Quantifying cardiac‐induced brain tissue expansion using DENSE

Abstract

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 −4 (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.

Accuracy of cardiac‐induced brain motion measurement using displacement‐encoding with stimulated echoes (DENSE) magnetic resonance imaging (MRI): A phantom study

“…This error represents between 2.4%‐4% of the maximum cardiac displacement (cardiac displacement has been reported to be between 6‐10 mm 30 ). Although this displacement error (240 µm) is acceptable for cardiac displacement, it is higher than the maximum average displacement reported for healthy brain tissue (100‐187 µm) 12,13 . In this study, we compared the displacement from DENSE to that of LDV in 4 locations on the moving plate with peak displacement ranging from 1.04 mm to 0.22 mm.…”

“…Although this displacement error (240 µm) is acceptable for cardiac displacement, it is higher than the maximum average displacement reported for healthy brain tissue (100-187 µm). 12,13 In this study, we compared the displacement from DENSE to that of LDV in 4 locations on the moving plate with peak displacement ranging from 1.04 mm to 0.22 mm. Peak displacements of 1.04 mm and 0.22 mm represent in vivo brain tissue displacement reported for pathological 34 and healthy subjects 12 , respectively.…”

“…12 Adams et al determined cardiac-induced brain tissue expansion using DENSE MRI and demonstrated that tissue-specific volumetric strain quantification was possible with DENSE. 13 Also, Adams et al reported that cerebral pulsatility between intersubjects showed a consistent peak value and was also strongly correlated to cerebrospinal fluid flow volume changes in healthy subjects. 14 Recently, in a study to determine cardiac-and respiratory-induced brain deformation using a novel high-field MRI, Sloots et al determined that the heartbeat-induced volumetric strain was 3 times larger than respiratory-induced volumetric strain, which was determined using an optimal tag spacing of 0.15 mm/pi.…”

“…In 2018, Pahlavian et al quantified regional brain tissue displacement and strain in healthy subjects using DENSE MRI 12 . Adams et al determined cardiac‐induced brain tissue expansion using DENSE MRI and demonstrated that tissue‐specific volumetric strain quantification was possible with DENSE 13 . Also, Adams et al reported that cerebral pulsatility between intersubjects showed a consistent peak value and was also strongly correlated to cerebrospinal fluid flow volume changes in healthy subjects 14 .…”

Novel strain analysis informs about injury susceptibility of the corpus callosum to repeated impacts

“…Recent development of movement-based imaging modalities such as DENSE-MRI ( Aletras et al , 1999 ; Adams et al , 2019 ) and amplified magnetic resonance imaging (aMRI) has shown promising results for studying the complex motions of the brain, based on physiological dynamics ( Holdsworth et al , 2016 ; Terem et al , 2018 ). aMRI uses the periodic cardiac-induced blood pulsation as a loading force to visualize and quantify sub-voxel displacement of brain tissues.…”