加速径向回波平面波谱成像采用黄金角度视序和全变差正则化的压缩感知重建。
Accelerated radial echo-planar spectroscopic imaging using golden angle view-ordering and compressed-sensing reconstruction with total variation regularization.
机构信息
Department of Radiological Sciences, University of California Los Angeles, Los Angeles, California, USA.
Physics and Biology in Medicine Interdepartmental Graduate Program, University of California Los Angeles, Los Angeles, California, USA.
出版信息
Magn Reson Med. 2021 Jul;86(1):46-61. doi: 10.1002/mrm.28728. Epub 2021 Feb 18.
PURPOSE
To implement a novel, accelerated, 2D radial echo-planar spectroscopic imaging (REPSI) sequence using undersampled radial k-space trajectories and compressed-sensing reconstruction, and to compare results with those from an undersampled Cartesian spectroscopic sequence.
METHODS
The REPSI sequence was implemented using golden-angle view-ordering on a 3T MRI scanner. Radial and Cartesian echo-planar spectroscopic imaging (EPSI) data were acquired at six acceleration factors, each with time-equivalent scan durations, and reconstructed using compressed sensing with total variation regularization. Results from prospectively and retrospectively undersampled phantom and in vivo brain data were compared over estimated concentrations and Cramer-Rao lower-bound values, normalized RMS errors of reconstructed metabolite maps, and percent absolute differences between fully sampled and reconstructed spectroscopic images.
RESULTS
The REPSI method with compressed sensing is able to tolerate greater reductions in scan time compared with EPSI. The reconstruction and quantitation metrics (i.e., spectral normalized RMS error maps, metabolite map normalized RMS error values [e.g., for total N-acetyl asparate, REPSI = 9.4% vs EPSI = 16.3%; acceleration factor = 2.5], percent absolute difference maps, and concentration and Cramer-Rao lower-bound estimates) showed that accelerated REPSI can reduce the scan time by a factor of 2.5 while retaining image and quantitation quality.
CONCLUSION
Accelerated MRSI using undersampled radial echo-planar acquisitions provides greater reconstruction accuracy and more reliable quantitation for a range of acceleration factors compared with time-equivalent compressed-sensing reconstructions of undersampled Cartesian EPSI. Compared to the Cartesian approach, radial undersampling with compressed sensing could help reduce 2D spectroscopic imaging acquisition time, and offers a better trade-off between imaging speed and quality.
目的
使用欠采样的径向 k 空间轨迹和压缩感知重建实现一种新颖的、加速的 2D 径向回波平面波谱成像（REPSI）序列，并将结果与欠采样笛卡尔波谱序列的结果进行比较。
方法
在 3T MRI 扫描仪上使用黄金角度视图排序实现 REPSI 序列。在六个加速因子下采集径向和笛卡尔回波平面波谱成像（EPSI）数据，每个因子的扫描时间相等，并使用总变差正则化的压缩感知进行重建。通过前瞻性和回顾性欠采样的体模和体内脑数据比较了估计浓度和克拉默-劳下界值、重建代谢物图的归一化均方根误差、完全采样和重建波谱图像之间的绝对百分比差异的结果。
结果
与 EPSI 相比，具有压缩感知的 REPSI 方法能够容忍更大的扫描时间减少。重建和定量指标（即光谱归一化均方根误差图、代谢物图归一化均方根误差值[例如，对于总 N-乙酰天冬氨酸，REPSI = 9.4%，EPSI = 16.3%；加速因子 = 2.5]、绝对百分比差异图以及浓度和克拉默-劳下界估计）表明，加速的 REPSI 可以将扫描时间缩短 2.5 倍，同时保持图像和定量质量。
结论
与时间等效的欠采样笛卡尔 EPSI 压缩感知重建相比，使用欠采样径向回波平面采集的加速 MRSI 可提供更高的重建精度和更可靠的定量，适用于各种加速因子。与笛卡尔方法相比，具有压缩感知的径向欠采样可以帮助减少 2D 波谱成像采集时间，并在成像速度和质量之间提供更好的折衷。
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