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Claims  |
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What is claimed is:
1. Apparatus for determining the location of an object adapted to be
inserted into the body of a patient, which comprises:
a transmitter, the transmitter including an oscillator for generating a
transmit signal, and a transmit coil coupled to the oscillator for
transmitting a signal corresponding to the transmit signal;
a receiver, the receiver including a receive coil for receiving the signal
transmitted by the transmitter by mutual inductance between the two coils,
means for processing the signal received by the receive coil, one of the
transmit coil and the receive coil being situated on the object adapted to
be inserted into the patient's body, and the other of the receive coil and
the transmit coil being located externally to the patient's body, the
processing means providing an output signal which varies in accordance
with the strength of the signal received by the receive coil and detecting
the distance the transmit coil is form the receive coil based on the
strength of the signal received by the receive coil, the receiver further
including display means coupled to the processing means for indicating at
least the relative distance which the transmit coil is from the receive
coil, whereby the location of the object adapted to be inserted into the
patient's body may be located; and
means for controlling the strength of the signal transmitted by the
transmit coil in response to the output signal of the processing means of
the receiver, the control means being operatively coupled to the
processing means.
2. Apparatus for determining the location of an object adapted to be
inserted into the body of a patient, which comprises:
a transmitter, the transmitter including an oscillator, the oscillator
generating a first signal, means responsive to the first signal of the
oscillator for controlling the level of the first signal in accordance
with the strength of a signal received by a receiver operatively linked to
the transmitter and providing a second signal, and a transmit coil
responsive to the second signal and transmitting a third signal
corresponding to the second signal; and
a receiver, the receiver including a receive coil separated from the
transmit coil by a distance and for receiving the signal transmitted by
the transmit coil and providing a received signal, processing means for
processing the received signal to determine the distance between the
receive coil and the transmit coil and for providing a processed signal,
the control means being operatively coupled to the processing means of the
receiver and responsive to the processed signal, and display means
responsive to the processed signal for indicating at least the relative
distance between the transmit coil and the receive coil, one of the
transmit coil and the receive coil being situated on the object adapted to
be inserted into the patient's body, and the other of the receive coil and
the transmit coil being located externally to the patient's body, whereby
the location of the object adapted to be inserted into the patient's body
may be determined.
3. Apparatus for determining the orientation of an object adapted to be
inserted into a patient's body, which comprises:
a transmitter oscillator, the transmitter oscillator generating a first
signal;
a transmit coil situated externally to the patient's body, the transmit
coil being responsive to the first signal and transmitting a second signal
corresponding to the first signal;
means for rotating the transmit coil in a direction transverse to a
longitudinal axis of the transmit coil;
a receive coil situated on the object adapted to be inserted into the
patient's body, the receive coil receiving the second signal transmitted
by the rotating transmit coil and providing a third signal in response
thereto;
rectifying means responsive to the third signal for providing a rectified
fourth signal;
strobe means for providing strobes of light in response to the rectified
fourth signal; and
bar image forming means operatively cooperating with the strobe means for
providing an image of a bar, the bar image being aligned with a
longitudinal axis of the receive coil and thereby being indicative of the
orientation of the object on which the receive coil is situated.
4. The apparatus as defined by claim 3, wherein the bar image forming means
includes a slotted template, the slotted template being synchronously
rotatable with the transmit coil and having an elongated slot formed
therein, the slot being aligned with the longitudinal axis of the transmit
coil.
5. The apparatus as defined by claim 4, wherein the slotted template of the
bar image forming means is coupled to the transmit coil rotating means so
as to rotate with the transmit coil.
6. Apparatus for determining the location of an object adapted to be
inserted into a patient's body, which comprises:
a transmitter oscillator, the transmitter oscillator generating a first
signal;
means responsive to the first signal for controlling the level of the first
signal in accordance with the strength of a signal received by a receiver
operatively linked to the transmitter oscillator and providing a second
signal;
a transmit coil situated externally to the patient's body, the transmit
coil being responsive to the second signal and transmitting a third signal
corresponding to the second signal;
a receive coil situated on the object adapted to be inserted into the
patient's body, the receive coil receiving the third signal transmitted by
the transmit coil and providing a fourth signal in response thereto;
rectifying means responsive to the fourth signal for providing a rectified
fifth signal;
filter means responsive to the rectified fifth signal for providing a
filtered sixth signal in response thereto, the control means being
operatively coupled to the filter means and responsive to the filtered
sixth signal and controlling the level of the second signal in response
thereto; and
means for providing an indication of the location of the object adapted to
be inserted into the patient's body, the location indicating means being
responsive to the filtered sixth signal.
