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Purpose: Magnetic resonance-guided laser-induced thermal therapy (MRgLITT) is a minimally invasive procedure used to treat various intracranial pathologies. This study investigated the effects of variable power on maximal estimated thermal damage during ablation and duration required to reach maximal ablation. Materials/Methods: All ablations were performed using the Visualase Thermal Therapy System (Medtronic Inc., Minneapolis, Minnesota), which uses a 980 nm diffusing tip diode laser. Cases were stratified into low, medium and high power. Maximal thermal damage estimate (TDEmax) achieved in a single plane and time to reach maximal damage (ttdemax) were measured and compared between groups using a 2×3 Fixed Factor Analysis of Covariance. Ablation area change for cases in which an initial thermal dose was followed by a subsequent dose, with increased power, was also assessed. Results: We used real-time ablation data from 93 patients across various intracranial pathologies. ttdemax (mean ± SEM) decreased linearly as power increased (low: 139.2 ± 10.4 s, medium: 127.5 ± 4.3 s, high: 103.7 ± 5.8 s). In cases where a second thermal dose was delivered at higher power, the TDE expanded an average of 51.4 mm2 beyond the initial TDE generated by the first ablation, with the second ablation approaching TDEmax at a higher rate than the initial ablation. Conclusion: Increased power results in a larger TDEmax and an increased ablation rate. In cases where an initial thermal dose does not fully ablate the target lesion, a second ablation at higher power can increase the area of ablation with an increased ablation rate. [ABSTRACT FROM AUTHOR]

Background: Magnetic resonance-guided laser interstitial thermal therapy (MRgLITT) uses intraoperative temperature mapping and thermal damage estimates to guide ablations of intracranial targets. In select cases, signal artifact presents at the target site and impairs intraprocedural decision-making by obscuring the visualization of both temperature imaging and the thermal damage estimate calculation. To date, the etiology and impact of signal artifact are unknown. However, user-selected MRgLITT software settings may play a role in generating artifact., Objective: To assess the effect of the thresholding feature in MRgLITT software on signal artifact generation during intracranial ablations., Methods: Ablations were performed with the Visualase MRI-guided Laser Ablation System (Medtronic). For each LITT procedure, raw thermal data were extracted at a reference threshold of 40 and reprocessed at 5 additional threshold values ranging from 35 to 60. Artifact growth rates relative to threshold values were derived using simple linear regressions and then assessed within the context of laser power and duration using Pearson correlations., Results: A total of 33 patients were included, with 28 artifact-containing and 5 artifact-free cases. For artifact-containing cases, a 13% increase in artifact area occurred for every 1-point increase in threshold (R2 > 0.99). Artifact growth rates were not correlated with laser power (r = 0.15, P = .44) or duration (r = 0.0049, P = .98). One of the 5 artifact-free cases developed artifact at a threshold of 60., Conclusion: Artifact generation is likely multifactorial involving tissue properties and software settings. Operators can minimize software-introduced artifact by reducing threshold values., (Copyright © Congress of Neurological Surgeons 2021. All rights reserved.)

Background: Magnetic resonance-guided laser interstitial thermal therapy (MRgLITT) is a minimally invasive procedure that utilizes intraoperative magnetic resonance thermal imaging (MRTI) to generate a thermal damage estimate (TDE) of the ablative area. In select cases, the MRTI contains a signal artifact or defect that distorts the ablative region. No study has considered the impact of this artifact on TDE accuracy., Objective: To determine the effect of intraoperative MRTI signal artifact on postoperative magnetic resonance imaging (MRI)-predicted ablative area., Methods: All ablations were performed using the Visualase MRI-Guided Laser Ablation System (Medtronic). Patients were grouped based on whether the intraoperative MRTI contained signal artifact that distorted the ablative region. 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 and compared between groups with and without intraoperative MRTI artifact., Results: A total of 91 patients undergoing MRgLITT for various surgical indications were examined. MRTI artifact was observed in 43.9% of cases overall. The mean absolute difference between TDE and the postoperative MRI cross-sectional area was 94.8 mm2 (SEM = 11.6) in the group with intraoperative MRTI artifact and 54.4 mm2 (SEM = 5.5) in the nonartifact group., Conclusion: MRTI signal artifact is common during LITT. The presence of signal artifact during intraoperative MRTI results in higher variation between intraoperative TDE and postoperative MRI cross-sectional ablative area. In cases in which intraoperative MRTI artifact is observed, there may be a larger degree of variation between observed intraoperative TDE and measured postoperative MRTI ablative area., (Copyright © 2019 by the Congress of Neurological Surgeons.)

Objective: Intraoperative dynamics of magnetic resonance-guided laser-induced thermal therapy (MRgLITT) have been previously characterized for ablations of naive tissue. However, most treatment sessions require the delivery of multiple doses, and little is known about the ablation dynamics when additional doses are applied to heat-damaged tissue. This study investigated the differences in ablation dynamics between naive versus damaged tissue., Methods: The authors examined 168 ablations from 60 patients across various surgical indications. All ablations were performed using the Visualase MRI-guided laser ablation system (Medtronic), which employs a 980-nm diffusing tip diode laser. Cases with multiple topographically overlapping doses with constant power were selected for this study. Single-dose intraoperative thermal damage was used to calculate ablation rate based on the thermal damage estimate (TDE) of the maximum area of ablation achieved (TDEmax) and the total duration of ablation (tmax). We compared ablation rates of naive undamaged tissue and damaged tissue exposed to subsequent thermal doses following an initial ablation., Results: TDEmax was significantly decreased in subsequent ablations compared to the preceding ablation (initial ablation 227.8 ± 17.7 mm2, second ablation 164.1 ± 21.5 mm2, third ablation 124.3 ± 11.2 mm2; p = < 0.001). The ablation rate of subsequent thermal doses delivered to previously damaged tissue was significantly decreased compared to the ablation rate of naive tissue (initial ablation 2.703 mm2/sec; second ablation 1.559 mm2/sec; third ablation 1.237 mm2/sec; fourth ablation 1.076 mm/sec; p = < 0.001). A negative correlation was found between TDEmax and percentage of overlap in a subsequent ablation with previously damaged tissue (r = -0.164; p < 0.02)., Conclusions: Ablation of previously ablated tissue results in a reduced ablation rate and reduced TDEmax. Additionally, each successive thermal dose in a series of sequential ablations results in a decreased ablation rate relative to that of the preceding ablation. In the absence of a change in power, operators should anticipate a possible reduction in TDE when ablating partially damaged tissue for a similar amount of time compared to the preceding ablation.