Journal Article

Strain Tensor Imaging: Cardiac-induced brain tissue deformation in humans quantified with high-field MRI

de Luca, Alberto, Biessels, Geert Jan, Zwanenburg, Jaco J.M., Sloots, Jacob Jan

2021

Overview

•Cardiac-induced 3D brain tissue strain tensor measured using MRI.•Single-shot simultaneous multi-slice DENSE MRI is suitable to acquire tissue strain for voxel-wise assessment.•Strain tensor field is consistent over healthy subjects and has good repeatability.•Brain tissue shows the Poisson effect, where longitudinal expansion is accompanied by transverse compression. The cardiac cycle induces blood volume pulsations in the cerebral microvasculature that cause subtle deformation of the surrounding tissue. These tissue deformations are highly relevant as a potential source of information on the brain's microvasculature as well as of tissue condition. Besides, cyclic brain tissue deformations may be a driving force in clearance of brain waste products. We have developed a high-field magnetic resonance imaging (MRI) technique to capture these tissue deformations with full brain coverage and sufficient signal-to-noise to derive the cardiac-induced strain tensor on a voxel by voxel basis, that could not be assessed non-invasively before. We acquired the strain tensor with 3 mm isotropic resolution in 9 subjects with repeated measurements for 8 subjects. The strain tensor yielded both positive and negative eigenvalues (principle strains), reflecting the Poison effect in tissue. The principle strain associated with expansion followed the known funnel shaped brain motion pattern pointing towards the foramen magnum. Furthermore, we evaluate two scalar quantities from the strain tensor: the volumetric strain and octahedral shear strain. These quantities showed consistent patterns between subjects, and yielded repeatable results: the peak systolic volumetric strain (relative to end-diastolic strain) was 4.19⋅10−4 ± 0.78⋅10−4 and 3.98⋅10−4 ± 0.44⋅10−4 (mean ± standard deviation for first and second measurement, respectively), and the peak octahedral shear strain was 2.16⋅10−3 ± 0.31⋅10−3 and 2.31⋅10−3 ± 0.38⋅10−3, for the first and second measurement, respectively. The volumetric strain was typically highest in the cortex and lowest in the periventricular white matter, while anisotropy was highest in the subcortical white matter and basal ganglia. This technique thus reveals new, regional information on the brain's cardiac-induced deformation characteristics, and has the potential to advance our understanding of the role of microvascular pulsations in health and disease.

• Publisher: Elsevier Inc,Elsevier Limited,Elsevier
• Subject: Algorithms / Anisotropy / Basal ganglia / Blood / Brain Deformation / Deformation / Heart / Magnetic Resonance Imaging / Microvasculature / Neuroimaging / Noise / Physiology / Poisson effect / Respiration / Shear strain / Single-Shot DENSE / Small Vessel Disease / Strain Tensor / Substantia alba / Tissue Strain