Comparison of bone mineral density with dual energy x-ray absorptiometry, quantitative ultrasound and single energy x-ray absorptiometry

OBJECTIVE: We conducted this prospective study to establish the correlation between dual energy x-ray absorptiometry (DXA), quantitative ultrasound (QUS) and single energy x-ray absorptiometry (SXA) and to establish the role of QUS and SXA as a screening tool for osteoporosis.

METHODS: We carried out measurements of bone mineral density (BMD) of lumbar spine and femoral neck using DXA, QUS of heel using ultrasound densitometer, and BMD of forearm using SXA. We performed all the measurements at the Nuclear Medicine Division of King Khalid University Hospital, Riyadh, Kingdom of Saudi Arabia between 2002 and 2004. We obtained the measurements of 437 female adult patients, aged 20-87 years.

RESULTS: We expressed all the values as mean ± SD. The BMD (g/cm2) of lumbar spine was 1 ± 0.18, and femoral neck was 0.88 ± 0.17. The broad band ultrasound attenuation (BUA) of the heel was 74.9 ± 39.1 dB/MHz, the speed of sound (SOS) was 1542.5 ± 81.4 m/s, and the estimated BMD was 0.52 ± 0.15 (g/cm2). The BMD of forearm showed a value of 0.44 ± 0.10 g/cm2. The best correlation was between absolute values of BMD of lumbar spine and femoral neck (r=0.71, p=0.000). The correlation between BMD of lumbar spine, QUS heel and forearm BMD was significant, but low to moderate (r=0.43-0.64, p=0.000). A strong correlation existed between the various parameters of heel, namely, BUA, SOS and estimated BMD (r=0.85-0.96, p=0.000). We used the World Health Organization (WHO) criterion of T-score to diagnose the patients with osteoporosis or osteopenia with each modality. We diagnosed a maximum number of patients to have osteoporosis with BMD estimation of lumbar spine (31%), followed by femoral neck (14%), forearm (11%), and heel (6%).

CONCLUSION: The correlation between all modalities was significant, but varied from high to low. It was high between lumbar spine and femoral neck, moderate between lumbar spine and forearm and low between lumbar spine and QUS of heel. When we used the same WHO criterion of T-score (more than -2.5 SD below normal), QUS detected significantly less numbers with osteoporosis. We conclude that with the present cut-off of T-score, the QUS may not be used as a screening tool. It may need some modification of T-score. However, we need larger multi-center studies with a larger number of patients for further validation.