Can I suggest that you *don't* use a pie chart. In the field of data
representation pie charts are considered the bastard child of the graph
family, for valid reasons.
Google people like Edward Tufte for leading thinking on data representation.
There will always be a chart type that will display data better than a
pie chart.
Pie charts are bad enough, but 3D, exploded pie charts displayed at an
angle just begger belief.