Regional Quantification of Brain Tissue Strain Using Displacement-Encoding With Stimulated Echoes Magnetic Resonance Imaging

Abstract

Intrinsic cardiac-induced deformation of brain tissue is thought to be important in the pathophysiology of various neurological disorders. In this study, we evaluated the feasibility of utilizing displacement encoding with stimulated echoes (DENSE) magnetic resonance imaging (MRI) to quantify two-dimensional (2D) neural tissue strain using cardiac-driven brain pulsations. We examined eight adult healthy volunteers with an electrocardiogram-gated spiral DENSE sequence performed at the midsagittal plane on a 3 Tesla MRI scanner. Displacement, pixel-wise trajectories, and principal strains were determined in seven regions of interest (ROI): the brain stem, cerebellum, corpus callosum, and four cerebral lobes. Quantification of small neural tissue motion and strain along with their spatial and temporal variations in different brain regions was found to be feasible using DENSE. The medial and inferior brain structures (brain stem, cerebellum, and corpus callosum) had significantly larger motion and strain compared to structures located more peripherally. The brain stem had the largest peak mean displacement (PMD) (187 ± 50 μm, mean ± SD). The largest mean principal strains in compression and extension were observed in the brain stem (0.38 ± 0.08%) and the corpus callosum (0.37 ± 0.08%), respectively. Measured values in percent strain were altered by as much as 0.1 between repeated scans. This study showed that DENSE can quantify regional variations in brain tissue motion and strain and has the potential to be utilized as a tool to evaluate the changes in brain tissue dynamics resulting from alterations in biomechanical stresses and tissue properties.

Demonstration of circumferential heterogeneity in displacement and strain in the abdominal aortic wall by spiral cine DENSE MRI

“…38 In addition, the recent literature has demonstrated the use of DENSE imaging in quantifying smaller displacements in larger anatomical structures like the central nervous system. 39 However, the mean (homogenized) circumferential strain in this study (calculated by averaging the circumferential strain of all regions) is 0.14 ± 0.05, which is in close agreement to previously reported mean values of abdominal aortic circumferential strain via ultrasound of 0.132 ± 0.065 (Karatolios et al) and 0.123 ± 0.014 (Wittek et al). 31,40 Furthermore, Goergen et al report a consistent mean circumferential strain of the abdominal aorta even across multiple species from mice to humans of 0.12-0.16.…”

“…Additionally, DENSE imaging has not yet been validated for strain estimates in thin‐walled tubes; however, it has been validated for larger displacements . In addition, the recent literature has demonstrated the use of DENSE imaging in quantifying smaller displacements in larger anatomical structures like the central nervous system . However, the mean (homogenized) circumferential strain in this study (calculated by averaging the circumferential strain of all regions) is 0.14 ± 0.05, which is in close agreement to previously reported mean values of abdominal aortic circumferential strain via ultrasound of 0.132 ± 0.065 (Karatolios et al) and 0.123 ± 0.014 (Wittek et al) .…”

Quantifying cardiac‐induced brain tissue expansion using DENSE

“…However, despite the important potential of brain tissue volumetric strain in evaluating small vessel function, a complete picture of its variation over the cardiac cycle has not yet been obtained. Previous investigations of brain tissue motion did not assess brain tissue volumetric strain, or reported it only in relatively small regions of interest (ROIs) within at most a few slices, or measured only 2D strain . These measurements (even those made at 3 T) also probably suffered considerably from noise, since utilizing DENSE to encode brain tissue motion results in an inherent 50% signal loss due to the use of a single stimulated echo in the acquisition window .…”

“…Previous investigations of brain tissue motion did not assess brain tissue volumetric strain, 4 or reported it only in relatively small regions of interest (ROIs) within at most a few slices, 14,15 or measured only 2D strain. 13 These measurements (even those made at 3 T) also probably suffered considerably from noise, since utilizing DENSE to encode brain tissue motion results in an inherent 50% signal loss due to the use of a single stimulated echo in the acquisition window. 16 Additionally, the derivation of volumetric strain requires the computation of spatial derivatives, which amplifies the noise present in the displacement maps.…”

“…General improvements in available hardware, software and imaging techniques since the early exploration of brain tissue motion using MRI have allowed renewed interest in the phenomenon of brain tissue motion in healthy subjects as well as patients . Displacement encoding via stimulated echoes (DENSE), a non‐invasive MRI technique, was shown to be a feasible method for capturing the displacement vector fields that characterize brain tissue pulsatility, thereby allowing the derivation of brain tissue volumetric strain. However, despite the important potential of brain tissue volumetric strain in evaluating small vessel function, a complete picture of its variation over the cardiac cycle has not yet been obtained.…”