Article Development of voxelised numerical

ABSTRACT Although great efforts had been made to improve the physical phantoms used for ca-librating in vivo measurement systems, for technical reasons they can oniy provide a rough representation of human tissue. Substantial corrections m w t therefore be made to calibration factors obtained with such caiibration phantoms for extrapola-tion to a given individuai. These corrections are particularly crucial and delicate in low-energy in vivo measurement when absorption in tissue is significant. To improve caiibration for such special conditions, the posîibility has been raised of using voxe-lised numerical phantoms associated with Monte Carlo computing techniques. In the method described below, a mathematical phantom, consisting of a voxelised repre-sentation derived from scanner images is used, with a specially-designed interface making it possible to not only reconstruct widely-differing contamination confgura-tions and specify associated tissue compositions, but also automatically create an MCNP4b input file. After validation of the different sources and geometries, the complete procedure of reconstruction of the phantom and simulation of "'Am lung measurement was carried out using a tissue equivalent calibration phantom of th