7. The apparatus as defined in claim 6, wherein the object location
indicating means includes means for providing a bar display indicating the
relative proximity of the transmit coil to the receive coil, the bar
display means being responsive to the filtered sixth signal.
8. The apparatus as defined in claim 6, wherein the object location
indicating means includes means for providing a numeric display of the
distance between the receive coil and the transmit coil, the distance
display means being responsive to the filtered sixth signal.
9. The apparatus as defined in claim 6, which further determines the
orientation of the object in the patient's body, and which further
comprises:
means for rotating the transmit coil in a direction transverse to a
longitudinal axis of the transmit coil;
strobe means for providing strobes of light in response to the rectified
fifth signal; and
bar image forming means, the bar image forming means including a slotted
template synchronously rotatable with the transmit coil and having an
elongated slot formed therein, the slot being aligned with the
longitudinal axis of the transmit coil, the bar image forming means
operatively cooperating with the strobe means to provide an image of a
bar, the bar image being aligned with a longitudinal axis of the receive
coil and thereby being indicative of the orientation of the object on
which the receive coil is situated.
10. Apparatus for determining the location and orientation of an object
adapted to be inserted into a patient's body, which comprises:
a transmitter oscillator, the transmitter oscillator generating a first
signal;
a transmitter modulator responsive to the first signal and providing a
modulated second signal;
a transmit coil situated externally to the patient's body, the transmit
coil being responsive to the modulated second signal and transmitting a
third signal corresponding to the second signal;
means for rotating the transmit coil in a direction transverse to a
longitudinal axis of the transmit coil;
a receive coil situated on the object adapted to be inserted into the
patient's body, the receive coil receiving the third signal transmitted by
the rotating transmit coil and providing a fourth signal in response
thereto;
rectifying means responsive to the fourth signal for providing a rectified
fifth signal;
filter means responsive to the rectified fifth signal for providing a
filtered sixth signal in response thereto, the transmitter modulator being
further responsive to the filtered sixth signal and controlling the level
of the modulated second signal in response thereto;
strobe means for providing strobes of light in response to the rectified
fifth signal;
bar image forming means, the bar image forming means including a slotted
template synchronously rotatable with the transmit coil and having an
elongated slot formed therein, the slot being aligned with the
longitudinal axis of the transmit coil, the bar image forming means
operatively cooperating with the strobe means to provide an image of a
bar, the bar image being aligned with a longitudinal axis of the receive
coil and thereby being indicative of the orientation of the object on
which the receive coil is situated; and
means for providing an indication of the location of the object adapted to
be inserted into the patient's body with respect to the transmit coil, the
location indicating means being responsive to the filtered sixth signal.
11. A method for locating an object inserted into a patient's body, which
comprises the steps of:
generating a first signal;
transmitting the first signal from a transmit coil located externally to
the patient's body;
receiving the transmitted signal by a receive coil situated on the object
in the patient's body;
rectifying the signal received by the receive coil;
filtering the rectified signal and providing a filtered signal;
controlling the level of the first signal in response to the filtered
signal; and
displaying an indication of the relative location of the object from the
transmit coil in response to the filtered rectified signal.
12. A method for determining the orientation of an object inserted into a
patient's body, which comprises the steps of:
transmitting a signal from a transmit coil situated externally to the
patient's body;
rotating the transmit coil in a direction transverse to a longitudinal axis
of the transmit coil;
receiving the transmitted signal by a receive coil situated on the object
inserted into the patient's body;
rectifying the received signal;
providing strobes of light in response to the rectified received signal;
and
forming an image of a bar in response to the strobes of light, the bar
image being aligned with a longitudinal axis of the receive coil and
thereby being indicative of the orientation of the object on which the
receive coil is situated.
