Apparent diffusion coefficient and MR relaxation during osmotic manipulation in isolated turtle cerebellum

Abstract

The apparent diffusion coefficient (ADC) and relaxation times of water were measured by magnetic resonance imaging (MRI) in the isolated turtle cerebellum during osmotic cell volume manipulation. The aim was to study effects of cell volume changes, a factor in ischemia and spreading depression, in isolation from considerations of blood flow and metabolism. Cerebella were superfused at 12–14°C with solutions ranging from 50–200% normal osmolarity. Hypotonic solutions, which are known to cause cell swelling, led to reductions of ADC and increases of T2, while hypertonic solutions had the opposite effect. This supports the concept that ADC varies with the extracellular space fraction and, combined with published data on extracellular ion diffusion, is consistent with fast or slow exchange models with effective diffusion coefficients that are approximately 1.7 times lower in intracellular than in extracellular space. Spin‐spin relaxation can be affected by osmotic disturbance, though such changes are not seen in all pathologies that cause cell swelling. Magn Reson Med 44:427–432, 2000. © 2000 Wiley‐Liss, Inc.

Magnetic resonance quantification of water and metabolites in the brain of cirrhotics following induced hyperammonaemia

“…DTI, therefore, provides a sensitive tool to monitor brain water homeostasis in vivo, and this is supported by in vitro data in brain slice preparations and cultured cells in the context of detection of osmotic changes. In isolated turtle cerebellum exposed to a hypotonic environment, ADC was reported to fall, while under hypertonic conditions, ADC rose significantly [12], supporting the hypothesis that changes in ADC can reflect cellular swelling. A similar finding has also been reported in rat brain hippocampal slices [13].…”

Transient decrease in water diffusion observed in human occipital cortex during visual stimulation

“…Extracellular water diffusion in the brain is exquisitely sensitive to changes in cell size. Changes in cell volume induced by osmotic agents are accompanied by changes in water diffusion (an increase in cell diameter resulting in a decrease ADC and vice versa) (28)(29)(30)(31). So far, the best-known example of an ADC decrease linked to cell swelling is brain ischemia, where the ADC decreases at a very early stage in the infarcted areas (12,32).…”

Direct and fast detection of neuronal activation in the human brain with diffusion MRI

“…Diffusion MRI provides valuable information on the microscopic obstacles which hinder diffusing molecules, such as membranes or macromolecules, and in turn, on the tissue cellular structure (11). Based on other MRI reports of water diffusivity decrease during intense neuronal activation (12,13) or during other physiological or pathological conditions inducing cell swelling (14)(15)(16)(17), the observed diffusion findings have been putatively ascribed to a transient swelling of cortical cells and a shrinking of the extracellular space, increasing its tortuosity (18) for diffusing molecules. However, no confirmation has been found so far for this mechanism.…”