Broad-area irradiation of small near-field targets using ultrasound

Abstract

An ultrasonic transducer system for treating a portion of tissue. The ultrasonic transducer system includes a frequency generator, an ultrasonic transducer, and a transmitter element. The transducer receives an AC voltage from the frequency generator and produces an ultrasonic energy pulse at an ultrasonic frequency for a pulse width. The transmitter element is coupled to the transducer and is for irradiating a portion of skin tissue. The transmitter element has a chilled surface in contact with the skin tissue and an acoustic aperture for producing a substantially collimated energy beam. The beam has a width greater than 4 mm.

1 . An ultrasonic transducer system for treating tissue comprising:
 a frequency generator for generating an AC voltage;   a unitary transducer receiving the AC voltage from the frequency generator for producing an ultrasonic energy pulse at an ultrasonic frequency for a pulse width; and   a transmitter element coupled to the transducer for irradiating a portion of skin tissue, the transmitter element having an acoustic aperture for producing a substantially collimated energy beam, the beam having a width greater than 4 mm wherein the cross-sectional area of the substantially collimated energy beam does not vary by more than 20% over a distance of at least 5 mm from the surface of the skin tissue to a treatment plane and wherein the substantially collimated energy beam is produced by a single transducer.   
     
     
         2 . The ultrasonic transducer system of  claim 1  further including a chilled surface in contact with the skin tissue. 
     
     
         3 . The ultrasonic transducer system of  claim 1 , wherein the intensity of the ultrasonic energy pulse at the transducer is greater than 150 W/cm 2 . 
     
     
         4 . The ultrasonic transducer system of  claim 1 , wherein the pulse width is less than 100 milliseconds. 
     
     
         5 . The ultrasonic transducer system of  claim 1 , wherein the ultrasonic frequency is between 5 and 20 MHz. 
     
     
         6 . The ultrasonic transducer system of  claim 1 , wherein the ultrasonic energy pulse has an acoustic wavelength, and the square of half the acoustic aperture, divided by the product of the acoustic wavelength and the distance from the acoustic aperture to 5 mm below the skin surface, is greater than 3. 
     
     
         7 . The ultrasonic transducer system of  claim 1 , wherein the ultrasonic energy pulse has an acoustic wavelength, and the square of half the acoustic aperture, divided by the product of the acoustic wavelength and the distance from the acoustic aperture to 5 mm below the skin surface, is greater than 10. 
     
     
         8 . The ultrasonic transducer system of  claim 1 , wherein the Fresnel number of the beam is greater than 3. 
     
     
         9 . The ultrasonic transducer system of  claim 1 , wherein the Fresnel number of the beam is greater than 10. 
     
     
         10 . The ultrasonic transducer system of  claim 1 , wherein the substantially collimated energy beam has a cross sectional area at least 16 mm 2  from the surface of the skin tissue to 5 mm below the surface of the of skin tissue. 
     
     
         11 . The ultrasonic transducer system of  claim 1 , wherein the intensity of the ultrasonic energy pulse is greater than or equal to 150 W/cm, the ultrasonic frequency is between 5 and 20 MHz, and the pulse width is less than 100 milliseconds. 
     
     
         12 . The ultrasonic transducer system of  claim 1 , wherein the acoustic aperture has a non-circular shape. 
     
     
         13 . The ultrasonic transducer system of  claim 1 , wherein the transducer produces a plurality of ultrasonic energy pulses, each energy pulse at a different frequency and pulse width. 
     
     
         14 . The ultrasonic transducer system of  claim 1 , wherein the transducer produces a plurality of ultrasonic energy pulses and the difference between a highest pulse frequency and a lowest pulse frequency is greater than 0.25% of an average frequency of the plurality of ultrasonic energy pulses. 
     
     
         15 . The ultrasonic transducer system of  claim 1 , wherein the transducer produces a pulse that is continuously swept over a range of frequencies. 
     
     
         16 . The ultrasonic transducer system of  claim 1 , wherein the transducer produces an ultrasonic frequency that is swept at a rate greater than or equal to 0.25% of the average frequency per 100 milliseconds. 
     
     
         17 . The ultrasonic transducer system of  claim 1 , wherein the edge of the acoustic aperture is apodized to attenuate the transmitted power near a perimeter of the energy beam. 
     
     
         18 . The ultrasonic transducer system of  claim 17 , wherein the transmitter element includes an apodizing annulus for attenuating the transmitted power near the perimeter of the energy beam. 
     
     
         19 . A method of inhibiting hair growth in a skin tissue, the method comprising:
 placing a unitary ultrasonic transducer in contact with the skin tissue, the transducer having an acoustic aperture for producing a substantially collimated energy beam over a treatment area greater than 16 mm 2 , wherein the substantially collimated energy beam is produced by a single transducer, herein the cross-sectional area of the substantially collimated energy beam does not vary by more than 20% over a distance of at least 5 mm from the surface of the skin tissue to a treatment plane, the tissue having a plurality of hair follicles within the treatment area; and   generating one or more ultrasonic energy pulses, each energy pulse at a corresponding frequency and pulse width.   
     
     
         20 . The method of  claim 19  further including the step of cooling the tissue surface. 
     
     
         21 . The method of  claim 19 , wherein the frequency of the ultrasonic energy is varied. 
     
     
         22 . The method of  claim 21  wherein the ultrasonic frequency is swept at a rate greater than or equal to 0.25% of the average frequency per 100 milliseconds. 
     
     
         23 . The method as recited in  claim 21  wherein the variation between the highest and lowest frequencies of the ultrasonic energy is at least 1.0% of the average drive frequency. 
     
     
         24 . The method of  claim 19 , wherein the combined pulse widths of all of the energy pulses total less than 100 ms. 
     
     
         25 . The method if  claim 19 , wherein the intensity of the ultrasonic energy pulse at the transducer is greater than 150 W/cm 2 . 
     
     
         26 . The method of  claim 25 , wherein the frequency of the ultrasonic energy pulse is between 5 and 20 MHz.