ULTRASOUND IMAGING OF THERMAL THERAPY IN IN-VITRO LIVER

The objective of this work was to image liver tissue heated to tempera tures below the vaporization threshold as a function of time, to test the feasibility of real-time ultrasound monitoring to control lesion s ize during minimally invasive thermal therapy (MITT), Two experiments were devised. In one experiment, a thermal gradient was established in a rectangular volume of tissue to correlate changes in ultrasound ima ge echogenicity (B-mode image brightness) with tissue temperature. In the other, a thermal lesion was produced in a rectangular volume of ti ssue by an interstitial microwave antenna, and the progression of the lesion was monitored by ultrasound. In both experiments, the echogenic ity of the tissue increased slightly for tissue temperatures up to 40 degrees C, but became lower than that of unheated tissue for temperatu res above 40 degrees C, In the second experiment, images uf the lesion were compared with a photograph of the lesion taken after the experim ent was complete. The final lesion was composed of two concentric regi ons-an inner region of heavily coagulated tissue and an outer region o f less-damaged tissue. These two damaged regions indicated that increa sed ultrasound attenuation was largely responsible for the decreased e chogenicity observed in the ultrasound images, and the increase in ech ogenicity of tissue heated to temperatures up to 40 degrees C is thoug ht to be due to decreased ultrasound attenuation at these temperatures . (C) 1998 World Federation for Ultrasound in Medicine & Biology.