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Investigation of a spherical-section ultrasound phased array for hepatic ablation

A 3D ultrasound thermal model with a 3D finite element representation for modeling the thermal diffusion effects for hepatic ablation induced by spherical-section ultrasound phased array was developed. The model was first validated against available published measured data in rat liver. Using the validated model, effects of blood perfusion and heating schemes on lesion formation were studied for both single focus and split-focus intensity patterns. It was shown that for single focus sonication pattern the short-duration (∼2 s) and high-intensity (∼1250 W/cm2) heating scheme can completely reduce the cooling effect of the blood perfusion. The lesion shape and size were significantly altered by perfusion for split-focus pattern even with a rapid heating scheme when the focus spacing was larger than 2.4 mm. Underdosed areas might be present between two foci. Prolonging exposure time or shortening focus spacing can reduce the cool region between two foci. In addition, the influences of thermal and acoustic parameters were also studied. When the therapy depth is short (<5 cm), the lesion size monotonically increases with increasing attenuation coefficient that ranges from 5.4 to 11 Np/(m·MHz).