Patent Application
20050055018
The invention relates to methods and devices for non-invasive ultrasonic destruction of living tissue in sub-dermal layer, in particular using CW focused ultrasonic energy.
During a long period, researchers have tried to use focused ultrasonic energy for non-invasive destruction of internal tissue. For example, U.S. Pat. No. 5,143,063 describes thermal fat destruction using focused ultrasonic energy. Parameters of the acoustic waves are adjusted to create thermal effect. The disadvantage of this method is the pain associated with thermal lysis of the living tissue.
Patent U.S. Pat. No. 5,624,382 describes thermal destruction of tumors. Cavitation is described there as a negative phenomenon, because bubbles created due to cavitation scatter ultrasonic energy and prevent its focusing.
U.S. Pat. No. 6,450,979 describes a device for lipolysis by continuous wave (CW) ultrasonic emission where safety is maintained by limiting ultrasonic energy intensity at a very low level, so as to avoid cavitation.
Thus, most devices invented for deep tissue necrosis such as removing of tumors or lipolysis have been designed for pure thermal effect without cavitation.
There are also devices trying to use cavitation induced by focused ultrasonic energy. U.S. Pat. No. 6,113,558 describes a device based on focused ultrasonic energy with parameters optimized for creating cavitation inside the tissue. The thermal damage is avoided by producing pulses shorter than 100 ms and duty cycle ratios over 5.
Patent application U.S. Ser. No. 2002/0082589 describes similar invention for lysis of adipose tissue using pulsed ultrasonic energy and cavitation, with duty cycle low enough to avoid thermal damage inside the skin. Detectors of cavitation are proposed for feed-back and control of a frame moving the transducer incrementally or continuously over the body and rupturing cells in a generally planar layer of adipose tissue.
In accordance with one aspect of the present invention, there is provided a system for non-invasive lysis of sub-dermal tissue such as adipose (fat) tissue by means of focused ultrasonic energy comprising
The source of ultrasonic energy is preferably accommodated in a hand-held applicator, the displacement being provided by an operator.
The system has means for measurement of current speed and indication for adjustment of the current speed to the safe speed. The indication may be, for example, visual or audio indication.
The system may also comprise a powered traction system, for example with driving wheels, adapted to displace the applicator with the safe speed. The operator in this case only holds the applicator against the patient's body.
The system preferably comprises safety means adapted to limit the delivery of the ultrasonic energy if the safe speed is not maintained.
The source of ultrasonic energy is preferably a piezoelectric transducer. It may be shaped as a spherical transducer, cylindrical transducer, a phase array, Fresnel lens, etc. The transducer may be shaped for rolling over the skin surface.
According to another aspect of the present invention, there is provided a method for non-invasive lysis of sub-dermal tissue such as adipose (fat) tissue, comprising:
The method further comprises measurement of current displacement speed of the source and indication for adjustment of the current speed towards the safe speed.
According to the method, the calculation of the safe speed depends on intensity of ultrasonic energy in the focus and the absorption coefficient of ultrasonic energy by the tissue.
For lysis of adipose tissue, the method preferably uses ultrasonic energy intensity at least 1000 mW/cm2, frequency 0.5 to 1.5 MHz, focal zone dimension at the most 1 cm, and safety speed 0.2 to 2 cm/sec.
The present invention thus provides an apparatus and method for treatment of adipose or other tissue by continuous emission of focused ultrasound energy in the subcutaneous fat layer, for example at a depth of 0.3 to 3 cm, and adjusting the energy level to destroy fat cells by cavitation without thermal damage to the connective tissue and the blood vessels. This effect is achieved due to the continuous displacement of the source over the skin surface at a safe speed.
The apparatus advantageously calculates the safe speed of the source and provides indication for speed adjustment. The speed optimization allows usage of relatively high energy intensity over 1000 mW/cm2 and effective destruction of the fat tissue without thermal damage or pain.
The accommodation of the source in a hand-held applicator provides portability and flexibility in the usage of the method. The powered traction system assists the operator to maintain the optimal safe speed and relieves his physical and psychical load which is very important for treatments like fat removal that require destruction of relatively large volume of adipose tissue.
In order to understand the invention and to see how it may be carried out in practice, preferred embodiments will now be described, by way of non-limiting examples only, with reference to the accompanying drawings, in which:
Referring now to
In operation, the operator turns on the control unit 12 and sets the energy intensity. The processor 28 calculates and indicates the safe speed of the applicator. The operator further takes the applicator by the handle 42, activates the traction system, and passes the rolling transducer 44 over the skin of the patient following the safe speed established by the traction system.
Another embodiment of the inventive system is presented in
As a non-limiting example, the safe speed may be calculated in the following way. For given ultrasonic power density P[W/cm2] in the focal zone, and known absorption coefficient of ultrasound energy in the tissue A[cm−1], the power absorption, D[W/cm3] will be:
D=PA
Noting specific heat of the tissue by c[J/(cm3*K)], and the tolerable (painless) temperature raise by ΔT[K], we obtain the maximal energy E that a unit volume of tissue may absorb as E=ΔT/c. The emitted energy in the focal zone for exposure time t is E=Dt. Thus, the maximal exposure time tMAX will be
The minimal (safe) displacement speed V can be calculated as ratio of focus size S[m] in the displacement direction, and maximal exposure time:
The absorption coefficient of ultrasound energy in the tissue is known to be A=0.3 cm−1. The specific heat of the tissue may be assumed similar to water c=4.2 [J/(cm3*K)], while the temperature raise should not exceed ΔT=10° K. Then, for a focus size S=0.8 cm and power density 10 W/cm2, the safe speed will be about 1 cm/sec.
The optimal parameters for adipose tissue destruction were found to be:
Although a description of specific embodiments has been presented, it is contemplated that various changes could be made without deviating from the scope of the present invention. For example, the present invention could be used for lysis of other tissues than adipose tissue, suitably selecting parameters of treatment. The system may employ various indication means, both disposed in the control unit or in the applicator. The traction system may for example employ belts (caterpillars), etc.
