McMaster School of Biomedical Engineering, McMaster University, Hamilton, Ontario, Canada.
Phys Med Biol. 2018 Oct 23;63(21):215005. doi: 10.1088/1361-6560/aae4d5.
Magnetic resonance imaging (MRI) has superior soft tissue contrast and lower interobserver variability compared to computed tomography and advances in equipment and pseudo-CT estimation have allowed for MR-only radiation therapy planning. Dedicated MR sequences have been used to localize paramagnetic structures with positive contrast, and most implanted seeds are gold fiducial markers (GFMs). We used a fast, dual-plane co-RASOR sequence to localize implanted GFMs with positive contrast in phantom and tissue to assess their resolution and registration accuracy of registration to CT. Off-resonant reconstructions of co-RASOR images were able to resolve GFMs down to 5 mm apart at 12 cm FOV. No systematic biases were observed by comparing registration of co-RASOR and bSSFP to CT images in an MR-compatible Lego phantom with a set of highly visible known points. The standard deviations of the MR to CT distance errors were <0.5 mm in all directions. We separated the component due to registration by comparing the two MR sequences, which had a maximum standard deviation of 0.36 mm in the SI-direction. Registration using the positive contrast points in a porcine sample phantom showed increased errors, but co-RASOR still performs acceptably with a target registration error of <0.75 mm. The dual-plane co-RASOR sequence could then be used for both registration and image tracking when performing MR-only radiation therapy planning.
磁共振成像（MRI）在软组织对比度方面优于计算机断层扫描（CT），且观察者间变异性较低，并且设备和伪 CT 估算方面的进步使得仅使用 MRI 进行放射治疗计划成为可能。专用的磁共振序列已被用于定位具有正对比度的顺磁性结构，大多数植入的种子是金基准标记物（GFM）。我们使用快速的双平面共 RASOR 序列在体模和组织中定位具有正对比度的植入 GFM，以评估其对 CT 的分辨率和配准精度。共 RASOR 图像的离谐重建能够在 12cm FOV 下分辨出相距 5mm 的 GFM。在具有一组高度可见已知点的 MR 兼容乐高体模中，通过比较共 RASOR 和 bSSFP 与 CT 图像的配准，没有观察到系统偏差。在所有方向上，MR 与 CT 距离误差的标准偏差均<0.5mm。我们通过比较两个 MR 序列来分离配准引起的组件，在 SI 方向上的最大标准偏差为 0.36mm。在猪样本体模中使用正对比度点进行注册显示出更大的误差，但共 RASOR 的性能仍然可以接受，目标注册误差<0.75mm。然后，当进行仅使用 MRI 的放射治疗计划时，双平面共 RASOR 序列可用于注册和图像跟踪。
