Schrantee Anouk, Najac Chloe, Jungerius Chris, van der Zwaag Wietske, Jbabdi Saad, Clarke William T, Ronen Itamar
Department of Radiology and Nuclear Medicine, Amsterdam University Medical Center, University of Amsterdam, Amsterdam, The Netherlands.
C.J. Gorter MRI Center, Department of Radiology, Leiden University Medical Center, Leiden, The Netherlands.
Imaging Neurosci (Camb). 2023 Nov 17;1. doi: 10.1162/imag_a_00031. eCollection 2023.
Functional magnetic resonance spectroscopy (fMRS) is a non-invasive technique for measuring dynamic changes in neurometabolites. While previous studies have observed concentration changes in metabolites during neural activation, the relationship between neurometabolite response and stimulus intensity and timing requires further investigation. To address this, we conducted an interleaved fMRS and functional magnetic resonance imaging (fMRI) experiment using a visual stimulus with varying contrast levels. A total of 20 datasets were acquired on a 7T MRI scanner. The visual task consisted of two STIM blocks (30 s/20 s ON/OFF, 4 min), with 10% or 100% contrast, interleaved with a 5 min REST block. A dynamic fitting approach was used for fMRS data analysis. For metabolite level changes, the STIM conditions were modeled in two different ways: either considering the full STIM block as active condition (full-block model) or only modeling the ON blocks as active condition (sub-block model). For linewidth changes due to the BOLD effect, STIM conditions were modeled using the sub-block model. For both models, we observed significant increases in glutamate levels for both the 10% and 100% visual contrasts, but no significant difference between the contrasts. Decreases in aspartate, and glucose, and increases in total N-acetylaspartate and total creatine were also detected, although less consistently across both 10% and 100% visual contrasts. BOLD-driven linewidth decreases and fMRI-derived BOLD increases within the MRS voxel were observed at both 10% and 100% contrasts, with larger changes at 100% compared to 10% in the fMRI-derived BOLD only. We observed a non-linear relation between visual contrast, the BOLD response, and the glutamate response. Our study highlights the potential of fMRS as a complementary technique to BOLD fMRI for investigating the complex interplay between visual contrast, neural activity, and neurometabolism. Future studies should further explore the temporal response profiles of different neurometabolites and refine the statistical models used for fMRS analysis.
功能磁共振波谱成像（fMRS）是一种用于测量神经代谢物动态变化的非侵入性技术。虽然先前的研究已经观察到神经激活过程中代谢物浓度的变化，但神经代谢物反应与刺激强度和时间之间的关系仍需进一步研究。为了解决这个问题，我们使用具有不同对比度水平的视觉刺激进行了一项交错式fMRS和功能磁共振成像（fMRI）实验。在一台7T磁共振成像扫描仪上共采集了20个数据集。视觉任务由两个刺激块（开启/关闭时间为30秒/20秒，共4分钟）组成，对比度为10%或100%，并与一个5分钟的静息块交错进行。采用动态拟合方法对fMRS数据进行分析。对于代谢物水平变化，刺激条件以两种不同方式建模：要么将整个刺激块视为活动条件（全块模型），要么仅将开启块建模为活动条件（子块模型）。对于由于血氧水平依赖（BOLD）效应导致的线宽变化，刺激条件使用子块模型进行建模。对于这两种模型，我们观察到在10%和100%视觉对比度下谷氨酸水平均显著升高，但对比度之间无显著差异。还检测到天冬氨酸和葡萄糖水平降低，以及总N-乙酰天门冬氨酸和总肌酸水平升高，不过在10%和100%视觉对比度下的一致性较差。在10%和100%对比度下均观察到MRS体素内BOLD驱动的线宽减小和fMRI衍生的BOLD增加，仅fMRI衍生的BOLD在100%对比度下的变化比10%时更大。我们观察到视觉对比度、BOLD反应和谷氨酸反应之间存在非线性关系。我们的研究突出了fMRS作为BOLD fMRI的补充技术在研究视觉对比度、神经活动和神经代谢之间复杂相互作用方面的潜力。未来的研究应进一步探索不同神经代谢物的时间反应特征，并完善用于fMRS分析的统计模型。
