Mathematical Modeling of Thermal Damage Estimate Volumes in MR‐guided Laser Interstitial Thermal Therapy

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BACKGROUND AND PURPOSE Magnetic resonance‐guided laser interstitial thermal therapy (MRgLITT) is a minimally invasive procedure that produces real‐time thermal damage estimates (TDEs) of ablation. Currently, MRgLITT software provides limited quantitative parameters for intraoperative monitoring, but orthogonal TDE‐MRI slices can be utilized to mathematically estimate ablation volume. The objective of this study was to model TDE volumes and validate using post‐24 hours MRI ablative volumes. METHODS Ablations were performed with the Visualase Laser Ablation System (Medtronic). Using ellipsoidal parameters determined for dual‐TDEs from orthogonal MRI planes, TDE volumes were calculated by two definite integral methods (A and B) implemented in Matlab (MathWorks). Post‐24 hours MRI ablative volumes were measured in OsiriX (Pixmeo) by two‐blinded raters and compared to TDE volumes via paired t ‐test and Pearson's correlations. RESULTS Twenty‐two ablations for 20 patients with various intracranial pathologies were included. Average TDE volume calculated with method A was 3.44 ± 1.96 cm 3 and with method B was 4.83 ± 1.53 cm 3 . Method A TDE volumes were significantly different than post‐24 hours volumes ( P < .001). Method B TDE volumes were not significantly different than post‐24 hours volumes ( P = .39) and strongly correlated with each other ( r = .85, R 2 = .72, P < .0001). A total of eight of 22 (36%) method A versus 17 of 22 (77%) method B TDE volumes were within 25% of the post‐24 hours ablative volume. CONCLUSION We present a viable mathematical method integrating dual‐plane TDEs to calculate volumes. Future algorithmic iterations will incorporate additional calculated variables that improve ablative volume estimations.