At its opposite side resistor R8 is connected to 
one input of a DC voltage comparator 48, and through a resistor R9 to the 
output 49 of the comparator. The other input of comparator 48 is connected 
through a resistor R10 to a potentiometer P1, which can be adjusted to set 
the reference voltage which must be applied through resistor R8 to the 
first-named input of the comparator in order to maintain a predetermined 
signal level at its output 49. 
The output 49 of comparator 48 is designed to control the energization of 
an alarm device 50, comprising a conventional audio signaling device 52, 
which is connected at one side to a comparator output 49 and at its 
oppsite side to the five volt power supply. This signal device 52, which 
may be of the type sold under the trademark "Sonalert", is positioned in 
housing 14 so that it registers with the screened opening 16, whereby when 
it is energized its high frequency output signal will be clearly audible 
through the housing opening 16. Connected in series with each other and in 
parallel with the audio device 52 are another resistor R11, and a 
light-emitting diode D4 which registers with the lamp element 20. Diode D4 
is energized simultaneously with the audio device 52 whenever the probe 10 
senses a metallic object, thus to provide a visual indication of its 
presence as well as the audible signal provided by the device 52. 
As noted above, the battery 32 is of the rechargeable variety. For this 
reason housing 14 contains a battery charging circuit denoted generally in 
FIG. 2 by the numeral 60, and comprising a pair of banana connectors 61 
located in the sockets 17 at the bottom of the housing, and connected to 
the input of a rectifier 63, which is fixed on a circuit board in the 
housing. One of the outputs of rectifier 63 is grounded at 64 and the 
other output 65 is connected through a capacitor C5 to ground, and to the 
input of a voltage regulator 66. One output of regulator 66 is connected 
through a potentiometer P2 to ground, and the other output, the value of 
which is controlled by the pot P2, is applied by a conductor 67 through a 
capacitor C6 to ground, and through a diode D5 and the resistor R1 to the 
diode D2 which registers with the lamp element 19. The conductor 67 is 
also connected through a resistor R12 and a diode D6 with the OFF contact 
of the switch 15. 
The banana connectors 61 are adapted releasably to be attached by mating 
connectors in the battery charging stand 18 with the secondary coil of a 
step-down transformer T1 of conventional design, which is mounted in the 
stand 18 to supply an AC input of approximately 12 volts to the rectifier 
63. When the connectors 61 are plugged into the stand 18 and switch 15 is 
engaged with its OFF contact (as shown in FIG. 2), the voltage regulator 
66 can produce on line 67 a recharging voltage which is supplied to the 
positive terminal of battery 32, and in an amount determined by the 
setting of the pot P2. The same voltage is applied through the diode D5 
and the resistor R1 to the diode D2, which therefore illuminates the red 
lamp element 19 to indicate to an observer that the battery charging 
circuit is active, and that the battery is being recharged. 
Obviously when the housing 14 is removed from stand 18 the battery charging 
circuit is automatically deenergized. The diode D6 and the resistor R12 
prevent any DC voltage from the battery from causing current flow in the 
reverse direction through the battery charging circuit. 
Referring again to oscillator 41, the five volt power supply for the 
crystal 42 is connected through a capacitor C7 to ground, and a resistor 
R12 and a line 71 to one side of crystal 42. Crystal 42 is connected in 
series with a capacitor C8 and resistor R13, and in parallel with a pair 
of 2-input positive NAND gates G1 and G2, which form part of an integrated 
circuit commonly identified as an IC 7400 of the dual-in-line variety; and 
which is adapted to be powered from the five volt supply in a conventional 
manner (not illustrated). These gates form part of a feed back circuit 
including resistors R14 and R15 connected across gates G1 and G2, 
respectively, and in series with a resistor R16 connected between the 
output of gate G1 and the input of gate G2. 
In the embodiment illustrated in FIGS. 1 and 2, and merely by way of 
example, the cable 12 is approximately six feet in length; the tube 22 is 
approximately six inches long and has a 1/4 inch OD and a 1/8 inch ID; and 
coil 24 comprises approximately seventy-five turns of wire. Sample values 
for the capacitors and resistors disclosed in FIG. 2 are as follows: 
______________________________________ 
Capacitors 
C1 - 22 .mu.fd C5 - 22 .mu.fd 
C2 - .05 .mu.fd C6 - .47 .mu.fd 
C3 - .05 .mu.fd C7 - .47 .mu.fd 
C4 - .05 .mu.fd C8 - 15 pfd 
Resistors (.OMEGA.) 
R1 - 1K R6 - 1 Meg R11 - 1K 
R2 - 1 Meg R7 - 1.8K R12 - 5.6K 
R3 - 1 Meg R8 - 10K R13 - 270 
R4 - 1K R9 - 10 Meg R14 - 580 
R5 - 4.7 Meg R10 - 10K R15 - 1.8K 
R16 - 240 
______________________________________ 
As noted above, one of the features of the invention is the fact that the 
probe 10 and its associated coaxial cable 12 and connector 13 are designed 
at the time of manufacture to be tuned to the frequency of the signal 
output of the oscillator 41. In this connection these elements form an 
assembly which functions as the tank circuit of the oscillator, and once 
they have been tuned to the oscillator frequency, the pot P1 can be 
adjusted to require that the alarm device 50 be deenergized until such 
time that the voltage drop across the sensing coil 24 is lowered or 
diminished by a predetermiend value. In the embodiment illustrated, once 
this voltage has dropped below a predetermined value the output 49 of the 
comparator 48 drops to a value that permits the alarm device 50 to be 
energized, and to remain energized until the drop across probe 24 once 
again increases to the set point value as determined by pot P1. 
