The characterization of the lesion growth in time

Abstract

Thermal heating effects of high intensity focused ultrasound (HIFU) on the dynamics of lesion formation were characterized automatically to assess the role of vapor bubbles in distorting the shape. Tissue mimicking phantom was used in experiments by a 4.2 MHz curve-linear transducer with 44 mm diameter and 44 mm radius of curvature. A variety of HIFU intensities were produced by different amplitudes. Images were acquired by a CCD camera and HDI-1000 ultrasound imager, recorded to VHS, and digitized to measure lesion size and shape. Each image was subtracted with noise reduction in order to detect the HIFU on time and to segment the boundaries of the lesions performed by Matlab programming. Area, length, width, and ratio of lesion area proximal to center line over area distal to center line were calculated along HIFU exposure time. Slight increase in HIFU intensity, means hyperecho forms earlier, and lesion shape change. The data supported the hypothesis that lesion dramatically distorts well after hyperecho with only small increase in HIFU intensity. [Work supported by National Space and Biomedical Research Institute.]