Department of Biomedical Engineering, University of Alberta, Edmonton, Canada.
Department of Biomedical Engineering, University of Alberta, Edmonton, Canada.
Magn Reson Imaging. 2022 Oct;92:224-231. doi: 10.1016/j.mri.2022.06.010. Epub 2022 Jun 27.
To optimize quantitative susceptibility-weighted imaging also known as true susceptibility-weighted imaging (tSWI) for strong susceptibility sources like hemorrhage and compare to standard susceptibility-weighted imaging (SWI) and quantitative susceptibility mapping (QSM).
Ten patients with known intracerebral hemorrhage (ICH) were scanned using a 3D SWI sequence. The magnitude and phase images were utilized to compute QSM, tSWI and SWI images. tSWI parameters including the upper threshold for creating susceptibility-weighted masks and the multiplication factor were optimized for hemorrhage depiction. Combined tSWI was also computed with independent optimized parameters for both veins and hemorrhagic regions. tSWI results were compared to SWI and QSM utilizing region-of-interest measurements, Pearson's correlation and Kruskal-Wallis test.
Fifteen hemorrhages were found, with mean susceptibility 0.81 ± 0.37 ppm. Unlike SWI which utilizes a phase mask, tSWI uses a mask computed from QSM. In tSWI, the weighted mask required an extended upper threshold far beyond the standard level for more effective visualization of hemorrhage texture. The upper threshold was set to the mean maximum susceptibility in the hemorrhagic region (3.24 ppm) with a multiplication factor of 2. The blooming effect, seen in SWI, was observed to be larger in hemorrhages with higher susceptibility values (r = 0.78, p < 0.001) with reduced blooming on tSWI. On SWI, 4 out of 15 hemorrhages showed phase wrap artifacts in the hemorrhagic region and all patients showed some phase wraps in the air-tissue interface near the auditory and frontal sinuses. These phase wrap artifacts were absent on tSWI. In hemorrhagic regions, a higher correlation was observed between the actual susceptibility values and mean gray value for tSWI (r = -0.93, p < 0.001) than SWI (r = -0.87, p < 0.001).
In hemorrhage, tSWI minimizes both blooming effects and phase wrap artifacts observed in SWI. However, unlike SWI, tSWI requires an altered upper threshold for best hemorrhage depiction that greatly differs from the standard value. tSWI can be used as a complementary technique for visualizing hemorrhage along with SWI.
优化定量磁化率加权成像（也称为真实磁化率加权成像，tSWI）以适应强磁化率源，如出血，并与标准磁化率加权成像（SWI）和定量磁化率映射（QSM）进行比较。
对 10 名已知患有颅内出血（ICH）的患者进行 3D SWI 序列扫描。利用幅度和相位图像计算 QSM、tSWI 和 SWI 图像。针对出血描绘优化了 tSWI 参数，包括用于创建磁化率加权掩模的上限阈值和乘法因子。还使用静脉和出血区域的独立优化参数计算了联合 tSWI。利用感兴趣区域测量、皮尔逊相关和克鲁斯卡尔-沃利斯检验比较 tSWI 结果与 SWI 和 QSM。
共发现 15 个出血灶，平均磁化率为 0.81 ± 0.37 ppm。与利用相位掩模的 SWI 不同，tSWI 使用从 QSM 计算得到的掩模。在 tSWI 中，加权掩模需要一个远远超过标准水平的扩展上限阈值，以便更有效地可视化出血纹理。上限阈值设置为出血区域的平均最大磁化率（3.24 ppm），乘法因子为 2。在具有更高磁化率值的出血灶中，SWI 中观察到的blooming 效应（r = 0.78，p < 0.001）更大，tSWI 上的 blooming 效应较小。在 SWI 上，15 个出血灶中有 4 个在出血区域出现相位缠绕伪影，所有患者在靠近听小骨和额窦的空气-组织界面都出现了一些相位缠绕伪影。这些相位缠绕伪影在 tSWI 上不存在。在出血区域，tSWI 中实际磁化率值与平均灰度值之间的相关性高于 SWI（r = -0.93，p < 0.001）。
在出血中，tSWI 可最大限度地减少 SWI 中观察到的 blooming 效应和相位缠绕伪影。然而，与 SWI 不同，tSWI 需要一个用于最佳出血描绘的改变的上限阈值，该阈值与标准值有很大不同。tSWI 可作为 SWI 可视化出血的补充技术。
