Department of Biomedical Engineering, University of Alberta, Edmonton, Alberta, Canada.
Departments of Radiology and Clinical Neurosciences, Hotchkiss Brain Institute, University of Calgary, Calgary, Alberta, Canada.
NMR Biomed. 2022 Nov;35(11):e4788. doi: 10.1002/nbm.4788. Epub 2022 Jul 1.
Iron concentration in the human brain plays a crucial role in several neurodegenerative diseases and can be monitored noninvasively using quantitative susceptibility mapping (QSM) and effective transverse relaxation rate (R *) mapping from multiecho T *-weighted images. Large population studies enable better understanding of pathologies and can benefit from pooling multisite data. However, reproducibility may be compromised between sites and studies using different hardware and sequence protocols. This work investigates QSM and R * reproducibility at 3 T using locally optimized sequences from three centers and two vendors, and investigates possible reduction of cross-site variability through postprocessing approaches. Twenty-four healthy subjects traveled between three sites and were scanned twice at each site. Scan-rescan measurements from seven deep gray matter regions were used for assessing within-site and cross-site reproducibility using intraclass correlation coefficient (ICC) and within-subject standard deviation (SDw) measures. In addition, multiple QSM and R * postprocessing options were investigated with the aim to minimize cross-site sequence-related variations, including: mask generation approach, echo-timing selection, harmonizing spatial resolution, field map estimation, susceptibility inversion method, and linear field correction for magnitude images. The same-subject cross-site region of interest measurements for QSM and R * were highly correlated (R ≥ 0.94) and reproducible (mean ICC of 0.89 and 0.82 for QSM and R *, respectively). The mean cross-site SDw was 4.16 parts per billion (ppb) for QSM and 1.27 s for R *. For within-site measurements of QSM and R *, the mean ICC was 0.97 and 0.87 and mean SDw was 2.36 ppb and 0.97 s , respectively. The precision level is regionally dependent and is reduced in the frontal lobe, near brain edges, and in white matter regions. Cross-site QSM variability (mean SDw) was reduced up to 46% through postprocessing approaches, such as masking out less reliable regions, matching available echo timings and spatial resolution, avoiding the use of the nonconsistent magnitude contrast between scans in field estimation, and minimizing streaking artifacts.
人脑内的铁含量在多种神经退行性疾病中起着关键作用，可通过多回波 T *加权图像的定量磁化率映射（QSM）和有效横向弛豫率（R *）映射进行非侵入性监测。大型人群研究有助于更好地了解病理学，并可以从多站点数据中受益。然而，使用不同硬件和序列协议的站点和研究之间的可重复性可能会受到影响。本研究使用来自三个中心和两个供应商的局部优化序列，在 3T 下研究了 QSM 和 R *的可重复性，并通过后处理方法研究了减少跨站点变异性的可能性。二十四名健康受试者在三个站点之间旅行，并在每个站点进行两次扫描。使用七个深部灰质区域的扫描-重扫测量值，通过组内相关系数（ICC）和个体内标准差（SDw）测量值评估站点内和站点间的可重复性。此外，还研究了多种 QSM 和 R *后处理选项，目的是最小化跨站点序列相关的变化，包括：掩模生成方法、回波时间选择、协调空间分辨率、磁场图估计、磁化率反转方法以及幅度图像的线性磁场校正。相同受试者的 QSM 和 R *跨站点感兴趣区测量值高度相关（R ≥0.94）且可重复（QSM 和 R *的平均 ICC 分别为 0.89 和 0.82）。QSM 的平均跨站点 SDw 为 4.16 皮培（ppb），R *为 1.27 秒。对于 QSM 和 R *的站点内测量，平均 ICC 分别为 0.97 和 0.87，平均 SDw 分别为 2.36 ppb 和 0.97 秒。精度水平与区域有关，在额叶、靠近脑边缘和白质区域会降低。通过后处理方法，如屏蔽不可靠区域、匹配可用回波时间和空间分辨率、避免在磁场估计中使用扫描之间不一致的幅度对比度以及最小化条纹伪影，跨站点 QSM 变异性（平均 SDw）可降低多达 46%。
