RadiAnt is actually one of the most affordable professional viewers on the market (costing roughly the same as two CT scans). Furthermore, the – it is a permanent free version with limitations.
The "killer app" for rib reading is the tool. In RadiAnt, you can draw a precise line along the center of a specific rib on an axial or coronal image. The software then "straightens" that curved rib into a single, flat 2D image. Radiant Dicom Viewer Cracked Rib