Introduction: Magnetic Resonance-guided Laser Induced Thermal Therapy (MRgLITT) is a minimally invasive procedure used to treat various intracranial pathologies. The technology utilizes intraoperative magnetic resonance thermal imaging (MRTI) to generate a thermal damage estimate (TDE) of the ablative area. Previous studies have shown that the intraoperative TDE correlates strongly with postoperative MRI ablative cross-sectional area. However, no studies have evaluated this correlation when the intraoperative MRTI contains a signal artifact or defect that distorts the ablative region.

Methods: All ablations were performed using the Visualase MRI-Guided Laser Ablation System (Medtronic). Patients were grouped based on whether or not the intraoperative MRTI contained signal artifact that distorted the ablative region. Intraoperative TDE from the Visualase console and postoperative T1-weighted images were acquired. Cross-sectional area of the ablative lesion from the MRI image was measured, and the difference between intraoperative TDE and postoperative MRI cross-sectional area was calculated. Mean differences were compared between the group with intraoperative MRTI artifact and the group without MRTI artifact.

Results: 47 patients undergoing MRgLITT for various surgical indications were examined. The mean difference between TDE and the postoperative MRI cross-sectional area in the group with intraoperative MRTI artifact was 152.7 mm2 (SEM = 32.36), while the difference in the non-artifact group was 54.2 mm2 (SEM = 32.26). This indicated a statistically significant difference between the two groups (p = 0.0037).

Conclusions: The presence of signal artifact during intraoperative MRTI results in a larger degree of variation between intraoperative TDE and postoperative MRI cross-sectional ablative area. The presence of intraoperative MTRI artifact may be indicative of an underlying intralesional defect capable of altering the accuracy of the intraoperative TDE. Operators should be advised that in cases where intraoperative MRTI artifact is observed, patients may require more frequent follow-up due to reduced postoperative MRI concordance with intraoperative TDE.

Patient Care: This research will help inform postoperative management of patients with intraoperative MRTI signal artifact.

Learning Objectives: By the conclusion of this session, participants should be able to recognize the appearance of MRTI signal artifact and its implications.

References: Patel, Nitesh V., Kiersten Frenchu, and Shabbar F. Danish. "Does the Thermal Damage Estimate Correlate With the Magnetic Resonance Imaging Predicted Ablation Size After Laser Interstitial Thermal Therapy?." Operative Neurosurgery (2017).