In vivo measurement of ADC change due to intravascular susceptibility variation

The apparent diffusion coefficient (ADC) of extravascular tissue water in r at brains was measured in response to step-wise injections of the superpara magnetic intravascular contrast agent AMI-227, These data were normalized a nd compared with measured changes in R-2* and blood magnetic susceptibility . Linear regression showed that ADC changes 33%/ppm shift of intravascular susceptibility and 0.43% s(-1) change in R-2*. These changes correspond to a predicted ADC change of approximate to 6% far a change between fully oxyg enated and fully deoxygenated blood. The source of these ADC changes was co nfirmed to be background gradients within the sample by the use of diffusio n weighting with bipolar gradients of odd symmetry designed to cancel such background gradient effects on ADC, The results suggest that diffusion-weig hted imaging is sensitive to blood-oxygenation and may provide a means of m easuring changes in blood oxygen. They also provide estimates of the potent ial contribution of susceptibility changes to changes in ADC that occur, fo r example, in stroke and seizure. (C) 1999 Wiley-Liss, Inc.