Homogeneous orthogonal diffusion of drugs in the rat brain

The study introduced a homogeneous orthogonal diffusion model to describe the diffusion pattern of agents in the rat brain. Magnetic resonance imaging was performed post-injection of paramagnetic drugs into the caudatum of the rat brain at predetermined time intervals. The signal intensity on magnetic resonance images was converted to agents' concentration, and the standard least square method was employed to estimate the diffusion coefficients. The diffusion coefficients calculated along the three orthogonal axes were D₁ = (0.0097 ± 0.0036) mm² /h, D₂ = (0.0153 ± 0.0033) mm² /h, and D₃ = (0.0293 ± 0.0155) mm² /h; the clearance rate constant was k = (0.2177 ± 0.0112)/h. The theoretical homogeneous orthogonal model can enhance our knowledge on both the biophysical characteristics of brain extracellular space and the interstitial drug delivery in the brain.