3D gradient echo snapshot CEST MRI with low power saturation for human studies at 3T
3D gradient echo snapshot CEST MRI with low power saturation for human studies at 3T
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DOI：
10.1002/mrm.27569
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发表时间：
2019-04-01
影响因子：
3.3
通讯作者：
Scheffler, Klaus
中科院分区：
文献类型：
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作者：
Deshmane, Anagha;Zaiss, Moritz;Scheffler, Klaus
目的：对于临床实施，化学交换饱和转移（CEST）成像序列必须是快速的，具有高信噪比（SNR）、3D覆盖，并且产生鲁棒的对比度。然而，光谱选择性CEST对比度需要Z光谱的密集采样，这增加了扫描持续时间。本文提出了一个折衷方案：使用3D快照梯度回波（GRE）读出与优化CEST预饱和，采样和后处理，在3 T的高分辨率Z-光谱是可能的3D覆盖几乎没有额外的时间cost.Methods：3D快照CEST序列进行了优化，低功耗CEST MRI在3 T。脉冲饱和的饱和功率和饱和持续时间进行了优化。光谱采样和后处理（B-0校正，去噪）进行了优化，光谱选择性洛伦兹CEST效应提取。结果：在54个照射频率偏移下，由80个脉冲组成的脉冲串达到低功率饱和，脉冲持续时间t（p）= 20 ms（50%占空比时总饱和时间t（sat）= 3.2 s），B-1 = 0.6 μ T。使用3D快照CEST序列，在每个偏移7秒内采集180 x 220 x 54 mm的视野。使用多洛伦兹拟合定量+3.5和-3.5 ppm处的光谱选择性CEST效应。在CEST对比中，重复性高，受试者间变异系数低于10%。酰胺和核overhauser效应CEST效应在肿瘤和坏死中表现出类似的相关性，如在以前的超高fieldwork.Conclusion：一个复杂的CEST工具准备用于临床应用的开发和可行性测试。
Purpose: For clinical implementation, a chemical exchange saturation transfer (CEST) imaging sequence must be fast, with high signal-to-noise ratio (SNR), 3D coverage, and produce robust contrast. However, spectrally selective CEST contrast requires dense sampling of the Z-spectrum, which increases scan duration. This article proposes a compromise: using a 3D snapshot gradient echo (GRE) readout with optimized CEST presaturation, sampling, and postprocessing, highly resolved Z-spectroscopy at 3T is made possible with 3D coverage at almost no extra time cost.Methods: A 3D snapshot CEST sequence was optimized for low-power CEST MRI at 3T. Pulsed saturation was optimized for saturation power and saturation duration. Spectral sampling and postprocessing (B-0 correction, denoising) was optimized for spectrally selective Lorentzian CEST effect extraction. Reproducibility was demonstrated in 3 healthy volunteers and feasibility was shown in 1 tumor patient.Results: Low-power saturation was achieved by a train of 80 pulses of duration t(p) = 20 ms (total saturation time t(sat) = 3.2 seconds at 50% duty cycle) with B-1 = 0.6 mu T at 54 irradiation frequency offsets. With the 3D snapshot CEST sequence, a 180 x 220 x 54 mm field of view was acquired in 7 seconds per offset. Spectrally selective CEST effects at +3.5 and -3.5 ppm were quantified using multi-Lorentzian fitting. Reproducibility was high with an intersubject coefficient of variation below 10% in CEST contrasts. Amide and nuclear overhauser effect CEST effects showed similar correlations in tumor and necrosis as show in previous ultra-high field work.Conclusion: A sophisticated CEST tool ready for clinical application was developed and tested for feasibility.