ISCD CBDT key terms

Bone mineral content divided by the projected two-dimensional bone area measured by DXA, expressed in g/cm². It is not a true volumetric density, so results are influenced by bone size and patient thickness.

The total mass of mineral within the region scanned, expressed in grams. Software derives it from differential X-ray attenuation, and it is used to calculate areal bone mineral density when divided by area.

The number of standard deviations a patient's bone mineral density lies above or below the mean of a young adult reference population of the same sex. The World Health Organization diagnostic thresholds are applied to this value.

The number of standard deviations a patient's bone mineral density lies above or below the mean of an age-, sex-, and usually ethnicity-matched reference population. Values of −2.0 or lower prompt evaluation for secondary causes.

A skeletal disorder of compromised bone strength that increases fracture risk. Clinically it is defined by a T-score of −2.5 or lower at a validated site or by the occurrence of a low-trauma fragility fracture.

Bone mineral density that is below the young adult reference mean but not low enough for osteoporosis, conventionally a T-score between −1.0 and −2.5. It signals increased fracture risk and warrants attention to modifiable factors.

A fracture resulting from a fall from standing height or less, or from trauma that would not normally break healthy bone. Its presence can establish a diagnosis of osteoporosis regardless of the measured density.

A validated risk-assessment algorithm that estimates the ten-year probability of major osteoporotic fracture and hip fracture from clinical risk factors, with or without bone mineral density. It guides treatment decisions beyond density alone.

Dual-energy X-ray absorptiometry of the spine, hip, or forearm used for diagnosis and monitoring. It is the standard technique for osteoporosis diagnosis because those sites are validated against fracture outcomes.

Dual-energy X-ray absorptiometry of sites such as the heel, wrist, or finger using compact devices. Results are useful for screening and risk prediction but cannot be used with the World Health Organization diagnostic T-score criteria.

An imaging method that acquires two X-ray spectra of differing energies and uses the difference in attenuation to separate bone mineral from soft tissue. It provides low-dose, high-precision bone density measurement.

Interaction in which an X-ray photon transfers all its energy to a bound inner-shell electron, producing strong attenuation that rises sharply at lower photon energies. It dominates bone attenuation at the low-energy DXA beam.

Interaction in which a photon transfers part of its energy to an electron and is deflected. Its probability depends mainly on electron density and changes little with photon energy, so it dominates soft-tissue attenuation at the higher DXA beam energy.

A defined area on the scan image within which bone mineral content and area are measured. Correct placement, such as excluding osteophytes or metal, is essential for accurate and comparable results.

The standard central DXA site that averages bone mineral density across the first through fourth lumbar vertebrae. Vertebrae with focal structural changes or artifacts are excluded, and at least two evaluable vertebrae are required.

A central DXA site comprising the femoral neck, trochanter, and intertrochanteric region of one hip. The total hip or femoral neck value is used for diagnosis, and the same hip should be scanned on follow-up.

A subregion of the proximal femur DXA scan used for diagnosis and fracture-risk prediction. Its relatively thin cortical bone makes precise repositioning important for reproducible monitoring.

A peripheral DXA site on the distal forearm used when the spine and hip cannot be measured or interpreted. It is also useful in hyperparathyroidism and in patients with very large body size.

The normative data set, matched for sex and usually ethnicity, from which T-scores and Z-scores are calculated. Using an inappropriate or mismatched reference population can misclassify a patient's risk category.

True three-dimensional bone density in mg/cm³, estimated by techniques such as quantitative computed tomography or by correcting DXA for bone size. It is less affected by body and bone thickness than areal density.

A three-dimensional technique that measures volumetric bone density, typically of the lumbar spine, using a calibration phantom. It separates trabecular from cortical bone but delivers a higher radiation dose than DXA.

A texture index derived from lumbar spine DXA images that reflects trabecular microarchitecture independently of density. Lower values indicate degraded structure and add fracture-risk information to bone mineral density.

The smallest difference between two measurements that exceeds measurement error at a chosen confidence level, usually 95 percent. A change must exceed this value to be considered real rather than technical variation.

The closeness of repeated measurements of the same quantity under unchanged conditions. It is expressed as a coefficient of variation and determines whether a change over time is meaningful.

The standard deviation of repeated measurements divided by their mean, usually expressed as a percentage. It is the standard way to report precision for bone density measurements.

A formal study in which a technologist scans volunteers or patients repeatedly to calculate that operator's measurement error. It must be performed before monitoring patients and repeated after major hardware or software changes.

A manufactured object with known or stable attenuation properties used to calibrate a densitometer and verify its performance over time. Regular scanning detects drift before it affects patient results.

The routine scanning and evaluation of a phantom to confirm that a densitometer is stable and operating within acceptable limits. Trends or abrupt shifts trigger investigation and service before clinical results are compromised.

The process of adjusting or verifying instrument output against a known standard so that measured attenuation correctly maps to bone mineral values. It underpins comparability between scans and between systems.

Any feature on a scan that is not true patient anatomy and that alters the measured density, such as metal hardware, contrast material, or external objects. Recognition and correction or exclusion are required before interpretation.

Findings that make a vertebra uninterpretable for diagnostic density measurement, including fracture, focal sclerosis, laminectomy, or overlying hardware. Excluded vertebrae are omitted and the remaining evaluable vertebrae are averaged.

The use of whole-body DXA to estimate total and regional fat mass and lean soft-tissue mass. It requires specific software and attention to patient positioning and scan boundaries.

A radiation-protection quantity that reflects the overall risk from a partial or whole-body exposure, expressed in sieverts. A central DXA scan delivers a very small effective dose compared with most radiological procedures.

X-rays deflected from their original path within the patient or room, contributing to occupational exposure. Shielding, distance, and collimation reduce dose to the technologist.

The two major manufacturers of clinical densitometers, whose systems differ in reference databases, calibration, and analysis conventions. Results from different manufacturers are not directly interchangeable for monitoring.

The professional who positions patients, acquires and analyzes scans, performs quality control and precision testing, and communicates results within scope of practice. Certification demonstrates competence in these tasks.

The acquisition setting that determines beam width and speed according to patient thickness and body size. Choosing the wrong mode degrades image quality and accuracy, especially in very thin or obese patients.