Are you using this function?
http://zone.ni.com/reference/en-XX/help/370281W-01/imaqvision/imaq_find_circles/
If so, you can wire the Circles Data array into a for loop and unbundle the x,y, and radius. You can wire each of those out of the array which will autoindex each measurement into individual arrays. You can then wire each measurement array into Mean.vi which will give you the mean x, y, and radius.
Also, for future questions, there's a machine vision board here:
http://lavag.org/forum/10-machine-vision-and-imaging/
or here
http://forums.ni.com/t5/Machine-Vision/bd-p/200