Uhl Quentin, Pavan Tommaso, Molendowska Malwina, Jones Derek K, Palombo Marco, Jelescu Ileana Ozana
Department of Radiology, Lausanne University Hospital (CHUV), Lausanne, Switzerland.
School of Biology and Medicine, University of Lausanne, Lausanne, Switzerland.
Imaging Neurosci (Camb). 2024 Mar 6;2. doi: 10.1162/imag_a_00104. eCollection 2024.
Biophysical models of diffusion tailored to quantify gray matter microstructure are gathering increasing interest. The two-compartment Neurite EXchange Imaging (NEXI) model has been proposed recently to account for neurites, extra-cellular space, and exchange across the cell membrane. NEXI parameter estimation requires multi-shell multi-diffusion time data and has so far only been implemented experimentally on animal data collected on a preclinical magnetic resonance imaging (MRI) set-up. In this work, the translation of NEXI to the human cortex in vivo was achieved using a 3 T Connectom MRI system with 300 mT/m gradients, that enables the acquisition of a broad range of b-values (0 - 7.5 ms/µm²) with a window covering short to intermediate diffusion times (20 - 49 ms) suitable for the characteristic exchange times (10 - 50 ms). Microstructure estimates of four model variants: NEXI, NEXI(its extension with the addition of a dot compartment), and their respective versions that correct for the Rician noise floor (NEXIand NEXI) that particularly impacts high b-value signal, were compared. The reliability of estimates in each model variant was evaluated in synthetic and human in vivo data. In the latter, the intra-subject (scan-rescan) versus between-subjects variability of microstructure estimates was compared in the cortex. The better performance of NEXIhighlights the importance of correcting for Rician bias in the NEXI model to obtain accurate estimates of microstructure parameters in the human cortex, and the sensitivity of the NEXI framework to individual differences in cortical microstructure. This application of NEXI in humans represents a significant step, unlocking new avenues for studying neurodevelopment, aging, and various neurodegenerative disorders.
为量化灰质微观结构而定制的扩散生物物理模型正越来越受到关注。最近提出了双室神经突交换成像（NEXI）模型，以解释神经突、细胞外空间以及跨细胞膜的交换。NEXI参数估计需要多壳多扩散时间数据，并且到目前为止仅在临床前磁共振成像（MRI）设置上收集的动物数据上进行了实验实施。在这项工作中，使用具有300 mT/m梯度的3T连接组MRI系统实现了NEXI在人体皮质中的体内转化，该系统能够获取广泛的b值范围（0 - 7.5 ms/µm²），其窗口覆盖适合特征交换时间（10 - 50 ms）的短至中间扩散时间（20 - 49 ms）。比较了四种模型变体的微观结构估计值：NEXI、NEXI（通过添加一个点状隔室进行扩展）以及它们各自校正了特别影响高b值信号的莱斯噪声底限的版本（NEXI和NEXI）。在合成数据和人体体内数据中评估了每个模型变体估计值的可靠性。在后者中，比较了皮质中微观结构估计值的受试者内（扫描 - 重扫描）与受试者间变异性。NEXI的更好性能突出了在NEXI模型中校正莱斯偏差以获得人体皮质微观结构参数准确估计值的重要性，以及NEXI框架对皮质微观结构个体差异的敏感性。NEXI在人体中的这种应用代表了重要的一步，为研究神经发育、衰老和各种神经退行性疾病开辟了新途径。