13. A method for determining the location and orientation of an object
inserted into a patient's body, which comprises the steps of:
generating a first signal;
modulating the first signal;
transmitting the modulated signal from a transmit coil situated externally
to the patient's body;
rotating the transmit coil in a direction transverse to a longitudinal axis
of the transmit coil;
receiving the transmitted signal by a receive coil situated on the object
inserted into the patient's body;
rectifying the received signal;
filtering the rectified received signal, the first signal being modulated
in response to the filtered and rectified received signal;
providing strobes of light in response to the rectified and filtered
received signal;
forming an image of a bar in response to the strobes of light, the bar
image being aligned with a longitudinal axis of the receive coil and
thereby being indicative of the orientation of the object on which the
receive coil is situated; and
providing an indication of the location of the object with respect to the
transmit coil in accordance with the strength of the filtered and
rectified received signal. |
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Claims |
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Description |
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BACKGROUND OF THE INVENTION
1. Field Of The Invention
The present invention relates to medical equipment generally, and more
particularly to medical equipment used to aid in the tracking of catheters
inserted into a patient's body by indicating the orientation and distance
of the catheter in the body.
2. Description Of The Prior Art
The tracking of catheters which have been inserted into a body has been
accomplished in the past by a method which required the medical team to
first insert a guide wire into the vein or artery in which the catheter
would be inserted. The catheter is then led along this guide wire for a
predefined distance, such distance being less than the distance required
to place the catheter in its intended destination. The patient is x-rayed
to determine if the path which the catheter and guide wire has followed is
the same as the intended path. If so, the catheter is guided on to its
ultimate and final destination. If the path which the guide wire and the
catheter have taken is different from the intended path, the catheter and
guide wire must be withdrawn and the process repeated. This sequence is
repeated until the catheter and guide wire reach the desired destination.
The disadvantages of this process lie in the expense and danger involved in
subjecting a patient to repeated x-ray treatment and the delay caused by
the need to take x-ray photographs before completing the catheter
insertion. Also, the conventional "trial-and-error" method of inserting
and tracking a catheter described previously subjects the patient to undue
stress.
OBJECTS AND SUMMARY OF THE INVENTION
It is an object of the present invention to provide a means to determine
the location and orientation of a medical object which has been inserted
into a living body.
It is a further object of the present invention to provide a device which
can quickly and accurately determine the position and orientation of a
catheter in a body.
It is another object of the present invention to provide a catheter tracer
which can determine the distance and orientation of a catheter inserted
into a patient's body.
It is yet another object of the present invention to provide a hand-held
device for tracking a catheter inserted into a patient's body, which
device is simple in construction and inexpensive to manufacture.
It is yet a further object of the present invention to provide the
combination of a locator wire which is inserted into the catheter and a
catheter tracer adapted to interact with the locator wire in determining
the position of the catheter within a body.
It is still another object of a present invention to provide a method and a
device for tracking catheters inserted into a body, which method and
device overcome the inherent disadvantages of known methods of tracking
catheters.
In accordance with one form of the present invention, a catheter tracer
basically comprises a transmitter portion and a receiver portion. The
transmitter portion is mounted in a hand-held probe and includes an
oscillator which generates a carrier frequency signal, and a transmit coil
to which the carrier frequency signal is provided.
The transmitter further includes a drive mechanism for rotating the coil at
a predetermined rate. Because of the rotation of the coil, the transmitter
transmits an amplitude modulated or "pulsating" signal, the signal being
modulated at a frequency which is equal to the rotational rate of the
coil.
The receiver portion of the catheter tracer includes a receive coil. In one
form of the invention, the receive coil is mounted on, or defines, the tip
of a catheter or its guide wire adapted to be inserted into a patient's
body. Alternatively, the receive coil may be mounted on the end of a
"locator" wire. The catheter guide wire is removed and the locator wire is
inserted into the catheter in its place when determining the position of
the catheter.
As the transmit coil is rotated, a time varying, pulsating current and
voltage signal is electromagnetically induced in the receive coil. The
amplitude of the received signal is greatest when, for a given distance
between the two coils, the longitudinal axis of the transmit coil is
aligned with the longitudinal axis of the receive coil. This relationship
between the two coils will help identify the orientation of the receive
coil and, correspondingly, the location and direction of the catheter.
The receiver has additional circuitry for processing the signal induced in
the receive coil. This additional circuitry is carried in the hand-held
probe with the transmitter. The processing circuitry of the receiver
includes a differential amplifier which is coupled to the receive coil and
which amplifies the received signal. The output signal of this amplifier
is provided to a rectifier circuit, which rectifies the amplifier's output
signal.
