A biexponential DWI study in rat brain intracellular oedema

PurposeTo examine the changes in MR parameters derived from diffusion weighted imaging (DWI) biexponential analysis in an in vivo intracellular brain oedema model, and to apply electron microscopy (EM) to shed more light on the morphological background of MR-related observations.Materials and methodsIntracellular oedema was induced in ten male Wistar rats (380–450 g) by way of water load, using a 20% body weight intraperitoneal injection of 140 mmol/L dextrose solution. A 3T MRI instrument was used to perform serial DWI, and MR specroscopy (water signal) measurements. Following the MR examination the brains of the animals were analyzed for EM.ResultsFollowing the water load induction, apparent diffusion coefficient (ADC) values started declining from 724 ± 43 μm2/s to 682 ± 26 μm2/s (p < 0.0001).ADC-fast values dropped from 948 ± 122 to 840 ± 66 μm2/s (p < 0.001). ADC-slow showed a decrease from 226 ± 66 to 191 ± 74 μm2/s (p < 0.05).There was a shift from the slow to the fast component at 110 min time point. The percentage of the fast component demonstrated moderate, yet significant increase from 76.56 ± 7.79% to 81.2 ± 7.47% (p < 0.05). The water signal was increasing by 4.98 ± 3.52% compared to the base line (p < 0.01).The results of the E.M. revealed that water was detected intracellularly, within astrocytic preivascular end-feet and cell bodies.ConclusionThe unexpected volume fraction changes (i.e. increase in fast component) detected in hypotonic oedema appear to be substantially different from those observed in stroke. It may suggest that ADC decrease in stroke, in contrast to general presumptions, cannot be explained only by water shift from extra to intracellular space (i.e. intracellular oedema).