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Design and performance of a new a-Si flat-panel imager for use in cardiovascular and mobile C-arm imaging systems

This paper describes a new flat panel imager designed for use in cardiovascular and mobile C-arm imaging systems. The a-Si sensor array has a 1024 x 1024 matrix with a pixel pitch of 194 μm, resulting in an active area of 198.7 mm x 198.7 mm. The imager allows frame rates of up to 30 fps in full resolution fluoroscopy mode and up to 60 fps in a 2 x 2 binned low dose fluoroscopy mode. Typically, a 600 μm thick deposited columnar CsI(Tl) layer is used as the scintillator. Improvements in the pixel architecture, charge amplifier ASICs, and system level electronics resulted in a very low electronic noise floor, such that both the fluoroscopy and low dose fluoroscopy modes of the panel are x-ray quantum limited below 1 μR/frame. Low power consumption electronics combined with a mechanical design optimized for heat transfer and dissipation makes air-cooling sufficient for most environments. The small size of 24.1 x 24.1 x 6 cm and the weight of only 4.1 kg meet the requirements of C-Arm systems. Special consideration was given to the border around the active area, which has been reduced to 2 cm. Reported performance parameters include linearity, lag, contrast ratio, MTF, and DQE. For the full resolution mode, the MTF is greater than 0.53 and 0.21 at 1 and 2 lp/mm, respectively. DQE measured at 22 nGy/frame was greater than 0.68, 0.50, and 0.23 at 0, 1, and 2 lp/mm, respectively.