Effect of intra-abdominal fat on the accuracy of DXA lumbar spine bone mineral density measurement using DXA body composition measurements

Doctoral thesis English OPEN
Darlington, Sarah Elizabeth
  • Subject: T1 | R1
    mesheuropmc: musculoskeletal system | musculoskeletal diseases

In the diagnosis of osteoporosis, dual-energy X-ray absorptiometry (DXA) is the accepted method for measuring bone mineral density (BMD) due to its good precision. However, accuracy is compromised by two assumptions: (1) the body is composed of only soft tissue and bone mineral and (2) the composition of tissue overlying bone is equal to that adjacent to bone. To diagnosis osteoporosis, BMD is compared to that of a young healthy population to calculate a T-score. BMD is normal if T-score>-1 and osteoporotic if < -2.5.\ud The aim of this study was to use DXA whole body (WB) scans to quantify variation in abdominal fat thickness and to explore whether this information could be used to improve the accuracy of lumbar spine (LS) BMD measurement. Relevant data were extracted from archived DXA images for groups of patients who had received both LS and WB scans.\ud LS BMD increased with the width of the associated soft tissue baseline and BMD was correlated with fat thickness within the baseline.\ud For individuals, the bone mineral equivalence of the difference in fat thickness between a standard width baseline and a region over the spine corresponded to a maximum T-score difference of 0.6. However, the average for the groups gave a T-score difference of 0.2.\ud The predicted inaccuracy in LS BMD measurement resulting from a non-uniform fat distribution was within 0.013 g/cm2 for groups and 0.017 g/cm2 for individuals. From these measurements, errors in BMD of up to 6% and 3% for a standard width baseline were observed for individuals and groups respectively.\ud In the majority of patients, errors introduced by a non-uniform distribution of fat are unlikely to cause a mis-diagnosis. However, significant errors may occur in certain individuals. The clinical application of the proposed method to quantify errors in BMD requires further investigation
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