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Claims  |
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We claim:
1. A system for ultrasonically imaging internal tissues through the biopsy
channel of an endoscope, comprising:
a catheter having a diameter that is sufficiently small to pass through
said biopsy channel;
an ultrasound probe mounted at one end of said catheter, said ultrasound
probe having a maximum transverse dimension that is sufficiently small to
pass through said biopsy channel, said ultrasound probe having a
transversely directed beam pattern;
position measuring means coupled to said catheter and adapted to be coupled
to said endoscope for generating an ultrasound probe position signal
indicative of the longitudinal position of said catheter with respect of
said endoscope;
latch means actuatable to manually disengage said catheter from said
position measuring means so that said catheter can move longitudinally
without varying said ultrasound probe position signal; and
imaging means connected to said ultrasound probe by conductors extending
through said catheter, said imaging means generating an ultrasound signal
that is applied to said probe to generate an acoustic signal, said imaging
means further receiving an ultrasound signal from said ultrasound probe
corresponding to ultrasound acoustic signals reflected from said tissues
to said ultrasound probe, said ultrasound imaging means generating said
ultrasound image from said received ultrasound signal and from said
ultrasound probe position signal.
2. The ultrasound imaging system of claim 1 wherein said position measuring
means comprises:
a linear potentiometer having a resistance between a pair of leads that
varies according to the linear position of a potentiometer wiper contact
arm, said potentiometer being adapted for mounting on said endoscope
adjacent the proximal end of said biopsy channel; and
a releasable fastener mounted on said wiper contact arm, said fastener
releasably engaging said catheter
so that the resistance between the leads of said potentiometer varies
according to the longitudinal position of said catheter when said
releasable fastener is engaged with said catheter.
3. The ultrasound imaging system of claim 2 wherein said releasable
fastener comprises:
a stop member secured to said catheter;
a fastener body mounted on said wiper contact arm, said fastener body
having a recess adapted to receive said stop member; and
a latchpiece pivotally mounted on said fastener body, said latchpiece being
movable to at least partially enclosed said recess to retain said stop
member in said recess, thereby releasable securing said catheter to said
potentiometer wiper contact arm.
4. The ultrasound imaging system of claim 3 wherein said latchpiece further
includes an arcuate cutout to provide clearance for said catheter, thereby
allowing said latchpiece to enclose substantially all of said stop member.
5. The ultrasound imaging system of claim 2 wherein the resistance between
the leads of potentiometer is a linear function of the linear position of
said wiper contact arm.
6. A system for ultrasonically imaging internal tissues through the biopsy
channel of an endoscope, comprising:
a catheter having a diameter that is sufficiently small to pass through
said biopsy channel;
an ultrasound probe mounted at one end of said catheter, said ultrasound
probe having a maximum transverse dimension that is sufficiently small to
pass through said biopsy channel, said ultrasound probe having a
transversely directed beam pattern;
an elongated layer of resistive material covering at least a portion of
said catheter along its length;
a conductor lead extending through said catheter from at least one end of
said resistive material to an external location;
a conductive wiper adapted for mounting on said endoscope and making
contact with said resistive material so that the resistance between said
conductor lead and said wiper is indicative of the longitudinal position
of said catheter with respect to said endoscope; and
imaging means connected to said ultrasound probe by conductors extending
through said catheter, said imaging means generating an ultrasound signal
that is applied to said probe
to generate an acoustic signal, said imaging means further receiving an
ultrasound signal from said ultrasound probe corresponding to ultrasound
acoustic signals reflected from said tissues to said ultrasound probe,
said ultrasound imaging means generating said ultrasound image from said
received ultrasound signal and from said ultrasound probe position signal.
7. The ultrasound imaging system of claim 6 wherein said conductive wiper
is adapted for mounting on said endoscope adjacent the proximal end of
said endoscope and said resistive material covers said catheter in an area
in which said catheter enters the biopsy channel of said endoscope when
the distal end of said catheter is in a position to image internal
tissues.
