Center for Image Sciences, University Medical Center Utrecht, Utrecht, The Netherlands.
Department of Radiology and Biomedical Imaging, Magnetic Resonance Research Center, Yale University School of Medicine, New Haven, Connecticut, USA.
NMR Biomed. 2024 Oct;37(10):e5195. doi: 10.1002/nbm.5195. Epub 2024 Jun 6.
The neuronal tricarboxylic acid and glutamate/glutamine (Glu/Gln) cycles play important roles in brain function. These processes can be measured in vivo using dynamic H-[C] MRS during administration of C-labeled glucose. Proton-observed carbon-edited (POCE) MRS enhances the signal-to-noise ratio (SNR) compared with direct C-MRS. Ultra-high field further boosts the SNR and increases spectral dispersion; however, even at 7 T, Glu and Gln H-resonances may overlap. Further gain can be obtained with selective POCE (selPOCE). Our aim was to create a setup for indirect dynamic H-[C] MRS in the human brain at 7 T. A home-built non-shielded transmit-receive C-birdcage head coil with eight transmit-receive H-dipole antennas was used together with a 32-channel H-receive array. Electromagnetic simulations were carried out to ensure that acquisitions remained within local and global head SAR limits. POCE-MRS was performed using slice-selective excitation with semi-localization by adiabatic selective refocusing (sLASER) and stimulated echo acquisition mode (STEAM) localization, and selPOCE-MRS using STEAM. Sequences were tested in a phantom containing non-enriched Glu and Gln, and in three healthy volunteers during uniformly labeled C-glucose infusions. In one subject the voxel position was alternated between bi-frontal and bi-occipital placement within one session. [4-C]Glu-H4 and [4-C]Gln-H4 signals could be separately detected using both STEAM-POCE and STEAM-selPOCE in the phantom. In vivo, [4,5-C]Glx could be detected using both sLASER-POCE and STEAM-POCE, with similar sensitivities, but [4,5-C]Glu and [4,5-C]Gln signals could not be completely resolved. STEAM-POCE was alternately performed bi-frontal and bi-occipital within a single session without repositioning of the subject, yielding similar results. With STEAM-selPOCE, [4,5-C]Glu and [4,5-C]Gln could be clearly separated. We have shown that with our setup indirect dynamic H-[C] MRS at 7 T is feasible in different locations in the brain within one session, and by using STEAM-selPOCE it is possible to separate Glu from Gln in vivo while obtaining high quality spectra.
神经元三羧酸和谷氨酸/谷氨酰胺（Glu/Gln）循环在大脑功能中发挥着重要作用。这些过程可以通过在给予 C 标记葡萄糖期间使用动态 H-[C]MRS 在体内进行测量。质子观察碳编辑（POCE）MRS 与直接 C-MRS 相比可以提高信噪比（SNR）。超高场进一步提高了 SNR 并增加了光谱色散；然而，即使在 7T 下，Glu 和 Gln H 共振也可能重叠。通过选择性 POCE（selPOCE）可以进一步获得增益。我们的目标是在 7T 下为人体大脑创建间接动态 H-[C]MRS 设置。使用带有八个发射-接收 H 偶极子天线的自制非屏蔽发射-接收 C 鸟笼头线圈和一个 32 通道 H 接收阵列。进行了电磁模拟，以确保采集仍在局部和全局头部 SAR 限制范围内。使用半局部化的切片选择激发通过绝热选择性重聚焦（sLASER）和受激回波采集模式（STEAM）进行定位进行了 POCE-MRS，并用 STEAM 进行了 selPOCE-MRS。在含有非富集 Glu 和 Gln 的幻影中以及在三个健康志愿者中，在均匀标记 C-葡萄糖输注期间测试了序列。在一个受试者中，在一个会话中，在额-额和枕-枕之间交替了体素位置。在幻影中，使用 STEAM-POCE 和 STEAM-selPOCE 可以分别检测到[4-C]Glu-H4 和[4-C]Gln-H4 信号。在体内，使用 sLASER-POCE 和 STEAM-POCE 都可以检测到[4,5-C]Glx，灵敏度相似，但无法完全分辨[4,5-C]Glu 和[4,5-C]Gln 信号。在单个会话中，无需重新定位受试者，交替进行 STEAM-POCE 额-额和枕-枕，结果相似。使用 STEAM-selPOCE，可以清楚地分离[4,5-C]Glu 和[4,5-C]Gln。我们已经表明，使用我们的设置，在一个会话内可以在大脑的不同位置进行 7T 间接动态 H-[C]MRS，并且通过使用 STEAM-selPOCE，在体内可以将 Glu 与 Gln 分离，同时获得高质量的光谱。
