CAREER: Interactions of Radiofrequency Electromagnetic Fields with Biological Tissue: New Tools to Address Challenges and Exploit Opportunities

New York University Medical Center, New York NY

Investigators

Abstract

Abstract Nontechnical: Although numerous ex vivo or in situ animal measurements have been made over time, experimental access to in vivo electrical property distributions of human tissue have remained extremely limited, and indeed fundamental questions regarding the origin and distribution of these properties have tantalized scientists for decades. The research objective of this CAREER proposal is to develop, validate and disseminate a new method for reliable, non-invasive cross-sectional mapping of tissue electrical properties, based on measurements obtained with magnetic resonance (MR) imaging systems. This will provide insight on the distribution of electromagnetic (EM) fields in tissue, which in this project will be used to improve the diagnostic power of MR imaging, but could also enable marked improvement in speed and accuracy over current probe-based EM field mapping approaches used to satisfy safety regulatory requirements for wireless devices. Furthermore, in vivo electrical properties maps could be employed as biomarkers for cancer (and other pathologies), as well as to improve the effectiveness of existing therapeutic modalities, such as radiofrequency (RF) ablation, RF hyperthermia and electrochemotherapy. The Principal Investigator (PI) also expects that knowledge of electrical properties will provide an important new window into tissue structure and function, and will represent a rich new area for basic and applied research. A high priority of this proposal is the integration of educational and research activities. The PI will develop new courses that offer hands-on training activities, and will mentor and motivate students in research. Students at various levels and grades will learn how to make broad connections across disciplines, embracing concepts from electrodynamics, physics, biomedical engineering and medicine. The PI will publicly release a variety of software and tutorials, which is expected to generate new research projects and have an impact in education and training at other institutions. Technical: This project aims at extending general understanding of the interactions of EM fields with biological tissue, in order to dramatically improve high-field MR imaging performance. Maxwell's equations dictate the relationship between the electrical conductivity and permittivity of a body and the curvature of electromagnetic fields applied to that body. "Local Maxwell Tomography" (LMT) is a recently introduced technique that uses MR-based measurements of local field curvature to derive unknown electrical property distributions, effectively inverting Maxwell's equations. This project will establish a new generalized LMT technique that allows for high spatial resolution maps and accounts for boundaries of electrical properties for practical in vivo utilization. This will be employed for a wide range of applications, as: i) develop techniques to allow for the first time local RF power deposition monitoring and prediction in MR imaging; ii) engineer tailored RF pulses that enable practical control of MR signal profile and local RF power distribution; iii) create novel RF coil types and design concepts, using electrodynamic simulations of the theoretically optimal performance as a guideline. In vivo experiments will focus on collecting high-resolution in vivo information on electrical properties of brain tissue types. This information, currently not available, is expected to be of interest to researchers in a variety of fields (e.g, transcranial magnetic stimulation). As a lead-in to future studies, the PI will begin to investigate the biological basis of observed electromagnetic contrast. Since, depending upon the measurement frequency, permittivity and conductivity are believed to represent some combination of tissue cellularity, cell membrane integrity, and water content, the degree of correlation between conductivity images with spin-density MR images will be assessed to begin to tease out some of the components of this mixture.