Surgery: kinesitherapy – Kinesitherapy – Ultrasonic
Reexamination Certificate
2000-01-31
2003-01-28
Lateef, Marvin M. (Department: 3737)
Surgery: kinesitherapy
Kinesitherapy
Ultrasonic
Reexamination Certificate
active
06511444
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates generally to ultrasonic systems used for the vaporization of tissue, and more particularly to a phased array ultrasonic system used for creating channels within organs by ablating tissue.
Cardiac ischemia is a condition in which oxygenated blood is reduced or cutoff to a section of the heart, usually as the result of cholesterol-laden plaque narrowing the coronary arteries and preventing blood flow. Untreated ischemia may lead to ischemic heart disease often with disabling angina. Angina is severe chest pain caused by insufficient oxygenated blood reaching the heart often during times of exercise or emotional stress. Untreated ischemic heart disease with its associated angina may lead to heart attacks and death or in somewhat less severe cases to a great reduction in the quality of life for the patient.
There are currently three treatments for the treatment of cardiac ischemic disease and angina. The first therapy is pharmacological. Drugs for reducing cholesterol and for managing the pain of the patient are administrated in conjunction with exercise in order to increase the amount of oxygenated blood reaching the cardiac tissue. The second treatment is balloon angioplasty. In this treatment a catheter is worked into the coronary arteries carrying with it a balloon, when the catheter reaches the portions of the coronary arteries that are clogged with plaque, the balloon is expanded compressing the plaque and opening the coronary artery wider in order to allow greater blood flow. The third current treatment is a coronary graft by-pass operation. The coronary by-pass operation is one where new arteries are grafted around the clogged coronary arteries creating new, unobstructed, blood passageways.
Recently a new treatment for cardiac ischemic disease has been developed called transmyocardial revascularization (TMR). In TMR tiny channels, approximately 1 mm in diameter, are drilled through the heart muscle to allow oxygenated blood from the left ventricle to flow through these channels into the damaged muscle tissue to bring oxygenated blood to those areas. Currently, TMR utilizes high powered lasers to drill these holes in the cardiac muscle. TMR is an invasive procedure since currently TMR techniques still require the chest to be opened sufficiently to visualize the heart. The laser is then used to drill holes from outside of the heart muscle through the entire heart muscle into the left ventricle. Although current studies show that the outer portion of the drilled channel does heal, more tissue is still damaged than is needed to bring oxygenated blood to the damaged tissues. In addition, the lasers used for TMR are expensive to obtain and to operate. In another method of laser TMR, the laser is threaded into the left ventricle and the channels are drilled into the wall directly. While this method does not destroy more tissue than necessary, it is still invasive, in that the laser is threaded through the circulatory system into the interior of the heart, and in particular to the left ventricle chamber of the heart, in order to be proximate to the target areas.
While TMR is a new procedure, the use of lasers to vaporize tissue, and the problems associated therewith, are not new. The present invention is superior to using lasers to vaporize tissue, since a laser can destroy more tissue than is necessary, or can perforate tissue causing additional complications, whereas the present invention is more easily controlled.
Other methods that exist to destroy tissue have other problems as well. For example, direct current cardiac tissue ablation requires a catheter to be inserted into the interior of the heart and 2,000 to 4,000 volts of electricity are applied to the target tissue over several milliseconds. In addition to being invasive, the severe muscle contractions which result, require the patient to be under general anesthesia.
RF and microwave ablation of cardiac tissue is invasive since it requires a catheter inserted into the interior of the heart. In addition the energy is difficult to focus and the size of the target tissue to be ablated is limited due to the lower energy available.
There are two methods currently used to deliver ultrasonic energy to target tissue. The first is to use a catheter with an ultrasonic transducer or transducer array on the tip. The catheter must be inserted into the interior of the heart and be in close proximity to the target tissue, due to the inability to narrowly focus the beam. Although phased array catheter probes have been discussed in the literature there are none commercially available. In addition, the size of the probe will limit the number of available phased array elements. The fewer the number of elements, the wider the main lobe of the antenna becomes. This will result in heating a wider area of tissue and hence cause the collateral destruction of healthy tissue during treatment. In addition more energy will be in the sidelobes of the phased array which will reduce the efficiency and possibly damage collateral tissue as well.
The second method of delivering ultrasonic energy is the use of an external ultrasonic transducer, having a phased array antenna in conjunction with a hydrophone array. The hydrophone is invasively placed to provide detection of the ultrasonic energy to determine its focus point. The hydrophone measurement provides the necessary feedback to adjust the beam focus properly so as to limit collateral tissue damage. However, the hydrophone array must be placed proximate to the target tissue so as to be effective.
Vaporization of tissue using ultrasound has not been described in the prior art. Although it has been known generally in the art that small cavities are formed in tissue during ultrasonic exposures with high power. However, there have not been any attempts to control this cavity and use it for tissue removal. In addition, the exposure parameters that cause desired, controlled tissue vaporization have not been known. There is a need for an apparatus to produce the energy required at the appropriate frequency to create tissue vaporization.
Therefore what is needed is an ultrasonic apparatus capable of producing sufficient pressure at the acoustic focus to vaporize tissue, and an ultrasound phased array with a feedback control system capable of measuring and controlling the power and phase from each individual array element such that TMR channels are created noninvasively within the myocardium by vaporizing tissue at the acoustic focus of the phased array. This will enable tissue to be vaporized without opening the patient's body in order to actually see the tissue to be vaporized without having to invasively thread a catheter or hydrophone array into the patient's body.
SUMMARY OF THE INVENTION
According to the invention, phased array ultrasonic devices are provided for use in vaporizing tissue non-invasively during medical treatment. The device includes a plurality of ultrasonic transducer elements which transmit ultrasonic waves each having a particular power and phase. The control of an individual ultrasonic transducer element to produce ultrasonic energy having a particular power and phase is needed to achieve constructive interference at the desired acoustic focus, and is achieved by a focusing means that is responsive to a feedback signal. This constructive interference creates high pressure amplitudes for vaporizing the target tissue at the focus. The individual ultrasonic transducer elements are supplied energy by a channel driver element that is responsive to the focusing means.
To achieve this desired acoustic focus, in one embodiment, the driver element is responsive to a focusing element and feedback means to properly drive the ultrasonic transducer elements. The focusing element comprises a controller that determines an operating parameter of the ultrasonic transducer element. The controller is responsive to the feedback signal and in the preferred embodiment determines the phase and power to be transmitted by each individual ultrasonic
Buchanan Mark T.
Daum Douglas R.
Fjield Todd
Hynynen Kullervo
Brigham and Women's Hospital
Lahive & Cockfield LLP
Lateef Marvin M.
Mantis Mercader Eleni
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