8. A system for ultrasonically imaging internal tissues through the biopsy
channel of an endoscope, comprising:
a catheter having a diameter that is sufficiently small to pass through
said biopsy channel;
an ultrasound probe mounted at one end of said catheter, said ultrasound
probe having a maximum transverse dimension that is sufficiently small to
pass through said biopsy channel, said ultrasound probe having a
transversely directed beam pattern;
a potentiometer housing adapted for mounting on said endoscope adjacent the
proximal end of said biopsy channel;
a rotary potentiometer mounted in said potentiometer housing, said
potentiometer having an arcuate resistance element and a rotatable wiper
contact slidable along said resistance element, said wiper contact being
coupled to a hollow shaft through which said catheter extends, said hollow
shaft being coaxial with said arcuate resistance element;
a releasable fastener releasably securing said catheter to said hollow
shaft so that said catheter and shaft rotate with each other; and
imaging means connected to said ultrasound probe by conductors extending
through said catheter, said imaging means generating an ultrasound signal
that is applied to said prode to generate an acoustic signal, said imaging
means further receiving an ultrasound signal from said ultrasound probe
corresponding to ultrasound acoustic signals reflected from said tissues
to said ultrasound probe, said ultrasound imaging means generating said
ultrasound image from said received ultrasound signal and from said
ultrasound probe position signal.
9. The ultrasound imaging system of claim 8 wherein said releasable
fastener includes a compression screw having a hollow center axis threaded
into the hollow shaft of said potentiometer in coaxial alignment with said
shaft so that said catheter extends through the hollow center axis of said
screw, said compression screw frictionally engaging said catheter when
said compression screw is threaded into said shaft to secure said catheter
to said shaft.
10. A system for ultrasonically imaging internal tissues through the biopsy
channel of an endoscope, comprising:
a catheter having a diameter that is sufficiently small to pass through
said biopsy channel;
an ultrasound probe having a tranversely directed beam pattern mounted at
one end of said catheter, said ultrasound probe having a maximum
transverse dimension that is sufficiently small to pass through said
biopsy channel, said ultrasound probe having a probe casing mounted at the
end of said catheter, said casing having at least one acoustically
transparent area , a transducer support member mounted in said casing , an
ultrasound transducer mounted on said transducer support member beneath
said acoustically transparent area , and actuating means for selectively
moving said transducer support member longitudinally within said casing,
thereby longitudinally scanning said transducer;
position measuring means coupled to said catheter and adapted to be coupled
to said endoscope for generating an ultrasound probe position signal
indicative of the longitudinal position of said catheter with respect to
said endoscope;
imaging means connected to said ultrasound probe by conductors extending
through said catheter, said imaging means generating an ultrasound signal
that is applied to said transducer to generate an acoustic signal, said
imaging means further receiving an ultrasound signal from said ultrasound
probe corresponding to ultrasound acoustic signals reflected from said
tissues to said ultrasound probe, said ultrasound imaging means generating
said ultrasound image from said received ultrasound signal and from said
ultrasound probe position signal.
11. The ultrasound imaging system of claim 10 wherein said catheter
includes a fluid channel extending along its length and communicating with
the interior of said probe casing, and wherein said transducer support
member includes a piston slidably engaging the inside wall of said probe
casing, and wherein said actuating means includes fluid control means for
selectively applying fluid to the interior of said catheter to cause said
piston to move said transducer support member longitudinally in said probe
casing.
12. The ultrasound imaging system of claim 11, further including a pressure
release tube extending through the catheter and piston into the interior
of said probe casing to allow said fluid to flow into and out of the
distal end of said casing when fluid flowing through said catheter moves
said piston.
13. The ultrasound imaging system of claim 11 wherein said actuating means
comprise a drive piston slidably mounted in the interior of said catheter
to force said fluid toward and away from said probe, said drive piston
being coupled to an electromechanical actuator and to said position
measuring means.
14. The ultrasound imaging system of claim 13, further including a flexible
bag positioned outside said endoscope and a pressure release tube
extending from said bag through said catheter and piston into the interior
of said probe casing to allow said fluid to flow into and out of the
distal end of said casing when fluid flowing said catheter moves said
piston.
