Investigation of image lag in a high-speed flat panel detector-based cone beam CT imaging system

Abstract

A cone beam CT (CBCT) imaging system has been developed based on a high-speed flat panel detector specially designed for cone beam CT. This system has shown great potential for early breast cancer detection with high contrast and spatial resolution, and the potential for high-speed dynamic studies. Image lag always plays an important role in cone beam CT imaging by affecting the image quality. This paper investigated the relationship of the image lag with various parameters of this new system, which include frame number, detector mode, frame rate, detector signal strength and kVp value. A simulated breast phantom was designed to demonstrate how image lag causes artifacts in the image and affects the reconstructed linear attenuation coefficient of tumor in different tissues. Experimental results illustrate that lag on this system is less than 3%, and is independent of kVp value and detector mode. When the detector signal strength increases from 10% to 80% saturation, lag decreases by 10%. Lag is also a function of the frame rate increasing by 20% when the frame rate changed from 3.75 fps to 30 fps. Computer simulations reveal that lag on this new system caused less than 6 HU reduction in the CT# for simulated tumors and soft tissue and 20 HU reduction for high contrast objects. This work tells us that lag on this new CBCT system for breast imaging can be ignored. However, when this system is used for dynamic study, which requires a high readout speed from the detector, image lag correction will need to be considered to achieve good image quality.