From: Proceedings 10th World Congress of Cryosurgery
New Methods for Monitoring Cryosurgery, MRI

November 1998
Boris Rubinsky Biomedical Engineering Laboratory, University of California Berkeley, Berkeley CA
Magnetic resonance imaging (MRI) produces images of tissue by subjecting the tissue to a variable magnetic field and monitoring the consequent time response (relaxation time), of tissue protons. Because the relaxation time of the protons in ice (frozen tissue) is considerable different from their relaxation time in water (unfrozen tissue), the part of the tissue that is frozen produces no image under conventional MRI. Therefore MRI can be used to monitor the extent of the frozen region in relation to unfrozen tissue, in real time and in three dimensions. The use of MRI in cryosurgery will be illustrated with applications in skin cryosurgery, brain and prostate cryosurgery. Because MRI can produce a three-dimensional image, practically instantaneous in the time scale of a process of freezing, MRI images can be used to calculate the temperature distribution in the frozen region during cryosurgery. The technique for calculating temperatures in the frozen tissue with MRI will be described and the accuracy of the predictions illustrated with examples from cryosurgery.

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