The receiver processing circuitry further includes a low pass filter or
integrator circuit, which receives the rectified output signal of the
rectifier circuit and provides an output signal which is, essentially, a
voltage level having an amplitude which varies with the peak amplitude of
the rectified output signal.
The catheter tracer of the present invention also includes a bar display
circuit and a digital voltmeter circuit, each of which is provided with
the filter output signal. The bar display circuit includes a bar display
mounted on the hand-held probe, which bar display provides the physician
with an indication of the relative strength of the signal received and,
accordingly, the relative proximity of the probe to the catheter. The
digital voltmeter circuit includes a numeric display, which display
provides the physician with a numeric indication of the distance between
the rotating transmit coil in the handheld probe and the receive coil
mounted on the catheter, its guide wire or the locator wire.
The catheter tracer further includes circuitry and an associated display
for indicating to the physician the orientation of the catheter, guide
wire or locator wire within the patient's body. The catheter orientation
circuitry effectively translates the time relation of the amplitude peaks
of the received signal into a display of the orientation of the receive
coil mounted on the catheter, locator wire or guide wire tip. The
orientation circuitry includes a pulse amplifier and shaper circuit which
is provided with the output signal of the rectifier circuit. The pulse
amplifier and shaper circuit provides gain and an offset adjustment to the
rectified signal, and eliminates the 2,200 Hertz carrier frequency from
the signal. The output signal from the pulse amplifier and shaper circuit
is, effectively, the amplified envelope of the rectified signal,
adjustable in offset. The output signal of the pulse amplifier and shaper
circuit is provided to a monostable multivibrator and is adjusted in
offset to trigger the monostable multivibrator at the peaks of the
envelope, which correspond to the peaks in the received signal. The
multivibrator provides a logic output signal in the form of a pulse each
time a peak in the received signal occurs.
The output signal of the monostable multivibrator is connected to a drive
circuit, which in turn drives light emitting diodes (LEDs). The LEDs are,
in effect, strobed on for a predetermined duration whenever a pulse is
generated by the monostable multivibrator.
The hand-held probe includes an essentially opaque template which includes
a diametrically extending slot. The slotted template rotates synchronously
with the rotating transmit coil, with the slot being in alignment
lengthwise with the longitudinal axis of the transmit coil. The LEDs are
arranged in a circle spaced apart from each other and positioned below the
slotted template. Whenever the LEDs are strobed on, they project light
through the slot in the rotating template. The slot projects the image of
a bar or line on a translucent face lens on the probe and above the
rotating slotted template so that the image is viewable through the lens
by the physician.
As mentioned previously, the amplitude of the received signal is greatest
when the longitudinal axis of the transmit coil is aligned with the
longitudinal axis of the receive coil. It is at these times of coil
alignment that the LEDs are strobed, and their light is projected through
the template slot to form the bar image on the lens. Accordingly, the
direction of the bar image will correspond to the longitudinal axis of the
receive coil, and thus will be indicative of the orientation of the
catheter, locator wire or guide wire on which the receive coil is mounted.
A preferred form of the catheter tracer, as well as other embodiments,
objects, features and advantages of this invention, will be apparent from
the following detailed description of illustrative embodiments thereof,
which is to be read in connection with the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a perspective view of the combination of a catheter tracer and a
locator wire for a catheter, formed in accordance with one form of the
present invention.
FIG. 2 is a top view of a hand-held probe forming a portion of the catheter
tracer of the present invention.
FIG. 3 is a cross-sectional view of the hand-held probe shown in FIG. 2,
taken along line 3--3 of FIG. 2.
FIG. 4 is an exploded view of the gearing and other mechanical parts housed
within the hand-held probe.
FIG. 5 is a cross-sectional view of a locator wire of a catheter, formed in
accordance with the present invention.
FIG. 6a is an enlarged perspective view of a portion of the locator wire
shown in FIG. 5 and shown encircled by circle A.
FIG. 6b is an enlarged perspective view of a portion of the locator wire
shown in FIG. 5 and shown encircled by circle B.
FIG. 7 is a block diagram of an electronic circuit used in the catheter
tracer of the present invention.
FIGS. 8a through 8c are schematic diagrams of the circuit used in the
catheter tracer of the present invention.
