Supplementary Material for: Compact Intraoperative MRI: Stereotactic Accuracy and Future Directions

<b><i>Background:</i></b> Intraoperative imaging must supply data that can be used for accurate stereotactic navigation. This information should be at least as accurate as that acquired from diagnostic imagers. <b><i>Objectives:</i></b> The aim of this study was to compare the stereotactic accuracy of an updated compact intraoperative MRI (iMRI) device based on a 0.15-T magnet to standard surgical navigation on a 1.5-T diagnostic scan MRI and to navigation with an earlier model of the same system. <b><i>Methods:</i></b> The accuracy of each system was assessed using a water-filled phantom model of the brain. Data collected with the new system were compared to those obtained in a previous study assessing the older system. The accuracy of the new iMRI was measured against standard surgical navigation on a 1.5-T MRI using T1-weighted (W) images. <b><i>Results:</i></b> The mean error with the iMRI using T1W images was lower than that based on images from the 1.5-T scan (1.24 vs. 2.43 mm). T2W images from the newer iMRI yielded a lower navigation error than those acquired with the prior model (1.28 vs. 3.15 mm). <b><i>Conclusions:</i></b> Improvements in magnet design can yield progressive increases in accuracy, validating the concept of compact, low-field iMRI. Avoiding the need for registration between image and surgical space increases navigation accuracy.**背景**：术中成像必须提供可用于精准立体定向导航的数据，此类信息的精度至少应与诊断成像设备获取的结果相当。**研究目的**：本研究旨在对比基于0.15-T磁体的升级款紧凑型术中磁共振成像（intraoperative MRI, iMRI）设备，与基于1.5-T诊断扫描磁共振成像的标准手术导航系统，以及该系列早期型号的立体定向导航精度。**研究方法**：采用充水脑部体模对各系统的精度进行评估。将新系统采集的数据与既往针对该系列早期型号的研究中获取的数据进行对比。新型术中磁共振成像的精度，以基于T1加权（T1-weighted, T1W）图像的1.5-T磁共振成像标准手术导航为参照进行测量。**研究结果**：采用T1W图像的术中磁共振成像的平均误差低于1.5-T扫描图像的平均误差（1.24 mm vs. 2.43 mm）。新型术中磁共振成像获取的T2加权（T2-weighted, T2W）图像所对应的导航误差，也低于该系列早期型号的结果（1.28 mm vs. 3.15 mm）。**研究结论**：磁体设计的优化可逐步提升导航精度，验证了紧凑型低场强术中磁共振成像的可行性。无需在图像与手术空间间进行配准操作，可进一步提升导航精度。