Optimum design of multi-layer K-edge filter and multi-stage detectors for triple energy bone densitometer

Dual X-ray bone densitometry may cause some errors in diagnosis due to heterogeneous distribution of adipose tissue. It is necessary to develop a more accurate technique to consider the effects of fat. In this research, a triple energy X-ray method has been introduced and conceptual design of a system consisting of 160 kV X-ray tube, multi-layer K-edge filter and multi-stage detector has been presented. Design calculations have been performed using MCNP4C Monte Carlo code to select the type of filters and detectors with the best thicknesses for better distinguishing materials. The energy peaks (37 keV, 50 keV and 105 keV) can be separated optimally with a multi-layer filter composed of barium (170 μm) and gadolinium (100 μm) as the first and second layers, respectively which are coated on a 1 mm aluminum plate placed between the source and tissue. The transmitted photons have been counted by a multi-stage linear array of detectors consisting of ZnSe(Te) and CsI(Tl) with 400 μm and 5 mm thicknesses, respectively. Monte Carlo simulations show that the triple energy X-ray technique has better accuracy than that of the standard dual energy X-ray technique.