Surgery – Truss – Pad
Patent
1987-05-27
1990-07-24
Smith, Ruth S.
Surgery
Truss
Pad
128 24A, A61B 1722
Patent
active
049428780
DESCRIPTION:
BRIEF SUMMARY
During the use of an extracorporeal lithotriptor for destroying gall stones by pressure waves, the degree of fragmentation thereof, the knowledge of which is important for determining the moment when the firing should be stopped, is somtimes difficult to assess.
In fact, from the very beginning of fragmentation, small fragments may be deposited under the stone and form a screen in front of the locating device, for example an echography device, which the lithotriptor comprises. The image which then appears on the screen of this device is that of the layer formed by the fragment which then merges with the rest of the stone. The resolution of the device is not sufficient to separate each elementary particle and the operator, deceived by the aspect of the image, may stop the treatment prematurely.
Another case of error is that in which, with the gall stone enclosed in a cavity, the fragments remain in position. The result is that the echographic image may remain unchanged even when the fragmentation is complete.
The invention has as an object a method of locating the stones and fragments thereof comprising the formation of an image and observation thereof in real time, characterized in that said fragments are subjected to pulsed and focused elastic waves emitted with a relatively small power with respect to that of the firing, but appreciably higher than that used for the echography, and at a rate of the order of a few hertz, advantageously 5 to 10 Hz and in that the shape modifications undergone by the echoes of the fragments are interpreted so as to obtain information relative to the size of the fragments.
The invention is based on the discovery that small sized fragments (less than 3 mm for example), subjected to such an elastic wave, undergo a movement of an amplitude inversely proportional to their size. Because of interference phenomena there partly results therefrom a substantial and characteristic modification of the shape of the echoes reflected by the fragment. The echo may disappear completely if the size of the fragment is less than a certain limit, it will on the other hand be stable for a fragment of a size greater than a given threshold.
In a preferred embodiment, the stone and its fragments subjected to said elastic waves are observed with type A echography effected on a line which passes through the focal spot of the elastic wave beam and the disappearance or modification of the echo are observed on each of the fragments for indicating that the above mentioned lower limit of size has been reached and that it is no longer necessary to resume firing.
In an improvement, a zone containing fragments whose sizes it is desired to analyse more finely is subject, during application of said elastic waves, to elastic examination pulses and the variation of the carrier frequency of these examination pulses by reflection from the fragments is measured so as to give an indication of the speed of movement of said fragments under the impact of said elastic waves.
The invention also has as an object a device for implementing the above mentioned process. In its preferred embodiment, this device uses the main ultrasonic pulse emitter of the lithotriptor at reduced power and at a pulse rate appropriate to setting in motion the gall stone fragments and displays the echoes in echography A.
Other characteristics, as well as the advantages of the invention, will clearly appear from the light of the following description.
The single FIGURE of the accompanying drawing is the general diagram of a lithotriptor equipped with an apparatus for locating gall stone fragments in accordance with a preferred embodiment of the invention.
A transducer 1 has been shown in the drawing in the form of a spherical skull cap, constructed and mounted so as to be able to be positioned along three orthogonal axes, as was described in U.S. Pat. No. 4,617,931, filed on Nov. 26, 1984 in the name of Jacques Dory for: "Ultrasonic pulse apparatus for destroying calculuses" and which is incorporated in the present disclosure as a part thereof. An
REFERENCES:
patent: 4526168 (1985-07-01), Hassler et al.
patent: 4669483 (1987-06-01), Hepp et al.
Drucker William A.
Smith Ruth S.
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