Manganese-Enhanced Magnetic Resonance Imaging as a Diagnostic and Dispositional Tool after Mild-Moderate Blast Traumatic Brain Injury

Rodriguez et al.
Journal of Neurotrauma. April 2016, 33(7): 662-671.

   In this paper, they used a form of manganese-enhanced MRI (MEMRI) to study the effects of blast traumatic brain injury, a severe form of TBI which sometimes leads to long term neuropsychiatric problems. They were looking for markers in mouse brains which might lead to markers to identify injury in humans. In order to do this, they worked with a specially designed chamber that used compressed helium to send blast waves of different strengths at anesthetized mice.  Mice were then given IP injections of 40mg/kg manganese. Mice brains were imaged using T2 scans to be sure there were no major structural changes or damage, and T1 weighted scans to examine manganese uptake at 6, 24, 48, 72hrs, and 14 and 28 days after the helium blast.
   Blast-exposed mice showed greater transmission of manganese across the blood-csf barrier at 6 hours post-injection compared to controls. By 24 hours, this increased uptake caused greater signal throughout the brain in blast mice. The differences lasted for at least a week in all regions, in some regions after two weeks, and disappeared after a month. They found that in a few tissues, signal intensity kept increasing for 72 hours before going back down.
   One very interesting thing in this study was that they tried to use a 0.01M Mn phantom in their scans as a control, but found that its image values were more variable than expected from scan to scan (presumably due to microscopic air bubbles and changes in position of the phantoms), but the brain ROIs they studied didn't show the same variability, so they resorted to using non-blast-exposed saline-vehicle-injected mice as image quality controls for normalizing T1 values.
   There was also one other finding that I have a hard time understanding. They found that if mice underwent the blast treatment while wearing little mousey body armor, the manganese enhancement in the brain was attenuated and happened at levels similar to those in a mouse not exposed to a blast. -DH