Ultrasound imaging and catheters for use therein

Details Ultrasound imaging and catheters for use therein Ultrasound imaging and catheters for use therein

1994-07-27

1995-11-14

Manuel, George

Surgery

Truss

Pad

12866206, A61B 812

Patent

active

054657261

DESCRIPTION:

BRIEF SUMMARY
The present invention relates to medical ultrasound imaging and to catheters for use therein.
Our International Patent Application Nos. GB88/00971 (Publication No. WO89/04142) and GB90/00830 (Publication No. WO90/14601) disclose ultrasound systems for producing 3-dimensional and 2-dimensional images respectively of human internal organs and to catheters for use with such systems.
In these systems a catheter is provided at its distal end, with a piezo-electric transducer crystal array for generating ultrasonic signals and for receiving their echoes from which a visual representation is obtained.
Typically, such catheters are designed for insertion into an artery of the patient and the 2-dimensional and/or 3-dimensional images obtained are of the interior of the artery.
There is a problem with such ultrasound arrangements in that a dead space or blind spot, as far as the imaging is concerned, exists in the immediate vicinity of the transducer array. This caused by the fact that the mechanical vibration of the transducer elements to produce the ultrasonic signals takes some time to die down after an energisation pulse. This time is sufficiently long for the energisation vibration to interfere with the vibration of the crystal caused by the returning echo signal. This phenomena is sometimes referred to as "ringdown". The time it takes for the transducer element to stop vibrating as a result of its initial energisation is also sometimes referred to as the "ringdown" time.
This phenomenon is described, for example, in U.S. Pat. No. 4,899,757 and one solution to the "ringdown" problem is disclosed in that patent.
The arrangement disclosed in U.S. Pat. No. 4,899,757 deals with this "ringdown" problem by including the "dead space" within the catheter itself. In other words the initial path of the outgoing ultrasound signal and the final part of the path of the incoming echo signal are both contained within the catheter itself. It is thus possible with such an arrangement for any target, such as the interior wall of a blood vessel, to be visualised even though that target is immediately adjacent to or in contact with the external surface of the catheter.
The present invention is concerned with providing an ultrasonic catheter which overcomes the "ringdown" problem and also provides an ultrasonic beam which is more effective than the single element beam provided by the prior art.
According to the present invention a catheter including an ultrasonic transducer element positioned in relation to the catheter to emit an ultrasonic signal substantially parallel to or co-axial with the axis of the catheter and a mirror arranged within the catheter to deflect the ultrasonic signal in a substantially radial direction in relation to the axis of the catheter, the path length of the ultrasonic signal within the catheter being such that it overcomes the "ringdown" problem, is characterised by the following features: substantially diametral plane of the catheter; interface located within the catheter at a specified distance from the transducer; and conical interface are so selected that the initial path of the emitted ultrasonic signal and the final path of the returning ultrasonic echo signal are contained within the catheter itself so as to overcome the "ringdown" problem.
The term "conical interface" refers to any conical interface between two media or materials such that the effect of the interface is to reflect the ultrasonic beam, or returning echo beam, through an angle sufficient for the beam to exit from the side of the catheter. In practice the conical surface would preferably be inclined at substantially 45.degree. to the catheter axis to thus cause the outgoing ultrasonic beam and the returning echo beam no be turned through substantially 90.degree..
The "ringdown" distance depends on a number of variables which include the frequency with which the transducer is excited the transducer material, the mounting of the transducer including the backing materials and front layers. Thus it will be a question of detailed desig

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patent: 5081993 (1992-01-01), Kitney et al.
patent: 5156144 (1992-10-01), Iwasaki et al.
patent: 5257629 (1993-11-01), Kitney et al.

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