15. A system for ultrasonically imaging internal tissues through the biopsy
channel of an endoscope, comprising:
a catheter having a diameter that is sufficiently small to pass through
said biopsy channel;
an ultrasound probe having a tranversely directed beam pattern mounted at
one end of said catheter, said ultrasound probe having a maximum
transverse dimension that is sufficiently small to pass through said
biopsy channel, said ultrasound probe having a probe body having a planar
transducer mounting surface and a partially spherical recess positioned
above said transducer mounting surface, an ultrasound transducer mounted
on said transducer mounting surface, and an impedance matching material
filling said partially spherical recess;
position measuring means coupled to said catheter and adapted to be coupled
to said endoscope for generating an ultrasound probe position signal
indicative of the longitudinal position of said catheter with respect to
said endoscope; and
imaging means connected to said ultrasound probe by conductors extending
through said catheter, said imaging means generating an ultrasound signal
that is applied to said transducer to generate an acoustic signal, said
imaging means further receiving an ultrasound signal from said ultrasound
probe corresponding to ultrasound acoustic signals reflected from said
tissues to said ultrasound probe, said ultrasound imaging means generating
said ultrasound image from said received ultrasound signal and from said
ultrasound probe position signal.
16. The ultrasound imaging system of claim 15 wherein the probe body of
said probe further includes a second partially spherical recess concentric
with said first partially spherical recess, said second partially
spherical recess having a radius of curvature that is smaller than the
radius of curvature of said first partially spherical recess, and wherein
the transducer of said probe includes outer and inner elements having
respective diameters approximately equal to the diameters of said first
and second partially spherical recesses, thereby allowing said probe to
focus at at least two depth ranges.
17. The ultrasound imaging system of claim 16 wherein said transducer
comprises a cylindrical plate of a piezoelectric material having first and
second planar faces, said first planar face being plated with a metal over
substantially its entire surface, said second planar face being plated
with a metal in two semicircular areas having a diameter that is
substantially smaller than the diameter of said cylindrical plate and in
two separate arcuate areas surrounding said semicircular areas, said
ultrasound imaging system being connected between the plating on said
semicircular areas to focus at a relatively shallow depth and between the
plating on said arcuate areas to focus at a relatively large depth, the
piezoelectric material beneath the semicircular area and arcuate area on
one side of said plate being polarized oppositely from the polarization of
the piezoelectric material beneath the other semicircular and arcuate
areas.
18. The ultrasound imaging system of claim 17 wherein said semicircular
plated areas are separated from each other and said plated arcuate areas
are separated from each other by a common diameter of said cylindrical
plate.
19. The ultrasound imaging system of claim 15 wherein said ultrasound
transducer comprises a cylindrical plate of piezoelectric material having
first and second planar faces, said first planar face being plated with a
metal over substantially its entire surface and said second planar face
being plated with a metal in two separate semicircular areas between which
said ultrasound imaging system is connected, the piezoelectric material
beneath one of said semicircular areas being polarized oppositely from the
polarization of the piezoelectric material beneath the other of said
semicircular areas.
20. A catheter for allowing an ultrasound image to be made through the
biopsy channel of an endoscope, comprising:
a tube having a diameter that is sufficiently small to pass through said
biopsy channel, said tube having sufficient rigidity so that the position
and orientation of the ends of the tube correspond to each other, said
tube having sufficient flexibility to conform to the curved configuration
of an endoscope biopsy channel;
an ultrasound probe mounted at one end of said tube, said ultrasound probe
having a maximum transverse dimension that is sufficiently small to pass
through said biopsy channel, said ultrasound probe having a transversely
directed beam pattern;
position measuring means coupled to said tube and adapted to be coupled to
siad endoscope for generating an ultrasound probe position signal
indicative of the longitudinal position of said tube with respect to said
endoscope; and
latch means actuated to manually disengage said tube from said position
measuring means so that said tube can move longitudinally without varying
said ultrasound probe position signal.
21. The catheter of claim 20 wherein said position measuring means
comprises:
a linear potentiometer having a resistance between a pair of leads that
varies according to the linear position of a potentiometer wiper contact
arm, said potentiometer being adapted for mounting on said endoscope
adjacent the proximal end of said biopsy channel; and
a releasable fastener mounted on said wiper contact arm, said fastener
releasably engaging said tube as it exits from said biopsy port so that
the resistance between the leads of said potentiometer varies according to
the longitudinal position of said tube when said releasable fastener is
engaged in said tube.
