A Study of DQE Dependence with Beam Quality, GE Senographe Essential Detector for Mammography

摘要

This paper deals with the analysis of objective image quality parameters for the new GE Senographe Essential FFDM system at several beam qualities. The detector consists of an indirect conversion a-Si flat panel coupled to a CsI:Tl scintillator. The system under study has gone through a series of relevant modifications in flat-panel with respect to the previous model (GE Senographe DS 2000). These changes modify its performance and are intended to favor advanced low dose applications like tomosynthesis, which uses harder beam spectra and lower doses per exposure than conventional FFDM. Although our system does not have tomosynthesis implemented, we have determined that most clinical explorations are performed by automatically selecting a Rh/Rh anode/filter combination at kV values within the range from 28 to 30 kV, which means a harder spectrum than that of typical use in FFDM. Flat-panel optimization for tomosynthesis has a clear influence in usual FFDM clinical performance and the new detector behavior needs to be investigated. Our study was extended to several beam qualities, namely, Mo/Mo and Mo/Rh at 28 kV and Rh/Rh at 26, 28, 30, and 34 kV. We found that flat-panel optimization results in higher DQE values as beam quality increases, which is contrary to the expected behavior. This positive correlation between beam quality and DQE is also diametrically opposite to that of the previous model. As a direct consequence, usual FFDM takes advantage of the changes in the detector, as less exposure is needed to achieve the same DQE if harder beams are used.