Abstract
Selective intracellular (IC) and extracellular (EC) brain water apparent diffusion coefficient (ADC) values were measured in normal and ischemic rat brain. Selective T~1~‐relaxation enhancement of the EC water, using intracerebroventricular (ICV) infusion of an NMR contrast reagent (CR), was used to separate the IC and EC signal contributions. In the CR‐infused, normal brain (n = 4), T~1~ = 235 ± 10 ms and T~2~ = 46 ± 2 ms for IC water (85%) and T~1~ = 48 ± 8 ms and T~2~ = 6 ± 2 ms for EC water (15%). Volume‐localized ADC~z~ (z‐gradient axis) values were 0.90 ± 0.02 (EC+IC), 0.81 ± 0.05 (IC), 0.51 ± 0.02 (EC+IC), and 0.53 ± 0.07 (IC), for normal, CR‐infused, ischemic, and ischemic/CR‐infused groups, respectively (ADC values are ×10^‐3^ mm^2^/s; n = 5 for each group). Imaging ADC~z~ values were 0.81 ± 0.03 (EC+IC), 0.75 ± 0.05 (IC), 0.51 ± 0.04 (EC+IC), and 0.52 ± 0.05 (IC), respectively, for the same groups. Imaging ADC~av~ (average diffusivity) values for the same groups were 0.70 ± 0.05 (EC+IC), 0.69 ± 0.06 (IC), 0.45 ± 0.06 (EC+IC), and 0.44 ± 0.06 (IC), respectively. These results suggest that the IC water ADC determines the overall water ADC value in normal and ischemic rat brain. Magn Reson Med 48:826–837, 2002. © 2002 Wiley‐Liss, Inc.