Applied Mathematics Colloquium: Application of Waveguide Elastography to TBI
Friday, November 15, 2019
3206 Kirwan Hall (Mathematics Department)
An Overview of Waveguide Elastography and its Application to the Study of Traumatic Brain Injury
Anthony Romano and William G. Szymczak
Naval Research Laboratory
Background: Previously, we introduced Waveguide Elastography which utilizes a fusion of Magnetic Resonance Elastography (MRE), Diffusion Tensor Imaging (DTI), and a combination of isotropic and anisotropic inversion algorithms for the evaluation of the viscoelastic stiffness and anisotropy of the human brain. This approach was developed as a non-invasive diagnostic tool for the study of brain health or pathology.
Aims: The aims of this work are i) to evaluate the viscoelastic properties of the brains of both healthy controls and patients who present with Traumatic Brain Injury (TBI) from known causes and ii) to demonstrate the alterations to the stiffness and anisotropy of healthy brain structures as a result of insult/injury.
Methods: MRE was developed at The Mayo Clinic in Rochester, MN in 1995, and uses Magnetic Resonance Imaging (MRI) with a phase contrast imaging method to measure elastic waves propagating in biological tissue that is excited using an actuator in contact with the region under interrogation. By utilizing dynamical equations of motion appropriate for wave propagation in the tissues, the stiffness can be evaluated and utilized as a metric for diagnostic purposes, as it has been observed that many diseases can alter tissue stiffness such as cancer. Therefore this method is often referred to as non-invasive palpation.
DTI was developed at The National Institutes of Health in Bethesda, MD in 1994 and utilizes MRI to evaluate the diffusion of water molecules along waveguides such as muscle and white matter. In combination with MRE, this allows for the evaluation of the waves propagating along the waveguides and anisotropic inversion algorithms are implemented for the evaluation of an orthotropic stiffness tensor.
Both of these measurements methods will be explained, as well as the associated inversion algorithms to obtain both isotropic and anisotropic stiffness. This approach will be demonstrated in the evaluation of the stiffness and diffusion metrics in the brains of patients who have suffered TBI, and will be compared with the same metrics within the brains of healthy age and gender matched controls.
Results: When compared to the healthy controls, there were significant differences in the stiffness as well as the anisotropic models of the white matter in the TBI patients, with alterations in dependence upon the insult/injury experienced. Additionally, this method has been proven to diagnose Amyotrophic Lateral Sclerosis (ALS, or Lou Gherig’s Disease) as a result of a reduction of the anisotropic shear stiffness within the Cortico-Spinal Tracts of the patients.
Conclusions: Preliminary studies indicate that this fusion of measurement and analytical modalities can provide metrics, based on differences in material stiffness and anisotropy, for differentiation between healthy controls and TBI patients for diagnostic purposes. This work supported by Tim Bentley, ONR Code 34, Warfighter Protection.
Dr. Anthony Romano is a Research Physicist and Dr. William Szymczak is a Mathematician.