Physical image properties of a complementary metal-oxide-semiconductor imager for mammography systems

We acquired a direct-type flat panel detector (FPD) developed for mammography systems and investigated its physical image properties, as its characteristics may affect future mammography in the clinic. The pixel size of the detector is 50 µm, the smallest size used in clinical mammography. Amorphous selenium (a-Se) film is used in direct-type FPDs. Due to its inferior temperature properties, the temperature of the imaging room should be set to approximately 25 °C. A novel a-Se film with superior heat resistance has been developed by the HAMAMATSU photonics KK Electron Tube Division that is suitable for high electric field driving. However, the associated trade-offs in image properties are unknown. The purposes of the current study were to investigate whether the detector maintains a high image quality in the presence of a high electric field, and to evaluate the image properties. The signal readout mechanism incorporates a complementary metal-oxide-semiconductor with superior noise properties. We measured the input-output characteristics, resolution, noise properties, and detection quantum efficiency, and investigated the effects of the exposure of the a-Se film to different applied voltages under standard mammography conditions prescribed by the International Electrotechnical Commission. The resolution and noise properties associated with the direct-type FPD were not affected by differences in applied voltage. The CMOS imager had a higher resolution than conventional systems with an equivalent pixel size. It also had a high detective quantum efficiency value. Thus, this detector may be useful in mammography.