Improved measurement of brain deformation during mild head acceleration using a novel tagged MRI sequence

Abstract

In vivo measurements of human brain deformation during mild acceleration are needed to help validate computational models of traumatic brain injury and to understand the factors that govern the mechanical response of the brain. Tagged magnetic resonance imaging is a powerful, noninvasive technique to track tissue motion in vivo which has been used to quantify brain deformation in live human subjects. However, these prior studies required from 72 to 144 head rotations to generate deformation data for a single image slice, precluding its use to investigate the entire brain in a single subject. Here, a novel method is introduced that significantly reduces temporal variability in the acquisition and improves the accuracy of displacement estimates. Optimization of the acquisition parameters in a gelatin phantom and three human subjects leads to a reduction in the number of rotations from 72–144 to as few as 8for a single image slice. The ability to estimate accurate, well-resolved, fields of displacement and strain in far fewer repetitions will enable comprehensive studies of acceleration-induced deformation throughout the human brain in vivo.

Mechanistic Insights into Human Brain Impact Dynamics through Modal Analysis

“…Confirming this hypothesis, strain in the brain and specifically strain in the periventricular region of the brain-with the highest density of axon fibers-have been shown to correlate best with acute concussion and longterm neurological deficits [21][22][23][24]. However, dynamical behavior of the brain during rapid head motions with various amplitudes, durations, and directions, as well as the reason for higher susceptibility of these deep regions of the brain to strain are still largely unknown [22,25].As a complex dynamical system with an intricate geometry, nonuniformly compliant boundary conditions and significantly inhomogeneous material properties, understanding the mechanical characteristics of the brain requires a multifaceted approach that takes into account both the spatial and temporal aspects of this system. A force impulse on the head creates nonlinear traveling shear waves inside the brain, which propagate at different speeds and attenuate at different rates, and can create localized strain concentrations at different regions of a linear [26] and nonlinear [27] viscoelastic medium.…”

“…Confirming this hypothesis, strain in the brain and specifically strain in the periventricular region of the brain-with the highest density of axon fibers-have been shown to correlate best with acute concussion and longterm neurological deficits [21][22][23][24]. However, dynamical behavior of the brain during rapid head motions with various amplitudes, durations, and directions, as well as the reason for higher susceptibility of these deep regions of the brain to strain are still largely unknown [22,25].…”

“…There are several limitations associated with the work presented here. The FE model used in this study had previously been partially validated with sparse cadaver experiments and not thoroughly validated against in vivo MRI data [25,68]. We believe that more accurate and region specific material properties and more detailed geometries, particularly the cortical gyri, will render the dynamic differences more pronounced.…”

Test suite for image-based motion estimation of the brain and tongue

“…1 Researchers studying brain motion under mild acceleration use specialized hardware, and the study of the tongue is aided by a metronome. 3,4 However, no technique yields perfect results when the motion under investigation is voluntary. Consequentially, characterizing any effects arising from inconsistency is useful to determine estimation accuracy.…”

“…Consequentially, characterizing any effects arising from inconsistency is useful to determine estimation accuracy. 3 …”