Department of Diagnostic Physics, Division of Radiology and Nuclear Medicine, Oslo University Hospital, Oslo, Norway.
Department of Diagnostic Physics, Division of Radiology and Nuclear Medicine, Oslo University Hospital, Oslo, Norway.
Eur J Radiol. 2020 Nov;132:109278. doi: 10.1016/j.ejrad.2020.109278. Epub 2020 Sep 16.
Relative cerebral blood volume (rCBV) from dynamic susceptibility contrast (DSC)-MRI is a valuable biomarker in patients with glioblastoma for assessing treatment response and predicting overall survival. DSC-MRI based on echo planar images (EPI) may possess severe geometric distortions from magnetic field inhomogeneities up to the order of centimeters. The aim of this study is to assess how much two readily available EPI-based geometric distortion correction methods, FSL TOPUP and EPIC, affect rCBV values from DSC-MRI in patients with confirmed glioblastoma.
We used a combined single-shot 2D gradient-echo (T2*), spin-echo (T2) EPI sequence to estimate both T2* and T2-weighted rCBV from the same contrast agent injection. Effects of distortion correction on the positive phase-encoded T2- and T2*-images were assessed in healthy anatomical brain regions in terms of Wilcoxon signed rank tests on median rCBV change and on Dice coefficients, as well as in tumor lesions in terms of Wilcoxon signed rank tests on median rCBV change.
Our results show that following distortion correction, both gradient-echo and spin-echo rCBV increased in cortical areas of the frontal, temporal and occipital lobe, including the posterior orbital gyri in the frontal lobe and middle frontal gyri (p < 0.0008). Similar, improved Dice coefficients were observed for gradient-echo EPI in temporal, occipital and frontal lobe. Only spin-echo rCBV in enhancing lesion increased with correction (p = 0.0002).
Our study sheds light on the importance of performing geometric distortion correction on EPI-based MRI data before assessing functional information such as rCBV values. Our findings may indicate that uncorrected rCBV values can be underestimated from positive phase-encoding EPI and that geometric distortion correction is warranted when comparing EPI-based data to conventional MRI.
动态对比磁共振成像（DSC-MRI）中的相对脑血容量（rCBV）是评估胶质母细胞瘤患者治疗反应和预测总生存期的有价值的生物标志物。基于回波平面图像（EPI）的 DSC-MRI 可能会因磁场不均匀性而产生高达厘米级的严重几何变形。本研究旨在评估两种易于获得的基于 EPI 的几何变形校正方法，FSL TOPUP 和 EPIC，对经证实的胶质母细胞瘤患者的 DSC-MRI 中 rCBV 值的影响。
我们使用了一种组合的单次 2D 梯度回波（T2*）、自旋回波（T2）EPI 序列，从相同的对比剂注射中估计 T2和 T2 加权 rCBV。通过Wilcoxon 符号秩检验，评估了校正对健康解剖脑区正相位编码 T2-和 T2-图像的影响，评估指标为中位数 rCBV 变化和 Dice 系数；以及在肿瘤病变中，评估指标为中位数 rCBV 变化的 Wilcoxon 符号秩检验。
我们的结果表明，校正后，皮质区的额、颞和枕叶，包括额叶的眶后回和中额回，梯度回波和自旋回波 rCBV 均增加（p < 0.0008）。类似地，也观察到颞叶、枕叶和额叶的梯度回波 EPI 的 Dice 系数得到了改善。只有增强病变中的自旋回波 rCBV 随校正而增加（p = 0.0002）。
本研究强调了在评估功能信息（如 rCBV 值）之前，对基于 EPI 的 MRI 数据进行几何变形校正的重要性。我们的发现可能表明，未校正的 rCBV 值可能会因正相位编码 EPI 而被低估，并且在将基于 EPI 的数据与常规 MRI 进行比较时，需要进行几何变形校正。
