Evaluation of MRI protocols for the assessment of lumbar facet joints after MR-guided focused ultrasound treatment

Abstract

BackgroundMR-guided focused ultrasound (MRgFUS) might be a very safe and effective minimally invasive technique to treat facet joint pain caused by arthritis and other degenerative changes. However, there are still safety concerns for this treatment and challenges regarding MR imaging and temperature mapping due to susceptibility effects between the bone and soft tissue near the joint, which has resulted in poor MR image quality. The goal of this research was to evaluate multiple magnetic resonance imaging (MRI) pulse sequences for characterizing ablated lumbar facet joint lesions created by high-intensity focused ultrasound (FUS) and compare the findings to histological tissue assessment. In particular, we investigated the use of T2-weighted MRI to assess treatment effects without contrast administration.MethodsAn IACUC approved study (n = 6 pigs) was performed using a 3T widebore MRI system equipped with an MRgFUS system. Facet joints of the lumbar vertebra were ablated using 1-MHz frequency and multiple sonication energies (300–800 J). In addition to T2-weighted MRI for treatment planning, T1-, T2-, and T2*-weighted and perfusion MRI sequences were applied. Signal intensity ratios of the lesions were determined. Histopathology was used to characterize cellular changes.ResultsAblation of the facet joint, using MRgFUS, was successful in all animals. T2-weighted images showed high signal intensity in the edematous facet joint and adjacent muscle, while delayed contrast-enhanced T1-weighted images showed an enhanced ring surrounding the target volume. T2*-weighted GRE images revealed inconsistent lesion visualization. Histopathology confirmed the presence of cellular coagulation (shrinkage), extracellular expansion (edema), and hemorrhage in the bone marrow.ConclusionsMRgFUS provided sufficient precision and image quality for visualization and characterization of ablated facet joints directly after ablation. MRI may help in monitoring the efficacy of FUS ablation without contrast after treating patients with back pain.

Magnetic Resonance Imaging–Guided Focused Ultrasound Ablation of Lumbar Facet Joints of a Patient With a Magnetic Resonance Image Non-Conditional Pacemaker at 1.5T

“…We report a first case of MRgFUS ablation of lumbar facet joints in a patient with refractory low back pain and MRI non-conditional pacemaker. Facet joint MRgFUS is a relatively new treatment for facet joint pain 8,10,11 ; this procedure has the advantage of not requiring skin incision, and uses MRI for treatment planning and monitoring of the ablation in the real-time.…”

Comparison of Noninvasive High-Intensity Focused Ultrasound with Radiofrequency Ablation of Osteoid Osteoma

“…This is supported by recent reports demonstrating ability to safely perform MR-HIFU ablation close to the spine in treatment of spinal facet-related joint pain. [24][25][26] The single patient with partial response following MR-HIFU ablation had an osteoid osteoma located in the medullary cavity of the femur, rather than the cortex. This location required lethal heating deep within the bone to reach the nidus, pushing the current technical limits of this technology.…”

Potentials, Limitations and Future Directions of MR Contrast Media in Ablation Therapies

“…Figure 5 shows the correlation between a contrast enhanced MR image and macroscopic section of the ablated soft tissue; such as the kidney. In the bones (femur and lumber vertebrate), contrast enhanced MR images provided no enhancement of the bones, but of the adjacent soft tissue (Figure 6 and 7) [99][100][101]. : Left: Axial T1-weighted MR image of ablated lumber facet joint acquired one hour after thermal ablation (arrows).…”

“…Gd-DTPA (0.15 mmol/kg) was intravenously injected to delineate the ablated tissue. Again, the peri-ablated zone was enhanced, but not the core of ablated region; Center: Sagittal view shows the left ablated facet joint (arrow); Right: Coronal view shows of the enhanced rim of the ablated facet joint [99] …”