Predictability of the size of laser-induced lesions in T1-weighted MR images obtained during interstitial laser-induced thermotherapy of benign prostatic hyperplasia

The purpose of this study was to predict diameters of lesions induced by la ser-induced thermotherapy (LITT) of benign prostatic hyperplasia (BPH) from MRI signal/tissue temperature correlations during on-line monitoring with a temperature-sensitive fast low-angle shot (FLASH) sequence. Twenty LITT p rocedures with Nd:YAG (1.064 nm) and diode (830 nm) lasers were monitored o n line with a T1-weighted FLASH sequence at 1.5 Tesla. Interstitial prostat e temperature (T) was measured on line in 10 LITT procedures and laser ener gy deposition in 12, Slopes of linear regression curves for signal intensit y (SI) over T were applied to determine SI at 60 degrees C to estimate diam eters of intraprostatic LITT lesions. Diameters of unperfused LITT lesion c ores in contrast-enhanced T1-weighted images served as gold standards. Line ar regression curves with an average slope of -.54% SI/degrees C were obtai ned in 17 LITT procedures. Correlation coefficients were r = .92-.95 for SI /T and SI/energy deposition. Baseline variation of SI at body temperature w as +/- 3.9%, corresponding to +/- 7 degrees C. prediction of size (13 lesio ns) from on-line FLASH imaging was correct in 10 of 13, whereas 3 lesions w ere overestimated. Prediction of LITT lesion diameters from on-line MRI mon itoring is possible with a temperature-sensitive FLASH sequence in the pros tate. Accuracy may suffice to assign target regions of interest to tissue l ocations to be protected from coagulation.