Peripheral quantitative computed tomography (pQCT) and dual energy x-ray absorptiometry (DXA) are fundamental imaging technologies in the assessment of bone in children and adolescents. However, they may both produce misleading outcomes, particularly in growing subjects. The goal of this thesis is to quantify and minimize the shortcomings of pQCT and DXA. We have isolated factors that lead to potential errors in pQCT and DXA, offered corrections for those errors or alternative measures, and introduced an automated MRI (magnetic resonance imaging) bone feature extraction program.

A major limitation of pQCT measurements arises from scan positioning in metaphyseal density determinations. Due to a considerable gradient of cancellous bone in the region, the density reported by a conventional single slice is dependent on the location of the scan and may not come from the same exact anatomical site in different individuals or over time. As a result, interpretation of these data may be difficult. We have presented a method to measure the gradient of cancellous bone with pQCT and obtain overall measures of cancellous bone such as average density.

DXA’s limitations are a product of its two-dimensional design. To derive bone measures, it assumes a homogeneous soft-tissue distribution, which leads to errors when the distribution is actually inhomogeneous. In addition, the inclusion of the vertebral posterior elements in anterior-posterior projections of the spine may misrepresent actual spine strength, which is usually associated with the vertebral body. These two factors impact DXA bone measures and may lead to recommendations that deviate analogous outcomes from QCT (quantitative computed tomography), a three-dimensional modality. In a series of three studies, we have investigated the extent of the error due to these limitations, and attempted to reduce those errors.

Lastly, we explore the possibility of extracting bone features with MRI. Since MRI does not use ionizing radiation, it would be advantageous to use in lieu of QCT or pQCT. However, since bone suffers poor contrast in MRI, manual tracing or semiautomatic methods are usually required. To reduce operator error and improve efficiency, we have designed a fully automatic program and compared its results with established QCT methods.