School of Biological and Health Systems Engineering, Arizona State University, Tempe, AZ, USA.
Banner M D Anderson Cancer Center, Gilbert, AZ, USA.
NMR Biomed. 2019 Mar;32(3):e4046. doi: 10.1002/nbm.4046. Epub 2019 Jan 14.
Magnetic resonance spectroscopic imaging (MRSI) is an important technique for assessing the spatial variation of metabolites in vivo. The long scan times in MRSI limit clinical applicability due to patient discomfort, increased costs, motion artifacts, and limited protocol flexibility. Faster acquisition strategies can address these limitations and could potentially facilitate increased adoption of MRSI into routine clinical protocols with minimal addition to the current anatomical and functional acquisition protocols in terms of imaging time. Not surprisingly, a lot of effort has been devoted to the development of faster MRSI techniques that aim to capture the same underlying metabolic information (relative metabolite peak areas and spatial distribution) as obtained by conventional MRSI, in greatly reduced time. The gain in imaging time results, in some cases, in a loss of signal-to-noise ratio and/or in spatial and spectral blurring. This review examines the current techniques and advances in fast MRSI in two and three spatial dimensions and their applications. This review categorizes the acceleration techniques according to their strategy for acquisition of the k-space. Techniques such as fast/turbo-spin echo MRSI, echo-planar spectroscopic imaging, and non-Cartesian MRSI effectively cover the full k-space in a more efficient manner per T . On the other hand, techniques such as parallel imaging and compressed sensing acquire fewer k-space points and employ advanced reconstruction algorithms to recreate the spatial-spectral information, which maintains statistical fidelity in test conditions (ie no statistically significant differences on voxel-wise comparisions) with the fully sampled data. The advantages and limitations of each state-of-the-art technique are reviewed in detail, concluding with a note on future directions and challenges in the field of fast spectroscopic imaging.
磁共振波谱成像（MRSI）是评估体内代谢物空间变化的重要技术。MRSI 的长扫描时间由于患者不适、增加成本、运动伪影和协议灵活性有限，限制了其临床应用。更快的采集策略可以解决这些限制，并有可能在不增加当前解剖学和功能采集协议的成像时间的情况下，将 MRSI 更广泛地应用于常规临床方案。毫不奇怪，已经投入了大量精力来开发更快的 MRSI 技术，这些技术旨在以大大减少的时间捕获与常规 MRSI 获得的相同的基础代谢信息（相对代谢峰面积和空间分布）。在某些情况下，成像时间的提高会导致信噪比和/或空间和光谱模糊的损失。这篇综述检查了二维和三维快速 MRSI 中的当前技术和进展及其应用。这篇综述根据其在 k 空间中的采集策略对加速技术进行分类。诸如快速/涡轮回波 MRSI、回波平面波谱成像和非笛卡尔 MRSI 之类的技术可以更有效地在每个 T 内覆盖整个 k 空间。另一方面，并行成像和压缩感知等技术采集的 k 空间点较少，并采用先进的重建算法来重建空间频谱信息，在测试条件下（即在体素比较方面没有统计学上显著差异）保持统计保真度与完全采样数据。详细回顾了每种最先进技术的优缺点，并就快速光谱成像领域的未来方向和挑战进行了说明。
