Dual-Energy X-ray Absorptiometry, commonly known as DEXA or DXA, is a specialized medical imaging test that uses a small amount of ionizing radiation to measure bone mineral density. This non-invasive procedure is the standard method for diagnosing osteoporosis and assessing an individual’s risk of bone fracture. Because the scan uses X-rays, many people are naturally concerned about the amount of radiation exposure involved. Understanding the precise radiation dose delivered during a typical examination helps to clarify the safety profile of this diagnostic tool.
Quantifying the DEXA Radiation Dose
A standard DEXA scan, which typically includes measurements of the hip and lower spine, delivers a small effective radiation dose. The measurement unit for this dose is the microSievert (µSv); one thousand microSieverts equals one milliSievert (mSv). The effective dose for a diagnostic DEXA scan generally falls within a range of less than 1 µSv to about 15 µSv.
The exact dose depends on the specific technology utilized. Older fan-beam systems may result in doses between 1 and 10 µSv. Modern pencil-beam scanners often deliver a dose of less than 1 µSv. Even a whole-body composition scan, which covers a larger area, typically results in a dose of only 4 to 5 µSv.
The X-ray beam energy levels are kept low to achieve necessary contrast between soft tissue and bone while minimizing exposure. This focus on low energy and brief scan times ensures the total radiation dose is minimal compared to most other radiological procedures.
Putting the Exposure into Perspective
To understand the DEXA dose, it is helpful to compare it to the radiation people encounter in everyday life. The average person in the United States is exposed to natural background radiation from the environment at a rate of approximately 8 to 10 µSv per day. This natural exposure comes from cosmic rays, soil, rocks, and naturally occurring radioactive elements in food and water. Therefore, a typical DEXA scan’s radiation exposure is often equivalent to what a person receives over just one day of normal background exposure.
The DEXA scan delivers a much lower dose than other common medical imaging tests. A standard chest X-ray typically delivers an effective dose ranging from 20 to 50 µSv, which is several times higher than most DEXA scans. A mammogram is associated with a dose of approximately 130 µSv. Procedures like quantitative computed tomography (QCT), another method for measuring bone density, range from 50 to 100 µSv.
Everyday activities also provide context. For instance, a cross-country airplane flight from New York to Los Angeles exposes a passenger to about 35 µSv of cosmic radiation. The radiation from a single flight is generally greater than the radiation received during a combined hip and spine DEXA scan. The DEXA procedure is among the lowest-dose imaging modalities used in medicine.
Safety Protocols and Minimizing Risk
Medical radiation procedures are guided by the principle of “As Low As Reasonably Achievable” (ALARA). This mandates that the dose must be minimized while still obtaining the diagnostic image quality necessary for an accurate assessment. Technologists and physicists regularly calibrate DEXA equipment to ensure the lowest possible dose is used.
While the dose from a single DEXA scan is minimal, clinicians remain mindful of the cumulative radiation dose, particularly for patients who require monitoring over many years. The benefit of diagnosing and managing conditions like osteoporosis, which can lead to fractures, significantly outweighs the theoretical risk. Physicians must justify the necessity of the scan before it is performed.
Protocols exist to manage risk, primarily concerning pregnancy. Because a developing fetus is more sensitive to radiation, DEXA scans are generally avoided in individuals who are pregnant or who may be pregnant. Although the dose reaching the uterus is extremely low, medical practice avoids unnecessary exposure during this sensitive period. The technician confirms the patient’s status before proceeding with the examination.