Center for Metabolic Imaging in Precision Medicine (CAMIPM), Department of Radiology, Perelman School of Medicine at the University of Pennsylvania, Philadelphia, Pennsylvania, USA.
Magn Reson Med. 2023 Jun;89(6):2295-2304. doi: 10.1002/mrm.29600. Epub 2023 Feb 6.
Nuclear Overhauser effect (NOE) is based on dipolar cross-relaxation mechanism that enables the indirect detection of aliphatic protons via the water proton signal. This work focuses on determining the reproducibility of NOE magnetization transfer ratio (NOE ) and isolated or relayed NOE (rNOE) contributions to the NOE MRI of the healthy human brain at 7 Tesla (T).
We optimized the amplitude and length of the saturation pulse by acquiring NOE images with different values with multiple saturation lengths. Repeated NOE MRI measurements were made on five healthy volunteers by using optimized saturation pulse parameters including correction of B and inhomogeneities. To isolate the individual contributions from z-spectra, we have fit the NOE z-spectra using multiple Lorentzians and calculated the total contribution from each pool contributing to the overall NOE contrast.
We found that a saturation amplitude of 0.72 μT and a length of 3 s provided the highest contrast. We found that the mean NOE value in gray matter (GM) was 26%, and in white matter (WM) was 33.3% across the 3D slab of the brain. The mean rNOE contributions from GM and WM values were 8.9% and 9.6%, which were ∼10% of the corresponding total NOE signal. The intersubject coefficient of variations (CoVs) of NOE from GM and WM were 4.5% and 6.5%, respectively, whereas the CoVs of rNOE were 4.8% and 5.6%, respectively. The intrasubject CoVs of the NOE range was 2.1%-4.2%, and rNOE range was 2.9%-10.5%.
This work has demonstrated an excellent reproducibility of both inter- and intrasubject NOE and rNOE metrics in healthy human brains at 7 T.
核 Overhauser 效应（NOE）基于偶极子交叉弛豫机制，通过水质子信号实现脂肪质子的间接检测。本工作旨在确定在 7 特斯拉（T）下健康人脑的 NOE 磁共振成像（MRI）中 NOE 磁化转移比（NOE）和孤立或传递 NOE（rNOE）的重复性。
我们通过使用不同的饱和长度获取具有不同 值的 NOE 图像，优化了饱和脉冲的幅度和长度。通过使用包括 B 和 不均匀性校正的优化饱和脉冲参数，对五名健康志愿者进行了重复的 NOE MRI 测量。为了从 z 谱中分离出各个贡献，我们使用多个洛伦兹函数拟合了 NOE z 谱，并计算了每个池对整体 NOE 对比的总贡献。
我们发现，饱和幅度为 0.72 μT，长度为 3 s 可提供最高的对比度。我们发现，灰质（GM）中的平均 NOE 值为 26%，白质（WM）中的平均 NOE 值为 33.3%，跨越大脑的 3D 切片。GM 和 WM 的平均 rNOE 贡献值分别为 8.9%和 9.6%，约占相应总 NOE 信号的 10%。GM 和 WM 的 NOE 的受试者间变异系数（CoV）分别为 4.5%和 6.5%，而 rNOE 的 CoV 分别为 4.8%和 5.6%。NOE 的受试者内 CoV 范围为 2.1%-4.2%，rNOE 的范围为 2.9%-10.5%。
本工作在 7T 下健康人脑的 NOE 和 rNOE 指标的跨受试者和受试者内均表现出极好的可重复性。