FIGS. 9a through 9d are various signal waveforms associated with the
circuitry of the catheter tracer of the present invention.
FIG. 10 is a graph of voltage versus distance, showing the correlation
between the amplitude of the received signal and the distance between the
hand-held probe and the tip of the catheter locator wire.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
Apparatus for tracking a catheter in a patient's body, or hereinafter
referred to as a "catheter tracer", formed in accordance with the present
invention, is constructed basically in two interconnectable parts: 1) a
hand-held probe 2; and 2) a locator wire 4 constructed to include a
receive coil 6, as will be described.
The probe 2 has a shape which allows for easily handling. It includes a
handle 8 which is held by the physician, and an enlarged portion or head
10 situated opposite the handle, which head 10 includes a rounded lower
portion 12 which is placed over the patient's body near the area which is
suspected to contain the tip of the catheter guide wire 4 on which the
receive coil 6 is mounted.
The receive coil 6, which may be mounted on the catheter itself, its guide
wire or the catheter locator wire 4, as shown in FIG. 1, is connected to
the hand-held probe by an electrical conduit 14. This conduit 14 carries
the signal which is received by the receive coil to the hand-held probe 2
for processing and for display on its face, as will be described below.
As shown in FIG. 2, the hand-held probe includes a translucent face lens 16
on the enlarged head portion 10 of the probe on a side opposite to the
rounded lower portion 12. The face lens 16 of the hand-held probe, which
is viewable to the physician, displays three forms of information: 1)
distance in centimeters between the rounded lower portion 12 of the probe
(in which a transmit coil 18 is located) and the receive coil 6 mounted on
the tip of the catheter locator wire; 2) coarse proximity information in
the form of a bar graph display 20, which the physician relies on in
locating the tip of the catheter, the number of lights of the bar graph
display 20 which are illuminated being proportional to the receiver signal
strength; and 3) the orientation of the catheter, displayed as an
illuminated bar or line 22 on the central portion of the face lens 16 of
the hand-held probe.
In the preferred form of the invention, the indicator which displays the
distance from the hand-held probe 2 to the tip of the catheter, guide wire
or locator wire 4 is in the form of two numeric display LEDs 24 which are
mounted side-by-side for the purpose of giving a two digit display of
distance in centimeters. The two digit display 24 is centered along the
longitudinal axis of the hand-held probe 2 under the face lens 16 of the
head portion, and each digit of the display is preferably oriented with
its bottom toward the probe handle 8.
The proximity display 20, which indicates the receiver signal strength, is
preferably formed of twenty LEDs 26 which are arranged arcuately spaced
just under the face lens of the hand-held probe, that is, in a curved bar
graph style array.
As shown in FIG. 3 of the drawings, the hand-held probe 2 defines a first
chamber 28 in the handle portion 8 of the probe, which chamber 28 houses
two printed circuit boards containing the electronic circuitry of the
transmitter and receiver portions of the catheter tracer, a second chamber
30 situated at the free end of the handle 8, which chamber 30 preferably
houses six nickel cadmium batteries 31 shown double-stacked three high, a
third chamber 32 in the head 10 of the probe for receiving a third
circular shaped printed circuit board 34 containing the display circuitry,
and a fourth chamber 36 in which the mechanical parts and gearing of the
catheter tracer are housed. The rounded lower portion 12 of the probe is
formed with a plastic or rubber covering or "radome".
The mechanical parts and gearing of the catheter tracer of the present
invention is shown in FIG. 3 and in the exploded view of FIG. 4. The
mechanical portion of the catheter tracer includes a gear motor 40, which
rotates at between about 200 and about 300 r.p.m. Mounted on the shaft of
the motor 40 is a main drive gear 42. The main drive gear 42 engages a
secondary drive gear 44. The secondary drive gear 44 is fixedly mounted on
a secondary drive shaft 46 which extends upwardly through the head 10 of
the hand-held probe between the face lens 16 and the rounded lower portion
12.
On one end of the secondary drive shaft 46 is mounted a slotted template
48. The slotted template 48 includes a disc portion 50 having a slot 52
extending partially diametrically across the disc and through the
thickness of the disc. The template 48 is formed of an opaque material so
that light can only be transmitted through the slot 52.
