[Sequential MRI and CT monitoring in cryosurgery--an experimental study in polyvinyl alcohol gel phantom]

The purpose of this investigation is to detect a cryolesion by MRI and CT during cryosurgery. A fundamental study was performed to demonstrate MR and CT images of polyvinyl alcohol (PVA) gel, which was used as a phantom for MRI, under the condition of low temperature. MRI was performed on a 0.1 Tesla system (ASAHI MR Mark-J). As the temperature lowered, the unfrozen PVA gel showed decreases in T1 and T2, and an increase in signal intensity on the low flip (LF) angle images, which were obtained using 60 degrees of flip angle, Tr of 100 msec, Te of 18 msec with gradient echo acquisition method. The frozen PVA gel showed no signal intensity on the LF images and zero in T1 and T2. On the other hand, the CT images revealed the frozen area of the PVA gel as a hypodense area. From the facts described above, it may be concluded that MRI and CT will be able to detect cryolesions during cryosurgery.