DEXA Accuracy and Calibration

How we ensure the data you receive is within +/- 0.5% accuracy?

You’ll hear our DEXA technicians quote some amazing accuracy stats. But it’s well worth asking the question, where do those statistics come from? Let’s talk about DEXA accuracy and our practices for ensuring the quality of the data.

How does a DEXA work?

DEXA stands for Dual Energy X-ray Absorptiometry. It uses two different energy levels of x-ray beams to determine the composition of a body. One energy wavelength is attuned to a density associated with fat tissue, the least dense tissue. The other is attuned to a density associated with bone, the densest tissue. Everything else is categorized into the lean tissue category.

So, while the DEXA accounts for skeletal muscle in "lean tissue", it will also include organs, tendons, and other internal fluids, including bone marrow.

Primary calibration

Think of this as very similar to calibrating a scale. This happens during routine maintenance to configure the scanner for use. There are two tools used: an aluminum step wedge, and an acrylic step wedge.

Aluminum is used to calibrate DEXA to bone tissue, acrylic is most similar to fat. By running tests of the scanner against known quantities, we can determine if the DEXA is ready for client tests.

The acrylic block and the aluminum step wedge are placed on top of each other to provide a stepwise ladder system for electrons that have been excited by the X-ray tube.

This allows our operations team to measure the functional amount of X-ray that is reaching the detector on the other side. This is an analog process, and only by running tests on these analog systems can we ensure quality data.

To help visualize the function of this process, think back to science class or your kitchen. Imagine we have a known quantity of sugar, 5lbs, and we need to measure it on the DEXA.

Each day we run QA (Quality Assurance) to make sure we have zeroed out the scale. That way, if the amount of x-ray that passes through the sugar and reaches the detector looks more like 5.08 lbs, we calibrate the software to understand it is 5lbs.

Daily Quality Assurance

Each DEXA scanner in our fleet has to pass a daily Quality Assurance (QA) test before being used by our technicians. This daily QA is performed with a block that has known weight and approximations of each of the tissue type densities.

This QA is a crucial component of BodySpec’s operation. If a single aspect of the QA self-checks fails, the system cannot proceed. To use the earlier analogy, the daily QA is like measuring a bag of sugar, an apple, and a brick each day to ensure those density quantities are accurately being relayed to the software.

All QA data is saved and stored remotely for further analysis by our operations team. They can monitor how each machine is performing, and ensure QA data across the fleet is trending appropriately.

Accuracy vs. Precision

Consider this. Accuracy is a measurement of how close the measure is to the true value: we offer accuracy of +/- 0.5% based on our daily QA testing. Precision is how close measurements are to each other. That’s where you, the DEXA scan client, play a role!

Even if the DEXA was perfectly accurate in every situation, your body is in a constant state of change with eating, drinking, sweating, and using the restroom. Keeping your body in the same state each time you scan is a great way to improve the precision of your scans.

Since free water and undigested food fall under the lean tissue category, it is hence the most variable category from time to time. Our rule of thumb is that if your lean tissue change is under 2%, it’s more likely to be due to hydration or food status.

The Bottom Line

BodySpec takes the utmost care in providing ongoing data quality checks. Book a scan today to begin putting this accuracy to work in conceptualizing your goals, and tracking your progress over time.