A transmit coil 18 is mounted on the other end of the secondary drive shaft
46. The transit coil 18 is formed of a ferrous core or support 54 which is
disposed with its longitudinal axis perpendicular to the axis of the
secondary drive shaft 46. A continuous length of wire 56 is wound about
the oppositely extending legs of the core 54 to define the coil, which is
formed, effectively, as a Miller coil. More specifically, the transmit
coil 18 is preferably formed by layer winding #26 AWG wire on a Miller
ferrite core #2006 until its finished dimensions are #" in length and 1/2"
in diameter. Such a winding should provide a D.C. resistance of about 1.10
ohms, an inductance of 2.2 Mh and a Q of 10. With a 1 microfarad capacitor
in parallel with it, the transmit coil 18 should resonate at about 2200
Hertz. The secondary drive shaft 46 intersects the core of the transmit
coil 18 at its center so that the transmit coil is balanced as it rotates.
When the motor 40 is energized, its main drive gear 42 engages the
secondary drive gear 44, causing the secondary drive shaft 46 to rotate.
This in turn causes the transmit coil 18 and the slotted template 48 to
rotate in synchronism. The slotted template 48 is arranged relative to the
transmit coil 18 such that the longitudinal axis of the slot 52 is aligned
with the longitudinal axis of the transmit coil.
A pair of slip rings 58 are provided on the secondary drive shaft 46. Each
slip ring 58 is connected to a respective end of the transmit coil lead
wire. A pair of contacts (not shown) engage the slip rings 58 and are
connected to the transmitter circuitry of the catheter tracer.
Four discrete LEDs 60 are mounted on the underside of the slotted template
48 in a circular array. Each LED 60 is positioned ninety degrees from its
adjacent LEDs. As will be described in greater detail, these LEDs will be
strobed on at predetermined times. Light from the LEDs 60 will pass
through the slot 52 in the disc portion of the template. The light from
the LEDs will pass through the slot and will be projected as an image on
the face lens 16 disposed above the slotted template 48. The projected
image 22 formed by the LEDs 60 will be in the shape of an elongated bar or
line, which image is visible to the physician. The LEDs 26 of the
proximity display 20, as well as the digit LEDs 24 of the distance
indicator, are also positioned below the face lens 16 of the probe and
viewable through the lens.
FIGS. 5 and 6 show the locator wire 4 and a receive coil 6 located near or
on the free end of the wire. The locator wire 4 is preferably formed as a
single strand wire 62 such as 0.012 inch diameter piano wire. The receive
coil 6 is preferably formed by winding 800 turns of #43 AWG wire 64 around
the tip portion of the piano wire 62. The tip portion of the piano wire 62
may be annealed to increase its permeability.
The lead wires 66 which carry the received signal from the receive coil 6
along the locator wire 4 are wrapped in a helical manner along the locator
wire to a connector Pl which plugs into the hand-held probe 2. Each of the
two lead wires 66 is wrapped in opposite directions, one following a
right-hand helix and the other following a left-hand helix. Both lead
wires are wrapped with similar spacing. This configuration aids in the
cancellation of any electromagnetic interference which is induced in the
lead wires 66. The receive coil 6 and lead wires 66 may be sprayed with a
urethane varnish or the like to maintain their wrapped configuration about
the locator wire 4.
Although not shown but envisioned to be within the scope of the invention,
a catheter or the catheter guide wire may be formed with the receive coil
located at its free end, instead of using a locator wire. If the locator
wire is used, the medical team periodically removes the guide wire during
the catheter insertion operation, and inserts the locator wire 4 in its
place, in order to determine the present location and orientation of the
catheter within the patient's body.
The electronic circuitry of the catheter tracer of the present invention
will now be described in greater detail, and with reference to FIGS. 7-9
of the drawings.
FIG. 7 shows, in block diagram form, the relationship of the various
functional blocks of the electronic circuitry. This relationship can best
be seen by tracing the transmit signal through the circuitry, starting
with the transmitter portion of the catheter tracer.
The transmitter includes an oscillator 68 which generates a transmit signal
preferably of constant amplitude and a carrier frequency of approximately
2,200 hertz. The output signal of the oscillator 68 is provided to a
modulator 70, whose function will be described in greater detail, and the
modulator's output signal is provided to the transmit coil 18.
