Type:
Educational Exhibit
Authors:
R. M. Lorente-Ramos, Y. del Valle-Sanz, F. J. Azpeitia-Armán, J. Acosta-Batlle; Madrid/ES
DOI:
10.1594/ecr2009/C-577
Background
DXA is the technique of choice in the assessment of bone mineral density (BMD).
The scanner consists of a low dose X-ray tube employing two different energies to separate mineral and soft tissue components and a high-resolution multi-detector array.
Devices may use two different systems: either a fan-beam emitting alternating high (140 kVp) and low (70-100 kVp) X- rays, which sweeps across a scan area, or a constant X-ray beam with a rare earth filter with energy-specific absorption, which separates photons of higher (70 KeV) and lower energy (40 KeV).
Understanding every step of the procedure is important.
Technical factor implies adequate patient positioning, and including in the study the complete region of interest.
Once the correct imaging is achieved, care should be taken on analysis. ROI placement should be careful and artefacts should be detected in order to exclude them from the ROI.
Interpretation is the last step. The scanner calculates bone mineral density (BMD) in grams per square centimetre (g/cm2). Comparing with reference database, values and curves are obtained: Z-score (comparing with healthy population of the same ethnicity, sex, and age) and T-score (comparing with young adults of the same ethnicity and age). The diagnosis of osteoporosis according to WHO (World Health Organization) is based on the number of SD (standard deviation) values that the patient´s BMD value differs from the mean BMD of a young-adult reference population (T-score).
Artifacts should also be stated in the report, as they may be due to disorders previously diagnosed or that require further exams.