The Existence of Biexponential Signal Decay in Magnetic Resonance Diffusion-Weighted Imaging Appears to Be Independent of Compartmentalization

Abstract

It is generally believed that the apparent diffusion coefficient (ADC) changes measured by diffusion-weighted imaging (DWI) in brain pathologies are related to alterations in the water compartments. The aim of this study was to elucidate the role of compartmentalization in DWI via biexponential analysis of the signal decay due to diffusion. DWI experiments were performed on mouse brain over an extended range of b-values (up to 10000 mm-2 s) under intact, global ischemic, and cold-injury conditions. DWI was additionally applied to centrifuged human erythrocyte samples with a negligible extracellular space. Biexponential signal decay was found to occur in the cortex of the intact mouse brain. During global ischemia, in addition to a drop in the ADC in both components, a shift from the volume fraction of the rapidly diffusing component to the slowly diffusing one was observed. In cold injury, the biexponential signal decay was still present despite the electron-microscopically validated disintegration of the membranes. The biexponential function was also applicable for fitting of the data obtained on erythrocyte samples. The results suggest that compartmentalization is not an essential feature of biexponential decay in diffusion experiments. © 2004 Wiley-Liss, Inc.