Vanderbilt University Institute of Imaging Science, Vanderbilt University Medical Center, Nashville, TN, USA.
Vanderbilt University Institute of Imaging Science, Vanderbilt University Medical Center, Nashville, TN, USA; Department of Radiology and Radiological Sciences, Vanderbilt University Medical Center, Nashville, TN, USA.
Magn Reson Imaging. 2021 Dec;84:1-11. doi: 10.1016/j.mri.2021.05.006. Epub 2021 May 28.
Measurements of the variations of spin-locking relaxation rates (R) with locking field amplitude allow the derivation of quantitative parameters that describe different dynamic processes, such as slow molecular motions, chemical exchange and diffusion. In some samples, changes in R values between locking frequency 0 and 200 Hz may be dominated mainly by diffusion of water in intrinsic field gradients, while those at higher locking fields are due to exchange processes. The exchange and diffusion effects act independently of each other, as confirmed by simulation and experimentally. In tissues, the relevant intrinsic field gradients may arise from the magnetic inhomogeneities caused by microvascular blood so that R dispersion over weak locking field amplitudes (≤ 200 Hz) is affected by changes in capillary density and geometry. Here we first review the theoretical and experimental background to the interpretation of R dispersions caused by intrinsic magnetic susceptibility variations within the tissue. We then provide new empirical results of R dispersion imaging of the human brain and skeletal muscle at low locking field amplitudes for the first time and identify potential applications of R dispersion imaging in clinical studies.
自旋锁定弛豫率（R）随锁定场幅度的变化的测量可以得出描述不同动态过程的定量参数，例如缓慢的分子运动、化学交换和扩散。在某些样品中，锁定频率为 0 和 200 Hz 之间的 R 值变化可能主要由固有场梯度中水中的扩散引起，而在较高的锁定场中则是由于交换过程。交换和扩散效应是相互独立的，这已通过模拟和实验得到证实。在组织中，相关的固有场梯度可能是由微血管血液引起的磁场不均匀性引起的，因此，在弱锁定场幅度（≤200 Hz）下的 R 弥散受到毛细血管密度和几何形状变化的影响。在这里，我们首先回顾了在组织内固有磁化率变化引起的 R 弥散的解释的理论和实验背景。然后，我们首次提供了在低锁定场幅度下对人脑和骨骼肌进行 R 弥散成像的新的经验结果，并确定了 R 弥散成像在临床研究中的潜在应用。
