Department of Neurosurgery, Medical College of Wisconsin, 8701 Watertown Plk Rd., Milwaukee, WI 53226, USA.
Department of Radiology, Medical College of Wisconsin, 8701 Watertown Plk Rd., Milwaukee, WI 53226, USA; Center for Imaging Research, Medical College of Wisconsin, 8701 Watertown Plk Rd., Milwaukee, WI 53226, USA.
Magn Reson Imaging. 2022 Feb;86:46-54. doi: 10.1016/j.mri.2021.11.003. Epub 2021 Nov 19.
Advanced diffusion MRI models are being explored to study the complex microstructure of the brain with higher accuracy. However, these techniques require long acquisition times. Simultaneous Multi-Slice (SMS) accelerates data acquisition by exciting multiple image slices simultaneously and separating the overlapping slices using a mathematical model, which makes use of the distinct information coming from an array of receive coils. However, SMS acceleration introduces increased noise in reconstructed images and crosstalk between simultaneously excited slices. These compounded effects from SMS acceleration could affect quantitative MRI techniques such as diffusion imaging. In this study, the effects of SMS acceleration on the accuracy of propagator metrics obtained from a model-free advanced diffusion technique called Mean Apparent Propagator MRI (MAP-MRI) was investigated. Ten healthy volunteers were scanned with SMS accelerated multi-shell diffusion MRI acquisitions. Group analyses were performed to study brain regions affected by SMS acceleration. In addition, diffusion metrics from atlas-based fiber tracts of interest were analyzed to investigate how propagator metrics in major fiber tracts were biased by 2- and 3-band SMS acceleration. Both zero-displacement metrics and non-Gaussianity metrics were significantly altered when SMS acceleration was used. MAP-MRI metrics calculated from SMS-3 showed significant differences with respect to SMS-2. Furthermore, with the shorter TR afforded by SMS acceleration, the characteristics of this bias have changed. This has implications for studies using diffusion MRI with SMS acceleration to investigate the effects of a disease or injury on the brain tissues.
高级弥散磁共振成像模型正在被探索用于以更高的精度研究大脑的复杂微观结构。然而，这些技术需要较长的采集时间。同时多层激发（SMS）通过同时激发多个图像层并使用数学模型分离重叠的层来加速数据采集，该数学模型利用来自一组接收线圈的独特信息。然而，SMS 加速会在重建图像中引入更多噪声，并在同时激发的层之间产生串扰。这些来自 SMS 加速的复合效应可能会影响定量磁共振成像技术，如扩散成像。在这项研究中，研究了 SMS 加速对从一种称为平均表观扩散系数磁共振成像（MAP-MRI）的无模型高级扩散技术获得的扩散系数测量值的准确性的影响。十名健康志愿者接受了 SMS 加速多壳层扩散 MRI 采集的扫描。进行了群组分析以研究受 SMS 加速影响的大脑区域。此外，还分析了基于图谱的感兴趣纤维束的扩散指标，以研究在主要纤维束中，2 波段和 3 波段 SMS 加速如何使扩散系数发生偏差。当使用 SMS 加速时，零位移指标和非高斯指标都发生了显著变化。SMS-3 计算的 MAP-MRI 指标与 SMS-2 相比有显著差异。此外，由于 SMS 加速提供的较短 TR，这种偏差的特征发生了变化。这对使用 SMS 加速的扩散 MRI 研究疾病或损伤对脑组织的影响具有重要意义。