22. The catheter of claim 21 wherein said releasable fastener comprises:
a stop member secured to said tube;
a fastener body mounted on said wiper contact arm, said wiper body having a
recess adapted to receive said stop member; and
a latchpiece pivotally mounted on said fastener body, said latchpiece being
movable to at least partially enclose said recess to retain said stop
member in said recess, thereby releasably securing said tube to said
potentiometer wiper contact arm.
23. The catheter of claim 22 wherein said latchpiece further includes an
arcuate cutout to provide clearance for said tube, thereby allowing said
latchpiece to enclose substantially all of said stop member.
24. The catheter of claim 21 wherein the resistance between the leads of
said potentiometer is a linear function of the linear position of said
wiper contact arm.
25. A catheter for allowing an ultrasound image to be made through the
biopsy channel of an endoscope, comprising:
a tube having a diameter that is sufficiently small to pass through said
biopsy channel, said tube having sufficient rigidity so that the position
and orientation of the ends of the tube correspond to each other, said
tube having sufficient flexibility to conform to the curved configuration
of an endoscope biopsy channel;
an ultrasound probe mounted at one end of said tube, said ultrasound probe
having a maximum transverse dimension that is sufficiently small to pass
through said biopsy channel, said ultrasound probe having a transversely
directed beam pattern;
an elongated layer of resistive material covering at least a portion of
said tube along its length;
a conductor lead extending through said tube from at least one end of said
resistive material to an external location; and
a conductive wiper adapted for mounting on said endoscope at a location
that allows said wiper to make contact with said resistive material when
the distal end of said tube is in a position to image internal tissues so
that the resistance between said conductor lead and said wiper is
indicative of the longitudinal position of said tube with respect to said
endoscope.
26. The catheter of claim 25 wherein said conductive wiper is adapted for
mounting on said endoscope adjacent the proximal end of the biopsy channel
of said endoscope, and said resistive material covers said tube in an area
in which said tube enters the biopsy channel of said endoscope when the
distal end of sid tube is in a position to image internal tissues.
27. A catheter for allowing an ultrasound image to be made through the
biopsy channel of an endoscope, comprising:
a tube having a diameter that is sufficiently small to pass through said
biopsy channel, said tube having sufficient rigidity so that the position
and orientation of the ends of the tube correspond to each other, said
tube having sufficient flexibility to conform to the curved configuration
of an endoscope biopsy channel;
an ultrasound probe mounted at one end of said tube, said ultrasound probe
having a maximum transverse dimension that is sufficiently small to pass
through said biopsy channel, said ultrasound probe having a transversely
directed beam pattern;
a potentiometer housing adapted for mounting on said endoscope adjacent the
proximal end of said biopsy channel;
a rotary potentiometer mounted in said potentiometer housing, said
potentiometer having an arcuate resistance element and a rotatable wiper
contact slidable along said resistance element, said wiper contact being
coupled to a hollow shaft through which said tube extends, said hollow
shaft being coaxial with said arcuate resistance element; and
a releasable fastener releasably securing said tube to said hollow shaft so
that said tube and shaft rotate with each other.
28. The catheter of claim 27 wherein said releasable fastener includes a
compression screw having a hollow center axis threaded into the hollow
shaft of said potentiometer in coaxial alignment with said shaft so that
tube extends through the hollow center axis of said screw, said
compression screw frictionally engaging said tube when said compression
screw is threaded into said shaft to secure said tube to said shaft.
29. A catheter for allowing an ultrasound image to be made through the
biopsy channel of an endoscope, comprising:
a tube having a diameter that is sufficiently small to pass through said
biopsy channel, said tube having sufficient rigidity so that the position
and orientation of the ends of the tube correspond to each other, said
tube having sufficient flexibility to conform to the curved configuration
of an endoscope biopsy channel;
an ultrasound probe having a transversely directed beam pattern mounted at
one end of said tube, said ultrasound probe having a maximum transverse
dimension that is sufficiently small to pass through said biopsy channel,
said ultrasound probe having
a probe casing mounted at the end of said tube, said casing having at least
one acoustically transparent area , a transducer support member mounted in
said tube, an ultrasound transducer mounted on said transducer support
member beneath said acoustically transparent area , and actuating means
for selectively moving said transducer support member longitudinally
within said tube, thereby longitudinally scanning said transducer; and
position measuring means coupled to said tube and adapted to be coupled to
said endoscope for generating an ultrasound probe position signal
indicative of the position of said tube with respect to said endoscope.
