Effects of systematic partial volume errors on the estimation of gray matter cerebral blood flow with arterial spin labeling MRI
Effects of systematic partial volume errors on the estimation of gray matter cerebral blood flow with arterial spin labeling MRI
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DOI：
10.1007/s10334-018-0691-y
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发表时间：
2018-12-01
影响因子：
2.3
通讯作者：
Asllani, Iris
中科院分区：
文献类型：
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作者：
Petr, Jan;Mutsaerts, Henri J. M. M.;Asllani, Iris
部分容积（PV）校正是动脉自旋标记（ASL）MRI中的一个重要步骤，用于在计算平均灰质（GM）灌注时将灌注与结构效应分离。有三种主要方法用于执行该校正：（1）GM阈值，其仅包括具有高于预设阈值的GM体积的体素;（2）GM加权，其使用与阈值化相结合的逐体素GM贡献;以及（3）PVC，其应用空间线性回归算法来估计给定体素处的每个组织的流量贡献。在所有情况下，使用从T1加权（T1 w）图像的分割中提取的PV图获得GM体积。因此，由于ASL和T1 w图像之间的读出类型和空间分辨率差异，PV标测图包含错误。在这里，我们估计这些错误，并评估其影响的性能，每个PV校正方法计算GM脑血流量（CBF.Materials and MethodsTwenty-two志愿者进行扫描，使用二维回波平面成像（EPI）和三维螺旋ASL。对于每种PV校正方法，使用模拟PV图计算GM CBF，以包含由于ASL和T1 w图像之间读出不匹配引起的空间分辨率不匹配和几何失真引起的估计误差。结果进行了分析，以评估每个错误的影响，估计GM CBF ASL data.ResultsGeometric失真的影响最大的二维EPI数据，而3D螺旋是最受影响的分辨率不匹配。PVC方法优于GM阈值，即使在存在来自分辨率失配和几何失真的组合误差的情况下。对于2D和3D ASL，PVC的定量优势分别为16%和10%。与理论预期一致，对于无误差PV图，PVC方法提取了真实的GM CBF。相比之下，GM加权高估GM CBF 5%，而GM阈值低估了16%。PV地图错误的存在降低了计算GM CBF的所有methods.ConclusionThe PV地图的质量提出没有参数的优先使用GM阈值方法PVC在ASL的临床应用。
ObjectivePartial volume (PV) correction is an important step in arterial spin labeling (ASL) MRI that is used to separate perfusion from structural effects when computing the mean gray matter (GM) perfusion. There are three main methods for performing this correction: (1) GM-threshold, which includes only voxels with GM volume above a preset threshold; (2) GM-weighted, which uses voxel-wise GM contribution combined with thresholding; and (3) PVC, which applies a spatial linear regression algorithm to estimate the flow contribution of each tissue at a given voxel. In all cases, GM volume is obtained using PV maps extracted from the segmentation of the T1-weighted (T1w) image. As such, PV maps contain errors due to the difference in readout type and spatial resolution between ASL and T1w images. Here, we estimated these errors and evaluated their effect on the performance of each PV correction method in computing GM cerebral blood flow (CBF).Materials and methodsTwenty-two volunteers underwent scanning using 2D echo planar imaging (EPI) and 3D spiral ASL. For each PV correction method, GM CBF was computed using PV maps simulated to contain estimated errors due to spatial resolution mismatch and geometric distortions which are caused by the mismatch in readout between ASL and T1w images. Results were analyzed to assess the effect of each error on the estimation of GM CBF from ASL data.ResultsGeometric distortion had the largest effect on the 2D EPI data, whereas the 3D spiral was most affected by the resolution mismatch. The PVC method outperformed the GM-threshold even in the presence of combined errors from resolution mismatch and geometric distortions. The quantitative advantage of PVC was 16% without and 10% with the combined errors for both 2D and 3D ASL. Consistent with theoretical expectations, for error-free PV maps, the PVC method extracted the true GM CBF. In contrast, GM-weighted overestimated GM CBF by 5%, while GM-threshold underestimated it by 16%. The presence of PV map errors decreased the calculated GM CBF for all methods.ConclusionThe quality of PV maps presents no argument for the preferential use of the GM-threshold method over PVC in the clinical application of ASL.