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Description  |
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BACKGROUND OF THE INVENTION
In ultrasonic systems used to image the interior of a patient's body, a
transducer transmits acoustic energy into the body and receives echoes
from structures therein. It converts the energy in these echoes into
electrical signals that are used to form an image. In many cases,
structures close to the surface of the body are not in a region of sharp
focus because of their proximity to the transducer, but they can be placed
farther away from the transducer so as to be in a region of better focus
by insertion of a stand-off device between the transducer and the
patient's body. A plastic bag filled with liquid may be used for this
purpose. Furthermore, in a system producing an image in the form of a
sector, it is difficult to identify structures near the apex because of
the limited field of view. This problem can also be eliminated by use of a
stand-off device because the structures previously at the apex can be
placed properly within the sector where more of the surrounding structure
is visible.
In some known stand-off devices, the surface of the stand-off device that
contacts the body has been made of flexible material, but the volume
within the device has been filled with liquid so that pressure must be
applied to bring a desired amount of the surface into intimate contact
with the patient's body. This causes the relative positions of the
structures being observed to be disturbed.
BRIEF DESCRIPTION OF THE INVENTION
A stand-off device constructed in accordance with this invention is
comprised of a cup section made of flexible material having its lip joined
to the lip of a cup section made of relatively stiff material, enough
bubble-free liquid contained in said cup sections to fill the volume of
the stiff cup section and partially fill the volume of the flexible cup
section, the remainder of the volume being gas-free, and an opening in the
bottom of the stiff cup section whereby a transducer may be acoustically
coupled to the liquid. When the flexible cup section is lightly pressed
against the body of a patient, its geometry is modified to a point where
good acoustical coupling is established between the body of the patient
and the liquid. The transducer itself may close the opening in the bottom
of the stiff cup, or a flexible membrane may be used for this purpose and
the transducer mounted in intimate contact therewith. In either case, good
acoustical coupling must be provided between the transducer and the
liquid. The stand-off device can be separate from the transducer and have
means for holding the transducer in its proper position, or it can be an
integral part of the transducer.
The stiff cup section generally but not necessarily occupies most of the
distance between the transducer and the body of the patient and is strong
enough to maintain its shape when the flexible cup section is pressed
against the body. Alternatively, the walls of the stiff cup section can be
strong enough to retain their general shape and yet flexible enough to
permit the depth of the cup section to be changed by squeezing it with the
hand.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1A is a view looking down in a flexible cup section of a stand-off
device constructed in accordance with this invention;
FIG. 1B is an elevational section BB of FIG. 1A;
FIG. 1C is a bottom view of the stand-off device;
FIG. 1D is the elevational section DD of FIG. 1A;
FIG. 1E is the elevational section EE of FIG. 1A;
FIG. 2 is the elevational section of FIG. 1B with a transducer mounted for
operation; and
FIG. 3 is an exterior projection view of a stand-off device with a
transducer adjoined thereto.
DETAILED DESCRIPTION OF THE INVENTION
In the following description, corresponding components in the various
figures of the drawings are designated in the same way.
Reference is now made to FIG. 1B. A stiff cup section 2 has a rectangular
opening 4 formed in its bottom, and a membrane 6 is tautly stretched
across the opening 4. In this particular embodiment, a circular top 8 of a
cap 9 having a hollow cylindrical skirt 10 extending perpendicularly below
its periphery is bonded to a recess in the outer surface of the bottom of
the rigid cup 2 with such orientation that a rectangular opening 12 in the
top 8 is in registration with the rectangular opening 4. An annular groove
14 on the inner surface of the skirt 10 is located at a given distance
from the top 8. A transducer retaining clip 16, which is in the general
form of a hollow cylinder, has an annular base 18 and four fingers
f.sub.1, f.sub.2, f.sub.3 and f.sub.4 extending perpendicularly therefrom,
but only fingers f.sub.1, f.sub.2 and f.sub.3 appear in FIG. 1B. The outer
diameter of the base 18 is slightly less than the inner diameter of the
skirt 10, and an annular ridge 20 is located on the outer surface of the
base 18 at a distance from the top of the clip 16 that is slightly less
than the distance of the groove 14 from the top 8 of the cap 9. Thus, when
the membrane 6 is stretched taut over the base 18 of the clip 16 and down
its sides and the clip 16 is inserted into the skirt 10, the ridge 20
engages the groove 14 so as to hold the membrane 6 in position across the
bottom of the opening 12 and therefore across the opening 4.