30. The catheter of claim 29, further including a fluid channel extending
along the length of said catheter and communicating with the interior of
said probe casing, and wherein said transducer support member includes a
piston slidably engaging the inside wall of said probe casing, and wherein
said actuating means includes fluid control means for selectively applying
fluid to the interior of said catheter to cause said piston to move said
transducer support member longitudinally in said probe casing.
31. The catheter of claim 30, further including a pressure release tube
extending through said catheter and piston into the interior of said probe
casing to allow said fluid to flow into and out of the distal end of said
casing when fluid flowing through said catheter moves said piston.
32. The catheter of claim 30 wherein said actuating means comprise a drive
piston slidably mounted in the interior of said catheter to force said
fluid toward and away from said probe, said drive piston being coupled to
an electromechanical actuator and to said position measuring means.
33. A catheter for allowing an ultrasound image to be made through the
biopsy channel of an endoscope, comprising:
a tube having a diameter that is sufficiently small to pass through said
biopsy channel, said tube having sufficient rigidity so that the position
and orientation of the ends of the tube correspond to each other, said
tube having sufficient flexibility to conform to the curved configuration
of an endoscope biopsy channel;
an ultrasound probe having a transversely directed beam pattern mounted at
one end of said tube, said ultrasound probe having a maximum transverse
dimension that is sufficiently small to pass through said biopsy channel,
said ultrasound probe having a probe body having a planar transducer
mounting surface and a partially spherical recess positioned above said
transducer mounting surface , an ultrasound transducer mounted on said
transducer mounting surface , and an impedance matching material filling
said partially spherical recess; and
position measuring means coupled to said tube and adapted to be coupled to
said endoscope for generating an ultrasound probe position signal
indicative of the position of said tube with respect to said endoscope.
34. The catheter of claim 33 wherein the probe body of said probe further
includes a second partially spherical recess, said second partially
spherical recess having a radius of curvature that is smaller than the
radius of curvature of said first partially spherical recess, and wherein
the transducer of said probe includes outer and inner elements having
respective diameters approximately equal to the diameters of said first
and second partially spherical recesses, thereby allowing said probe to
focus at at least two depth ranges.
35. The catheter of claim 34 wherein said transducer comprises a
cylindrical plate of a piezoelectric material having first and second
planar faces, said first planar face being plated with a metal over
substantially its entire surface, said second planar face being plated
with a metal in two separate semicircular areas having a diameter that is
substantially smaller than the diameter of said cylindrical plate and in
two separate arcuate areas surrounding said semicircular areas, each of
said plated areas being connected to leads extending from said probe
through said tube so that an ultrasound signal applied between the plating
on said semicircular areas causes said probe to focus at a relatively
shallow depth and an ultrasound signal applied between the plating on said
arcuate areas causes said probe to focus at a relatively large depth, the
piezoelectric material beneath the semicircular area and arcuate area on
one side of said plate being polarized oppositely from the polarization of
the piezoelectric material beneath the other semicircular and arcuate
areas.
36. The catheter of claim 35 wherein said semicircular plated areas are
separated from each other and said plated arcuate areas are separated from
each other by a common diameter of said cylindrical plate.
37. The catheter of claim 33 wherein said ultrasound transducer comprises a
cylindrical plate of piezoelectric material having first and second planar
faces, said first planar face being plated with a metal over substantially
its entire surface, and said second planar face being plated with a metal
in two separate semicircular areas, the piezoelectric material beneath one
of said semicircular areas being polarized oppositely from the
polarization of the piezoelectric material beneath the other of said
semicircular areas, said catheter further including a pair of leads
extending between respective semicircular plated areas of said probe
through said tube.
