Walsh, E.G., “Basic MR Physics: Considerations for Behavioral Medicine and Neurophysiology”, for “Brain Imaging in Behavioral Medicine and Clinical Neuroscience”. R.A. Cohen, L.H. Sweet (Editors), Springer, 2011, p.11-36.
Walsh, E.G., “Cardiovascular MR Instrumentation”, for “Textbook of Cardiovascular MRI”, G.M. Pohost , K. Nayak (Editors), Informa Healthcare, 2007, p31-49.
Magnetic resonance imaging of physiologic function represent areas that benefit from the development and implementation of rapid parametric imaging techniques. My collaborators and I study approaches to these problems with the aim of developing real-time display of information related to parameters such as blood flow, BOLD fMRI contrast, and temperature. Applications include functional brain imaging and mapping of temperature during thermal ablation procedures. To facilitate this, I collaborate with a group of applied mathematicians in the investigation of underlying mathematical principles that can be applied to these problems. There is also active work in the development of nanoparticle contrast/therapy agents for use in magnetic resonance imaging for target identification and acceleration of thermal therapy procedures.
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 addressing conditioning problems associated with this technique using a mathematical formalism (in collaboration with five applied mathematicians) designed to overcome the conditioning problems associated with a direct inverse solution to the MR signal equation. Our group was awarded with the opportunity to spend three sessions at the American Institute of Mathematics using their resources to research our questions and approaches as a group.
An active program in nanoparticle contrast agent development is underway in which we are investigating the design of targeted contrast agents for antigen specific binding, as well as for use as accelerants in targeted microwave tumor ablation therapy. This work includes implementation of real-time magnetic resonance temperature mapping for accurate depiction of treatment zones to reduce recurrence associated with thermal therapy.
2014 DEANS Award: Neuroprotective Effects of Anti-Inflammatory Treatments on Neonatal Brain Ischemia. Start 10/14 end 12/15. Prinicpal Investigator, total award $80,000.
Industry, Codman/Johnson&Johnson: Magnetic Resonance Compatibility of Hydrocephaly Shunt Devices: Start 5/12 end 5/16. Principal Investigator, total award $36000.
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.