Experimental assessment of power and temperature penetration depth controlwith a dual frequency ultrasonic system

A novel ultrasound applicator for superficial simultaneous thermoradiothera py consisting of two parallel-opposed linear arrays and a double-sided scan ning reflector was constructed and tested for penetration depth control. In this design the arrays operate at different frequencies (1 and 5 MHz, in t his study) and the input power to each array element (five 2x 2 cm(2) eleme nts per array) is computer adjustable. The ultrasonic beams from the arrays are aimed at the scanning reflector which in rum deflects them simultaneou sly and in parallel toward the treatment volume. Relative intensity distrib utions generated by the prototype were measured in a degassed water phantom using a thermal technique for a selected reflector position; these showed that the ultrasonic intensity distribution can be controlled in the lateral dimensions by varying the input power level to individual array elements. A fixed-perfused canine kidney phantom was employed to demonstrate experime ntally that real time penetration depth control is possible by varying the excitation magnitude of one array (frequency) relative to that of the other . It is concluded that the dual-frequency scanned-reflected ultrasound appl icator offers a degree of dynamic three-dimensional control of the power de position pattern of clinical significance. (C) 1999 American Association of Physicists in Medicine. [S0094-2405(99)01105-0].