• Marte Thuen, Martin Berry, Tina Bugge Pedersen, Pål Erik Goa, Mike Summerfield, Olav Haraldseth, Axel Sandvig, and Christian Brekken.
• Department of Circulation and Medical Imaging, NTNU, Trondheim, Norway. marte.thuen@ntnu.no
• J Magn Reson Imaging. 2008 Oct 1; 28 (4): 855-65.

PurposeTo provide dose-response data for the safe and effective use of MnCl(2) for manganese (Mn(2+)) -enhanced MRI (MEMRI) of the visual pathway.Materials And MethodsRetinal ganglion cell (RGC) toxicity, CNR in MEMRI, axon density resolution for MEMRI, mode of axonal transport and clearance of Mn(2+) from the vitreous after ivit were investigated. After 0, 30, 150, 300, 1500, and 3000 nmol ivit MnCl(2), neural toxicity was measured by counting surviving RGC back-filled with FluroGold (FG), CNR of the vitreous body and visual pathway by three-dimensional (3D) MEMRI, resolution of ON axon density by correlating CNR with axon density, and axonal transport of Mn(2+) by studying CNR in 3D MEMRI of the ON after ion of 200 nmol MnCl(2).ResultsThere were no changes in RGC density after ivit MnCl(2) 0 were recorded distally from the ion site, but there was no signal in the retina. At ivit doses >1500 nmol, clearance from the vitreous body was impaired.ConclusionThe optimal dose for MEMRI of the rat visual pathway was found to be 150-300 nmol ivit MnCl(2). Higher doses are toxic, causing RGC death, impair active clearance from the vitreous, and loss of Mn(2+) enhancement throughout the visual pathway. Mn(2+) traffic within RGC axons is mediated mainly by anterograde transport.(c) 2008 Wiley-Liss, Inc.

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