Wolfson Brain Imaging Centre, University of Cambridge, Cambridge, UK.
Oxford Centre for Clinical Magnetic Resonance Research (OCMR), University of Oxford, Oxford, UK.
NMR Biomed. 2021 Jul;34(7):e4513. doi: 10.1002/nbm.4513. Epub 2021 Apr 7.
Cardiac proton spectroscopy ( H-MRS) is widely used to quantify lipids. Other metabolites (e.g. creatine and choline) are clinically relevant but more challenging to quantify because of their low concentrations (approximately 10 mmol/L) and because of cardiac motion. To quantify cardiac creatine and choline, we added water-suppression cycling (WSC) to two single-voxel spectroscopy sequences (STEAM and PRESS). WSC introduces controlled residual water signals that alternate between positive and negative phases from transient to transient, enabling robust phase and frequency correction. Moreover, a particular weighted sum of transients eliminates residual water signals without baseline distortion. We compared WSC and the vendor's standard 'WET' water suppression in phantoms. Next, we tested repeatability in 10 volunteers (seven males, three females; age 29.3 ± 4.0 years; body mass index [BMI] 23.7 ± 4.1 kg/m ). Fat fraction, creatine concentration and choline concentration when quantified by STEAM-WET were 0.30% ± 0.11%, 29.6 ± 7.0 μmol/g and 7.9 ± 6.7 μmol/g, respectively; and when quantified by PRESS-WSC they were 0.30% ± 0.15%, 31.5 ± 3.1 μmol/g and 8.3 ± 4.4 μmol/g, respectively. Compared with STEAM-WET, PRESS-WSC gave spectra whose fitting quality expressed by Cramér-Rao lower bounds improved by 26% for creatine and 32% for choline. Repeatability of metabolite concentration measurements improved by 72% for creatine and 40% for choline. We also compared STEAM-WET and PRESS-WSC in 13 patients with severe symptomatic aortic or mitral stenosis indicated for valve replacement surgery (10 males, three females; age 75.9 ± 6.3 years; BMI 27.4 ± 4.3 kg/m ). Spectra were of analysable quality in eight patients for STEAM-WET, and in nine for PRESS-WSC. We observed comparable lipid concentrations with those in healthy volunteers, significantly reduced creatine concentrations, and a trend towards decreased choline concentrations. We conclude that PRESS-WSC offers improved performance and reproducibility for the quantification of cardiac lipids, creatine and choline concentrations in healthy volunteers at 3 T. It also offers improved performance compared with STEAM-WET for detecting altered creatine and choline concentrations in patients with valve disease.
心脏质子波谱（H-MRS）广泛用于定量脂质。其他代谢物（如肌酸和胆碱）具有临床相关性，但由于其浓度较低（约 10mmol/L）且受到心脏运动的影响，因此更难以定量。为了定量测量心脏肌酸和胆碱，我们在两种单体波谱序列（STEAM 和 PRESS）中添加了水抑制循环（WSC）。WSC 引入了受控的残留水信号，这些信号在瞬变之间交替出现正相和负相，从而实现了强大的相位和频率校正。此外，特定的瞬变加权和消除了没有基线失真的残留水信号。我们在体模中比较了 WSC 和供应商的标准“WET”水抑制。接下来，我们在 10 名志愿者（7 名男性，3 名女性；年龄 29.3±4.0 岁；体重指数 [BMI] 23.7±4.1kg/m ）中测试了重复性。STEAM-WET 定量的脂肪分数、肌酸浓度和胆碱浓度分别为 0.30%±0.11%、29.6±7.0μmol/g 和 7.9±6.7μmol/g；而 PRESS-WSC 定量的分别为 0.30%±0.15%、31.5±3.1μmol/g 和 8.3±4.4μmol/g。与 STEAM-WET 相比，PRESS-WSC 给出的谱线拟合质量通过克拉默-劳尔下限表示，肌酸提高了 26%，胆碱提高了 32%。肌酸和胆碱浓度测量的重复性分别提高了 72%和 40%。我们还在 13 名因主动脉瓣或二尖瓣狭窄严重且需要瓣膜置换手术的症状性患者（10 名男性，3 名女性；年龄 75.9±6.3 岁；BMI 27.4±4.3kg/m ）中比较了 STEAM-WET 和 PRESS-WSC。STEAM-WET 可分析 8 名患者的谱线，PRESS-WSC 可分析 9 名患者的谱线。我们观察到脂质浓度与健康志愿者相似，肌酸浓度显著降低，胆碱浓度有降低趋势。我们得出的结论是，在 3T 下，PRESS-WSC 为健康志愿者心脏脂质、肌酸和胆碱浓度的定量提供了更好的性能和可重复性。与 STEAM-WET 相比，它在检测瓣膜疾病患者肌酸和胆碱浓度变化方面也具有更好的性能。
