The two most common bone density scanning techniques are quantitative ultrasound (sometimes referred to as QUS) and dual x-ray absorptiometry (also known as DEXA or DXA). The ultrasound technique is typically a heel scan and DEXA is usually a whole body scan.
When to Get a QUS Scan: The QUS bone scan is often considered to be a “first look” at bone density (BMD). Since it is simple and safe, it could be done most any time. Sometimes QUS is even offered at health fairs.
What It Shows: Bone density at the heel generally reflects the bone density in other parts of the body. However, if heel bone density is low, based on a QUS scan, it is important to consider getting a DEXA scan that measures other parts of the skeleton. QUS is often used for early detection even in younger individuals since it can catch serious problems early.
The Bottom Line: QUS serves as a convenient and less expensive quick bone density screening technique when compared to the DEXA technique.
When to Get a DEXA Scan: When a QUS scan indicates low bone density, a DEXA scan is usually the next reasonable step to take. Also, if you have specific risk factors, your healthcare professional may recommend a DEXA scan.
What It Shows: There are several different types of DEXA scanners. Consequently, the information produced can vary. They all provide bone density measurements and some provide more detail than others. The newer scanners often provide more detail at the most common fracture sites. DEXA is especially good for measuring bone density in the spine and hip, two common bone sites where fractures can be very painful and debilitating. Some whole body DEXA scans produce body composition data, so you can see how much of your body is lean mass and fat mass.
The Bottom Line: DEXA is the current “gold standard” for clinical bone density assessment. It is more expensive than QUS, but it can provide a great deal of valuable information about your bone status to help you make good decisions about prevention and/or treatment to avoid bone fractures caused by osteoporosis.
A Z-score of zero means that your BMD is the same as the average person like you. Unlike T-scores, Z-scores are not generally used to rank individuals for the diagnosis of osteopenia and osteoporosis.
Quantitative Ultrasound (QUS)
How It Works: Since QUS uses sound waves, there is virtually no risk. Most commonly, the scan is done at the heel. While sitting, you place your bare foot into a slot that fits the shape of a foot and relax for about a minute while the scan takes place.When to Get a QUS Scan: The QUS bone scan is often considered to be a “first look” at bone density (BMD). Since it is simple and safe, it could be done most any time. Sometimes QUS is even offered at health fairs.
What It Shows: Bone density at the heel generally reflects the bone density in other parts of the body. However, if heel bone density is low, based on a QUS scan, it is important to consider getting a DEXA scan that measures other parts of the skeleton. QUS is often used for early detection even in younger individuals since it can catch serious problems early.
The Bottom Line: QUS serves as a convenient and less expensive quick bone density screening technique when compared to the DEXA technique.
Dual X-ray Absorptiometry (DEXA)
How It Works: DEXA exposes the body to low level x-ray radiation that is much lower than conventional x-rays. To put this into perspective, DEXA exposes you to less x-ray radiation than an airline flight from New York to London. The scan is usually conducted with the patient in lying on their back. The scan can take 4 to 10 minutes if it is a whole body scan or as little as 30 seconds if the scan is just targeting a particular part of the body.When to Get a DEXA Scan: When a QUS scan indicates low bone density, a DEXA scan is usually the next reasonable step to take. Also, if you have specific risk factors, your healthcare professional may recommend a DEXA scan.
What It Shows: There are several different types of DEXA scanners. Consequently, the information produced can vary. They all provide bone density measurements and some provide more detail than others. The newer scanners often provide more detail at the most common fracture sites. DEXA is especially good for measuring bone density in the spine and hip, two common bone sites where fractures can be very painful and debilitating. Some whole body DEXA scans produce body composition data, so you can see how much of your body is lean mass and fat mass.
The Bottom Line: DEXA is the current “gold standard” for clinical bone density assessment. It is more expensive than QUS, but it can provide a great deal of valuable information about your bone status to help you make good decisions about prevention and/or treatment to avoid bone fractures caused by osteoporosis.
What Are Bone Mineral Density T-Scores and Z-scores?
T-Scores: Bone Mineral Density (BMD) measurements are typically expressed as T-scores. This is a technique used to compare your bone density to that of a young adult with normal bone density. The average young adult has a T-score of zero. A T-score greater than minus one is considered to be within the range of normal bone density.These T-scores are commonly used to rank bone density into three categories:
- Greater than -1 = normal BMD
- Between -1 and -2.5 = low BMD (osteopenia)
- -2.5 or lower = osteoporosis
A Z-score of zero means that your BMD is the same as the average person like you. Unlike T-scores, Z-scores are not generally used to rank individuals for the diagnosis of osteopenia and osteoporosis.