PubMed · 16360773
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Ignac Fogelman, Glen M Blake. 2005-12-17. Bone densitometry: an update.. https://doi.org/10.1016/s0140-6736(05)67867-1
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In clinical research, it is often of interest to estimate the response rate (i.e. the proportion of subjects who achieve a clinically meaningful threshold) for a particular variable. The standard estimator of the response rate is generally biased in the presence of measurement error. The estimation accounting for the measurement error utilizing fully nonparametric (NP) methods is complicated and may not be efficient. Therefore, we propose a model-based approach assuming a parametric model for the true value and only the first few moments for the measurement error. The estimator for the true response rate and the variance for the estimator are derived. An innovative method using bootstrap simulation is proposed to check the model assumption. Simulations show that the proposed estimator outperforms a fully NP estimator if the model assumption for X holds. This method is applied to address a commonly occurring question in osteoporosis regarding response to treatment in terms of longitudinal changes in bone mineral density (BMD). Bootstrap simulations showed that the model utilized is appropriate. The proposed method can also be applied in other fields of clinical research.
PURPOSE: To investigate the use of quantitative computed tomography (QCT) and dual energy absorptiometry (DXA) for assessing bone mineral density (BMD) in the evaluation of children with malignant infantile osteopetrosis (MIOP). METHODS AND PATIENTS: We retrospectively reviewed QCT- and DXA-determined BMD in six patients with infantile osteopetrosis and correlated BMD measured during the initial evaluation with patient characteristics. RESULTS: Five male and one female infant met the eligibility criteria. BMD was markedly elevated in all patients as determined by each modality, QCT or DXA. For QCT, in which age-specific normal values are known, the BMD was found to be 22.4-32.6 standard deviations above the mean. Using DXA, the estimated BMD of the lumbar spine ranged from 0.45 to 0.8 g/cm(2); children with similarly appearing bone radiographs had quite disparate BMD. While the qualitative trend of BMD among the patients was similar for both measures, the units and numerical values of BMD differed. We found no correlation between BMD results and hematopoiesis observed in the bone marrow or with visual evaluation of the radiographs. CONCLUSION: Both QCT and DXA are effective quantitative measures of BMD in children with MIOP. However, the same modality should be employed for longitudinal evaluation of a given patient. Each technique has unique advantages and disadvantages and may complement one another in the evaluation of MIOP or other bone disorders. Quantitative assessment of BMD in children with MIOP will likely serve to further characterize this disease.
Iron L-edge, iron K-edge, and sulfur K-edge X-ray absorption spectroscopy was performed on a series of compounds [Fe(III)H(3)buea(X)](n-) (X = S(2-), O(2-), OH(-)). The experimentally determined electronic structures were used to correlate to density functional theory calculations. Calculations supported by the data were then used to compare the metal-ligand bonding and to evaluate the effects of H-bonding in Fe(III)(-)O vs Fe(III)(-)S complexes. It was found that the Fe(III)(-)O bond, while less covalent, is stronger than the Fe(III)(-)S bond. This dominantly reflects the larger ionic contribution to the Fe(III)(-)O bond. The H-bonding energy (for three H-bonds) was estimated to be -25 kcal/mol for the oxo as compared to -12 kcal/mol for the sulfide ligand. This difference is attributed to the larger charge density on the oxo ligand resulting from the lower covalency of the Fe-O bond. These results were extended to consider an Fe(IV)(-)O complex with the same ligand environment. It was found that hydrogen bonding to Fe(IV)(-)O is less energetically favorable than that to Fe(III)(-)O, which reflects the highly covalent nature of the Fe(IV)(-)O bond.