Abstract：
Functional understanding of the periaqueductal gray (PAG), a clinically relevant brainstem region, can be advanced using 1 H-MRS. However, the PAG\'s small size and high levels of physiological noise are methodologically challenging. This study aimed to (1) improve 1 H-MRS quality in the PAG using spectral registration for frequency and phase error correction; (2) investigate whether spectral registration is particularly useful in cases of greater head motion; and (3) examine metabolite quantification using literature-based or individual-based water relaxation times.
Spectra were acquired in 33 healthy volunteers (50.1 years, SD = 17.19, 18 females) on a 3 T Philipps MR system using a point-resolved spectroscopy (PRESS) sequence optimized with very selective saturation pulses (OVERPRESS) and voxel-based flip angle calibration (effective volume of interest size: 8.8 × 10.2 × 12.2 mm3 ). Spectra were fitted using LCModel and SNR, NAA peak linewidths and Cramér-Rao lower bounds (CRLBs) were measured after spectral registration and after minimal frequency alignment.
Spectral registration improved SNR by 5% (p = 0.026, median value post-correction: 18.0) and spectral linewidth by 23% (p < 0.001, 4.3 Hz), and reduced the metabolites\' CRLBs by 1% to 15% (p < 0.026). Correlational analyses revealed smaller SNR improvements with greater head motion (p = 0.010) recorded using a markerless motion tracking system. Higher metabolite concentrations were detected using individual-based compared to literature-based water relaxation times (p < 0.001).
This study demonstrates high-quality 1 H-MRS acquisition in the PAG using spectral registration. This shows promise for future 1 H-MRS studies in the PAG and possibly other clinically relevant brain regions with similar methodological challenges.
Spectra were acquired in 33 healthy volunteers (50.1 years, SD = 17.19, 18 females) on a 3 T Philipps MR system using a point-resolved spectroscopy (PRESS) sequence optimized with very selective saturation pulses (OVERPRESS) and voxel-based flip angle calibration (effective volume of interest size: 8.8 × 10.2 × 12.2 mm3 ). Spectra were fitted using LCModel and SNR, NAA peak linewidths and Cramér-Rao lower bounds (CRLBs) were measured after spectral registration and after minimal frequency alignment.
Spectral registration improved SNR by 5% (p = 0.026, median value post-correction: 18.0) and spectral linewidth by 23% (p < 0.001, 4.3 Hz), and reduced the metabolites\' CRLBs by 1% to 15% (p < 0.026). Correlational analyses revealed smaller SNR improvements with greater head motion (p = 0.010) recorded using a markerless motion tracking system. Higher metabolite concentrations were detected using individual-based compared to literature-based water relaxation times (p < 0.001).
This study demonstrates high-quality 1 H-MRS acquisition in the PAG using spectral registration. This shows promise for future 1 H-MRS studies in the PAG and possibly other clinically relevant brain regions with similar methodological challenges.
摘要：
目的：对导水管周围灰色（PAG）的功能理解，临床相关的脑干区域，可以使用1H-MRS。然而,PAG的小尺寸和高水平的生理噪声在方法上具有挑战性。这项研究旨在（1）使用频谱配准进行频率和相位误差校正来改善PAG中的1H-MRS质量；（2）研究频谱配准在头部运动较大的情况下是否特别有用；（3）使用基于文献或基于个体的水弛豫时间来检查代谢物定量。
方法：对33名健康志愿者（50.1岁，SD=17.19，18雌性）在3TPhilippsMR系统上使用点分辨光谱（PRESS）序列，该序列经过非常选择性的饱和脉冲（OVERPRESS）和基于体素的翻转角校准（有效感兴趣体积大小：8.8×10.2×12.2mm3）。使用LCModel和SNR拟合光谱，在光谱配准和最小频率对齐后，测量了NAA峰线宽和Cramér-Rao下界（CRLB）。
结果：光谱配准将SNR提高了5％（p=0.026，校正后中值：18.0），光谱线宽提高了23％（p<0.001，4.3Hz），并将代谢物CRLB降低1%至15%(p<0.026)。相关分析显示，使用无标记运动跟踪系统记录的头部运动（p=0.010）的SNR改善较小。与基于文献的水弛豫时间相比,使用基于个体的水弛豫时间检测到更高的代谢物浓度(p<0.001)。
结论：这项研究证明了使用光谱配准在PAG中进行高质量的1H-MRS采集。这显示了在PAG和其他可能具有类似方法学挑战的临床相关脑区域中的未来1H-MRS研究的希望。
方法：对33名健康志愿者（50.1岁，SD=17.19，18雌性）在3TPhilippsMR系统上使用点分辨光谱（PRESS）序列，该序列经过非常选择性的饱和脉冲（OVERPRESS）和基于体素的翻转角校准（有效感兴趣体积大小：8.8×10.2×12.2mm3）。使用LCModel和SNR拟合光谱，在光谱配准和最小频率对齐后，测量了NAA峰线宽和Cramér-Rao下界（CRLB）。
结果：光谱配准将SNR提高了5％（p=0.026，校正后中值：18.0），光谱线宽提高了23％（p<0.001，4.3Hz），并将代谢物CRLB降低1%至15%(p<0.026)。相关分析显示，使用无标记运动跟踪系统记录的头部运动（p=0.010）的SNR改善较小。与基于文献的水弛豫时间相比,使用基于个体的水弛豫时间检测到更高的代谢物浓度(p<0.001)。
结论：这项研究证明了使用光谱配准在PAG中进行高质量的1H-MRS采集。这显示了在PAG和其他可能具有类似方法学挑战的临床相关脑区域中的未来1H-MRS研究的希望。
