Log scale for choroid plexus contamination graphs?

[lweasel]

For the graph which plots choroid plexus contamination, the percentages are likely to be very small, even when the choroid plexus contamination is large (e.g. a "large" amount of contamination might be something like 0.5%).

Perhaps we could change the y-axis of this graph to be log scale (or something like that, if there's a better way)?