ARRT Bone Densitometry key terms

Imaging method that acquires two x-ray beams of different energies and uses the difference in attenuation to separate bone mineral from soft tissue, producing areal bone mineral density images.

A metal filter, commonly cerium or samarium, placed in the x-ray beam to shape the spectrum into distinct low- and high-energy peaks so the system can make two separable attenuation measurements.

Scanner design in which x-rays spread from the source to a multi-element detector array so an entire line is captured at once; faster scanning with higher resolution but slightly more dose.

Scanner design using a narrow collimated beam and a single detector that sweep across the patient line by line; produces less scatter and lower dose, but scan times are longer.

The row of detector elements that measures how much of the x-ray beam passes through the patient and converts it into the counts used to build the density image.

Compact densitometer that measures sites such as the heel, forearm or finger; used mainly for risk assessment, while central spine and hip measurements remain standard for diagnosis and monitoring.

Method that sends ultrasound through bone, usually the heel, and measures speed of sound and attenuation to estimate fracture risk without ionizing radiation; not used for diagnosis or monitoring.

Bone mineral content divided by the two-dimensional projected area of the measured region, reported in grams per square centimeter; it does not correct for bone thickness or depth.

The total mineral mass inside a measured region, reported in grams, before it is divided by that region's projected area to give bone mineral density.

The number of standard deviations a patient's bone mineral density lies above or below the mean of a young, healthy, sex-matched reference population; the basis for diagnosing osteoporosis.

The number of standard deviations a patient's bone mineral density differs from the mean of an age-, sex-, and ethnicity-matched reference group; preferred for children, premenopausal women and young men.

The outlined area on a scan in which density is measured; correct size and placement, especially at the hip, strongly influence the reported value and its reproducibility.

Software that automatically finds bone edges and places regions of interest on a scan; the technologist must review the result and correct it when placement is wrong.

The standard lumbar spine measurement, reported as the average of at least two evaluable vertebrae; vertebrae with fracture, surgery or artifact may be excluded from the average.

A hip region of interest combining the femoral neck, trochanter and intertrochanteric area; it is often the preferred site for following change in bone density over time.

The hip region of interest in the narrow area just below the femoral head; its measurement is sensitive to leg rotation and to how the software draws the neck box.

A low-density area in the proximal femur displayed by older hip analysis software; it is no longer recommended for diagnosing osteoporosis or for monitoring patients.

A forearm site one-third of the way from the wrist to the elbow, made mostly of cortical bone; measured when the spine and hip cannot be scanned or evaluated.

A lateral spine image made on a densitometer and reviewed for vertebral compression deformities, adding fracture information to the bone density result.

A texture measurement calculated from the lumbar spine scan that reflects trabecular microarchitecture and can refine fracture risk estimates beyond bone mineral density alone.

Any material on or in the patient, such as metal hardware, contrast, buttons or calcification, that changes x-ray attenuation and can falsely raise or lower the measured density.

Removing a vertebra or region from analysis when artifact or fracture makes its measurement unreliable, while still reporting the minimum number of valid sites required.

Stored bone density values from a defined population, built into the software, that convert a patient's raw measurement into T-scores and Z-scores.

Placing the patient on the table with correct spine alignment or leg rotation, and removing interfering objects, so regions of interest are placed accurately and repeat scans match.

Extra counts from a recent nuclear medicine study can distort a density scan; scanning is usually postponed, or the affected site avoided, until the radioactivity has cleared.

The principle of keeping radiation exposure as low as reasonably achievable while still obtaining the needed information; density scans use very low doses but are still minimized.

Explaining why the scan is done, how it works, its very low radiation dose, and what the patient must do, so the patient is comfortable and cooperates during the examination.

Asking patients of childbearing age whether they may be pregnant before any scanning begins, because densitometry uses ionizing radiation even at low dose.

The smallest difference between two bone density measurements that is likely to be a real change rather than measurement error, calculated from the site's precision at a chosen confidence level.

How closely repeated measurements of the same person or phantom agree; expressed as a standard deviation or coefficient of variation and used to determine the least significant change.

The standard deviation of repeated measurements divided by their mean and multiplied by 100, giving precision as a percentage that can be compared across sites and machines.

A manufactured object with stable, known attenuation that is scanned on a regular schedule to confirm the densitometer is still measuring consistently.

A graph of quality control results over time with lines at the mean and at two and three standard deviations, used to spot shifts, gradual drift and outliers.

Scanning the manufacturer's phantom at the start of each working day and comparing the results with established limits before any patient is scanned.

Repeating scans on the same people and calculating the standard deviation and least significant change for each technologist and site; needed to judge whether follow-up changes are real.

Scheduled service by qualified personnel, plus calibration checks confirming that measured attenuation still corresponds to known density values, keeping the system within specification.

Comparing measurements from two densitometers, or from before and after a major service, to establish a conversion so serial results from different systems can be interpreted together.

The standard file format and network protocol used to send scan images and reports from the densitometer to the picture archiving system and to referring physicians.