What is the difference between dexa scan and QCT-Pro software?

dexa asks for every day calibration (fantom scan), the software is checking for the errors of the scan and if it passes only then it allows you to perform examinations, so the examination results are much more precise and the x-ray dose is hundred times less than CT. 

Dexa Scan is a machine to perform or dignose bone-density of Patient. while QCT-Pro is software used with CT-Scan machine, it allow to draw image reconstraction and gives detail of bone-density.