Dual energy X-ray absorptiometry is also an accurate and precise method to measure the dimensions of human long bones

The accuracy, as well as the in vitro and in vivo precision of width and length measurements of human humerus and femur from dual energy X-ray absorptiometry (DXA) images, was investigated. The measurement was based on the bone area inside a specified region determined by the bone edge detection software of the scanner. The accuracy and in vitro precision studies were performed using a bone-simulating aluminum phantom embedded in different amounts of water. The in vivo precision was determined by measuring both limbs twice in 10 subjects (for humerus) and in 9 subjects (for femur). The accuracy was not significantly affected by the amount of water, and varied from 0.6 to 1.2%. Similarly, the in vitro precision varied from 0.4 to 0.6%. The average in vivo precision of the width measurement ranged from 0.4% (humeral and femoral midshaft) to 0.9% (proximal humerus), not depending on the size of the measured bone. The precision of the length measurement was 0.3% for the humerus and 3.7% for the femoral neck. In conclusion, the standard DXA technique provides a reliable measurement of the width and length in human humerus and femur in vivo, and thus may be useful in evaluating the properties of these bones in conjunction with the standard bone mineral measurements. Specifically, studies evaluating the effects of various types of mechanical loading (exercise) on bone may greatly benefit from this possibility because not only the bone mineral content and density but also the bone geometry change due to loading.