In point of fact, the probe assembly (probe 10, cord 12, connector 13) is 
tuned approximately to the f.sub.d or driving frequency of the oscillator 
41, and this tuning can be effected by adjusting the number of turns in 
the sensing coil 24. The reason for this is better explained by reference 
to FIGS. 3 and 4, wherein point A denotes a properly tuned probe assembly 
(10, 12, 13) and points B and C denote improperly tuned probe assemblies. 
The number of turns in the coil 24 represented by point A is such that the 
drop across the coil has a value slightly less than the maximum voltage 
capable of being produced in the coil by the oscillator circuit, and more 
importantly, this voltage is on the downside of the voltage-frequency 
curve (FIG. 3), so that as the coil 24, represented by point A, approaches 
a metal object, the drop across the coil 24 will steadily decrease. 
Each of the probe assemblies represented by points B and C, on the other 
hand, has too few turns in its probe coil 24, so that when the latter 
approaches a metallic object the voltage drop across the coil 24 will 
increase slightly (see arrows in FIG. 3) before decreasing. Assuming that 
the alarm 50 has been set to be energized when the probe voltage reaches 
the value indicated by the broken lines in FIGS. 3 and 4 the probe 
assembly denoted by C would be entirely unsatisfactory because it normally 
would energize the alarm, and would momentarily deenergize the alarm as 
the probe coil 24 approached a metallic object. 
As shown by FIG. 4, the probe assembly denoted by point B likewise would 
not be satisfactory because it would not be anywhere as near as sensitive 
as the probe assembly represented by point A. Since the voltage across the 
assembly denoted by point A steadily drops as its coil 24 approaches a 
metallic object, it would trigger the alarm 50 at a distance d.sub.A from 
the object, while the probe coil represented by point B would have to 
reach the lesser distance d.sub.B before triggering this alarm. 
During construction, a probe assembly 10, 12 and 13 can be tuned before 
fixing the core 23 in tube 22 by attaching the connector 13 to housing 14 
before the latter is sealed closed. A high input impedance voltmeter is 
connected at one side to the juncture of R7, R8 and the drain of Q2, and 
at its opposite side to ground. The turns of coil 24 are then adjusted 
(increased or decreased) until the voltage indicated by the meter begins 
to drop as the probe coil is moved into the vicinity of a metallic object. 
The pot P1 is then adjusted to set the alarm voltage which will be 
required across coil 24 in order to energize alarm 50. The voltmeter is 
then removed, and the housing is closed; the coil 24 is fastened by a glue 
to the core; and the core and one end of the cable are vacuum potted or 
otherwise secured in tube 22 with an epoxy resin filler of the type noted 
above, thereby to seal the core, coil and cable against movement in the 
tube. This construction causes the probe assembly 10, 12 13 to remain 
tuned (as at A in FIG. 3) throughout its use. 
From the foregoing it will be apparent that the present invention provides 
an extremely compact and reliable probe for detecting metal objects in 
human and animal bodies. The probe coil 24 is shock excited by the output 
of the oscillator 41, and unlike most prior art sensing devices, although 
it generates a sinusoidal wave it is not driven with a sinusoidal wave. 
The distributed capacitance represented by the fixed length of the probe 
assembly is connected in parallel with the inductance represented by the 
coil 24, and together they function as the tank circuit for the 
oscillator. As a consequence, if the probe assembly 10, 12, 13 is tuned 
exactly to the oscillator output, the current flow through coil 24 
normally will be at a minimum, and the voltage drop thereacross at a 
maximum, as shown in FIG. 3. However, by pre-tuning the assembly as noted 
above--i.e., by selecting the number of turns in the coil 24 so that its 
inductance normally causes the voltage drop across the coil to be slightly 
less than said maximum (point A in FIG. 3)--it has been possible to 
produce an extremely sensitive probe, and one which does not require any 
adjustment prior to its use. The only manual operation required is the 
manipulation of the ON-OFF switch in order to energize or deenergize the 
device. 
The high input impedance RF amplifier 45 serves to isolate the loading 
effects of the detector unit 46 from the probe circuit or coil. Likewise, 
the high input impedance DC amplifier 47 serves to isolate the comparator 
48 from the detector unit 46. The probe and detector circuits thus remain 
stable and produce no change in the output of the comparator 48 until such 
time that the coil 24 detects the presence of a metallic object. The 
distance between the coil 24 and the metallic object required to trigger 
the alarm 50 will, of course, depend to a greater extent upon the overall 
power supply of the system, and also upon the set point established by the 
pot P1. 
Still another advantage of this probe device is that it is very small and 
portable. The probe itself, as represented by the phenolic tube 22, need 
be no larger than the size of a pencil. By sealing the tube 22, with a 
plastic coating compatible to the human body (e.g., Teflon, nylon, etc.) 
the tube can be protected from body fluids and solids, and is readily 
sterilizable by use of a gas sterilization agent, or the like. Moreover, 
it will be readily apparent to one skilled in the art that by proper 
selection of the plastic from which the probe is made, it might even be 
capable of withstanding sterilization by radiation or auto-claving, or may 
be inexpensive enough to warrant the manufacture of disposable probes. 
Moreover, although in practice the probe is pretuned as noted above, it 
would be possible also to connect to line 44 a small, variable capacitor 
C.sub.x, such as shown in phantom by broken lines in FIG. 2, which would 
be adjustable from the exterior of housing 14 to correct any undesirable 
detuning that might occur because of temperature changes or replacement of 
the probe, cable, connector assembly (10, 12, 13). 
While this invention has been illustrated and described in detail in 
connection with only certain embodiments thereof, it will be apparent that 
it is capable of still further modification, and that this application is 
intended to cover any such modifications as may fall within the scope of 
one skilled in the art or the appended claims.