Counting NoData values in raster using ArcGIS Desktop?

I have created a raster in ArcGIS Desktop 10 with a large number of holes (NoData) in it.

I want to fill the holes using something like the the following:

rOut = arcpy.sa.Con(arcpy.sa.IsNull(rGround),
arcpy.sa.FocalStatistics(rGround, arcpy.sa.NbrCircle(FillRadius,"CELL"), "MEAN"),
rGround)

It is desirable to fill the holes by averaging across a circle with a relatively small radius, but a small radius leaves larger holes unfilled, so I need to iterate this operation.

To do that I would like to be able to get the number of NoData values in my raster, once it reaches zero I can stop filling.