38. An ultrasound probe for generating an ultrasound acoustic signal and
receiving reflected ultrasound acoustic signals, comprising:
a probe body having a planar transducer mounting surface and first and
second partially spherical recesses positioned above said transducer
mounting surface, said second partially spherical recess having a radius
of curvature that is smaller than the radius of curvature of said first
partially spherical recess;
an ultrasound transducer mounted on said transducer mounting surface, said
transducer having outer and inner elements having respective diameters
approximately equal to the diameter of said first and second partially
spherical recesses ; and
an impedance matching material filling said partially spherical recess.
39. The ultrasound probe of claim 38 wherein said transducer comprises a
cylindrical plate of a piezoelectric material having first and second
planar faces, said first planar face being plated with a metal over
substantially its entire surface, said second planar face being plated
with a metal in two separated semicircular areas having a diameter that is
substantially smaller than the diameter of said cylindrical plate and in
two arcuate areas surrounding said semicircular areas, said semicircular
areas causing said probe to focus at a relatively shallow depth when an
ultrasound signal is applied between said semicircular areas, and said
arcuate plated areas causing said probe to focus at a relatively large
depth when an ultrasound signal is applied between said arcuate plated
areas, the piezoelectric material beneath the semicircular area and
arcuate area on one side of said plate being polarized oppositely from the
polarization of the piezoelectric material beneath the other semicircular
and arcuate areas.
40. The ultrasound probe of claim 39 wherein said semicircular plated areas
are separated from each other and said plated arcuate areas are separated
from each other by a common diameter of said cylindrical plate.
41. An ultrasound probe for generating an ultrasound acoustic signal and
receiving reflected ultrasound acoustic signals, comprising:
a probe body having a planar transducer mounting surface and a partially
spherical recess positioned above said transducer mounting surface;
an ultrasound transducer mounted on said transducer mounting surface, said
ultrasound transducer including a cylindrical plate of piezoelectric
material having first and second planar faces, said first planar face
being plated with a metal over substantially its entire surface, and said
second planar face being plated with a metal with two separate
semicircular areas, the piezoelectric material beneath one of said
semicircular areas being polarized oppositely from the polarization of the
piezoelectric material beneath the other of said semicircular areas; and
an impedance matching material filling said semicircular areas partially
spherical recess.
42. An ultrasound transducer for generating an ultrasound acoustic signal
from an ultrasound electric signal and for generating an ultrasound
electric signal from a received ultrasound acoustic signal, said
transducer comprising a cylindrical plate of piezoelectric material having
first and second planar faces, said first planar face being plated with a
metal over substantially its entire surface, and said second planar face
being plated with a metal in two separate semicircular areas between which
said ultrasound electric signal is applied or generated, the piezoelectric
material between said first planar face and one semicircular area of said
second planar face being polarized opposite to the polarization of the
piezoelectric material between said first planar face and the other
semicircular area of said second planar face.
43. The ultrasound transducer of claim 42 wherein said semicircular areas
have a diameter that is substantially smaller than the diameter of said
cylindrical plate, said transducer further including two separate arcuate
areas surrounding said semicircular areas, thereby allowing said
transducer to focus at a relatively shallow depth when said electrical
signal is applied to or generated between said semicircular plated areas
and allowing said transducer to focus at a relatively large depth when
said ultrasound electric signal is applied to or generated between said
arcuate areas.
44. The transducer of claim 43 wherein said semicircular plated areas are
separated from each other and said plated arcuate areas are separated from
each other by a common diameter of said cylindrical plate. |
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Claims |
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Description |
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TECHNICAL FIELD
This invention relates to ultrasound imaging, and more particularly, to a
system for ultrasonically imaging internal body tissues using an
endoscopically deliverable imaging probe.
BACKGROUND ART
A wide variety of ultrasound systems have long been used for medical
diagnostic purposes. One of these ultrasound devices is the Doppler probe,
in which ultrasound energy is transmitted into the body and the change in
frequency of the return signal is detected to provide an indication of
blood flowing in veins and arteries. The characteristics of the
frequency-shifted Doppler signal indicate the presence of an adjacent
blood vessel and identify whether the vessel is a vein or an artery.
Recently, an endoscopically deliverable ultrasound Doppler probe has been
proposed and is described in U.S. Pat. No. 4,582,067, to Silverstein et
al. The endoscopically deliverable Doppler probe can be passed through the
biopsy channel of standard endoscopes and placed, under direct vision,
against the tissue to be examined. The system has been found to be useful
for evaluating the papilla of Vater to determine whether an abnormal blood
vessel is present which might cause life-threatening hemorrhage. The
system has also been used for locating arteries in ulcers that are
responsible for massive upper gastrointestinal hemorrhage before and after
the application of endoscopically delivered hemostatic therapy.