A flexible cup section 22 formed from thin flexible material has a lip 24
cemented to the outer surface of the lip 26 of the rigid cup 2. In order
to fit the contours of the body more readily, it is advantageous for the
bottom of the flexible cup 22 to be substantially planar.
An important aspect of the invention is the fact that the cups 2 and 22
contain a volume of liquid 23 that is greater than the volume of the cup
section 2 and less than the sum of the volume of the cup section 2 and the
maximum volume of the cup section 22 at normal ambient conditions. It is
important that the liquid 23 contain no air bubbles. With a configuration
generally like that shown in the drawings, good results have been attained
when the liquid fills 95% of the total cup volumes. In any event, 90% to
98% of the total volume of the cups should be filled.
Introduction of the required amount of liquid into the cup sections 2 and
22 without also introducing air bubbles is made possible by provision of
means such as a purging port 30 (FIGS. 1C and 1D) in the bottom of the cup
2. As can be seen in FIG. 1D, which is a vertical section DD of FIG. 1A,
the port 30 is comprised of a screw 32 threaded into a passageway 34 that
extends entirely through the bottom of the cup 2. The outer end of the
passageway 34 has an annular recess 36 which has a diameter slightly
larger than the head of the screw 32 and an O-ring 38 mounted in the
recess 36 so that when the screw 32 is screwed inwardly, its head squeezes
the O-ring 38 so as to form a seal. In order that the cup sections 2 and
22 may contain a desired amount of liquid, the stand-off device is
positioned with the axes of the cup sections vertically disposed and the
cup section 2 on the bottom. The screw 32 is removed and liquid is poured
through the passageway 34 until the cup sections 2 and 22 are filled to
overflowing. In this situation, the volume formed by the cup section 22 is
a maximum. At this point, the device is lowered onto a flat horizontal
surface so as to push the bottom of the flexible cup section 22 upward and
cause a desired amount of fluid to overflow from the passageway 34. The
screw 32 is then inserted and tightened against the O-ring 38 so as to
form a seal. If improper use should cause air bubbles to form in the
liquid, the process can be repeated. If this contingency is not provided
for, the passageway 34 could be permanently sealed off when the right
amount of fluid has overflowed.
If the cup section 2 and the maximum volume of the cup section 22 were
entirely filled with liquid, the bottom of the cup section 22 would be
curved and would have to be firmly pressed against the body of a patient
in order to ensure contact throughout the required surface area even
though the cup section 22 is molded with the surface 22' perpendicular to
the cup axis being flat. As previously pointed out, such firm pressure
would disturb the relative locations of structures in the body. But when
the combined volumes of the cup sections 2 and 22 are nearly filled, e.g.,
95%, as just described, very little pressure is required to make the
bottom 22' of the cup 22 conform to the shape of the body so that the
relative positions of structures within the body are not disturbed and the
interior of the body can be viewed as it is. More importantly, however,
good contact between the bottom 22' of the cup 22 and the body is easily
achieved.
It is equally important that the entire active area of a transducer lens be
in intimate contact with the outside of the membrane 6. This function is
peformed by the clip 16 for a transducer having the shape of the
transducer 40 depicted in FIGS. 2 and 3, but it is understood that the
design of the clip 16 may be different for transducers having a different
shape. The outside of the transducer 40 has a cylindrical cross-section at
the point indicated by the arrow dh, FIG. 2, and tapers to a smaller
nearly rectangular cross-section as it approaches its active area 42. The
area 42 may be covered by a rubber lens 43. Although not shown, the active
area 42 has a rectangular configuration that is proportional to the
rectangular openings 4 and 12. On the lower side of the arrow dh, the
outer diameter of the transducer 40 is reduced so as to form a step 44.
