Faculty of Advanced Sciences and Technologies, University of Isfahan, Isfahan, Iran.
Department of Biomedical Engineering, Aliabad Katoul Branch, Islamic Azad University, Aliabad-e-Katoul, Iran.
MAGMA. 2021 Apr;34(2):213-228. doi: 10.1007/s10334-020-00863-3. Epub 2020 Jul 6.
Inversion recovery-pointwise encoding time reduction with radial acquisition (IR-PETRA) is an effective magnetic resonance (MR) pulse sequence in generating pseudo-CTs. The hardware-related spatial-distortion (HRSD) in MR images potentially deteriorates the accuracy of pseudo-CTs. Thus, we aimed at characterizing HRSD for IR-PETRA.
gross-HRSD (Euclidean-sum of gross-HRSD (i = x, y, z)) for IR-PETRA was assessed using a brain-specific phantom for two MR scanners (1.5 T-Aera and 3.0 T-Prisma). Moreover, hardware imperfections were analyzed by determining gradient-nonlinearity spatial-distortion (GNSD) and B-inhomogeneity spatial-distortion (BISD) for magnetization-prepared rapid acquisition gradient-echo (MP-RAGE) which has well-known distortion characteristics.
In 3.0 T, maximum of gross-GNSD (Euclidean-sum of gross-GNSD) and gross-BISD for MP-RAGE was 2.77 mm and 0.57 mm, respectively. For this scanner, the mean and maximum of gross-HRSD for IR-PETRA were 0.63 ± 0.38 mm and 1.91 mm, respectively. In 1.5 T, maximum of gross-GNSD and gross-BISD for MP-RAGE was 3.41 mm and 0.78 mm, respectively. The mean and maximum of gross-HRSD for IR-PETRA were 1.02 ± 0.50 mm and 3.12 mm, respectively.
The spatial accuracy of MR images, besides being impacted by hardware performance, scanner capabilities, and imaging parameters, is mainly affected by its imaging strategy and data acquisition scheme. In 3.0 T, even without applying vendor correction algorithms, spatial accuracy of IR-PETRA image is sufficient for generating pseudo-CTs. In 1.5 T, distortion-correction is required to provide this accuracy.
反转恢复点编码时间减少径向采集（IR-PETRA）是一种有效的磁共振（MR）脉冲序列，可生成伪 CT。MR 图像中的硬件相关空间失真（HRSD）可能会降低伪 CT 的准确性。因此，我们旨在描述 IR-PETRA 的 HRSD。
使用特定于大脑的体模评估了两台磁共振扫描仪（1.5 T-Aera 和 3.0 T-Prisma）的 IR-PETRA 的总 HRSD（总 HRSD（i = x，y，z）的欧式和）。此外，通过确定磁化准备快速获取梯度回波（MP-RAGE）的梯度非线性空间失真（GNSD）和 B 不均匀性空间失真（BISD）来分析硬件缺陷，MP-RAGE 具有已知的失真特性。
在 3.0 T 中，MP-RAGE 的最大总 GNSD（总 GNSD 的欧式和）和总 BISD 分别为 2.77 mm 和 0.57 mm。对于该扫描仪，IR-PETRA 的总 HRSD 的平均值和最大值分别为 0.63 ± 0.38 mm 和 1.91 mm。在 1.5 T 中，MP-RAGE 的最大总 GNSD 和总 BISD 分别为 3.41 mm 和 0.78 mm。IR-PETRA 的总 HRSD 的平均值和最大值分别为 1.02 ± 0.50 mm 和 3.12 mm。
MR 图像的空间精度不仅受硬件性能、扫描仪功能和成像参数的影响，还主要受其成像策略和数据采集方案的影响。在 3.0 T 中，即使不应用供应商校正算法，IR-PETRA 图像的空间精度也足以生成伪 CT。在 1.5 T 中，需要进行失真校正以提供这种准确性。
