Department of Radiation Oncology, Henry Ford Health Systems, Detroit, Michigan.
Philips Healthcare, Cleveland, Ohio.
Int J Radiat Oncol Biol Phys. 2015 Nov 1;93(3):497-506. doi: 10.1016/j.ijrobp.2015.07.001. Epub 2015 Jul 9.
To incorporate a novel imaging sequence for robust air and tissue segmentation using ultrashort echo time (UTE) phase images and to implement an innovative synthetic CT (synCT) solution as a first step toward MR-only radiation therapy treatment planning for brain cancer.
Ten brain cancer patients were scanned with a UTE/Dixon sequence and other clinical sequences on a 1.0 T open magnet with simulation capabilities. Bone-enhanced images were generated from a weighted combination of water/fat maps derived from Dixon images and inverted UTE images. Automated air segmentation was performed using unwrapped UTE phase maps. Segmentation accuracy was assessed by calculating segmentation errors (true-positive rate, false-positive rate, and Dice similarity indices using CT simulation (CT-SIM) as ground truth. The synCTs were generated using a voxel-based, weighted summation method incorporating T2, fluid attenuated inversion recovery (FLAIR), UTE1, and bone-enhanced images. Mean absolute error (MAE) characterized Hounsfield unit (HU) differences between synCT and CT-SIM. A dosimetry study was conducted, and differences were quantified using γ-analysis and dose-volume histogram analysis.
On average, true-positive rate and false-positive rate for the CT and MR-derived air masks were 80.8% ± 5.5% and 25.7% ± 6.9%, respectively. Dice similarity indices values were 0.78 ± 0.04 (range, 0.70-0.83). Full field of view MAE between synCT and CT-SIM was 147.5 ± 8.3 HU (range, 138.3-166.2 HU), with the largest errors occurring at bone-air interfaces (MAE 422.5 ± 33.4 HU for bone and 294.53 ± 90.56 HU for air). Gamma analysis revealed pass rates of 99.4% ± 0.04%, with acceptable treatment plan quality for the cohort.
A hybrid MRI phase/magnitude UTE image processing technique was introduced that significantly improved bone and air contrast in MRI. Segmented air masks and bone-enhanced images were integrated into our synCT pipeline for brain, and results agreed well with clinical CTs, thereby supporting MR-only radiation therapy treatment planning in the brain.
利用超短回波时间（UTE）相位图像纳入一种新的成像序列，以实现稳健的空气和组织分割，并实现创新的合成 CT（synCT）解决方案，作为脑癌磁共振仅放疗治疗计划的第一步。
10 例脑癌患者在具有模拟功能的 1.0 T 开放式磁体上接受 UTE/Dixon 序列和其他临床序列扫描。从 Dixon 图像和反转 UTE 图像导出的水/脂肪图的加权组合生成骨增强图像。使用未缠绕的 UTE 相位图自动执行空气分割。通过计算使用 CT 模拟（CT-SIM）作为金标准的分割误差（真阳性率、假阳性率和 Dice 相似性指数）来评估分割准确性。synCT 使用基于体素的加权求和方法生成，该方法结合了 T2、液体衰减反转恢复（FLAIR）、UTE1 和骨增强图像。平均绝对误差（MAE）描述了 synCT 和 CT-SIM 之间的 Hounsfield 单位（HU）差异。进行了剂量学研究，并使用γ分析和剂量-体积直方图分析量化了差异。
平均而言，CT 和 MR 衍生的空气掩模的真阳性率和假阳性率分别为 80.8%±5.5%和 25.7%±6.9%。Dice 相似性指数值为 0.78±0.04（范围为 0.70-0.83）。synCT 和 CT-SIM 之间的全视场 MAE 为 147.5±8.3 HU（范围为 138.3-166.2 HU），最大误差发生在骨-气界面（骨的 MAE 为 422.5±33.4 HU，空气的 MAE 为 294.53±90.56 HU）。γ分析显示通过率为 99.4%±0.04%，该队列的治疗计划质量可接受。
引入了一种混合 MRI 相位/幅度 UTE 图像处理技术，该技术可显著提高 MRI 中的骨和空气对比度。分割的空气掩模和骨增强图像被集成到我们的 synCT 脑管道中，结果与临床 CT 非常吻合，从而支持脑癌的磁共振仅放疗治疗计划。