Another conventional, commonly used ultrasound system allows subcutaneous
tissues to be visualized. In ultrasound imaging, an ultrasound transducer
is generally placed in contact with the skin of the patient and pulses of
ultrasound energy are transmitted from the transducer into the tissues of
interest. Return echoes from the tissues are localized to a specific depth
by conventional range gating and used to modulate the intensity of a
cathode-ray tube display as the probe is either electrically or
mechanically scanned across the tissues. The scan of the probe modulates
one axis of the CRT, while the other axis of the CRT is modulated by the
range gate. The CRT thus displays a cross section of tissue. The internal
organs are visible primarily as a result of the changes in the acoustic
impedance of such organs in comparison to the surrounding tissues.
Ultrasound imaging has also been combined with the Doppler principle to
image blood flowing veins and arteries. In ultrasound Doppler imaging,
returns from non-moving tissues and organs are either ignored or processed
separately to display return echoes from moving blood.
Although tissues and internal organs, particularly those close to the
surface, can be imaged externally, the walls of the gastrointestinal track
cannot be externally imaged with any degree of accuracy for several
reasons. First, the wall of the gastrointestinal tract moves toward and
away from the transducer, thus making it extremely difficult to isolate
the relatively small thickness of the GI track as the depth of interest.
Furthermore, deep ultrasound imaging can be effectively accomplished only
by utilizing relatively low frequencies. However, the high resolution
required to usefully image the walls of the GI track require a
substantially higher ultrasound frequency. Yet this higher ultrasound
frequency is quickly attenuated in the body and never reaches the walls of
the GI track of interest.
In order to allow the walls of the gastrointestinal track to be
ultrasonically imaged without the many problems of external imaging,
attempts have been made to endoscopically image such tissues. Internal
ultrasound imaging offers several advantages over percutaneous ultrasound
and other imaging techniques. With internal ultrasound imaging,
penetration is less of a problem when the transducer is placed immediately
adjacent to the tissue target. The anterior abdominal wall and other
intervening structures do not have to be penetrated. Intervening
structures, especially air, can severely limit the percutaneous ultrasound
in certain clinical situations. The reduced penetration requirement allows
for the use of highfrequency ultrasound, which is capable of producing
images of high resolution. High-resolution ultrasound may reduce exposure
to ionizing radiation from other diagnostic procedures by eliminating
other less specific tests. Although ultrasound does have biological
effects, for use at diagnostic levels no significant effects have been
reported.
There is a critical need to be able to obtain during routine endoscopy
information about wall structure. This data may be useful to guide the
next diagnostic or therapeutic steps while the endoscope is still in
place. The earlier diagnosis which internal ultrasound imaging would allow
could have highly desirable effects upon the treatment of the patient in
terms of directing appropriate effective therapy and avoiding
inappropriate therapy. The advantages of an early, specific, inexpensive,
and noninvasive diagnosis are well recognized. For example, if the exact
extent of wall involvement by a sessile tumor could be determined, tumors
that could be ablated endoscopically without causing perforation could be
easily identified. Given the decision that the disease is localized to the
mucosa without deep invasion, laser or electrocautery could be applied.
If, however, the ultrasound image indicated that the tumor had spread to
adjacent structures, then palliative therapy would be appropriate.
Internal ultrasound imaging is particularly appropriate for diseases which
have certain common characteristics. Diseases which involve the
gastrointestinal wall, diseases which can be reached endoscopically,
diseases that are frequent, disabling, and currently not readily
diagnosed, and diseases that are now poorly treated because they are
diagnosed too late are all prime candidates.
One disease that could be advantageously diagnosed by internal ultrasound
imaging is Crohn's inflammatory bowel disease. Crohn's disease is a
disabling inflammatory disease of the gastrointestinal track which affects
the small and large bowel. The cause is unknown. It is one of the most
frequently encountered types of inflammatory bowel disease, the other
being mucosal ulcerative colitis. However, Crohn's disease involves the
entire thickness of the bowel wall (transmural disease), whereas
ulcerative colitis is limited to the mucosa of the colon. It has been
estimated that between one million and two million Americans have
inflammatory bowel diseases, and the frequency of these diseases is
increasing. Most of the new cases are diagnosed before the age of thirty.