The fingers f.sub.1 through f.sub.4 are respectively provided with ridges
r.sub.1 through r.sub.4 at the outer ends of their inside surfaces, but
only the fingers f.sub.2 and f.sub.3 of the clip 16 appear in FIG. 2. The
finger f.sub.1 also appears in FIG. 1B. As seen in FIG. 1B, the diameter
dr of the circle on which the innermost surfaces of the ridges r.sub.1
through r.sub.4 lie is less than the internal diameter db of the base 18
of the clip 16. The diameter db is slightly larger than the maximum outer
diameter dh of the transducer 40. Thus, as the transducer 40 is being
inserted within the fingers f.sub.1, f.sub.2, f.sub.3 and f.sub.4, there
comes a point when the outer surface of the transducer 40 engages the
inner ridges r.sub.1, r.sub.2, r.sub.3 and r.sub.4 so as to expand them in
a radially outward direction. When the annular step 44 reaches the ridges
r.sub.1, r.sub.2, r.sub.3 and r.sub.4, the fingers f.sub.1, f.sub.2,
f.sub.3 and f.sub.4 start to contract; and when the inner end of the
transducer reaches a point where it is in contact with the membrane 6 at
the corner 46 of the opening 12 in the top 8 of the cap 9, the interior
surfaces of the ridges r.sub.1 , r.sub.2, r.sub.3 and r.sub.4 are in
contact with the exterior surface of the step 44. The shape of the step 44
in an axial plane complements the shape of the ridges r.sub.1, r.sub.2,
r.sub.3 and r.sub.4 so as to provide good contact between them and firmly
retain the transducer 40 in position.
It is important to notice that when the transducer 40 is inserted in the
clip 16 in the manner just described, its lens 43 presses the diaphragm 6
upward into the opening 12 so as to establish intimate contact between
them.
Reference is now made to FIG. 3 for a description of the construction
details of the transducer 40 that permit its rectangular active area 42 to
be oriented with the rectangular opening 12 in the top 8 of the cap when
it is inserted into the clip 16. In FIG. 3, the annular step 44 of FIG. 2
is replaced by four steps S.sub.1 through S.sub.4 having the same shape in
an axial plane as the step 44. Only S.sub.4 appears in FIG. 3. When the
steps S.sub.1 through S.sub.4 are oriented so as to be respectively under
the fingers f.sub.1 through f.sub.4, they fit with the ridges r.sub.1
through r.sub.4 respectively in the same manner as the step 44, and the
registration between the active area 42 of the transducer 40 and the
rectangular opening 12 is obtained.
It would be possible to remove the transducer 40 from the clip 16 of FIG. 3
by exerting sufficient axial force so that the steps S.sub.1 through
S.sub.4 respectively push the fingers f.sub.1 through f.sub.4 in a
radially outward direction through interaction with the ridges r.sub.1
through r.sub.4, but this can be done more easily by rotating the
transducer 40 to the position shown in FIG. 3 wherein the steps S.sub.1
through S.sub.4 are between the fingers.
As the transducer 40 is rotated, an outward axial force is applied to it so
as to make its removal easier. This action results from the shape of the
outer surface of the transducer 40 surrounding the lens 43. The shape is
such that the transducer 40 contacts the edge 46 as indicated by a
dash-dot line 42' of FIG. 1C. Contact is made at the center of the sides
of the opening 12. As seen in FIG. 1E, the transducer 40 is curved in an
axial plane passing through the latter points of contact. It is curved in
a similar manner in axial planes on either side of the central one shown
in FIG. 1C. Therefore, when the transducer 40 is rotated about its
longitudinal axis, the surface surrounding the lens 43 rides up on the
edge 46 so as to force the transducer in an outward direction.
Although the stand-off device has been shown as being separate from the
transducer 40, it could be formed as an integral part thereof, in which
event the clip 16 would not be used.
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