Ex vivo magnetic resonance imaging of rat spinal cord at 9.4 T

The magnetic resonance (MR) properties of the rat spinal cord were characterized at the T9 level with ex vivo experiments performed at 9.4 T. The inherent endogenous contrast parameters, proton density (PD), longitudinal and transverse relaxation times T-1 and T-2, and magnetization transfer ratio (MTR) were measured separately for the grey matter (GM) and white matter (WM). Analysis of the measurements indicated that these tissues have statistically different proton densities with means PDGM=54.8± 2.5% versus PDWM=45.2± 2.4%, and different T-1 values with means T-1GM=2.28± 0.23 s versus T-1WM=1.97± 0.21 s. The corresponding values for T-2 were T-2GM=31.8± 4.9 ms versus T-2WM=29.5± 4.9 ms, and the difference was insignificant. The difference between MTRGM=31.2± 6.1% and MTRWM=33.1± 5.9% was also insignificant. These results collectively suggest that PD and T-1 are the two most important parameters that determine the observed contrast on spinal cord images acquired at 9.4 T. Therefore, in MR imaging studies of spinal cord at this field strength, these parameters need to be considered not only in optimizing the protocols but also in signal enhancement strategies involving exogenous contrast agents. © 2005 Elsevier Inc. All rights reserved.