Translator Disclaimer
18 March 2008 Parameter investigation and first results from a digital flat panel detector with forward bias capability
Author Affiliations +
Digital flat panel a-Si x-ray detectors can exhibit image lag of several percent. The image lag can limit the temporal resolution of the detector, and introduce artifacts into CT reconstructions. It is believed that the majority of image lag is due to defect states, or traps, in the a-Si layer. Software methods to characterize and correct for the image lag exist, but they may make assumptions such as the system behaves in a linear time-invariant manner. The proposed method of reducing lag is a hardware solution that makes few additional hardware changes. For pulsed irradiation, the proposed method inserts a new stage in between the readout of the detector and the data collection stages. During this stage the photodiode is operated in a forward bias mode, which fills the defect states with charge. Parameters of importance are current per diode and current duration, which were investigated under light illumination by the following design parameters: 1.) forward bias voltage across the photodiode and TFT switch, 2.) number of rows simultaneously forward biased, and 3.) duration of the forward bias current. From measurements, it appears that good design criteria for the particular imager used are 8 or fewer active rows, 2.9V (or greater) forward bias voltage, and a row frequency of 100 kHz or less. Overall, the forward bias method has been found to reduce first frame lag by as much as 95%. The panel was also tested under x-ray irradiation. Image lag improved (94% reduction), but the temporal response of the scintillator became evident in the turn-on step response.
© (2008) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.
Jared Starman, Carlo Tognina, Gary Virshup, Josh Star-lack, Ivan Mollov, and Rebecca Fahrig "Parameter investigation and first results from a digital flat panel detector with forward bias capability", Proc. SPIE 6913, Medical Imaging 2008: Physics of Medical Imaging, 69130L (18 March 2008);


Volume CT (VCT) enabled by a novel diode technology
Proceedings of SPIE (April 20 2005)
Amorphous silicon image sensor for x-ray applications
Proceedings of SPIE (April 10 1995)
Temporal artifacts in flat dynamic x-ray detectors
Proceedings of SPIE (June 28 2001)
X-ray matrix sensors
Proceedings of SPIE (April 30 1999)
Crosstalk modeling of a CT detector
Proceedings of SPIE (May 06 2004)
Performance of advanced a Si CsI based flat panel x...
Proceedings of SPIE (June 05 2003)
High-resolution amorphous silicon image sensor
Proceedings of SPIE (April 11 1996)

Back to Top