Manganese-enhanced magnetic resonance imaging in experimental spinal cord injury: Correlation between T1-weighted changes and Mn²⁺ concentrations

OBJECTIVE: Manganese (Mn²⁺)-enhanced magnetic resonance imaging (MEMRI) is a potentially important tool for assessing neural tissue regeneration after spinal cord injury (SCI). We evaluated the relation between Mn ²⁺ and T1-weighted magnetic resonance (MR) signals in an SCI rat model. METHODS: Rats were divided into 4 groups with or without SCI (T9-level transection) and with or without Mn²⁺ injection. Two microliters of 0.2 mol/L MnCl₂ was injected into the lateral ventricles. Magnetic resonance imaging (MRI) was performed 60 hours after injection. Signal intensities at cervical, thoracic, and lumbar levels were measured and normalized to the intensity of perivertebral muscles. Spinal cord sections were analyzed by inductively coupled plasma mass spectrometry (ICP-MS) for total Mn²⁺ content. The results of ICP-MS were compared with MR signal intensity. RESULTS: T1-weighted MR signal intensity and ICP-MS-measured Mn were significantly decreased below the SCI injury site in Mn-injected groups with or without SCI, and were similar to intensity and Mn²⁺ levels of noninjected animals. Signal intensity and Mn²⁺ concentration tended to decrease from cervical to lumbar spinal levels in the control rats. ICP-MS data correlated with MRI results. CONCLUSION: The results confirmed Mn ²⁺ uptake in the spinal cord after intraventricular injection. T1-weighted MR signal intensity correlates with spinal Mn²⁺ concentration as measured with ICP-MS. This work establishes the repeatability of MEMRI of the injured spinal cord and makes it possible to compare changes in axonal transport rates through the spinal cord after neuronal regeneration in vivo at different stages. MEMRI in animal models may improve understanding of the factors required to promote spinal cord regeneration.