Dual-energy CT hybridation and kernel processing effects on the estimation of bone mineral mass and density: a calcination study on ex vivo human femur.

INTRODUCTION: Recent technological advances with dual-energy quantitative computed tomography (DEQCT) allow to combine two images of different level of energy to obtain simulated mono-energetic images at 60 keV (SIM60KeV-QCT) with improved image contrast in clinical practice. This study includes three topics: (1) compare bone mineral content (BMC), areal and volumetric bone mineral density (aBMD, vBMD) obtained with SIM60KeV-QCT, single-energy QCT (SEQCT), and dual X-ray absorptiometry (DXA); (2) compare ash density and weight with respective vBMD and BMC assessed on SIM60KeV-QCT, SEQCT, and DXA; and (3) compare the influence of reconstruction kernels on the accuracy of vBMD and BMC using ash density and ash weight as the reference values. METHODS: DXA, SEQCT, and DEQCT acquisitions were performed ex vivo on 42 human femurs. Standard kernel (SK) and bone kernel (BK) were applied to each stack of images. Ten diaphyses and 10 femoral necks were cut, scanned, and reconstructed using the techniques described above. Finally, the bone specimens were calcined to obtain the ash weight. RESULTS: QCT analysis (SEQCT, SIM60KeV-QCT) underestimated BMC value compared to DXA. For femoral necks, all QCT analyses provided an unbiased estimate of ash weight but underestimated ash density regardless of the kernel used. For femoral diaphysis, SEQCT BK, SIM60KeV-QCT BK, and SK underestimated ash weight but not ash density. CONCLUSION: BMC and vBMD quantifications with the SIM60KeV-QCT gave similar results as the SEQCT. Further studies are needed to optimize the use of SIM60KeV-QCT in clinical situations. SK should be used given the effect of kernels on QCT assessment.

Mechanical behaviour of the in vivo paediatric and adult trunk during respiratory physiotherapy.

The load-deflection response of the human trunk has been studied using various methods. The different shapes observed may be due to the methodology and the population. The purpose of this study is to quantify and explain the in vivo mechanical response of paediatric and adult trunks during respiratory physiotherapy. Eight children aged 5-15 months and eight healthy adult volunteers aged 30-87 years participated in this study. The force applied by the physiotherapist and the displacement of the targets on his hands were recorded. Parameters were also measured and calculated to compare against other studies. Time lags between force time histories and displacement time histories were observed on both children and adults. Different time lags resulted in different shapes of the force-displacement curves. Factors including respiration, muscle contraction and loading pattern are part of the assumptions used to explain this phenomenon. The maximum displacements of the paediatric and adult trunks were 18 and 44 mm, respectively, with a maximum load of 208 and 250 N, respectively. This study provides a better explanation of the peculiar force-displacement characteristics of both living and active children and adults under a non-injurious, low-rate compression condition. Complementary data (e.g. muscle activity and breathing) should be collected in the future to go towards in vivo human trunk modelling.

In vivo analysis of thoracic mechanical response variability under belt loading: specific behavior and relationship to age, gender and body mass index.

Thoracic injuries are a major cause of mortality in frontal collisions, especially for elderly female and obese people. Car occupant individual characteristics like age, gender and Body Mass Index (BMI) are known to influence human vulnerability tolerance in crashes. The objective of the this study was to perform in vivo test experiments to quantify the influence of subject characteristics in terms of age, gender and anthropometry and on thorax mechanical response variability under belt loading. Thirty-nine relaxed volunteers of different anthropometries, genders and age were submitted to non-injurious sled tests (4 g, 8 km/h) with a sled buck representing the environment of a front passenger restrained by a 3-point belt. A resulting shoulder belt force FRes was computed using the external and internal shoulder belt loads and considering shoulder belt geometry. The mid sternal deflection D was calculated as the distance variation between markers placed at mid-sternum and at the 7th vertebra spinous process of the subject. Linear stiffness (K) and damping coefficient (µ) of a spring-dashpot model were identified from the FRes-D curves of each test. The analysis suggests that among subjects over 40 years old, thinness leads to higher K-values.

