Author: Richard Dortch, Thammathida Ketsiri, Zhiqiang Li, Shiv P. Srivastava 👨🔬
Affiliation: Barrow Neurological Institute, Dignity Health Cancer Institute, St. Joseph's Hospital & Medical Center 🌍
Purpose: Imaging the spinal cord post-surgery is challenging due to metal surgical implants, which induce signal loss and geometric distortions. Together, this hinders the visualization of the spinal cord and the accurate delineation of the target volumes for radiation therapy. Emerging methods (e.g., diffusion MRI) may overcome these challenges and provide quantitation of spine damage/recovery; however, these methods need to be systematically optimized. Toward this end, we designed a spine phantom that mimics the geometric and spine MRI properties, including diffusivity and water-fat content.
Methods: A titanium plate was fixed to the 3D-printed cervical spine model, and a microfiber bundle was placed inside the spinal canal to represent the spinal cord. The fat-water solution was injected into each vertebral body to mimic the bone marrow’s MR signals. MRI was acquired using two diffusion-weighted sequences: Multi-Shot Echo Planar Imaging (ms-EPI) and a Turbo spin-echo with Reduced field-of-view Imaging and Multi-Spectral modulation (TRIMS), which was designed by our group to overcome metal-related artifacts. T2-weighted and T1-weighted Dixon scans were acquired to reference and quantify the fat fraction within the spine.
Results: Distortion artifacts were observed in both T2 and diffusion-weighted images near the implants. The artifacts were less visible in the TRIMS than in ms-EPI, and the distortion of the spinal cord’s shape was nearly eliminated in the TRIMS. The artifacts observed in the phantom resembled those in previously acquired patient images. The generated fat fraction map also aligned well within the range of reported fat fraction values for the spine.
Conclusion: The proposed model effectively demonstrated the structure, water-fat content, and artifacts presented in spine MRI. This model shows potential to assist the development of novel imaging techniques for post-surgical spinal cord injuries, which could be applied to CT imaging and to assist treatment planning and response monitoring in radiotherapy.