Edward WalshEdit My Page
Functional magnetic resonance imaging (fMRI) is a powerful tool for the spatial and temporal localization of neuronal activity. My work involves the development and implementation of MRI acquisition and reconstruction techniques that reduce or eliminate difficulties associated with rapid functional acquisitions, including geometric distortion and signal loss in regions of the brain located near air-tissue interfaces, such as the orbitofrontal cortex.
In magnetic resonance imaging, field gradients are used for spatial encoding of the signals. A Fourier transform model is used to convert the data into the spatial domain for viewing of images. Difficulties with this model are that signal decay (a normal process) and local field gradients (arising in the tissue, especially near air-tissue interfaces) are not taken into account. Consequences include geometric distortion (which can result in misregistration of activation locations when mapping to anatomic reference images) and signal voids (no activation detection possible). The SS-PARSE techniques (Single-Shot Parameter Assessment by Retrieval from Signal Encoding) discards the Fourier transform model and instead casts the image reconstruction procedure as a nonlinear optimization process with the goal of providing an inverse solution to the MRI signal equation. Parametric maps of magnetization, decay rate, and frequency (a field map) are provided as the final solution in the reconstruction process. We are therefore able to map relaxation rate changes associated with the BOLD effect directly, rather than observing contrast changes in a conventional echo planar image as a consequence of the BOLD effect. Since frequency (field variation) is taken into account in the optimization process, geometric fidelity is enforced without any postprocessing.
An active program in nanoparticle contrast agent development is underway in the Chemistry Department at Brown. Variations of the PARSE technique are being considered for the rapid mapping of relaxation rates associated with nanoparticle agent uptake. This work will provide a means of rapidly assessing agent distribution and will permit time-resolved studies of agent uptake.
Alpha Eta Mu Beta
International Society for Magnetic Resonance in Medicine
IEEE Engineering in Medicine and Biology Society
ONR N66604-08-1-1616: Magnetic Resonance Imaging of Water Infiltration into Nanoparticle-Filled Polymers. Start 3/08 end 9/08, Principal Investigator, total award $15,614.
Industry, Cordis/Johnson&Johnson: Magnetic Resonance Compatibility of Hydrocephaly Shunt Devices: Start 2/08 end 3/09. Principal Investigator, total award $6000, possible follow-up funding.
NIH 1RO1-1HL084178-01A1: Hemodynamic and Cognitive Function in Cardiovascular Disease (L. Sweet, PI) start 8/07, end 5/11, PI on Brown subcontract for implementation of cerebral perfusion imaging, total award $2,534,047, subcontract award $36,392.
NIH 1RO1-DA020725-01: Amphetamine Effects on Brain fMRI and Behavior: Genetic and Personality Differences (T. White, PI) start 8/07 end 5/11, Co-investigator for physics support relating to imaging in high susceptibility gradient regions such as orbitofrontal cortex, 8.5% effort, total award $1,440,303.
Industry: Johnson & Johnson: Center for MRI Implant Device Characterization, 6/03-5/05, total award $35,000, Co-PI for quantitative assessment of image artifacts produced by NiTi stent prototypes.
NIH NINR R15-NR08210-01, Assessment of Pelvic Muscle Function in Women (PI V Johnson, Ph.D.) 3/03-2/05 total award $100,000, co-investigator for implementation of MR hardware, functional muscle imaging techniques and image processing.
- Xu, C., Xie, J., Kohler, N., Walsh, E.G., Chin, Y.E., Sun, S., Monodisperse Magnetite (Fe3O4) Nanoparticles Coupled with Nuclear Localization Signal (NLS) Peptide for Cell Nuclear Targeting, Chemistry Asian J 3:548-552, 2008.(2008)
- Walsh, E.G., Anayiotos, A., Brott, B., Johnson, V.Y., Venugopalan, R., Assessment of Cardiovascular Implant Devices for MRI Compatibility, Technology in Health Care 16(4):233-245, 2008.(2008)
- Xu. C., Xie, J., Ho, D., Wang, C., Kohler, N., Walsh, E.G., Morgan, J.R., Chin, Y.E., Sun, S., Au-Fe3O4 Dumbbell Nanoparticles as Dual Functional Probes, Angewandte Chemie. Int Ed 47:173-176, 2007.(2007)
- Zuo, J., Walsh, E.G., Deutsch, G., Twieg, D.B., Rapid Mapping of Flow Velocity Using a New PARSE Method, Magn Reson Med 55:147-152, 2006.(2006)
- Walsh, E.G., Holton, A.D., Brott, B.C., Venugopalan, R., Anayiotos, A.S., Magnetic Resonance Phase Velocity Mapping Through NiTi Stents in a Flow Phantom Model, J Magn Reson Imag 21:59-65, 2005.(2005)
- Holton, A.D., Walsh, E.G., Brott, B.C., Venugopalan, R., Hershey, B., Ito, Y., Shih, A., Koomullil, R., Anayiotos, A., Evaluation of In-Stent Stenosis by Magnetic Resonance Phase-Velocity Mapping in Nickel-Titanium Stents, J Magn Reson Imag 22:248-257, 2005.(2005)
- Zuo, J., Walsh, E.G., Twieg, D.B., Flow SS-PARSE: A New Method for Rapid Imaging and Mapping of Blood Flow Velocity, Proc IEEE EMBS International Conference 1:530-533, 2004.(2004)