系统部分容积误差对动脉自旋标记磁共振成像估计灰质脑血流量的影响。
Effects of systematic partial volume errors on the estimation of gray matter cerebral blood flow with arterial spin labeling MRI.
作者信息
Petr Jan, Mutsaerts Henri J M M, De Vita Enrico, Steketee Rebecca M E, Smits Marion, Nederveen Aart J, Hofheinz Frank, van den Hoff Jörg, Asllani Iris
机构信息
Helmholtz-Zentrum Dresden-Rossendorf, Institute of Radiopharmaceutical Cancer Research, Dresden, Germany.
Department of Biomedical Engineering, Rochester Institute of Technology, Rochester, NY, USA.
出版信息
MAGMA. 2018 Dec;31(6):725-734. doi: 10.1007/s10334-018-0691-y. Epub 2018 Jun 18.
OBJECTIVE
Partial 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 METHODS
Twenty-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.
RESULTS
Geometric 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.
CONCLUSION
The quality of PV maps presents no argument for the preferential use of the GM-threshold method over PVC in the clinical application of ASL.
目的
部分容积（PV）校正是动脉自旋标记（ASL）磁共振成像（MRI）中的重要步骤，在计算平均灰质（GM）灌注时用于将灌注与结构效应区分开来。执行此校正有三种主要方法：（1）GM阈值法，仅包括GM体积高于预设阈值的体素；（2）GM加权法，使用体素级GM贡献并结合阈值处理；（3）PVC法，应用空间线性回归算法估计给定体素处各组织的血流贡献。在所有情况下，GM体积通过从T1加权（T1w）图像分割中提取的PV图获得。因此，由于ASL和T1w图像在读出类型和空间分辨率上的差异，PV图包含误差。在此，我们估计了这些误差，并评估了它们对每种PV校正方法计算GM脑血流量（CBF）性能的影响。
材料与方法
22名志愿者接受了二维回波平面成像（EPI）和三维螺旋ASL扫描。对于每种PV校正方法，使用模拟包含由于空间分辨率不匹配和几何畸变导致的估计误差的PV图来计算GM CBF，这些误差是由ASL和T1w图像在读出上的不匹配引起的。分析结果以评估每种误差对从ASL数据估计GM CBF的影响。
结果
几何畸变对二维EPI数据影响最大，而三维螺旋数据受分辨率不匹配影响最大。即使存在分辨率不匹配和几何畸变的组合误差，PVC方法也优于GM阈值法。对于二维和三维ASL，无组合误差时PVC方法的定量优势为16%，有组合误差时为10%。与理论预期一致，对于无误差的PV图，PVC方法提取了真实的GM CBF。相比之下，GM加权法高估GM CBF 5%，而GM阈值法低估16%。PV图误差的存在降低了所有方法计算的GM CBF。
结论
在ASL的临床应用中，PV图的质量并不能成为优先使用GM阈值法而非PVC法的理由。
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