Analysis of the modifications of MRI signal of the brachial plexus of rats: Comparative study before and after freezing/thawing.

The aim of this study was to compare the MRI signal of the brachial plexus and surrounding muscles before and after freezing/thawing on a murine model. A first MRI going through the brachial plexuses of 5 healthy Wistar rats was performed immediately post-mortem. A second MRI was performed after freezing at -30°C and then thawing at 20°C for 24hours. All MRI images were segmented to make nerve and muscular structures appear and calculate the average intensity of the MRI signal using the program ImageJ. The average nerve and muscular MRI signals were compared before and after freezing/thawing and rated in grayscale units between 0 and 255. The average intensity of the MRI signal of nerve structures was 40.315 grayscale units before freezing and 31.943 after freezing/thawing. The average intensity of the MRI signal of muscular structures was 25.44 grayscale units before freezing and 35.710 after freezing/thawing. Our results have shown that the intensity of the MRI signal of the brachial plexus was higher before freezing/thawing. The intensity of the MRI signal of muscles was lower than the intensity of the brachial plexus before freezing/thawing and higher after freezing/thawing in muscles than in brachial plexus. The MRI could be used in clinical practice to monitor the reinnervation after frozen nerve allografts.