TEMPERATURE DETERMINATION IN THE FROZEN REGION DURING CRYOSURGERY OF RABBIT LIVER USING MR IMAGE-ANALYSIS

Cryosurgery currently is being used clinically to treat tumors in inte rnal organs such as the liver and prostate. Although performed at pres ent under ultrasound monitoring, magnetic resonance imaging (MRI)guida nce of these procedures not only permits monitoring of the frozen regi on during cryosurgery but also makes it possible to determine the temp erature distribution in the frozen region, which is not possible using ultrasound monitoring, A good estimate of the region of destruction i n the tissue can be obtained from correlating the temperature distribu tion and the time course of the freezing with the image of the frozen region, Unfortunately, MR pulse sequence-based temperature determinati on techniques such as diffusion, relaxation time, and chemical shift c annot be used for measuring the temperature in the frozen region becau se the T-2 Of the frozen region is so short that there is effectively no RF signal from the frozen region. This paper describes a numerical technique for determining the two dimensional temperature distribution the frozen region during MR image-guided cryosurgery of normal liver in rabbits, The technique involves solving the energy equation numeric ally in the frozen region to determine the temperature distribution th ere, The boundary conditions needed to solve the equation are determin ed from MR images of the frozen tissue during cryosurgery and from the measured temperature of the cryoprobe, The calculated temperature in the frozen region is then correlated with the damaged region (cryolesi on) determined from post mortem histologic evaluation. (C) 1997 Elsevi er Science Inc.