An experimental apparatus for analyzing the physical properties of biological tissues

The studies of X-ray attenuation of biological tissues are connected to the possibility of visualizing pathological tissues using new X-ray imaging techniques such as Multi-Energy subtraction X-ray Imaging. In fact the ability to distinguish pathological tissues is strictly related to an accurate knowledge of the X-ray absorption coefficients. A study of the attenuation properties of tissues was started at the University of Bologna in a facility based on a Bragg monochromator. The target of the Bragg monochromator is a LiF crystal able to produce monochromatic beams in a range of energies from 10 keV to 60 keV and with an energy resolution less than 2.0 keV. The absorption data are acquired by a CdTe detector. The energy resolution deterioration caused by the tailing effect at high energies is studied by a comparison with an HPGe detector. We implemented different algorithms for extracting chemical-physical information from X-ray absorption measurements, such as effective atomic number and electron density. The aim of this work is to present an instrumentation dedicated to the measure of the absorption coefficient of materials, in particular biological samples. An important feature of this apparatus is the possibility of selecting the energy of interest with high precision and repeatability. In addition, a study of the energy resolution of CdTe detector is reported, with a comparison with the energy resolution obtained with an HPGe detector for all the analyzed energy ranges. This study also analyzes the error propagation on the absorption curves, and evaluates the error introduced by the intrinsic characteristic of the detector used.