| Περίληψη: | Indirect detection digital imaging systems used in medical imaging, compromises powder phosphor scintillators as X-ray to light converters. Powder phosphors should combine image quality and light output parameters in order to produce high quality diagnostic images, with the parallel dose reduction to the patient. Additionally, they must be characterized by short decay times in order to be used in digital breast tomosynthesis (DBT) and dual energy imaging (DE). The aim of the present PhD thesis is the investigation of the optimum powder phosphor scintillator for use in a CMOS based digital imaging system and the investigation of the combination of the digital imaging system with the optimum scintillator for low energy medical applications, like DBT. Scintillating screens, were prepared using the method of sedimentation, by Lu2SiO5:Ce, Gd2O2S:Eu and Gd2O2S:Tb powder phosphors. Their properties were evaluated by experimentally determining parameters related to optical signal intensity and distribution at the scintillator exit surface, characterizing medical image quality and the patient’s dose. By comparing the luminescence efficiency and image quality properties of Lu2SiO5:Ce, Gd2O2S:Eu and Gd2O2S:Tb, the scintillating screen with the optimum characteristics was defined and placed, in close contact with the CMOS photodiode. MTF and DQE of our CMOS sensor were found better at the whole spatial frequency range with previously published data for a passive CMOS sensor, while NNPS was comparable. The evaluated CMOS sensor is characterized by high spatial resolution and detection efficiency properties that make it suitable for DBT. Additionally, image quality is acceptable at low exposure levels, which is crucial in DBT and DE applications where high patient’s dose is a drawback for the establishment of these methods.
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