Department of Radiology, Miller School of Medicine, University of Miami, Miami, Florida, USA.
J Magn Reson Imaging. 2014 Jan;39(1):224-34. doi: 10.1002/jmri.24130. Epub 2013 Apr 4.
To assess the impact of accelerated acquisitions on the spectral quality of volumetric magnetic resonance spectroscopic imaging (MRSI) and to evaluate their ability in detecting metabolic changes with mild injury.
The implementation of a generalized autocalibrating partially parallel acquisition (GRAPPA) method for a high-resolution whole-brain echo planar SI (3D-EPSI) sequence is first described and the spectral accuracy of the GRAPPA-EPSI method is investigated using lobar and voxel-based analyses for normal subjects and patients with mild traumatic brain injuries (mTBI). The performance of GRAPPA was compared with that of fully encoded EPSI for five datasets collected from normal subjects at the same scanning session, as well as on 45 scans (20 normal subjects and 25 mTBI patients) for which the reduced k-space sampling was simulated. For comparison, a central k-space lower-resolution 3D-EPSI acquisition was also simulated. Differences in individual metabolites and metabolite ratio distributions of the mTBI group relative to those of age-matched control subjects were statistically evaluated using analyses divided into hemispheric brain lobes and tissue types.
GRAPPA-EPSI with 16-minute scan time yielded robust and similar results in terms of MRSI quantitation, spectral fitting, and accuracy with that of fully sampled 3D-EPSI acquisitions and was more accurate than central k-space acquisition. Primary findings included high correlations (accuracy of 92.6%) between the GRAPPA and fully sampled results.
Although the reduced encoding method is associated with lower signal-to-noise ratio (SNR) that impacts the quality of spectral analysis, the use of the parallel imaging method can lead to the same diagnostic outcomes as the fully sampled data when using the sensitivity-limited volumetric MRSI.
评估加速采集对容积磁共振波谱成像（MRSI）谱质的影响，并评估其在检测轻度损伤时代谢变化的能力。
首先描述了一种高分辨率全脑回波平面 SI（3D-EPSI）序列的广义自校准部分并行采集（GRAPPA）方法的实现，并使用基于叶和体素的分析方法对正常受试者和轻度创伤性脑损伤（mTBI）患者进行研究，以评估 GRAPPA-EPSI 方法的光谱准确性。在相同的扫描会话中，将 GRAPPA 的性能与完全编码的 EPSI 进行了比较，比较了来自正常受试者的五个数据集，以及在模拟减少的 k 空间采样的 45 次扫描（20 名正常受试者和 25 名 mTBI 患者）上的性能。为了比较，还模拟了中央 k 空间低分辨率 3D-EPSI 采集。使用按半球脑叶和组织类型划分的分析方法，对 mTBI 组与年龄匹配的对照组个体代谢物和代谢物比分布的差异进行了统计学评估。
GRAPPA-EPSI 以 16 分钟的扫描时间进行，在 MRSI 定量、光谱拟合和准确性方面与完全采样的 3D-EPSI 采集具有相似的结果，并且比中央 k 空间采集更准确。主要发现包括 GRAPPA 和完全采样结果之间具有很高的相关性（准确性为 92.6%）。
尽管降低的编码方法与较低的信噪比（SNR）相关，会影响光谱分析的质量，但当使用灵敏度受限的容积 MRSI 时，并行成像方法的使用可以与完全采样数据产生相同的诊断结果。
