| MRI-guided cryoablation is a promising minimally invasive therapy for localized prostate cancer. Monitoring of temperatures achieved during freezing is essential for successful cryosurgery. MRI potentially allows temperature mapping in frozen tissue, and can also provide assessment of treatment efficacy. The two aims of this work were to develop methods to improve imaging and quantitation of frozen tissue for temperature mapping with MRI, and to investigate the ability of MRI to characterize the extent of cryoinjury.;Imaging of frozen tissue requires ultrashort echo times, usually achieved with half RF pulses. However, these pulses are sensitive to gradient imperfections such as eddy currents that cause errors in the slice profile. The goal of this work was to develop RF pulses that were less sensitive to these distortions, thereby improving MR imaging of frozen tissue. Three RF pulses were developed that achieved an improved slice profile and were robust to eddy current errors. Experimental results demonstrate substantially better slice selectivity and T2* quantitation accuracy with these pulses.;MRI can also provide the ability to non-invasively assess tissue injury after cryoablation. The appearance of acute and chronic cryolesions was evaluated on MRI, correlated with freezing protocol and compared to histopathology. The influence of various freezing protocol parameters such as freeze area, duration, rate, and number of freeze cycles on lesion appearance was evaluated. This characterization of cryolesion appearance and evolution can potentially be used to assess tissue response after cryoablation. |
