Thermal dosimetry studies of the Helios ultrasound system were performed in a tissue-equivalent phantom and in porcine tissues in vivo. SAR distributions in the phantom demonstrate the adjustability of the power deposition pattern from the 50 cm diameter annular array of 30 transducers. Examples are given of well-localized SAR patterns (< 3 cm diameter) in the phantom, and of peripherally enhanced (doughnut-shaped) SAR 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 as 20 cm3 and as large as 200 cm3 at depths of greater than 10 cm at a frequency of 0.5 MHz.
A computer controlled hyperthermia system has been developed for clinical evaluation. It is composed of a large aperture ultrasonic array applicator, an ultrasonic annular phased array imager and a multi-channel thermometry system. The applicator has a 50cm aperture which contains 30 broadband ultrasound transducers that operate from 500KHz to 1MHz. Each transducer is independently controllable in power, phase and mechanical orientation. The whole array is submersed in degassed water and is positionable in three dimensions plus rotation. Patient contact is through a thin water-tight plastic membrane. To assist in patient setup there is a sector scanning ultrasonic imager transducer in the center of the applicator. The patient treatment is monitored by a 30 channel thermometry system which accepts either T-type thermocouples or thermistors. The operator system interaction is through a touchscreen CRT and keyboard. Design details, phantom studies and simulations are presented.
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