Department of Integrated Health Sciences, Graduate School of Medicine, Nagoya University, Nagoya, Japan.
Department of Radiology, Graduate School of Medical Sciences, Nagoya City University, Nagoya, Japan.
J Appl Clin Med Phys. 2022 Feb;23(2):e13469. doi: 10.1002/acm2.13469. Epub 2021 Nov 2.
To investigate the spatial accuracy of delineating prostatic calcifications by quantitative susceptibility mapping (QSM) in comparison with computed tomography (CT), we conducted phantom and human studies. Five differently-sized spherical hydroxyapatites mimicking prostatic calcification (pseudo-calcification) were arranged in the order of their sizes at the center of a plastic container filled with gelatin. This calcification phantom underwent magnetic resonance (MR) imaging, including the multiple spoiled gradient-echo sequences (SPGR) for the QSM and CT as a reference. The volume of each pseudo-calcification and center-to-center distance between the pseudo-calcifications delineated by QSM and CT were measured. In the human study, eight patients with prostate cancer who underwent radiation therapy and had some prostatic calcifications were included. The patients underwent CT and SPGR and modified DIXON sequence for MR-only simulation. The hybrid QSM processing combined with the complex signals in the SPGR and water and fat fraction maps estimated from the modified DIXON sequence were used to reconstruct the pelvic susceptibility map in humans. The threshold of CT numbers was set at 130 HU, while the QSM images were manually segmented in the calcification phantom and human studies. In the phantom study, there was an excellent agreement in the pseudo-calcification volumes between QSM and CT (y = 1.02x - 7.38, R = 0.99). The signal profiles had similar trends in CT and QSM. The center-to-center distances between the pseudo-calcifications in the phantom were also identical in QSM and CT. The calcification volumes were almost identical between the QSM and CT in the human study (y = 0.95x - 9.32, R = 1.00). QSM can offer geometric and volumetric accuracies to delineate prostatic calcifications, similar to CT. The prostatic calcification delineated by QSM may facilitate image-guided radiotherapy in the MR-only simulation workflow.
为了研究定量磁化率映射（QSM）在与 CT 相比时描绘前列腺钙化的空间准确性，我们进行了体模和人体研究。五个不同大小的羟磷灰石球体模拟前列腺钙化（假钙化），按其大小顺序排列在充满明胶的塑料容器的中心。该钙化体模接受了磁共振（MR）成像，包括用于 QSM 和 CT 参考的多个扰相梯度回波序列（SPGR）。测量了每个假钙化的体积和 QSM 和 CT 描绘的假钙化之间的中心到中心距离。在人体研究中，纳入了 8 名接受放射治疗且存在一些前列腺钙化的前列腺癌患者。患者接受了 CT 和 SPGR 以及用于仅 MR 模拟的改良 Dixon 序列检查。使用混合 QSM 处理技术结合 SPGR 中的复杂信号以及从改良 Dixon 序列估计的水和脂肪分数图，重建了人体盆腔磁化率图。将 CT 数的阈值设置为 130 HU，而在体模和人体研究中手动对 QSM 图像进行了分割。在体模研究中，QSM 和 CT 之间的假钙化体积具有极好的一致性（y=1.02x-7.38，R=0.99）。信号曲线在 CT 和 QSM 中具有相似的趋势。体模中假钙化之间的中心到中心距离在 QSM 和 CT 中也相同。人体研究中 QSM 和 CT 之间的钙化体积几乎相同（y=0.95x-9.32，R=1.00）。QSM 可以提供描绘前列腺钙化的几何和体积准确性，与 CT 相似。QSM 描绘的前列腺钙化可能有助于仅在 MR 模拟工作流程中进行图像引导放疗。
