Lateral diffusion of Mn²⁺ in rat brain determined by T₁ relaxation time measured by ¹H magnetic resonance imaging

Abstract

Interstitial application of Mn²⁺ ion can be used to visualize neural activities in the brain by using T₁-weighted MRI. When we infuse Mn²⁺ in the cerebrospinal fluid (CSF), Mn²⁺ can be transferred into the interstitial space of brain through the ependymal cells. In order to optimize this entry process, we have analysed diffusion process of Mn²⁺ into the parenchyma. Mn²⁺ solution infused from the lateral ventricle of the rat brain, diffusion of Mn²⁺ was measured perpendicular direction from the third ventricle. T₁ relaxation times were measured at 4.7 T animal MR imaging system. Relaxivity of Mn²⁺ was used to convert T₁ relaxation time to Mn²⁺ concentration. From these results and the simple diffusion equation, apparent diffusion coefficient (Dap) of Mn²⁺ ion in the interstitial space is 2.5 x 10⁻³ mm²/min. However, the Dap tends to decrease when the distance from the third ventricle increased. It might be possible that 1) Mn²⁺ ion is trapped by neural/glial cells during diffusion, and/or 2) a presence of axial flux of the interstitial fluid in the brain. [Jpn J Physiol 55 Suppl:S72 (2005)]