Effect of porosity, tissue density, and mechanical properties on radial sound speed in human cortical bone

Purpose: The purpose of this study was to investigate the effect of simultaneous changes in cortical porosity, tissue mineral density, and elastic properties on radial speed of sound (SOS) in cortical bone. The authors applied quantitative pulse-echo (PE) ultrasound techniques that hold much potential especially for screening of osteoporosis at primary healthcare facilities. Currently, most PE measurements of cortical thickness, a well-known indicator of fracture risk, use a predefined estimate for SOS in bone to calculate thickness. Due to variation of cortical bone porosity, the use of a constant SOS value propagates to an unknown error in cortical thickness assessment by PE ultrasound. Methods: The authors conducted 2.25 and 5.00 MHz focused PE ultrasound time of flight measurements on femoral diaphyses of 18 cadavers in vitro. Cortical porosities of the samples were determined using microcomputed tomography and related to SOS in the samples. Additionally, the effect of cortical bone porosity and mechanical properties of the calcified matrix on SOS was investigated using numerical finite difference time domain simulations. Results: Both experimental measurements and simulations demonstrated significant negative correlation between radial SOS and cortical porosity (R ≥ 0.493, p < 0.01 and R ≥ 0.989, p < 0.01, respectively). When a constant SOS was assumed for cortical bone, the error due to variation of cortical bone porosity (4.9%-16.4%) was about 6% in the cortical thickness assessment in vitro. Conclusions: Use of a predefined, constant value for radial SOS in cortical bone, i.e., neglecting the effect of measured variation in cortical porosity, propagated to an error of 6% in cortical thickness. This error can be critical as characteristic cortical thinning of 1.10% ± 1.06% per yr decreases bending strength of the distal radius and results in increased fragility in postmenopausal women. Provided that the cortical porosity can be estimated in vivo, the relationship between radial SOS and cortical porosity can be utilized and a porosity based radial SOS estimate could be implemented to determine cortical thickness. This would constitute a step toward individualized quantitative ultrasound diagnostics of osteoporosis

Long-term dietary exposure to lead in young children living in different European countries. Scientific report submitted to EFSA

Long-term dietary exposure to lead in children aged 1 up to 14 years living in 12 different European countries was estimated using daily food consumption patterns and mean lead concentrations in various food commodities. Food consumption data were all categorised according to a harmonised system to allow for linkage with lead concentration data in a standardised way. Two different models were used for the calculations: the beta-binomial-normal (BBN) model and the observed individual means (OIM) model. For both models the lower bound exposure ranged from 0.4 to 1.7 µg/kg bw per day for median consumers. For 99th percentile consumers however the exposure differed between the two models with a lower bound exposure ranging from 0.7 to 4.1 µg/kg bw per day with the BBN model and 0.9 to 7.9 µg/kg bw per day with the OIM model. Upper bound exposures were on average a factor 1.8 higher for both models. Exposures on a body weight basis were higher in younger compared to older children. To assess the long-term exposure to lead in European children, a model, such as the BBN model, that corrects for the within-person variation is the preferred method to be used. The OIM method results in an overestimation of the percentage of the population exceeding a provisional tolerable weekly intake which is of relevance for risk management decisions