Magnetic Resonance Imaging-guided Laser Ablation Research Articles

Abstract No. 17 Prospective observational study of pain severity and pain interference outcomes following percutaneous magnetic resonance imaging–guided laser ablation or cryoablation of painful peripheral, soft tissue vascular anomalies: 6-month interim analysis

To prospectively evaluate the 6-month pain severity and pain interference outcomes following percutaneous MRI-guided laser ablation and cryoablation of focal painful, peripheral soft tissue vascular anomalies

Insular seizures and epilepsies: Ictal semiology and minimal invasive surgery.

The increased identification of seizures with insular ictal onset, promoted by the international development of stereo-electroencephalography (SEEG), has led to the recent description of larger cohorts of patients with insular or insulo-opercular epilepsies than those previously available. These new series have consolidated and extended our knowledge of the rich ictal semiology and diverse anatomo-clinical correlations that characterized insular seizures. In parallel, some experiences have been gained in the surgical treatment of insular epilepsies using minimal invasive procedures. The large majority of patients present with auras (mostly somatosensory and laryngeal) and motor signs (predominantly elementary and orofacial), an underlying focal cortical dysplasia, and an excellent postoperative seizure outcome. Many other subjective and objective ictal signs, known to occur in other forms of epilepsies, are also observed and clustered in five patterns, reflecting the functional anatomy of the insula and its overlying opercula, as well as preferential propagation pathways to frontal or temporal brain regions. A nocturnal predominance of seizure is frequently reported, whereas secondary generalization is infrequent. Some rare ictal signs are highly suggestive of an insular origin, including somatic pain, reflex seizures, choking spells, and vomiting. Minimal invasive surgical techniques have been applied to the treatment of insular epilepsies, including Magnetic Resonance Imaging-guided laser ablation (laser interstitial thermal therapy (LITT)), radiofrequency thermocoagulation (RFTC), gamma knife radiosurgery, and responsive neurostimulation. Rates of seizure freedom (about 50%) appear lower than that reported with open-surgery (about 80%) with yet a significant proportion of transient neurological deficit for LITT and RFTC. Significant progress has been made in the identification and surgical treatment of insular and insulo-opercular epilepsies, including more precise anatomo-clinical correlations to optimally plan SEEG investigations, and experience in using minimal invasive surgery to reduce peri-operative morbidity.

Characterization of Magnetic Resonance Thermal Imaging Signal Artifact During Magnetic Resonance Guided Laser-Induced Thermal Therapy.

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 attempted to characterize this artifact. To characterize MRTI signal the artifact in select cases to better understand its potential relevance and impact on the ablation procedure. All ablations were performed using the Visualase magnetic resonance imaging-guided laser ablation system (Medtronic). Patients were included if the MRTI contained signal artifact that distorted the ablative region during the first thermal dose delivered. Ablation artifact was quantified using MATLAB version R2018a (Mathworks Inc, Natick, Massachusetts). A total of 116 patients undergoing MRgLITT for various surgical indications were examined. MRTI artifact was observed in 37.0% of cases overall. Incidence of artifact was greater at higher powers (P<.001) and with longer ablation times (P=.024), though artifact size did not correlate with laser power or ablation duration. MRTI signal artifact is common during LITT. Higher powers and longer ablation times result in greater incidence of ablation artifact, though artifact size is not correlated with power or duration. Future studies should aim to evaluate effects of artifact on postoperative imaging and, most notably, patient outcomes.

