Phase-based manganese enhanced MRI, a new methodology to enhance brain cytoarchitectural contrast and study manganese uptake.

PURPOSE As the magnetic susceptibility induced frequency shift increases linearly with magnetic field strength, the present work evaluates manganese as a phase imaging contrast agent and investigates the dose dependence of brain enhancement in comparison to T(1) -weighted imaging after intravenous administration of MnCl(2). METHODS Experiments were carried out on 12 Sprague-Dawley rats. MnCl(2) was infused intravenously with the following doses: 25, 75, 125 mg/kg (n=4). Phase, T(1) -weighted images and T(1) maps were acquired before and 24 h post MnCl(2) administration at 14.1 Tesla. RESULTS Manganese enhancement was manifested in phase imaging by an increase in frequency shift differences between regions rich in calcium gated channels and other tissues, together with local increase in signal to noise ratio (from the T(1) reduction). Such contrast improvement allowed a better visualization of brain cytoarchitecture. The measured T(1) decrease observed across different manganese doses and in different brain regions were consistent with the increase in the contrast to noise ratio (CNR) measured by both T(1) -weighted and phase imaging, with the strongest variations being observed in the dentate gyrus and olfactory bulb. CONCLUSION Overall from its high sensitivity to manganese combined with excellent CNR, phase imaging is a promising alternative imaging protocol to assess manganese enhanced MRI at ultra high field.