Terminology	Acronym	Definition
Areal bone mineral density	aBMD	DXA calculates BMD using area. This is not an accurate measurement of the true bone mineral density, which is mass divided by volume. It is a reasonable estimate of BMC.
Bone mineral content	BMC	DXA measures the BMC of the spine, hip, wrist, femur, or any other selected part of the skeleton. It does this by focusing an x-ray on a body site and measuring the proportion of light rays that pass through the tissue as opposed to being blocked by minerals in the bone. Using computer software, it then divides that number by the surface area of the bone being measured to create BMD.
Bone mineral density	BMD	BMD refers to the amount of mineral matter per square centimeter of bone. BMD is used as a predictor of osteoporosis and fracture risk.
Computed tomography	CT	CT is an imaging procedure that uses special x-ray equipment to create a series of detailed pictures, or scans, of areas inside the body. It is also called computerized tomography and computerized axial tomography (CAT) scanning.
Cross-sectional moment of inertia	CSMI	CSMI is a measure of the distribution of material around a given axis. It is used to calculate bending stress.
Dual-energy x-ray absorptiometry	DXA	DXA is a means of measuring BMD. It is the most widely used and most thoroughly studied bone density measurement technology. Two x-ray beams with different energy levels are aimed at the patient’s bones. When soft tissue absorption is subtracted out, the BMD can be determined from the absorption of each beam by bone.
Hip structural analysis	HSA	HSA measures not only the BMD of the hip bone but also structural geometry of cross-sections traversing the proximal femur at specific locations. The bone mass image is used directly from the DXA scan, where pixel values are expressed in areal mass (g/cm2). The method employs the principle that a line of pixel values across the bone axis corresponds to a cut plane traversing the bone at that location and contains some of the information about the cross-section.
Percentage of undercarboxylated osteocalcin	%ucOC	%ucOC is a measure of vitamin K status. Osteocalcin is a vitamin K-dependent protein produced by the bone. The ratio of undercarboxylated to carboxylated or total osteocalcin has been regarded as a marker of inadequate vitamin K status.
Peripheral quantitative computed tomography	pQCT	pQCT is a type of quantitative CT used for making measurements of the BMD in a peripheral part of the body, such as the forearms or legs, as opposed to CT that measures BMD at the hip and spine. pQCT is useful for measuring bone strength.
Potential renal acid load	PRAL	PRAL is a measure of the acidic or basic effects that a food has on the body.
Quantitative computed tomography	QCT	QCT measures BMD using a standard CT scanner with a calibration standard to convert Hounsfield units (HU) of the CT image to BMD values. QCT scans are primarily used to evaluate BMD at the lumbar spine and hip.
Stress–strain index	SSI	The SSI of a bone is a surrogate measure of bone strength determined from a cross-sectional scan by QCT or pQCT. The SSI is used to compare the structural parameters determined by analysis of QCT/pQCT cross-sectional scans to the results of a three-point bending test.
Volumetric bone mineral density	vBMD	In addition to aBMD using DXA, a projected posteroanterior lateral vertebral scan is added to measure vertebral width, height, and depth to estimate vBMD. This permits direct measurement of bone depth, rather than estimation of projected posteroanterior dimensions.