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Three major imaging modalities are commonly used for osteoporosis in the clinical setting: DXA, quantitative computed tomography (QCT), and calcaneal ultrasonography. DXA is the most commonly used. QCT measures the lumbar spine as well as peripheral sites. The results are less likely to be affected by degenerative spinal changes than PA spine DXA scanning. Also, unlike DXA, QCT allows for selective assessment of both cortical and trabecular bone. Trabecular bone, because of its higher rate of turnover compared with cortical bone, would be expected to show metabolic changes earlier. Its ability to enable prediction of spinal fracture, however, is equal to that of DXA scanning; the cost and level of radiation exposure are higher.

Deciding which bone imaging modality to use is not always easy.Vertebral fractures are of much greater concern than hip fractures in women who are younger than 65 years of age or within 15 years of menopause. Any of the imaging modalities may be appropriate, especially those that include imaging of the spine. In women older than 65 years, hip fractures become more of a concern, and degenerative spinal changesand aortic calcification are more prevalent. Thus, in this population, hip imaging, lateral spine DXA, and peripheral imaging (e.g., calcaneal ultrasonography) may be suitable alternatives. PA spinal DXA should be avoided.

QCT measures the lumbar spine as well as peripheral sites. The results are less likely to be affected by degenerative spinal changes than PA spine DXA scanning. Also, unlike DXA, QCT allows for selective assessment of both cortical and trabecular bone. Trabecular bone, because of its higher rate of turnover compared with cortical bone, would be expected to show metabolic changes earlier.

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