MRI for in vivo Analysis of Ablation Zones Formed by Cooled Radiofrequency Neurotomy to Treat Chronic Joint Pain Across Multiple Axial Spine Sites

Abstract

Purpose: Radiofrequency (RF) ablation is the targeted damage of neural tissues to disrupt pain transmission in sensory nerves using thermal energy generated in situ by an RF probe. The present study aims to evaluate the utility of magnetic resonance imaging (MRI) for in vivo quantitative assessment of ablation zones in human subjects following cooled radiofrequency neurotomy for chronic pain at spinal facet or sacroiliac joints. Ablation zone size and shape have been shown in animal models to be influenced by size and type of RF probe – with cooled RF probes typically forming larger, more spherical ablation zones. To date, MRI of RF ablation zones in humans has been limited to two single retrospective case reports. Patients and Methods: A prospective, open-label pilot study of MRI for evaluation of cooled radiofrequency ablation zones following standard of care procedures in adult outpatients was conducted. Adult subjects (n=13) received monopolar cooled RF (CRF) ablation (COOLIEF™, Avanos Medical) of sensory nerves at spinal facet or sacroiliac joints, followed by an MRI 2–7 days after the procedure. MRI data were acquired using both Short Tau Inversion Recovery (STIR) and contrast-enhanced T1-weighted (T1C) protocols. T1C MRI was used to calculate 3-dimensional ellipsoid ablation zone volumes (V), where well-defined regions of signal hyperintensity were used to identify three orthogonal diameters (T, D, L) and apply the formula V=π/6×T×D×L. Results: Among 13 patients, 96 CRF ablation zones were created at 4 different anatomic sites (sacroiliac, lumbar, thoracic and cervical). CRF ablation zone morphology varied by anatomical location and structural features of surrounding tissues. In some cases, proximity to bone and striations of surrounding musculature obscured ablation zone borders. The volumes of 75 of the 96 ablation zones were measurable from MRI, with values (mean±SD) ranging from 0.4679 (±0.29) cm3 to 2.735 (±2.62) cm3 for the cervical and thoracic sites, respectively. Conclusion: In vivo T1C MRI analysis of cooled RF ablation zones at spinal facet and sacroiliac joints demonstrated variable effects of local tissues on ablation zone morphology. Placement of the CRFA probe very close to bone alters the ablation zone in a negative way, causing non-spherical and incomplete lesioning. These new data may serve to inform practicing physicians about optimal cooled RF probe placement in clinical procedures.