A random phased array device for delivery of High Intensity Focused Ultrasound

Randomised phased arrays can offer electronic steering of a single focus and simultaneous multiple foci concomitant with low levels of secondary maxima and so are potentially useful as sources of high intensity focused ultrasound (HIFU). This work describes laboratory testing of a 1 MHz random phased array consisting of 254 elements on a spherical shell of radius of curvature 130 mm and diameter 170 mm. A novel technique in which an infra-red camera is used to provide a rapid qualitative assessment of temperature changes in an absorbing target (and by inference relative intensity distributions) due to HIFU pulses for a range of focusing conditions is described. The results show that the array can steer a single focus laterally to at least ±15 mm off axis and axially to more than ±15 mm from the centre of curvature of the array and patterns of 4 and 5 simultaneous foci ±10 mm laterally and axially whilst maintaining low intensity levels in secondary maxima away from targeted area in good agreement with linear theoretical predictions. Experiments in which pork meat was thermally ablated indicate that contiguous lesions several cm3 in volume can be produced using the multiple foci patterns