Molecular Bioluminescence Imaging as a Noninvasive Tool for Monitoring Tumor Growth and Therapeutic Response to MRI-Guided Laser Ablation in a Rat Model of Hepatocellular Carcinoma

The objective of this study was to quantitatively compare tumor imaging by magnetic resonance imaging (MRI) and molecular bioluminescence imaging (BLI) and test the feasibility of monitoring the effect of MRI-guided laser ablation on tumor viability by 2-dimensional BLI and 3-dimensional diffuse luminescence tomography (3D DLIT) in an orthotopic rat model of hepatocellular carcinoma. This study was approved by the animal care committee. Rats underwent injection of N1S1 cells stably transfected with an empty vector (n = 3) or a heat shock element luciferase reporter (HSE-luc; n = 4) into the liver. All rats underwent MRI to assess tumor establishment and volume and 2-dimensional BLI to assess tumor luminescence at day 7 with subsequent MRI and 2D BLI and 3D DLIT in select animals at days 14 and 21. Magnetic resonance imaging-guided laser ablation of the tumor was performed with preablation and postablation 2D BLI and/or 3D DLIT (n = 2). The tumors underwent histopathologic analysis to assess tumor viability. The MRI scans demonstrated hyperintense T2-weighted lesions at 3 of 3 and 4 of 4 sites in the empty vector and HSE-luc rats, respectively. Two-dimensional BLI quantitation demonstrated 23.0-fold higher radiance in the HSE-luc group compared with the empty vector group at day 7 (P < 0.01) and a significant correlation with tumor volume by MRI (r = 0.86; P < 0.03). Tumor dimensions by 3D DLIT and MRI demonstrated good agreement. Three-dimensional DLIT quantitation demonstrated better agreement with the percentage of nonviable tumor by histopathology than did 2D BLI quantitation after the MRI-guided laser ablation. Bioluminescence imaging is feasible as a noninvasive, quantitative tool for monitoring tumor growth and therapeutic response to thermal ablation in a rat model of hepatocellular carcinoma.

Magnetic Resonance Imaging–Guided Laser Ablation of Bone Tumors

Image-guided thermal ablation of bone tumors is gaining acceptance in the oncology community. Computed tomography-guided radiofrequency ablation and cryoablation are widely available and are used in clinical practice. However, a potentially devastating complication of these techniques is thermal injury to the spinal cord and nerve roots in patients with tumors involving the vertebra, paraspinal tissues, or pelvis. Magnetic resonance imaging-guided laser ablation with quantitative magnetic resonance temperature imaging is a novel technique that allows for accurate imaging of the tumor, real-time placement of laser fibers, and real-time monitoring of the ablation zone. With this technique, target temperature thresholds are placed on critical neural elements to provide real-time feedback that allows for automatic deactivation of the laser when the threshold temperature is reached. The ablation zone is generated quickly, with sharp and well-demarcated boundaries. As such, magnetic resonance imaging-guided laser ablation may be a safer technique for ablating bone tumors in the vicinity of the spinal cord, nerve roots, and peripheral nerves.

Feasibility of 3.0T Magnetic Resonance Imaging-guided Laser Ablation of a Cadaveric Prostate

To demonstrate the feasibility of 3.0T magnetic resonance imaging (MRI)-guided laser ablation of the prostate. MRI-guided laser ablations in the intact prostate gland were performed in 5 cadavers. The cadavers were brought into the MRI suite and placed in a supine headfirst position. A needle guide grid was placed against the perineum, and MRI was performed to co-localize the grid with the prostate imaging data set. Using the guidance grid and 14-gauge Abbocath catheters, the laser applicators were placed in the prostate with intermittent MRI guidance. After confirmation of the position of the laser applicators, 2-minute ablations were performed with continuous MRI temperature feedback. Using the relative change in temperature and the Arrhenius model of thermal tissue ablation, the ablation margins were calculated. Laser ablation was successfully performed in all 5 cadaveric prostates using 15- and 30-W laser generators. Thermal mapping in the axial, sagittal, and coronal planes was performed with calculated ablation margins projected back onto the magnitude MR images. Deviations of the needles from the template projections ranged from 1.0 to 4.1 mm (average 2.1) at insertion depths of 75.5-116.5 mm (average 98.2). In the 2 cadavers for which histologic correlation was available, the extent of the ablation zone corresponded to the temperature mapping findings and the ablation transition zones were identifiable on hematoxylin-eosin staining. Transperineal laser ablation of the prostate gland is possible using 3.0T MRI guidance and thermal mapping and offers the potential for precise image-guided focal targeting of prostate cancer.