Surgery: kinesitherapy – Kinesitherapy – Ultrasonic
Reexamination Certificate
2000-03-09
2003-01-21
Lateef, Marvin M. (Department: 3737)
Surgery: kinesitherapy
Kinesitherapy
Ultrasonic
C601S001000, C600S439000
Reexamination Certificate
active
06508774
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to apparatus and methods for controlled heating of body tissues by high intensity focused ultrasound, commonly referred to by the acronym HIFU.
BACKGROUND OF THE INVENTION
Elevated temperature treatments are used for a variety of purposes in medical and veterinary practice. In HIFU treatment, ultrasonic energy is focused to a small spot within the body so as to heat the tissues to a temperature sufficient to create a desired therapeutic effect. This technique can be used to selectively destroy unwanted tissue within the body. For example, tumors or other unwanted tissues can be destroyed by applying focused ultrasonic energy so as to heat tissue to a temperature sufficient to kill the tissue, commonly about 60° to about 80° C., without destroying adjacent normal tissues. Other elevated-temperature treatments include selectively heating tissues so as to selectively activate a drug or to promote some other physiological change in a selected portion of the subject's body. The term “heating” is used herein as referring to all of these treatments, whereas the term “ablation” as used herein as specifically referring to procedures in which tissue is deliberately killed.
As disclosed in International Application PCT/US98/1062, published as International Publication WO/98/52465 the disclosure which is hereby incorporated by reference herein, HIFU heating typically is conducted using an ultrasonic emitter having an array of transducers. The transducers are actuated with a drive signal so as to emit therapeutic ultrasonic waves at a selected frequency. Differences in phase can be applied to the drive signal sent to each transducer so that the therapeutic ultrasonic waves tend to reinforce one another constructively at the focal location. As also disclosed in the '465 publication, the transducer array may be incorporated in a disposable device. As described, for example in copending, commonly assigned U.S. patent applications Ser. No. 09/496,988, filed Feb. 2, 2000 and 60/125,676, filed Mar. 22, 1999, the disclosures of which are also incorporated by reference herein, HIFU. may be applied but transducer arrays which are mounted on a probe such as a catheter which can be introduced into the body as, for example, within the vascular system or into a cavernous internal organ.
Application of intense ultrasonic energy to body tissues can result in a phenomenon referred to as “cavitation” in which small bubbles form and collapse. The occurrence of cavitation at any point within the body is dependent upon factors including the local temperature at that point, the composition of the tissue at that point and the characteristics of the ultrasonic energy applied to that point. In some medical procedures, cavitation is regarded as a desirable phenomenon for inducing tissue damage or for breaking up objects such as deposits within the body. However, in typical heating treatments, cavitation is regarded as highly undesirable because it can cause unwanted and unpredictable forms of tissue damage.
Various approaches have been proposed for monitoring cavitation in medical treatments of various types. Cavitation is accompanied by a wide band ultrasonic noise emissions from the region where cavitation is occurring. Vykhodtseva et al., Histologic Effects of High Intensity Focused Ultrasound Exposure with Subharmonic Emission in Rabbit Brain in vivo, Ultrasound in Med. and Biol. Vol. 21, No. 7, pp. 969-979, 1995, employs a hydrophone to monitor ultrasonic noise emission from the brain of rabbit during experimental application of ultrasound. The hydrophone is connected through a filter to an oscilloscope so that the ultrasonic noise emitted at the focal region can be displayed and observed. Grandia et al., U.S. Pat. No. 5,827,204 discloses a system in which cavitation is deliberately produced, and uses a hydrophone for detecting emitted noise with feedback control of the ultrasonic transmitter for the purpose of optimizing cavitation.
Cavitation is also accompanied by an increase in the tendency of the tissue where cavitation occurs to reflect ultrasonic waves as echoes, commonly referred to as “echogenicity”. That is, tissues with the bubbles produced in cavitation tend to reflect more ultrasound than the same tissues without such bubbles. Fujimoto et al., U.S. Pat. No. 5,694,936, discloses a system using a separate ultrasonic emitting transducer array for acquiring ultrasonic images of tissues during heating by directing a separate ultrasonic beam through the subject body and monitoring the reflected ultrasound. Areas where cavitation occurs appear as distinct features in such image. The image generated during the therapy is compared to an image taken prior to therapy wherein cavitation is present. If such comparison indicates a difference above a threshold level, the frequency or phase of the therapeutic ultrasonic waves used to produce the heating effect are altered so as to suppress cavitation.
Holland et al., In Vitro Detection of Cavitation Induced by a Diagnostic Ultrasound System, IEEE Transactions on Ultrasonics, Ferroelectrics and Frequency Control, Volume 39, No. 1, pp. 95-101, January, 1992, discloses monitoring of cavitation induced by a diagnostic ultrasound scanner using a separate ultrasonic scanner.
Fry et al., Ultrasound and Microbubbles: Their Generation, Detection and Potential Utilization in Tissue and Organ Therapy—Experimental, Ultrasound in Medicine and Biology, Vol. 21,. No. 9, pp. 1227-1237, 1995, conducts experimental procedures in tissues such as the brain and prostrate of experimental animals. A transrectal probe for producing lesions in the prostate is used to apply ultrasonic energy and also used to acquire ultrasonic images after each individual site exposure. The reference notes that cavitation can be induced “with potential therapeutic possibilities and benefits,” but that in certain circumstances the system can be operated in the intensity range which produces thermal lesions without cavitation.
Jing et al, U.S. Pat. No. 5,657,760 teaches the use of an ultrasonic technique for monitoring vaporization of tissue during heating induced by a laser beam so to provide feedback control of the laser beam. The reference suggests broadly that the laser used to provide heating can be replaced by other thermal therapy devices such as electromagnetic devices or ultrasound devices.
Despite all of the effects in the art however, further improvement would be desirable. For example, it would be desirable to provide improved methods and apparatus which can minimize the occurrence of cavitation in HIFU procedures, particularly in HIFU procedures using disposable ultrasonic transducers, and to provide such apparatus and methods in a form suitable for use with small ultrasonic transducer arrays suitable for introduction into small spaces within the body.
SUMMARY OF THE INVENTION
One aspect of the invention provides methods of applying and controlling high intensity focused ultrasound heating within the body of a living subject such as a human or non-human mammal. Methods according to this aspect of the invention desirably include the steps of applying drive signals to a first set of one or more transducers in an array of transducers to thereby cause said first set of transducers to emit therapeutic ultrasonic waves focused at a focal location and thereby heat tissue at such focal location, and acquiring received signals generated by a second set of one or more transducers in said array responsive to ultrasonic waves impinging on said transducers of second set. The received signals can be summed or otherwise processed to provide a detected signal representing ultrasonic waves reflected or emanating from said focal location. Most preferably, one or more of the transducers included in the first or transmitting set for least some part of the drive signal applying step is also included in the second or receiving set during at least some part of the received signal acquiring step. The method according to this aspect of the invention most
Acker David E.
Lopath Patrick David
Lateef Marvin M.
Lerner David Littenberg Krumholz & Mentlik LLP
Shah Devaang
Transurgical, Inc.
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