Surgery – Diagnostic testing – Detecting nuclear – electromagnetic – or ultrasonic radiation
Reexamination Certificate
1999-07-21
2001-09-11
Lateef, Marvin M. (Department: 3737)
Surgery
Diagnostic testing
Detecting nuclear, electromagnetic, or ultrasonic radiation
Reexamination Certificate
active
06287261
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates generally to ultrasonic imaging catheters, and more particularly, to ultrasonic transducers providing improved resolution for such catheters.
Intravascular imaging of blood vessels and surrounding tissues continues to be of great benefit in a wide range of medical fields. A particularly successful design for an intravascular imaging catheter
10
is shown in
FIGS. 1A and 1B
. Catheter
10
employs a rotatable imaging assembly
12
having a distal end
16
and a proximal end. An ultrasound transducer
14
is attached to distal end
16
. The proximal end is operably attached to a flexible drive cable (not shown). Transducer
14
typically is elliptical in shape with a flat outer face. The transducer outer face has its major axis aligned with a longitudinal axis
20
of the imaging assembly
12
. In other cases, the transducer
14
is round in shape with a flat outer face as shown in FIG.
1
C.
During operation, a flexible sheath
18
is inserted into a patient with the drive cable and imaging assembly
12
disposed within sheath
18
. The imaging assembly
12
typically is rotated within sheath
18
during transmission of ultrasound signals into the patient. During rotation of imaging assembly
12
, transducer
14
projects ultrasound signals into a 360 degree image plane. The image plane has an in-plane or X-plane component
22
created primarily by the rotation of transducer
14
. The image plane also has a cross-plane or Y-plane component
24
created primarily by the length of the major axis of transducer
14
for the transducer shown in FIG.
1
B. The transducer element
14
is connected to electronics, typically maintained outside the patient's body, to produce a video image of at least a portion of the image plane by well-known techniques.
To produce images, it is desirable to have ultrasound signals transmitted by transducer
14
pass through sheath
18
and reflect off of tissue or fluids. However, a portion of the ultrasound signals transmitted by the transducer
14
typically are reflected by the sheath
18
. Another portion of the ultrasound signals pass through sheath
18
, but are refracted by sheath
18
during passage.
Due at least in part to the sheath effects on the ultrasound signal and to the shape of the transducer, ultrasound signals typically have a different in-plane profile than a cross-plane profile. The in-plane profile typically is narrower or tighter than the cross-plane profile. This can be seen by comparing
FIG. 2A
(depicting an in-plane profile
26
for a round transducer) with
FIG. 2B
(depicting a cross-plane profile
28
for a round transducer). Further, the in-plane profile
26
has a focal length that is shorter compared to the focal length in the cross-plane profile
28
. As a result, the transducer
14
has better lateral resolution in the in-plane direction
22
than in the cross-plane direction
24
.
It is desirable, therefore, to produce a tighter beam profile in the cross-plane direction so that the focal point is closer to the transducer surface. Improved cross-plane lateral resolution will result. It is further desirable to provide a more circular or symmetrical cross-section for the ultrasound signal profile, so that lateral resolution is similar for both the in-plane and cross-plane.
SUMMARY OF THE INVENTION
The present invention provides ultrasound transducers, and imaging assemblies and catheters employing such transducers, that provide improved imaging capabilities. For example, the present invention provides improved lateral resolution as a result of the positioning of the transducer on the imaging assembly and/or the curvature profile of the transducer outer face. This produces a tighter imaging signal in the cross-plane direction, thereby improving lateral resolution.
In one embodiment, the present invention provides an ultrasound imaging assembly. The imaging assembly includes a housing having a distal end, a proximal end, and a longitudinal axis. The assembly includes a transducer element having a generally elliptical outer face which defines a major axis and a minor axis. The transducer element is operably attached to the distal end to position the minor axis to be generally parallel to the longitudinal axis. In this manner, a tighter cross-plane beam profile is produced due to the minor axis being generally parallel to, i.e. generally aligned with, the longitudinal axis of the imaging assembly.
In one aspect, the outer face of the transducer element is generally oval shaped. It will be appreciated by those skilled in the art, that other transducer shapes may be used within the scope of the present invention. In another aspect, the outer face is generally flat.
In one aspect, the outer face has a first radius of curvature along the minor axis and a second radius of curvature along the major axis. Preferably, the second radius of curvature is greater than the first radius of curvature. In this manner, the transducer element has a tighter radius of curvature in the cross-plane direction to provide a greater focussing effect in the cross-plane direction compared to the focussing effect in the in-lane direction. A tighter cross-plane beam profile will result compared to the device shown in FIG.
1
. Alternatively, the first and second radii of curvature are generally equal.
In one aspect, the proximal end is adapted to be coupled to a drive cable. In this manner, the drive cable can operate to rotate the imaging assembly. In another aspect, a matching layer or multiple matching layers are operably attached to the outer face of the transducer element. In this manner, improved efficiency and band-width can result.
In one aspect, the transducer element is a tapered focus transducer element. Alternatively, the transducer element is a true focus transducer element. Preferably, the transducer element is selected from a group of materials consisting of piezoplastics, piezocomposites, and piezoceramics.
In one particular aspect, the transducer element is adapted to propagate an ultrasound signal in response to electrical input. The ultrasonic beam includes an in-plane signal component that is generally perpendicular to the longitudinal axis, and a cross-plane signal component that is generally parallel to the longitudinal axis. The in-plane signal component has an in-plane focal length that is generally equal to a cross-plane focal length of the cross-plane signal component. In one aspect, the in-plane focal length is between about 0.25 mm and about 2.5 mm. Similarly, the cross-plane focal length is between about 0.25 mm and about 2.5 mm. In one particular aspect, the outer face has a shape and radius of curvature profile so that the ultrasound signal has a generally circular cross-sectional shape at a prescribed distance, for example between about 0.25 mm and about 2.5 mm, from the distal end.
The invention further provides an ultrasound imaging assembly which includes a housing having a distal end, a proximal end and a longitudinal axis. A transducer element having an outer face is included and coupled to the housing. The outer face has a first radius of curvature along a first axis and a second radius of curvature along a second axis. The transducer element is operably attached to the distal end to position the first axis to be generally parallel to the longitudinal axis. In one aspect, the second radius of curvature is greater than the first radius of curvature. Alternatively, the first and second radii of curvature are generally equal.
In one aspect, the first axis is a major axis of the outer face and the second axis is a minor axis of the outer face. Alternatively, the first axis is a minor axis of the outer face and the second axis is a major axis of the outer face. In this manner, elliptical or oval transducers are used. Alternatively, the outer face is generally round.
In still another aspect, the transducer element further includes a second face spaced apart from the outer face to define a transducer thickness therebetween. In one aspect, the second and oute
Bautista Richard
Mendoza Dennis
Suorsa Veijo T.
Imam Ali M.
Lateef Marvin M.
Sci-Med Life Systems, Inc.
Townsend and Townsend / and Crew LLP
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