Images were analysed using Image J software (http://rsbweb.nih.gov/ij/). Contrast enhancement maps were generated from the pre- and post-contrast T1 weighted scans according to the equation: Enh = (Spost – Spre) ÷ Spre where Spost = post contrast agent signal and Spre = pre-contrast agent signal. Regions of interest (ROIs) were manually defined to include the entire brain slice. Percentage signal change maps were generated by multiplying Enh by 100 and the mean percentage signal change for each brain slice calculated.