MR guidance and thermometry of percutaneous laser disc decompression in open MRI: an ex vivo study.

PURPOSE: To assess the feasibility of guidance and thermometry by open 1.0 T magnetic resonance (MR) imaging during percutaneous laser disc decompression (PLDD).

METHODS: A fluoroscopic proton-density-weighted turbo spin echo sequence was used for positioning a laser fiber and a reference thermosensor within the targeted spinal disc. In 30 lumbar discs from human donors, nonspoiled gradient-echo (GRE) sequences with different echo times (TE) were compared to monitor thermal laser effects (Nd:YAG laser, 1,064 nm). Temperature distribution was visualized in real time on the basis of T1-weighted images and the proton resonance frequency (PRF) technique. Image quality, temperature accuracy, and correlation with macroscopic lesion sizes were analyzed. Image quality was confirmed in healthy volunteers.

RESULTS: MR-guided placement of the laser fiber in the center of the targeted disk was precise. Best overall PLDD results-considering image quality (contrast-to-noise ratio), temperature accuracy (R (2) = 0.96), and correlation between the macroscopic and MR lesions (R (2) = 0.63)-were achieved with TE at 7 ms. The same TE value also gave the best image quality with healthy volunteers.

CONCLUSION: Instrument guidance and PRF-based thermometry of PLDD in the lumbar spine are feasible and accurate. Open 1.0 T MR imaging with fast spin-echo and GRE sequence designs may render laser discectomies more effective and controllable.