Magnetic resonance study of freezing damage development in rat liver tissue.

Abstract Cryolesions were produced by contact cryoprobes on male Wistar rat livers. The development of freezing damage was followed in vivo for 24 hr by morphological examinations, proton spin lattice relaxation times T 1 , and paramagnetic center concentration measurements. Significant proton T 1 increase, related to an increased tissue water content, as well as a concentration decrease of the paramagnetic centers, was observed for the cryolesion, as compared to the undamaged liver tissue of the same animal. The concentration decrease was observed for the g = 2.00 free radicals and g = 1.94 reduced state iron protein centers, specified by the parameter g indicating the position of their absorption lines in the electron paramagnetic resonance spectrum. It was also found that the rate of damage development following a single freezethaw cycle depends significantly on the cooling capacity of the cryoprobe. The final changes produced by 6- and 4-mm-diameter liquid nitrogen-cooled cryotips are comparable, but the development of damage was different.