7T下采用螺旋进出采样的人脑全层3D磁共振波谱成像
Whole-Slab 3D MR Spectroscopic Imaging of the Human Brain With Spiral-Out-In Sampling at 7T.
作者信息
Esmaeili Morteza, Strasser Bernhard, Bogner Wolfgang, Moser Philipp, Wang Zhe, Andronesi Ovidiu C
机构信息
Athinoula A. Martinos Center for Biomedical Imaging, Department of Radiology, Massachusetts General Hospital, Harvard Medical School, Boston, Massachusetts, USA.
Department of Diagnostic Imaging, Akershus University Hospital, Lørenskog, Norway.
出版信息
J Magn Reson Imaging. 2021 Apr;53(4):1237-1250. doi: 10.1002/jmri.27437. Epub 2020 Nov 12.
BACKGROUND
Metabolic imaging using proton magnetic resonance spectroscopic imaging (MRSI) has increased the sensitivity and spectral resolution at field strengths of ≥7T. Compared to the conventional Cartesian-based spectroscopic imaging, spiral trajectories enable faster data collection, promising the clinical translation of whole-brain MRSI. Technical considerations at 7T, however, lead to a suboptimal sampling efficiency for the spiral-out (SO) acquisitions, as a significant portion of the trajectory consists of rewinders.
PURPOSE
To develop and implement a spiral-out-in (SOI) trajectory for sampling of whole-brain MRSI at 7T. We hypothesized that SOI will improve the signal-to-noise ratio (SNR) of metabolite maps due to a more efficient acquisition.
STUDY TYPE
Prospective.
SUBJECTS/PHANTOM: Five healthy volunteers (28-38 years, three females) and a phantom.
FIELD STRENGTH/SEQUENCE: Navigated adiabatic spin-echo spiral 3D MRSI at 7T.
ASSESSMENT
A 3D stack of SOI trajectories was incorporated into an adiabatic spin-echo MRSI sequence with real-time motion and shim correction. Metabolite spectral fitting, SNR, and Cramér-Rao lower bound (CRLB) were obtained. We compared the signal intensity and CRLB of three metabolites of tNAA, tCr, and tCho. Peak SNR (PSNR), structure similarity index (SSIM), and signal-to-artifact ratio were evaluated on water maps.
STATISTICAL TESTS
The nonparametric Mann-Whitney U-test was used for statistical testing.
RESULTS
Compared to SO, the SOI trajectory: 1) increased the k-space sampling efficiency by 23%; 2) is less demanding for the gradient hardware, requiring 36% lower G and 26% lower S ; 3) increased PSNR of water maps by 4.94 dB (P = 0.0006); 4) resulted in a 29% higher SNR (P = 0.003) and lower CRLB by 26-35% (P = 0.02, tNAA), 35-55% (P = 0.03, tCr), and 22-23% (P = 0.04, tCho), which increased the number of well-fitted voxels (eg, for tCr by 11%, P = 0.03). SOI did not significantly change the signal-to-artifact ratio and SSIM (P = 0.65) compared to SO.
DATA CONCLUSION
SOI provided more efficient MRSI at 7T compared to SO, which improved the data quality and metabolite quantification.
LEVEL OF EVIDENCE
1 TECHNICAL EFFICACY STAGE: 2.
背景
使用质子磁共振波谱成像（MRSI）的代谢成像在≥7T的场强下提高了灵敏度和光谱分辨率。与传统的基于笛卡尔的波谱成像相比，螺旋轨迹能够更快地采集数据，有望实现全脑MRSI的临床应用。然而，7T时的技术因素导致螺旋-out（SO）采集中的采样效率欠佳，因为轨迹的很大一部分由重绕部分组成。
目的
开发并实施一种用于7T全脑MRSI采样的螺旋-out-in（SOI）轨迹。我们假设SOI将由于更高效的采集而提高代谢物图谱的信噪比（SNR）。
研究类型
前瞻性。
受试者/体模：五名健康志愿者（28 - 38岁，三名女性）和一个体模。
场强/序列：7T下的导航绝热自旋回波螺旋3D MRSI。
评估
将3D SOI轨迹堆栈纳入具有实时运动和匀场校正的绝热自旋回波MRSI序列。获得代谢物光谱拟合、SNR和克拉美-罗下限（CRLB）。我们比较了N-乙酰天门冬氨酸（tNAA）、肌酸（tCr）和胆碱（tCho）三种代谢物的信号强度和CRLB。在水图上评估峰值SNR（PSNR）、结构相似性指数（SSIM）和信躁比。
统计检验
采用非参数曼-惠特尼U检验进行统计检验。
结果
与SO相比，SOI轨迹：1）将k空间采样效率提高了23%；2）对梯度硬件要求较低，所需梯度强度（G）降低36%，切换率（S）降低26%；3）使水图的PSNR提高了4.94dB（P = 0.0006）；4）使SNR提高了29%（P = 0.003），CRLB降低了26% - 35%（P = 0.02，tNAA）、35% - 55%（P = 0.03，tCr）和22% - 23%（P = 0.04，tCho），这增加了拟合良好的体素数量（例如，tCr增加了11%，P = 0.03）。与SO相比，SOI在信躁比和SSIM方面没有显著变化（P = 0.65）。
数据结论
与SO相比，SOI在7T时提供了更高效的MRSI，提高了数据质量和代谢物定量。
证据水平
1 技术效能阶段：2。
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