Dr. Adam J. Pattison Profile

Dr. Adam J. Pattison

at Thayer School of Engineering at Dartmouth

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Proceedings Article | 29 March 2013 Paper

Development of a poroelastic dynamic mechanical analysis technique for biphasic media

Adam Pattison, Matthew D. J. McGarry, John Weaver, Keith Paulsen

Proceedings Volume 8672, 86721P (2013) https://doi.org/10.1117/12.2008777

KEYWORDS: Chemical elements, Magnetic resonance elastography, Elastography, Tissues, Fiber Bragg gratings, Reconstruction algorithms, Neodymium, Electroluminescent displays, Statistical analysis, Protactinium

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Magnetic resonance elastography is a technique where mechanical properties of materials are estimated by fitting a mechanical model to an MRI-acquired displacement field. These models have been primarily limited to viscoelasticity and linear elasticity, and only recently has poroelasticity been utilized as an applied model. To validate these estimates, the same material is measured via an independent dynamic mechanical analysis device. However, these devices only apply analytic viscoelastic models. In some cases, there is a model mismatch if a viscoelastic mechanical analysis is being compared to a poroelastic model in elastography. Thus, a poroelastic dynamic mechanical analysis technique is needed to properly measure porous media and compare the results with the appropriate elastography technique. A finite element technique was implemented on a TA-Q800 Dynamic Mechanical Analysis machine similar to the algorithm used in the corresponding MR elastography method. A viscoelastic version of the finite element code was created to validate the theory and show results similar to those obtained by the analytic DMA solution. Also, differences were seen that can be attributed to inertial forces not accounted for by an analytical solution. A poroelastic algorithm was then applied, showing great promise in the ability to measure properties of porous tissues.

Proceedings Article | 27 February 2009 Paper

MR elastography of hydrocephalus

Adam Pattison, S. Scott Lollis, Phillip Perríñez, John Weaver, Keith Paulsen

Proceedings Volume 7262, 72620A (2009) https://doi.org/10.1117/12.811820

KEYWORDS: Brain, Tissues, Magnetic resonance elastography, Magnetic resonance imaging, Control systems, Image segmentation, Protactinium, Elastography, Reconstruction algorithms, Actuators

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Hydrocephalus occurs due to a blockage in the transmission of cerebrospinal fluid (CSF) in either the ventricles or subarachnoid space. Characteristics of this condition include increased intracranial pressure, which can result in neurologic deterioration ^[1]. Magnetic resonance elastography (MRE) is an imaging technique that estimates the mechanical properties of tissue in vivo. While some investigations of brain tissue have been performed using MRE ^[2,3,4,5], the effects due to changes in interstitial pressure and fluid content on the mechanical properties of the brain remain unknown. The purpose of this work is to assess the potential of MRE to differentiate between the reconstructed properties of normal and hydrocephalic brains. MRE data was acquired in 18 female feline subjects, 12 of which received kaolin injections resulting in an acute form of hydrocephalus. In each animal, four MRE scans were performed during the process including one pre-injection and three post-injection scans. The elastic parameters were obtained using a subzone-based reconstruction algorithm that solves Navier's equations for linearly elastic materials ^[6]. The remaining cats were used as controls, injected with saline instead of kaolin. To determine the state of hydrocephalus, ventricular volume was estimated from segmenting anatomical images. The mean ventricular volume of hydrocephalic cats significantly increased (P ⪅ 0.0001) between the first and second scans. The mean volume was not observed to increase (P ⪆ 0.5) for the control cats. Also, there was an observable increase in the recorded elastic shear modulus of brain tissue in the normal and hydrocephalic acquisitions. Results suggest that MRE is able to detect changes in the mechanical properties of brain tissue resulting from kaolin-induced hydrocephalus, indicating the need for further study.

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