DXA vs MRI: they measure different things

A DXA scan and an MRI are sometimes confused, but they do completely different jobs — so it’s not really a case of one being “better.”

DXA measures bone strength

A DXA scan measures bone mineral density — how strong (or thin) your bones are. It’s the gold-standard test for diagnosing and monitoring osteoporosis, and it’s quick, painless and very low-dose.^[1] It gives a number (your T-score), not a detailed picture.

MRI shows detailed structure

An MRI produces detailed images of soft tissues and structures — bone marrow, joints, cartilage, discs, nerves and more — using magnets and radio waves, with no radiation.^[3] It shows what something looks like in fine detail, rather than measuring density.

When you’d have each

• You’d have a DXA to find out whether you have osteoporosis or to monitor your bone density over time.
• You’d have an MRI to investigate a specific structural problem — a joint injury, a disc, a suspicious area in the bone, or marrow disease.

They can even be complementary — but they’re not interchangeable. (For a spine with existing fractures or arthritis, where DXA is less reliable, a CT-based method may occasionally be used instead.)^[1]

Frequently asked questions

Can an MRI measure bone density instead of a DXA?

Not in the standard way DXA does. DXA is the established test for measuring bone density and diagnosing osteoporosis; MRI shows structure, not a density score.^[1]

Which has more radiation, DXA or MRI?

DXA uses a very low dose of radiation; MRI uses none. But they’re used for different purposes, so the choice is about what needs to be assessed.^[3]