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 prostatic hyperplasia (BPH) before, during, and after interstitial laser-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 patients, 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 patients, using T2-weighted FSE images and contrast-enhanced T1-weighted SE images. Results: The prostate was well delineated in all patients on T2-weighted FSE images, with a rather homogeneous peripheral gland and an inhomogeneous central gland. Volume measurements yielded reproducibilities of 3.2 %-4.7 %. Signal intensity in the FLASH sequence decreased during LITT, both in the prostate in vivo and in specimens of bovine prostate and seminal vesicles in vitro, with signal developments running in parallel. Areas of energy deposition and signal alteration were not sharply delineated. The latter margin of the laser-induced lesions could not be predicted from the FLASH images, while the tip of the laser fibre was easily recognized. Contrast-enhanced T1-weighted MR images immediately after LITT clearly demarcated low signal intensity laser lesions from high signal intensity surrounding prostate tissue. Follow-up examinations showed a decrease of 20 % of prostate volume over a period of 6-12 months after LITT. Correlation between prostate volume 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 recognition of intraprostatic alterations after LITT, including volume changes over a period of up to 1 year after therapy that can be predicted immediately after LITT. While laser energy deposition in the prostate can be monitored by MRI with T1-weighted FLASH sequences as a function of temperature alteration, it is not possible to determine the lesion margins immediately from the FLASH images. Online temperature development map generation will be necessary to influence ongoing LITT procedures with MRI.