Design and evaluation of a magnetic resonance-guided focused ultrasound system for the treatment of cervical spine pain

Abstract

Background: Neck pain is a common health problem, with a large percentage of individuals experiencing chronic or recurring pain. A considerable portion of chronic neck pain is attributed to the facet joints, which are small joints located at the back of the spinal column. Current treatments for this pain range from conservative treatments to invasive surgeries, each of which has potential risks and limitations. While radiofrequency ablation can be effective, it remains invasive and carries the risk of radiation exposure and long-term damage to paraspinal muscles. Magnetic resonance-guided focused ultrasound (MRgFUS) offers a promising alternative by enabling non-invasive and precise ablation of targeted tissue. However, the application of MRgFUS in the cervical spine requires careful consideration to avoid critical vascular and neural structures. Currently, there are no Food and Drug Administration approved focused ultrasound (FUS) devices for the cervical spine.

Purpose: This study aimed to design and evaluate a neck-specific MRgFUS system for the ablation of cervical facet joints in a preclinical setting. The goal was to demonstrate that MRgFUS could effectively target and ablate these joints while avoiding damage to surrounding critical structures.

Methods: The study involved the development of a specialized MRgFUS system consisting of an adjustable positioning gantry, a head support frame that supports the subject's head and neck above the transducer assembly, a transducer adjustment, and acoustic coupling system. The system included integrated magnetic resonance (MR) radiofrequency (RF) receive coils to enhance signal-to-noise ratio (SNR) and ensure accurate imaging during the procedure. The system was tested on five goats, where the cervical facet joints were targeted for ablation. Transducer position was located with the positioning coils, and the ultrasound focus was determined with MR-acoustic radiation force imaging (MR-ARFI) in adjacent muscle. Ablation of the facet joint was monitored in real-time with MR-temperature imaging (MRTI).

Results: The system demonstrated prediction accuracy of the geometric focus of 2.22 $\pm$ 0.74 mm. The MR imaging coil SNR was measured to be at least five times higher compared to the body coil. MR temperature precision was found to be 0.58 ${}^{\circ }C$ . The system successfully targeted and ablated the cervical facet joints using MR-ARFI and MRTI for guidance and monitoring.

Conclusions: The neck-specific MRgFUS system was able to target and ablate the cervical facet joints and monitor the treatment in real-time. The results suggest that this system has the potential for non-invasive treatment of facet joint related neck pain.

Keywords: ablation; cervical spine; focused ultrasound; magnetic resonance imaging.