Multiscale AnaLysIs of Children's bone growth: both advanced ultrasonic cross-sectional imaging and biomechanics model – MALICE

The analysis and the characterization of the growth of children's bones are still an open question and crucial for various applications. Regarding clinical concerns, it is important to progress in the knowledge of the metabolism of the children’s bone, and to give biological markers of this metabolism, or to analyze the effective molecules for the treatment of bone diseases in pediatrics such as osteopenia/osteoporosis. The evaluation of the bone mineral density (BMD) using the conventional X-ray modalities (Dual energy X-ray Absorptiometry or Peripheral Quantitative Computed x-ray Tomography) are not directly usable to the children's bone clinical exam without adapted protocols (anesthesia of the child, calculation of the radiation dosimetry, exams of children in protected areas), and the echography, which is frequently used in pediatrics, is not an adapted modality to measure BMD. The BMD measurement raises problems of interpretation at the child when the size of the bone varies, and\or must be corrected according to the statural age if the child is small-sized. The BMD measurement reporting exclusively the bone mineral contents, and no modality informs about the micro-architectural contents or about the mechanical resistance of the skeleton. Several studies show, particularly at the old woman, that the Quantitative Ultrasound Methods (by opposition to the purely qualitative echography) allow reaching more relevant information of the bone structure. For example, we know that the broadband ultrasonic attenuation fit well with the age. What about children? No clinical strategy of development and use of the ultrasounds is envisaged today or defined in pediatrics. Even from the point of view of the research, reference values according to the age for the young patients are missing. The lack of bibliographic references does not allow establishing statistics or mean values of physical parameters. Nevertheless, as for all biological materials, it is possible to determine properties such as the ultrasonic wave velocity or attenuation, even the elastic rigidity matrix using mechanical and acoustical measurements. But the problems are related to the small number of available samples for the laboratory tests and on the quality of these samples associated to pathology of the child. What about the case of the animal model? Today it cannot be reasonably used without gaining an insight into the elasticity, the anisotropy, the porosity, and the mineralization of this material in growth.
To conclude, the clinical modalities of the children and teenager’s bone exams still have constraints. The bone biomechanics is incomplete. Markers and references are missing. In the project MALICE, we shall progress in the knowledge of the quality and of the mechanisms of growth of the children’s bones by establishing a first base of biomechanical reference values. We shall propose then a numerical model of children's bone, which can evolve according to the age of newborn to the teenager. The geometrical and physical parameters could vary according to the mechanisms of bone modeling and mineralization. Thanks to the headways, we shall develop a new modality of examination, the quantitative ultrasonic tomography, completing the other clinical modalities. The cross-sectional image of the bone would be geometrical (size and shape) and parametrical (quantitative).
This project is ambitious and requires the pooling of several disciplines. It associates research teams in ultrasonic wave propagation, acoustical and X-ray imaging, in numerical modeling and biomechanics, in biology and bone quality, and clinical teams.