In-vivo analysis of thoracic mechanical response under belt loading: the role of body mass index in thorax stiffness.

Thoracic injuries are a major cause of mortality in frontal collisions, especially for elderly and obese people. Car occupant individual characteristics like BMI are known to influence human vulnerability in crashes. In the present study, thoracic mechanical response of volunteers quantified by optical method was linked to individual characteristics. 13 relaxed volunteers of different anthropometries, genders and age were submitted to non-injurious sled tests (4 g, 8 km/h) with a sled buck representing the environment of a front passenger restrained by a 3-point belt. A resulting shoulder belt force was computed using the external and internal shoulder belt loads and considering shoulder belt geometry. The mid sternal deflection was calculated as the distance variation between markers placed at mid-sternum and the 7th vertebra spinous process of the subject. Force-deflection curves were constructed using resulting shoulder belt force and midsternal deflection. Average maximum chest compression was 7.9±2.3% and no significant difference was observed between overweight subjects (BMI≥25 kg/m²) and normal subject (BMI<25 kg/m²). The overweight subjects exhibited significantly greater resultant belt forces than normal subjects (715±132 N vs. 527±111 N, p<0.05), higher effective stiffness (30.9±10.6N/mm vs. 19.6±8.9 N/mm, p<0.05) and lower dynamic stiffness (42.7±8.71 N/mm vs. 61.7±15.5 N/mm, p<0.05).

The mechanics of the in vivo infant and toddler trunk during respiratory physiotherapy.

BACKGROUND: The purpose of this study is to quantify the in vivo mechanical response of the child trunk under loading during physiotherapy treatments. METHODS: Twenty-six children aged 45 days to 7 years (14 girls and 12 boys) took part in this study. The forces applied by the physiotherapist were recorded using a force-plate embedded in the manipulation table supporting the child. Two synchronized cameras filmed the scene in a calibrated environment. The displacement of reflective targets glued on the physiotherapist's hands was calculated using an automatic tracking procedure and the 3D reconstruction "Direct Linear Transformation" algorithm. The progression of physical parameters was evaluated according to the age of the child. They included force, displacement, normalized displacement, loading speed, displacement and normalized displacement at the maximum force, force at the maximum displacement, viscous criterion and effective stiffness. FINDINGS: For all patients, the mean maximum displacement and load were 22 mm (SD 9 mm) and 240 N (SD 46 N) respectively. The force-displacement curves had shown the complexity of the in vivo behavior: four phases have been distinguished with cycles in respect with the respiratory phases. The increase in force always occurred before the increase in displacement. INTERPRETATION: This study helps to understand the in vivo behavior of the child trunk subjected to repetitive non-injurious mechanical loading. Further analysis in other populations and with different therapeutic maneuvers would refine the results.

Comparison of Hybrid III, Thor-alpha and PMHS Response in Frontal Sled Tests.

Two series of nine frontal sled tests were conducted to evaluate the behavior of the Hybrid III and Thor-alpha dummies. The first series was conducted at 50 kph with airbag and 4 kN force-limited shoulder belt and the second series at 30 kph and only a 4 kN force-limited shoulder belt. In each series, three replicate tests were conducted with each dummy and compared with three PMHS. The data provided by the same instrumentation located at the same position were compared to assess the biofidelity of both dummies. The results were mass scaled in order to account for the differences between the anthropometry of the cadaver. The good test-to-test repeatability for each dummy permitted to compare the mean value of each recorded parameter. Based on the cadaver response, the results show that the Thor-alpha provides responses that are more similar to those of PMHS than the Hybrid III. The flexible joints in the thoracic spine, the sternum design and the more humanlike ribcage give more similar accelerations than the Hybrid III as compared to those of the PMHS. Nevertheless, some parts have to be improved in order to better follow the behavior of the human subject. The head-neck complex, the chest, the shoulder and the pelvis of the Thor-alpha have a more humanlike behavior but some differences remain. The distribution of the deceleration between the components is sometimes different compared to those of the cadaver, even if the resultants are similar. The dummies and most particularly the Hybrid III are less sensitive to the change in restraint systems and tests conditions than a cadaver.