Magnetic resonance thermometry for predicting thermal damage: an application of interstitial laser coagulation in an in vivo canine prostate model.

Magnetic resonance image-guidance for interstitial thermal therapy has proven to be a valuable tool in its traditional role in device localization and, more recently, in monitoring heat deposition within tissue. However, a quantitative understanding of how temperature-time exposure relates to thermal damage is crucial if the predictive value of real-time MR thermal-monitoring is to be fully realized. Results are presented on interstitial laser coagulation of two canine prostate models which are shown to provide an opportunity to evaluate three models of thermal damage based on a threshold maximum temperature, an Arrhenius damage integral, and a temperature-time product. These models were compared to the resultant lesion margin as derived from post-treatment T(1)- and T(2)-weighted MR images, as well as from direct histological evaluation of the excised canine prostate. Histological evaluation shows that the thermal-injury boundary can be predicted from a threshold-maximum temperature of approximately 51 degrees C or an equivalent Arrhenius t(43) period of 200 minutes, but it is not reliably predicted using the temperature-time product. The methods described in this study are expected to have implications for the treatment of benign prostatic hyperplasia and prostate cancer with interstitial laser coagulation, which will be the focus of future human studies.