The receiver of the catheter tracer includes a receive coil 6, as mentioned
previously, which is mounted on the tip of the catheter, its guide wire or
the locator wire 4. As the transmit coil 18 is brought into proximity with
the receive coil 6 (at a distance of approximately 16 centimeters between
the two coils), the receive coil 6 begins to receive the signal sent by
the transmit coil 18 due to magnetic coupling between the two, which
causes a voltage and current to be induced in the receive coil. The
amplitude of the induced voltage and current is a function of the
orientation of the transmit coil with respect to the receive coil and the
distance between the two coils.
When the longitudinal axes of the two coils are in parallel, the magnetic
coupling between the two is the greatest, and the maximum current and
voltage is induced in the receive coil 6. When the axes of the two coils
are orthogonal, the induced current and voltage in the receive coil 6
drops to a minimum level. The electrical current and voltage amplitude
follows a periodic rise and fall with a steady rotational motion of the
transmit coil 18. The rotation of the transmit coil 18 amplitude modulates
the 2,200 hertz carrier transmit frequency of the transmitted signal (this
modulation is not performed by the transmitter modulator 70 mentioned
previously). The signal induced in the receive coil 6 is a 2,200 hertz
signal which increases and decreases in amplitude in a periodic fashion at
a rate of about 10 hertz. The resulting waveform of the received signal
induced in the receive coil is illustrated by FIG. 9a.
The receiver has additional circuitry for processing the signal induced in
the receive coil 6. This circuitry is preferably housed in the hand-held
probe 2 with the transmitter. The receiver processing circuitry includes
an amplifier 72 which is connected to the receive coil 6. The amplifier 72
amplifies the received signal and preferably has a gain of approximately
68. In its preferred form, the receiver amplifier 72 has a differential
input which is connected to the two leads of the receive coil (through
appropriate mating connectors P1 and J1), thereby reducing the effects of
common mode noise at the amplifier's input.
The receiver processing circuitry further includes a rectifier circuit 74
to which the amplified signal is provided. The rectifier circuit 74
rectifies the signal to provide an output signal which has only a positive
component. The output signal of the rectifier is shown in FIG. 9b.
The receiver processing circuitry further includes a low pass filter or
integrator circuit 76, which receives and averages the rectified output
signal of the rectifier circuit 74 and provides an output signal which is,
essentially, a voltage level having an amplitude which varies with the
peak amplitude of the rectified output signal and which changes slowly and
inversely with the strength of the received signal.
The receiver processing circuitry may also include a unity gain, buffer
amplifier 78 which is connected to the low pass filter circuit 76 and
which "buffers" the filter circuit by providing a high impedance load to
the filter circuit. The buffer amplifier 78 provides its output signal to
the transmitter modulator 70 and to the display circuitry.
The transmitter modulator 70 creates a 2,200 hertz carrier signal having a
strength which is inversely proportional to the strength of the received
signal, due to the negative feedback of the received signal through the
differential amplifier 72, rectifier circuit 74, filter circuit 76 and the
buffer amplifier 78 to the transmitter modulator 70. The negative feedback
of the received signal increases the operating range of the catheter
tracer by reducing the extreme variation in amplitude of the received
signal over varying distances and, in effect, linearizes the received
signal strength over the distance between the transmit coil 18 and the
receive coil 6.
As mentioned previously, the catheter tracer further includes circuitry and
an associated display for indicating to the physician the orientation of
the catheter within the patient's body. The catheter orientation circuitry
effectively translates the time relation of the amplitude peaks of the
received signal into a display of the orientation of the receive coil
mounted on the catheter, guide wire or locator wire tip. The orientation
circuitry includes a pulse amplifier and shaper circuit 80 which is
provided with the output signal of the rectifier circuit 74. The pulse
amplifier and shaper circuit 80 provides gain and an offset adjustment to
the rectified signal, and eliminates the 2,200 Hertz carrier frequency
from the signal. The output signal from the pulse amplifier and shaper
circuit 80 is, effectively, the amplified envelope of the rectified
signal, adjustable in offset.
