HEATING PATTERNS OF THE HELIOS ULTRASOUND HYPERTHERMIA SYSTEM

Thermal dosimetry studies of the Helios ultrasound system were perform ed in a tissue-equivalent phantom and in porcine tissues in vivo. SAR distributions in the phantom demonstrate the adjustability of the powe r deposition pattern from the 50 cm diameter annular array of 30 trans ducers. Examples are given of well-localized SAR patterns (< 3 cm diam eter) in the phantom, and of peripherally enhanced (doughnut-shaped) S AR patterns up to 10 cm in diameter at the focal plane. In vivo trials in porcine thigh muscle demonstrate the ability of the Helios system to produce regions of therapeutic heating (42-45-degrees-C) as small a s 20 cm3 and as large as 200 cm3 at depths of greater than 10 cm at a frequency of 0.5 MHz.