Patent Application
20120157891
The present invention generally relates to a system and method for treating tissue with a combination of thermal and pressure wave energy.
Tissue treatment by heating is used for diathermy, coagulation, surgery, hyperthermia, pain relief, drug delivery assistance, and many others. Heating tissue may be done by means of RF, ultrasound, laser light, electromagnetic induction, convection, mechanical stimulation and others.
Tissue treatment by non-heating pressure waves is used for urinary stones disintegration (lithotripsy), pain alleviation in joints, skin treatment, revascularization, massage and others. Non-heating pressure waves include sub-ultrasonic waves and shockwaves. Typical sub-ultrasonic waves are applied as pulses of sub-ultrasonic content and sub-ultrasonic repetition rate. Typical shockwaves have a steep wave front, followed by a shallower rarefaction tail that decays in oscillatory fashion. Extracorporeal shockwaves for medical applications are typically produced by electrohydraulic, electromagnetic or piezoelectric methods. Electrohydraulic shockwaves are formed with a high energy spark in water and an ellipsoidal reflector is used to focus the waves. Electromagnetic shockwaves are formed by producing a current pulse in a coil and inducing opposite current in an adjacent conducting membrane submerged in water. The repelling force of the opposing currents jerks the membrane and produces a wave. Focusing is by an acoustic lens, a reflector or by shaping a spherical membrane. Intracorporeal shockwaves are also used in lithotripsy, for example, and are produced by focusing laser light or creating a spark at the target.
The present invention seeks to provide improved treatment modalities by combining thermal energy with pressure wave energy without causing significant temperature increase for extended time, as is described more in detail hereinbelow.
In accordance with a non-limiting embodiment of the invention, pulsed heating is synchronized with pulses of pressure waves such that both pulses reach the target simultaneously. In one example, the propagation speed of the wave may be about 1.5 m/msec, and the time of releasing the heating pulse depends on the propagation speed of the heating pulse and the respective distances of the thermal and wave devices to the target. The heat of each pulse is dissipated prior to the arrival of the subsequent heating pulse.
There is thus provided in accordance with a non-limiting embodiment of the present invention a method including directing pressure waves at a tissue, and heating the tissue with thermal energy pulses, the thermal energy pulses synchronized to arrive at the tissue simultaneously with the pressure waves within a time tolerance range, and wherein heat of each thermal energy pulse is significantly dissipated in an environment that includes the tissue before a subsequent thermal energy pulse arrives at the tissue. The deposited heat energy per pulse, the number of pulses and the repetition rate of the pulses are determined by a processor according to the temperature and the heat dissipation capability of the tissue.
According to an embodiment of the present invention, the tissue temperature is measured by a sensor in communication with the processor. The heat dissipation capacity of the tissue may be based on prior measurements of tissue properties or properties based on the assumption that the tissue is similar to previously published tissue properties; these properties include, but are not limited to, thermal conductivity, specific heat, coefficients of thermal convection (forced and free), and others, both for dry and wet tissues.
The pressure waves may include sub-ultrasonic pulses or shockwaves or a combination of both. The pressure waves may include extracorporeal or intracorporeal pressure waves or a combination of both. The thermal energy may include RF heating, ultrasonic heating, optical heating or electromagnetic induction heating or any combination thereof.
In accordance with an embodiment of the present invention the method includes focusing at least one of the pressure waves and the thermal energy pulses. Focusing is according to the shape of the treated tissue: the focal volume may include spherical, ellipsoidal-like or generally elongated shapes.
In accordance with an embodiment of the present invention the method includes localizing the target by producing images of the target and processing the images with respect to a reference to calculate a location of the target with respect to a coordinate system. Imaging may be done by ultrasound, x-ray, CT, MRI, optical or electrical imaging or any combination thereof.
There is also provided in accordance with a non-limiting embodiment of the present invention system including a pressure wave source for directing pressure waves at a tissue, a heat source for heating the tissue with thermal energy pulses, and a controller for synchronizing the thermal energy pulses to arrive at the tissue simultaneously with the pressure waves within a time tolerance range, and such that heat of each thermal energy pulse is dissipated in an environment neighboring the tissue before a subsequent thermal energy pulse arrives at the tissue.
In accordance with an embodiment of the present invention a focusing element focuses the pressure waves.
In accordance with an embodiment of the present invention a focusing element focuses the thermal energy pulses.
The present invention will be understood and appreciated more fully from the following detailed description, taken in conjunction with the drawings in which:
Reference is now made to
The system includes a pressure wave source 10 for directing pressure waves 12 at a tissue 14 (typically a target 15 in the tissue). The system also includes a heat source 16 for heating tissue 14 with thermal energy pulses 18. In the embodiment of
The system includes a controller 24 for synchronizing the thermal energy pulses 18 to arrive at tissue 14 simultaneously with pressure waves 12 within a time tolerance range. The controller 24 controls the timing such that the heat of each thermal energy pulse 18 is dissipated in an environment neighboring tissue 14 before a subsequent thermal energy pulse 18 arrives at tissue 14. In accordance with one embodiment of the invention the time tolerance range is ±0.1 msec. In accordance with another embodiment of the invention the time tolerance range is ±0.5 msec. In accordance with yet another embodiment of the invention the time tolerance range is ±1 msec. Other ranges may be used, each having their own characteristics, advantages and tradeoffs, depending on the particular application.
The heat energy per pulse, the number of pulses and the repetition rate of the pulses are determined by controller 24 according to the temperature and the heat dissipation capability of the tissue. The tissue temperature can be measured by a sensor 25 in communication with controller 24. The heat dissipation capacity of the tissue may be based on prior measurements of tissue properties or properties based on the assumption that the tissue is similar to previously published tissue properties; these properties include, but are not limited to, thermal conductivity, specific heat, coefficients of thermal convection (forced and free), and others, both for dry and wet tissues
As seen in
Reference is now made to
The method includes directing pressure waves at a tissue (101), and heating the tissue with thermal energy pulses, wherein the thermal energy pulses are synchronized to arrive at the tissue simultaneously with the pressure waves within a time tolerance range (102). Heat of each thermal energy pulse is dissipated in an environment neighboring the tissue before a subsequent thermal energy pulse arrives at the tissue (103). The pressure waves may include sub-ultrasonic pulses or shockwaves or a combination of both. The pressure waves may include extracorporeal or intracorporeal pressure waves or a combination of both. The thermal energy may include RF heating, ultrasonic heating, optical heating or electromagnetic induction heating or any combination thereof.
The method further includes focusing at least one of the pressure waves and the thermal energy pulses (104).
The target may be localized by producing images of the target and processing the images with respect to a reference (e.g., an inertial reference frame of a coordinate system) to calculate a location of the target with respect to the coordinate system (105). Imaging may be done by ultrasound, x-ray, CT, MRI, optical or electrical imaging or any combination thereof (imaging system 30 shown in
The scope of the present invention includes both combinations and subcombinations of the features described hereinabove as well as modifications and variations thereof which would occur to a person of skill in the art upon reading the foregoing description and which are not in the prior art.