Crohn's disease is difficult to diagnose and treat. When the patient first
presents, the work-up may include history, physical exam, sigmoidoscopy,
barium enema and small intestine X-rays, colonoscopy, and rectal biopsy.
Even with this evaluation, diagnosis may be uncertain. Symptoms and
complications are variable. By rapidly examining the wall of the rectum
and colon with internal ultrasound imaging, an early specific diagnosis
may be made. When following such patients, internal ultrasound imaging may
also provide an essential parameter to evaluate whether the disease to
adjacent structures or formed an abscess.
Gastric malignancies, including adenocarcinoma and lymphoma, may also be
diagnosed using internal ultrasound imaging. Tumors of the upper
gastrointestinal tract are frequent. Currently, gastroenterologists use
endoscopy to evaluate the patient with epigastric symptoms suggesting an
ulcer or tumor. After visually inspecting an abnormal area, biopsies and
brush cytologies are taken. However, it is impossible for an endoscopist
to evaluate the area of the submucosa. There may be a lump, but the
biopsies will often contain only normal surface mucosa from over the mass.
If a cancer is suspected, the endoscopist cannot assess the degree of
extension of the tumor. Internal ultrasound imaging could be used
routinely during diagnostic endoscopy. Once an abnormal area was
visualized, an ultrasound probe could determine the nature of the
underlying wall. It could also answer such questions as whether there is a
mass present, whether the mass is abnormally thick, whether there are
abnormal lymph nodes adjacent to the stomach, or whether there are other
diagnostic features. This information might allow an earlier diagnosis,
expedite correct therapy, and avoid unnecessary intervention.
Internal ultrasound imaging may also be applicable to esophageal carcinoma.
Tumors of the esophagus have posed a significant problem for the clinician
for years. When a patient presents with symptoms caused by cancer, the
tumor is usually too expensive to be surgically resectable. The result is
that only 39% of esophageal cancers are considered resectable and the
five-year survival rate is only about 5%-10%. Since internal ultrasound
imaging would allow the endoscopist to evaluate an area which is
equivocal, the image might reveal diagnostic thickening of the mucosa
consistent with carcinoma. It can evaluate an obvious cancer to determine
whether the cancer has extended into the mediastinum, which would make the
patient inoperable. Internal ultrasound imaging may also be especially
helpful in the patient with a premalignant condition of the esophagus,
such as Barrett's epithelium, by early detection of possibly treatable
adenocarcinomas.
Tumors of the colon and rectum are one of the most common visceral tumors
in the Western Hemisphere. The instance of colon and rectal cancer has
increased over the past several years, and these tumors are now among the
three most frequent tumors in the United States. Colon and rectal cancers
account for approximately 15% of all newly diagnosed cancers in both men
and women in the United States. Significant progress in early detection of
these lesions has been made by screening stools for blood and by using
sigmoidoscopy and colonoscopy. However, it is usually difficult to stage
carcinomas of the colon and rectum preoperatively, despite CT scans and
other methods. But staging can be very important for patient management.
The extent of the tumor may dictate whether or not it is appropriate to
use preoperative radiation therapy. Internal ultrasound imaging could be
used to provide staging.
Finally, there is increasing interest in the motility of the
gastrointestinal tract since many diseases which trouble patients seem
related to motility. Such diseases include esophageal spasm, achalasia,
abnormal gastric emptying, functional bowel disease, and other motility
disfunctions.
Attempts have been made to provide internal ultrasound imaging through
endoscopes using linear arrays, phased arrays, and mechanical sector
scanners. The mechanical sector scanner endoscope, as described in
Hisanaga, "A New Trans-Digestive-Tract Scanner with a Gastro-Fiber-Scope,"
Proc. 23 AIUM 1978, uses a specially designed, side-viewing endoscope
having a transducer mounted on the end of a wire. The transducer has a
transversely directed beam pattern, and it is rotated ab | | |
