What is the difference between a qct and a dexa scan?

Different methods: Qct is quantitative computerized tomography. It uses calibration to measure bone density with a ct. It is very accurate, but does expose you to a fair dose of radiation, limited the number of times it should be done over the course of life. Dexa is dual energy x-ray absorptiometry is like a low dose x-ray. It too gives bone density, but since the radiation dose is lower, it can safely be repeated.