Bone mineral density measurement in children and adolescents
The clinical assessment of bone strength and fracture risk as well in children as in adults has always been a difficult challenge for its practical solution. The reason for that seems to be matter of both – focus and target. The problem concerns not only how or how well to measure, but essentially what to measure, and mostly how to interpret the data. The additional special challenge is interpretation of children’s data, what is related to the fact that bone mineral accrual throughout childhood and adolescence involves changes in bone size, geometry, and mineral content. The processes evolve at varying rates in different regions of the skeleton, with appendicular growth preceding spinal mineral acquisition. Trabecular and cortical compartments respond variably to sex steroids, calcium intake, and mechanical loading. The tempo of mineral accrual is more closely linked to pubertal and skeletal maturation than to chronological age, and these processes vary with gender and ethnicity. Additional problem is related to limited access to pediatric reference data.
Dual-Energy X-Ray Absorptiometry (DXA)
The most commonly used technique for the assessment of bone mineral content has became densitometric measurement with the use of DXA. DXA measurements are performed in the lumbar spine, femurs, forearms, and the whole body. Principle of operation of DXA measurement relies on the fact that when X-ray beam scans across the region of interest, bone attenuates the passing energy. The differences in relative attenuation are calculated and expressed as bone mineral content (BMC) in grams. Later on BMC values became divided by the projected area of the bones analyzed, referred conventionally as BMD and expressed as grams per square centimeter. Limitation is that referred as areal density DXA does not represent a volumetric density measurement. Additionally DXA cannot eliminate cancellous from cortical bone, and the resulting values reflect as the sum of both components. Beside substantial differences, a remarkable increase in BMD is observed in both sexes after the onset of puberty reaching a peak at approximately the time of cessation of longitudinal growth and epiphyseal closure. Source your medication needs online. Generic viagra online pharmacy
Quantitative Computed Tomography (QCT)
QCT is an established technique for measuring BMD in the axial and appendicular skeleton. CT image is formed by three dimensional voxels, which are small squares of different optical density depending on the tissue they represent. Unfortunately, beside significant irradiation, in small or sick children the size of cancellous and cortical bone is frequently smaller than the voxel size, therefore, not only bone but also marrow can be represented. The recent application of QCT to assess the appendicular skeleton as pQCT has significantly dropped potential irradiation and improved the ability to measure cortical bone in this area. By this means it can be measured: the cross-sectional area (cm2), bone geometry, and the cortical bone density. Results expressed as grams per cubic centimeter (vBMD) beside being true volumetric measurements are providing with information about bone geometry what allow to calculate noninvasively (using special algorithm) so called Strength-Strain Index (SSI). The SSI has been shown to provide a good estimate of bone mechanical strength at least of the human radius and tibia.