MRI MONITORING BEFORE, DURING, AND AFTER INTERSTITIAL LASER-INDUCED THERMOTHERAPY OF BENIGN PROSTATIC HYPERPLASIA - FIRST CLINICAL-EXPERIENCE

Purpose: To assess the clinical value of MRI in patients with benign p rostatic hyperplasia (BPH) before, during, and after interstitial lase r-induced thermotherapy (LITT) of the prostate. Methods: Ten patients with symptomatic BPH had MRI examinations of the prostate 48 h before and after LITT. Online monitoring with MRI at 1.5 T of interstitial Nd :YAG laser energy deposition in the prostate was performed in two pati ents, repeating a T1-weighted FLASH sequence (TR 100 ms, TE 5 ms, flip angle 90 degrees) every 20 s. Follow-up MRI examinations 2-3 weeks, 6 -8 weeks, and 6-12 months after LITT were carried out in eight patient s, using T2-weighted FSE images and contrast-enhanced T1-weighted SE i mages. Results: The prostate was well delineated in all patients on T2 -weighted FSE images, with a rather homogeneous peripheral gland and a n inhomogeneous central gland. Volume measurements yielded reproducibi lities of 3.2 %-4.7 %. Signal intensity in the FLASH sequence decrease d during LITT, both in the prostate in vivo and in specimens of bovine prostate and seminal vesicles in vitro, with signal developments runn ing in parallel. Areas of energy deposition and signal alteration were not sharply delineated. The latter margin of the laser-induced lesion s could not be predicted from the FLASH images, while the tip of the l aser fibre was easily recognized. Contrast-enhanced T1-weighted MR ima ges immediately after LITT clearly demarcated low signal intensity las er lesions from high signal intensity surrounding prostate tissue. Fol low-up examinations showed a decrease of 20 % of prostate volume over a period of 6-12 months after LITT. Correlation between prostate volum e development and lesion volume alteration was 0.85-0.90 (P = 0.002-0. 007) at all follow-up times. Conclusions: MRI allows rather precise re cognition of intraprostatic alterations after LITT, including volume c hanges over a period of up to 1 year after therapy that can be predict ed immediately after LITT. While laser energy deposition in the prosta te can be monitored by MRI with T1-weighted FLASH sequences as a funct ion of temperature alteration, it is not possible to determine the les ion margins immediately from the FLASH images. Online temperature deve lopment map generation will be necessary to influence ongoing LITT pro cedures with MRI.