Department of Radiology, University Medical Center Utrecht, Utrecht, The Netherlands.
Image Sciences Institute, University Medical Center Utrecht, Utrecht, The Netherlands.
NMR Biomed. 2019 Feb;32(2):e4050. doi: 10.1002/nbm.4050. Epub 2018 Dec 21.
Brain tissue undergoes viscoelastic deformation and volumetric strain as it expands over the cardiac cycle due to blood volume changes within the underlying microvasculature. Volumetric strain measurements may therefore provide insights into small vessel function and tissue viscoelastic properties. Displacement encoding via stimulated echoes (DENSE) is an MRI technique that can quantify the submillimetre displacements associated with brain tissue motion. Despite previous studies reporting brain tissue displacements using DENSE and other MRI techniques, a complete picture of brain tissue volumetric strain over the cardiac cycle has not yet been obtained. To address this need we implemented 3D cine-DENSE at 7 T and 3 T to investigate the feasibility of measuring cardiac-induced volumetric strain as a marker for small vessel blood volume changes. Volumetric strain over the entire cardiac cycle was computed for the whole brain and for grey and white matter tissue separately in six healthy human subjects. Signal-to-noise ratio (SNR) measurements were used to determine the voxel-wise volumetric strain noise. Mean peak whole brain volumetric strain at 7 T (mean ± SD) was (4.5 ± 1.0) × 10 (corresponding to a volume expansion of 0.48 ± 0.1 mL), which is in agreement with literature values for cerebrospinal fluid that is displaced into the spinal canal to maintain a stable intracranial pressure. The peak volumetric strain ratio of grey to white matter was 4.4 ± 2.8, reflecting blood volume and tissue stiffness differences between these tissue types. The mean peak volumetric strains of grey and white matter tissue were found to be significantly different (p < 0.001). The mean SNR at 7 T and 3 T of the DENSE measurements was 22.0 ± 7.3 and 7.0 ± 2.8 respectively, which currently limits a voxel-wise strain analysis at both field strengths. We demonstrate that tissue specific quantification of volumetric strain is feasible with DENSE. This metric holds potential for studying blood volume pulsations in the ageing brain in healthy and diseased states.
脑组织在心脏周期内随着其下的微血管中血液体积的变化而发生粘弹性变形和体积应变。因此，体积应变量测可能提供有关小血管功能和组织粘弹性特性的深入了解。通过受激回波进行位移编码（DENSE）是一种 MRI 技术，可定量测量与脑组织运动相关的亚毫米级位移。尽管先前的研究报告了使用 DENSE 和其他 MRI 技术进行脑组织位移的情况，但尚未获得整个心脏周期内脑组织体积应变量的完整图像。为了解决这一需求，我们在 7T 和 3T 上实现了 3D 电影 DENSE，以研究测量心脏诱导的体积应变为小血管血容量变化标志物的可行性。在六名健康人类受试者中，分别对整个大脑以及灰质和白质组织进行了整个心脏周期的体积应变量测。使用信噪比（SNR）测量来确定体素级别的体积应变量测噪声。7T 时（平均值±标准差）的整个大脑的平均峰值整体体积应变（mean ± SD）为（4.5 ± 1.0）×10-3（对应于 0.48 ± 0.1mL 的体积膨胀），这与文献中脑脊液位移到椎管以维持稳定颅内压的值一致。灰质与白质的峰值体积应变比为 4.4 ± 2.8，反映了这些组织类型之间的血容量和组织硬度差异。发现灰质和白质组织的平均峰值体积应变差异具有统计学意义（p < 0.001）。DENSE 测量的 7T 和 3T 的平均 SNR 分别为 22.0 ± 7.3 和 7.0 ± 2.8，这目前限制了两种场强下的体素级应变分析。我们证明了 DENSE 进行组织特异性体积应变定量是可行的。该指标有望用于研究健康和患病状态下老年人大脑的血容量脉动。
