Department of Medical Physics, Odette Cancer Centre, Sunnybrook Health Science Center, Toronto, ON, Canada.
Department of Medical Biophysics, University of Toronto, Toronto, ON, Canada; Medical Imaging, Sunnybrook Health Science Center, Toronto, ON, Canada; Department of Medical Imaging, University of Toronto, Toronto, ON, Canada.
Int J Radiat Oncol Biol Phys. 2014 Jul 1;89(3):649-57. doi: 10.1016/j.ijrobp.2014.03.028. Epub 2014 May 3.
To develop a practical method to localize bones in magnetic resonance (MR) images, to create "computed tomography-like" MR images (ctMRI) that could be used for radiation therapy verification, and to generate MR-based digitally reconstructed radiographs (DRR).
Using T1-weighted MR images, an air mask was derived from the manual contouring of all airways within the head and neck region using axial images at 6 anatomic levels. Compact bone, spongy bone, and soft tissue masks were then automatically generated using the statistical data derived from MR intensities and the air mask. ctMRI were then generated by mapping the MR intensities of the voxels within these masks into the CT number ranges of corresponding tissues. MR-based DRRs created from ctMRI were quantitatively evaluated using the co-registered MR and CT head images of 20 stereotactic radiosurgery patients. Ten anatomical points, positioned on the skull segmented using a threshold of 300 HU, in CT and ctMRI, were used to determine the differences in distance between MR-based DRRs and CT-based DRRs, and to evaluate the geometric accuracy of ctMRI and MR-based DRRs.
The bony structures were identified on ctMRI and were visible in the MR-based DRRs. From the 20 patient cases, the mean geometric difference and standard deviation between the 10 anatomical points on MR-based and CT-based DRRs was -0.05 ± 0.85 mm, respectively. This included uncertainty in image fusion. The maximum distance difference was 1.88 mm.
A practical method was developed to segment bone from MR images. The ctMRI created can be used for radiation treatment verification when MR-only simulation is performed. MR-based DRRs can be used in place of CT-based DRRs.
开发一种实用的方法来对磁共振（MR）图像中的骨骼进行定位，生成可用于放射治疗验证的“类似于 CT 的”MR 图像（ctMRI），并生成基于 MR 的数字重建射线照片（DRR）。
使用 T1 加权 MR 图像，通过在 6 个解剖水平的轴位图像上手动勾勒出头部和颈部区域内所有气道的轮廓，从气道中提取出空气掩模。然后，使用从 MR 强度和空气掩模中提取的统计数据自动生成致密骨、松质骨和软组织掩模。通过将这些掩模内的体素的 MR 强度映射到相应组织的 CT 数范围，生成 ctMRI。然后使用 20 例立体定向放射外科患者的配准的 MR 和 CT 头部图像对基于 MR 的 DRR 进行定量评估。在 CT 和 ctMRI 上，使用阈值为 300HU 对颅骨进行分割，选择 10 个位于颅骨上的解剖点，以确定基于 MR 的 DRR 和基于 CT 的 DRR 之间的距离差异，并评估 ctMRI 和基于 MR 的 DRR 的几何精度。
在 ctMRI 上可以识别出骨骼结构，并在基于 MR 的 DRR 中可见。在 20 例患者中，基于 MR 和 CT 的 DRR 上的 10 个解剖点之间的平均几何差异和标准差分别为-0.05±0.85mm，包括图像融合的不确定性。最大距离差异为 1.88mm。
开发了一种从 MR 图像中分割骨骼的实用方法。当仅进行 MR 模拟时，生成的 ctMRI 可用于放射治疗验证。可以替代 CT 基于 DRR 的基于 MR 的 DRR。
