[Study of diffusion phenomenon using an experimental magnetic resonance system (SIS 200/400) for small animals--reliability and apparent diffusion coefficient of normal animals].

We have developed a magnetic resonance (MR) spin echo method to obtain diffusion weighted imaging using motion probing gradient (MPG) pulses in orthogonal direction before and after a 180 degree pulse. Phantom models containing water, acetone, cupric sulfate and agar, and normal brains of Wistar rats and puppies were examined. MRI was performed using a SISCO SIS 200/400 MRI/MRS experimental system for small animals (4.7 tesla, 400 mm bore). The apparent diffusion coefficient (ADC) values, given in mm2/sec, were 2.19 +/- 0.02 x 10(-3) in water, 4.51 +/- 0.18 x 10(-3) in acetone, and the ADC of water was independent on longitudinal (T1) or transverse (T2) relaxation time. Time-dependent ADC changes were not demonstrated, however position-dependent ADC changes were significant. It is therefore important to set the sample at the same position for repeated MRI studies and for the evaluation of the time course of experimental studies. Mean ADC values of rat brains were 0.65 x 10(-3) for cortex, 0.69 x 10(-3) for caudate-putamen, 0.69 x 10(-3) (perpendicular to axon) for corpus callosum, 1.11 x 10(-3) (parallel to axon) for optic nerve, and 1.38 x 10(-3) (parallel to axon) for trigeminal nerve. Those of puppies were 1.14-1.42 x 10(-3) for gray matter, 1.17 (parallel to axon) and 0.89 (perpendicular to axon) x 10(-3) for white matter, 1.66 (parallel to axon) and 0.57 (perpendicular to axon) x 10(-3) for internal capsule, and 0.91-0.95 x 10(-3) for thalamus. On the in vivo ADC maps, white matter tracts successfully showed anisotropic diffusion. This technique has promising implications for the evaluation of the time course of cerebral damage and degenerative changes.