Evaluation of osteoporosis using CT image of proximal femur compared with dual energy x-ray absorptiometry (DXA) as the standard

Osteoporosis is a disorder of bone that leads to an increased risk of fracture, when it loses an excessive amount of mineral compositions. Bone densitometry techniques are useful to diagnose the disease as well as to predict the future risk of fracture. Dual energy x-ray absorptiometry (DXA) is currently considered as the `gold' standard for measuring areal bone mineral density, BMD (gcm
^-2
). Quantitative computed tomography (QCT) is used to measure volumetric BMD (g cm
^-3
) at lumbar spine using a phantom with a dedicated software; but it cannot be used to measure femur volumetric BMD. The aim of this study was to estimate apparent physical BMD (Est-vol. BMD, g cm
^-3
) of the proximal femur from CT image with good accuracy in the evaluation of post-menopausal osteoporosis. A total number of 50 Indian women, age ranged from 20-80 years were studied. No one had previous osteoporotic fractures. Each woman, the following investigations were carried out: i) BMD of the right proximal femur by DXA whole-body bone densitometer and ii) CT image of the right proximal femur. WHO's diagnostic criteria based on the measured femur neck BMD was used to classify the patients. According to this, total women were divided into the following groups: i) Normal (n=23, mean ± SD age = 42.8 ±11.1 years) ii) Osteopenia (n= 17, mean ± SD age = 49.6 ±12.5 years) and iii) Osteoporosis (n=10, mean ± SD age = 69.2 ±12.7 years) The CT image was analysed by Materialise's interactive medical image control system (MIMICS) software. Hounsfield Unit (HU) was measured in the regions of the proximal femur: i) Neck ii) Trochanter, iii) Head and iv) Shaft Using the measured mean HU value, Est-vol. BMD (g cm
^-3
) was estimated. Data was analysed by SPSS statistical software package. In osteoporotic Indian women group (n=10), the Est-vol. BMD (g cm
^-3
) of femur neck was correlated statistically significant (p=0.05) with BMD-DXA (g cm
^-2
) of all ROI's of the proximal femur, viz., femur neck, Ward's triangle, trochanter, femur shaft, and total hip. The obtained square of the correlation coefficients (r
²
) were 0.22, 0.25, 0.23, 0.41, and 0.34 respectively. In osteoporotic women, the mean values of BMD-DXA (g cm
^-2
) and Est-vol. BMD (g cm
^-3
) of femur neck were significantly (p=0.01) reduced by 36.7% and 71.8% respectively, when comparing to normal healthy women. Further, in osteoporotic women, the mean values of BMD-DXA as well as Est-vol. BMD of trochanter were significantly (p=0.01) reduced by 45.7% and 80.2% respectively, when comparing to normal healthy women. It was found that the percentage decrease in Est-vol. BMD was greater in osteoporotic women than the measured BMD-DXA, and it can be useful in the evaluation of the disease.