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In some of our most recent blogs we’ve discussed a few of the most interesting facts about x-rays (did you know that x-rays were the first form of diagnostic imaging and that the inventor’s wife was none too happy when she “saw her own death” upon viewing her skeletal hand?) We also wrote about some equally fascinating facts about MRI scans (they use materials that are extremely cold, making the inside of MRI machines only slightly warmer than outer space!). With so many unique facts act those two machines, we thought we’d take a look into another machine we use daily, the king of bone density scan machines: DEXA.

What Is DEXA?

Dual-energy x-ray absorptiometry, also known as a DEXA scan or DXA scan, is most often used to determine if the patient has osteoporosis. Once doctors have a baseline, they can tell how fast the disease is progressing with subsequent scans.

DEXA scans are most often used to scan the lower back and hips, though they can take density scans of other bones in the body. The entire procedure is non-invasive, painless, and generally takes less than 20 minutes. Because there’s no tunnel as there is with an MRI machine, claustrophobic patients don’t have to worry.

How DEXA Scans Work

The “dual-energy” part of the DEXA scan comes from two beams of extremely low-dose radiation used (see below). One of the beams has a wavelength peak that is absorbed primary by soft tissue, while the second peak is absorbed by bone. The soft tissue amount is subtracted from the total in order to find the patient’s bone mineral density.

The Radiation Is The Least Amount Use In Diagnostic Imaging

Perhaps the most amazing and comforting aspect of DEXA scans is that they use the least amount of radiation of any ionizing medical scan out there. It’s about a tenth of what you’d get in a chest x-ray, and less than you’d get in a dental x-ray.

How little radiation is it? Well, there’s something called “background radiation,” which is the amount of radiation that a person is subjected to every day simply by living on the planet. Some of it comes from the cosmic rays that penetrate our atmosphere, and another source is the breakdown of elements in the soil. The amount of radiation used in a DEXA scan is actually less than you’d get from simply being on Earth for a day!


When you get a DEXA scan, you’ll get a number called a T-score. This number tells a doctor if a person has normal bone density, low bone density, or osteoporosis.

But there’s a second score that you might hear about called a Z-score. Since bone density is going to go down over time whether a person has osteoporosis or not, it wouldn’t be fair to judge an elderly person’s bone density against someone who is young. The Z-score is a comparison between your score and that of someone who’s of the same age group, size, and gender.

Ready For Your Medical Imaging Scan?

Fair lawn Imaging is ready to help you determine your bone density in the most accurate way possible. Contact us today to schedule an appointment!