What is the difference between a dexa bone density scan and x-ray?

Dose and accuracy: The DEXA uses a very small dose of x-ray compared to a regular x-ray and it is designed to measure density not produce a high quality picture. A regular x-ray is designed to produce a high quality picture and is a poor measure of density.

DEXA uses CT: A DEXA scan uses cat scan and measures absorption of the x-ray to come up with a bone density measurement that can then be compared to age-matched normals. X-ray is a simple radiograph that makes an image, but is not able to quantitate bone density.

Nothing: The DEXA scan actually uses two low dose X-rays of different energy. By measuring the differences in how they are absorbed, bone density can be calculated.