Estimation of Brain Biomechanics using MRI

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Abstract

We have updated our IRB protocol to increase the age range of participants and to allow for telephone consent. Previously, the protocol had limited the age of participants to be less than 50. The modified age range now covers the planned ages of recruitment for this task (18-65). We have further optimized our acquisition protocol. Previously, we had required repeating four identical head motions to obtain one image slice for measuring each component of tissue displacement resulting from the impulsive load at the completion of the head rotation. Using a more efficient sampling of k-space and alterations of sequence of parameters, we now require only two repetitions of the identical head motions. In dong so, the time required to complete a given set of measurements is reduced by 50%. Because reproducing the same motion every time is critical to generating a high quality dataset, reducing the number of repetitions from 4 to 2 significantly improves the robustness of acquisition. Ideally we would like to measure the displacements with a single head/rotation impulse. And we continue to consider methods to enable this. Nevertheless, the reduction from 4 to 2 remains a significant improvement over the previous methods increasing the comfort of the patient with negligible loss in image quality. We have scanned and analyzed three post-mortem cadaver head/neck specimens. The first specimen was a fixed sample and we discovered that because the fixation process significantly increases the stiffness of the tissue, the deformations become too small for the data to be useful. The second and third specimens were fresh and provided good data. These two data sets include structural and diffusion MRI, computed tomography (CT), neck extension measurements, neck rotation measurements, and elastography measurements. In addition, the neck extension was performed with two different loading conditions. We have resumed scanning of healthy volunteers. Five participants have been scanned this year. We have developed a new collaboration with Drs. Michaelann Tartis/Ricardo MejiaAlvarez/Adam Willis (New Mexico Tech/Mich St/SAMMC) on the biomechanical evaluation of biofidelic blast phantom. This phantom is constructed of two layers of a polyacrylamide gel representing white and gray matter, and includes a convoluted surface resembling sulci/gyri We are extending the protocol to characterize the skull brain interface, specifically to characterixze the degree of slip at the brain skull interface and whether this is affected by traumatic meningeal in jury resulting from prior head trauma. We have received bench-to-bedside funding to support this aspect of the project, and hired a postdoc who had nearly completed the development of an interface phantom which will allow us to test methods for measuring slip using interfaces using tagged MRI and MR elastography.