Chapter 29: DXA in Adults and Children Judith Adams and Nick Bishop

Table 1: Causes of Artefacts Resulting in Errors in DXA BMD a © 2008 American Society for Bone and Mineral Research From the Primer on the Metabolic Bone Diseases and Disorders of Mineral Metabolism, 7 th Edition.

Figure 1 Figure 1 (A) DXA of normal lumbar spine L1–L4. Results are generally expressed as a mean “areal” density (BMDa; g/cm2) for all four vertebrae. (B) DXA of left hip; although BMDa is provided in a number of different sites (femoral neck, oblong box; Ward’s area, small box; trochanter; and total hip), for clinical diagnosis of osteoporosis (WHO T-score at or below −2.5), femoral neck and total hip are used. © 2008 American Society for Bone and Mineral Research From the Primer on the Metabolic Bone Diseases and Disorders of Mineral Metabolism, 7 th Edition.

Figure 2 Figure 2 Whole body DXA (in a child) is obtained in 1 min on fan beam scanners and provides total and regional information about the skeleton (less head) and body composition (lean muscle and fat mass). © 2008 American Society for Bone and Mineral Research From the Primer on the Metabolic Bone Diseases and Disorders of Mineral Metabolism, 7 th Edition.

Figure 3 Figure 3 Artefacts on DXA. (A) Lumbar spine vertebral fracture of L1 and L3. BMD at these levels will be falsely elevated (same BMC as nonfractured vertebra but in a smaller projected area, giving higher apparent BMD). (B) Laminectomy L4. Removal of the laminae and spinous process will falsely reduce the BMD of this vertebra. DXA images must be carefully scrutinized for such artefacts, and affected vertebra should be excluded from analysis. A minimum of two vertebrae are required for classification/interpretation. © 2008 American Society for Bone and Mineral Research From the Primer on the Metabolic Bone Diseases and Disorders of Mineral Metabolism, 7 th Edition.

Figure 4 Figure 4 VFA can be made on DXA scanners on (A) single-energy and (B) dual-energy images (grade 3 severe crush fracture of T8) at much lower radiations doses (1/100th to 1/50th) than in conventional spinal radiographs; some of the thoracic vertebrae are better visualized on dual, than on single, energy images. Six-point morphometry (MXA) and visual assessment of the vertebrae can be made. Aortic calcification can also be visualized and graded. © 2008 American Society for Bone and Mineral Research From the Primer on the Metabolic Bone Diseases and Disorders of Mineral Metabolism, 7 th Edition.