The output signal of the pulse amplifier and shaper circuit is provided to
a monostable multivibrator 82 and is adjusted in offset to trigger the
monostable multivibrator at the peaks of the envelope, which correspond to
the peaks in the received signal. The multivibrator 82 provides a logic
output signal in the form of a pulse each time a peak in the received
signal occurs. The pulse created is a square wave pulse, which is
preferably 20 milliseconds in duration. This pulse is provided for turning
on the high intensity light emitting diodes 60, which are strobed on
whenever the pulse is present. The pulse occurs ten times per second, and
is synchronized to the time the transmit coil 18 is aligned with the
receive coil 6.
The output signal of the monostable multivibrator 82 is connected to a
drive circuit 84, which in turn drives the strobe light emitting diodes
(LEDs) 60, which are connected in parallel. The LEDs 60 are, in effect,
strobed on for a predetermined duration whenever a pulse is generated by
the monostable multivibrator. The light of the high intensity light
emitting diodes 60 shines through the slot 52 formed in the rotating
slotted template 48, which slot projects an image of a bar or line 22 on
the face lens 16 of the hand-held probe. The image appears to be frozen in
time in a position indicative of the orientation of the receive coil 6.
Also as mentioned previously, the catheter tracer of the present invention
includes a proximity display circuit and a digital voltmeter circuit with
its associated numeric "distance" display. The proximity display circuit
includes a range and offset adjust circuit 86, which is provided with the
output signal from the buffer amplifier 78.
The range and offset adjust circuit 86 preferably has a gain of
approximately three and allows a variable DC offset to be introduced to
the buffer amplifier's output signal to adjust the proximity bar display
20, which indicates the received signal strength, so that the LED segment
of the bar display which indicates the lowest signal level remains
illuminated for small received signal levels. The output of the range and
offset adjust circuit 86 is provided to a driver circuit 88, which drives
the proximity LEDs 26.
The digital voltmeter circuit includes a range adjust circuit 90 to which
the buffer amplifier's output signal is provided. The output signal from
the range adjust circuit 90 is provided to an analog-to-digital converter
circuit 92, having outputs which drive the LED digit display 24. The
voltmeter circuit of the tracer provides a numeric display of the distance
between the hand-held probe and the receive coil in centimeters.
FIG. 8 schematically shows a preferred form of the electronic circuitry of
the catheter tracer. The actual values and part numbers of the components
used in the electronic circuitry shown in FIG. 8 are for illustrative
purposes only, and to facilitate an understanding of the invention.
However, alternative components, and values for these components, may be
substituted by one skilled in the art to provide the same or similar
results. The numbers positioned adjacent to the integrated circuits shown
in FIG. 8 represent the pin numbers of the circuits.
The oscillator 68 of the transmitter preferably is formed from a CMOS
timer/counter circuit U1, such as Intersil, Inc. integrated circuit ICM
7242 which internally consists of an RC oscillator followed by an eight
bit binary counter. The trigger (TR) input of the integrated circuit U1 is
connected to a voltage level of +5 volts through a fixed resistor R1,
which causes the integrated circuit U1 to output a square wave with a 50%
duty cycle on the "+2" output terminal. The "Vss" and reset (R) inputs are
grounded, and a capacitor C1 is connected between ground and the "RC"
input. The "V.sub.DD " input is connected to +5 volts and to one end of a
potentiometer R2 through a fixed resistor R3. The other end of the
potentiometer R2 and the wiper of the potentiometer are connected to the
"RC" input.
The potentiometer R2 allows the frequency of the output signal of the
oscillator 68 to be tuned to match the resonant frequency of the transmit
coil 18. The combination of the capacitor C1 and the resistance of the
potentiometer R2 and the fixed resistor R3 sets the RC time constant for
the oscillator circuit U1.
The transmitter modulator 70 includes an NPN transistor Q1 and a field
effect transistor (FET) Q2. The "+2" output of the oscillator circuit is
connected to the base of transistor Q1 through a base resistor R4. The
emitter of transistor Q1 is connected to ground, and the collector is
connected to the gate of transistor Q2. The source of transistor Q2 is
grounded, and the drain of transistor Q2 is connected to one lead of the
rotating transmit coil 18 through a diode D1 and one slip ring 58. The
collector of transistor Q1 is also connected to the output signal of the
buffer amplifier 78 (see U7 in FIG. 8) through a resistor R5.
Resistor R4 limits the base current which flows into transistor Q1.
Transistor Q1 allows the gate of transistor Q2 to have a potential equal
to the output of the buffer amplifier U7 or to be held at ground
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