Arc Finder Example of Tool Position for a Sector-type Region of Interest ACEUser's Guide, 3.6.x, 18316-000 Rev A Page 394 Object Definition Opening Angle between the two bounding radii of the tool sector. Radius The radius of the tool corresponds to the radius of the median annulus of the tool sector. Thickness Distance between the two bounding annuli of the tool sector. Note that the thickness cannot be more than twice the Radius, to prevent the ROI from over- lapping itself. Rotation Angle of rotation of the region of interest. Center X X coordinate of the origin of the tool. Center Y Y coordinate of the origin of the tool.