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 prov en to be a valuable tool in its traditional role in device localization and , more recently, in monitoring heat deposition within tissue. However, a qu antitative understanding of how temperature-time exposure relates to therma l damage is crucial if the predictive value of real-time MR thermal-monitor ing is to be fully realized. Results are presented on interstitial laser co agulation of two canine prostate models which are shown to provide an oppor tunity to evaluate three models of thermal damage based on a threshold maxi mum temperature, an Arrhenius damage integral, and a temperature-time produ ct. These models were compared to the resultant lesion margin as derived fr om post-treatment T-1- and T-2-weighted MR images, as well as from direct h istological evaluation of the excised canine prostate. Histological evaluat ion shows that the thermal-injury boundary can be predicted from a threshol d-maximum temperature of approximately 51 degreesC or an equivalent Arrheni us 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 focu s of future human studies. (C) 2000 Wiley-Liss, Inc.