Experimental Biological Physics

Emeritus Professor
PhD University of Pennsylvania, 1961

Research Summary:

Studies of localized brain activity by surface measurements of evoked electric potentials (EEG), and external measurements of evoked magnetic fields (MEG). With these measurements one can image cortical processes (i.g. visual) with millisecond resolution; no other imaging procedure can do this. On the other hand, in more traditional modalities such as CT and MRI there is a unique mathematical process for obtaining the final “picture”. In the electromagnetic case, the inverse problem of determining the magnitude and position of current sources from ptoential and field measurements does not have a unique solution-a factor which makes the problem rich and interesting from both a physics, and a physiological point of view. The work involves development and calculations of theoretical models, computer similations, and subsequent comparision of results with experimental measurements.

Recently Prof. Aaron realized that some techniques of EEG an MEG can be used to study exercise physiology. In this case on measures electric potentials and magnetic fields stimulated by surface electrodes (e.g., on the upper leg during knee extensions). The resulting measurements enable one to determine internal impedances which are related to water fluxes in the muscles. It is generally accepted that the fatigue process in skeletal muscles depends crucially on the intra- and extra-cellular water content of the exercising muscle tissue.

Recent Publications:

“Localized Muscle Impedence Measurement,” Skeletal Muscle: Pathology, Diagnosis and Management of Disease, ed. V. Preedy and T. Peters, Greenwich Medical Media (2002), R. Aaron and C. A. Shiffman.

“Localized Bioimpedance Measurements in the Evaluation of Neuromuscular Disease,” Submitted to Annual Meeting of the American Association of Electrodiagnostic Medicine (in Albuquerque) (2001), R. Aaron, C. A. Shiffman, and S. B. Rutkove.

“Spatial Dependence of the Phase in Localized Bioelectrical Impedance Analysis,&quo; Phys. Med. Biol. 46 (2001), R. Aaron, C. A. Shiffman, and A. Altman.

“Evaluation of Boundary Element Methods for the EEG Forward Problem: Effect of Linear Interpolation,” submitted to IEEE Transactions on Biomedical Engineering, December, 1993, H. A. Schlitt, L. Heller, R. Aaron, E.D. Best, and D. Ranken.

“Mesh Generation Issues in the EEG and MEG Forward Problem,” L. Heller, R. Aaron, E. D. Best, H. A. Schlitt, and D. M. Ranken submitted as a refereed contribution to the International Conference of Biomagnetism, Vienna (1993). Copies of overhead transparancies are available.