ABSTRACT. A comparison, in terms of image quality and glandular breast dose, was carried out between two similar digital mammography systems using amorphous selenium flat panel detectors. The two digital mammography systems currently available from Lorad-Hologic were compared. The original system utilises Mo/Mo and Mo/Rh as target/filter combinations, while the new system uses W/Rh and W/Ag. Images of multiple mammography phantoms with simulated compressed breast thicknesses of 4 cm, 5 cm and 6 cm and various glandular tissue equivalency were acquired under different spectral conditions. The contrast of five details, corresponding to five glandular compositions, was calculated and the ratio of the square of the contrast-tonoise ratio to the average glandular dose was used as a figure-of-merit (FOM) to compare results. For each phantom thickness and target/filter combination, there is an optimum voltage that maximises the FOM. Results show that the W/Rh combination is the best choice for all the detection tasks studied, but for thicknesses greater than 6 cm the W/Ag combination would probably be the best choice. In addition, the new system with W filter presents a better optimisation of the automatic exposure control in comparison with the original system with Mo filter. Over the past decade, several digital mammography systems based on different detector technologies have become available and the process of optimisation of digital systems has been developing in parallel with the adoption of those systems. On the one hand, this process involves the optimisation of digital detectors, but, on the other hand, it involves the optimisation of the X-ray sources and exposure factors with regards to the minimum radiation dose required to maintain the highest possible image quality. In conventional mammography this optimisation has mostly been achieved using the anode/filter combination Mo/Mo, but it may be questioned whether it is also optimal for digital mammography.In the past few years, several studies and simulation works have been carried out in order to investigate the factors that affect choice of X-ray spectra for mammography.Dance et al [1] in their Monte Carlo study concluded that in digital mammography with a gadolinium oxysulphide detector, the standard Mo/Mo combination is superior only for 2 cm compressed breasts. For all other compressed breast thicknesses and glandularities, each of the alternative anode/filter combinations (Mo/ Rh, W/Rh, Rh/Rh and Rh/Al) can offer a lower dose for the same contrast-to-noise ratio (CNR). In particular, for compressed breast thicknesses of 4 cm to 6 cm, W/Rh is recommended.In a previous work, Andre and Spivey [2] developed a parametric model for digital mammography to evaluate optimisation of X-ray spectra for a particular sensor. The model computes spectra and average glandular doses (AGD) for combinations of W target, beam filters (Al, Sn, Rh, Mo and Ag), kVp, breast type and thickness. On the basis of their results, the authors suggest the use of Mo filter for 30 mm bre...