[In vitro study on dosage level of HIFU for formation of line-shaped lesion in bovine liver].

The dot-shaped coagulative necrosis induced by a single HIFU exposure can be considered as a basis for HIFU ablation of tumour. For complete ablation of tumour mass with HIFU, the crucial point is to create a complete line-shaped lesion by way of dot-shaped coagulative necrosis. At the beginning of this in vitro study, a dot-shaped coagulative necrosis with focal width (W) 3mm was induced in ox liver by HIFU (acoustical intensity (I(SAL)) 6500W/cm2; exposure time 1s) at focal depth 2cm. And then, we investigated the formation of line-shaped lesion under two different modes, namely, multiple dot-shaped coagulative necrosis overlapping and linear scanning. Under multiple dot-shaped coagulative necrosis overlapping mode, line-shaped lesion is formed by the combination of multiple dot-shaped coagulative necroses. With acoustical intensity (I(SAL)) 6500W/cm2 and exposure time is for each single exposure, different intervals (D) between two successive single exposures (1mm, 2mm, 2.5mm, 3mm, 4.5mm, 5mm) were applied to obtain line-shaped lesion. Under linear scanning mode, the intensity (I(SAL)) 6500W/cm2 and cycle 1 were set constant, and various scanning speeds (V) 1mm/s, 3mm/s, 6mm/s, 7mm/s were adopted to create line-shaped lesion. After the procedures, the tissues were dissected to obtain the maximum section of the line-shaped lesion. The results were as follows: under multiple dot-shaped coagulative necrosis overlapping mode, a complete line-shaped lesion could be formed when D < or = W, while an incomplete line-shape lesion was formed when D > W; under linear scanning mode, a complete line-shaped lesion could be formed using the scanning speed 3mm/s and cycle 1. The results validate that the complete line-shaped lesion can be created with the dosage and exposure parameters optimized for the dimension of a single dot-shaped coagulative necrosis as shown in this study.