Comparison of thermal damage calculated using magnetic resonance thermometry, with magnetic resonance imaging post-treatment and histology, after interstitial microwave thermal therapy of rabbit brain

Clinical application of high-temperature thermal therapy as a treatment for solid tumours requires an accurate and close to real-time method for asses sing tissue damage. Imaging methods that detect structural changes during h eating may underestimate the extent of thermal damage. This is due to the o ccurrence of delayed damage manifested at tissue locations exposed to tempe ratures lower than those required to cause immediate structural changes. An alternative approach is to measure temperature and then calculate the expe cted damage based on the temperature history at each tissue location. Magne tic resonance (MR) imaging methods now allow temperature maps of the target and surrounding tissues to he generated in almost real-time. The aim of th is work was to evaluate whether thermal damage zones calculated on the basi s of MR thermometry maps measured during heating correspond to actual tissu e damage as measured after treatment by histological methods and MR imaging . Four male rabbits were treated with high-temperature thermal therapy delive red in the brain by a single microwave antenna operating at 915 MHz. MR sca nning was performed before, during and after treatment in a 1.5 T whole-bod y scanner. Temperature maps were produced using the proton resonance freque ncy (PRF) shift method of MR thermometry. In addition, conventional T-1-wei ghtcd and T-2-weighted spin-echo images were acquired after treatment. Ther mal damage zones corresponding to cell death, microvascular blood flow stas is and protein coagulation were calculated using an Arrhenius analysis of t he MR temperature/time course data. The calculated zones were compared with the lesions seen on histopathological examination of the brains which were removed within 6-8 h of treatment. The results showed that calculated damage zones based on MR thermometry agr eed well with areas of damage as assessed using histology after heating was completed. The data suggest that real-time calculations of final expected thermal damage based on an Arrhenius analysis of MR temperature data may pr ovide a useful method of real-time monitoring of thermal therapy when combi ned with conventional T-2-weighted images taken after treatment.