Author: Yaowen Cao, Yunwen Huang, Yidong Yang, Xiaogang Yuan, Ning Zhao, Cheng Zheng 👨🔬
Affiliation: Department of Life Sciences and Medicine, University of Science and Technology of China, Department of Engineering and Applied Physics, University of Science and Technology of China, University of Science and Technology of China 🌍
Purpose: MRI has better soft tissue contrast than cone beam CT which is commonly used in image guided radiotherapy. This study aims to develop a low-field MRI system for precision small animal radiation research.
Methods: The first stage involved verifying the performance of low-field MRI imaging and developing an offline MRI guidance system. A 0.5T neodymium magnet was used to construct the MRI system. In vivo imaging was performed on multiple mouse tumor models to evaluate the system's tumor detection capability. The uncertainty of offline guidance was measured using orthogonal 2D X-ray images after placing markers in both phantom and mouse. The offline guidance capability was tested on an orthotopic colon tumor model, with 10 mice in the radiotherapy group and another 10 in the control group. The radiotherapy prescription was 8 Gy × 4 fractions, for every 3 days. The planning target volume was segmented based on MRI, and the dose distribution was calculated based on CBCT. Online CBCT and radiotherapy were performed using the iSMARRT platform (45 kVp/0.9 mA for imaging and 225 kVp/13.3 mA for radiotherapy). Tumor volume changes were monitored via MRI over a two-week period following radiotherapy.
Results: Compared to H&E staining results, the low-field MRI system effectively identified and delineated all tumors in all models. The uncertainty of offline guidance was measured to be 1.19 ± 0.23 mm. A significant reduction in tumor volume was observed in the radiotherapy group compared to the control group (p < 0.01), demonstrating the efficacy of the offline MRI guidance system.
Conclusion: This study developed a low-field small animal MRI system and demonstrated its capability for tumor detection. By utilizing an existing radiotherapy platform, the system enabled MRI guided precision small animal radiotherapy.