A stand-off device for use with an acoustic transducer in the form of a volume having a flexible cup section and a stiff cup section with the lips of the cups joined together and almost filled with liquid. The bottom of the stiff cup section has an opening across which a membrane is mounted and a clip for holding the active section of a transducer in contact with the membrane.

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.

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.