METHOD FOR CORRECTING IMAGE ARTIFACTS IN DIGITAL X-RAY DETECTORS

METHOD FOR CORRECTING IMAGE ARTIFACTS IN DIGITAL X-RAY DETECTORS

FIELD OF INVENTION

The invention generally relates to correcting image artifacts in digital x-ray detectors and more particularly to correction of image artifacts due to field-effect-transistor (FET) leakage and row-correlated noise (RCN) in digital x-ray detectors.

BACKGROUND OF THE INVENTION

X-ray imaging is a widely used diagnostic tool. A typical X-ray imaging system includes an X-ray source and an X-ray sensor. A control system obtains the detected X-ray energy from the X-ray sensor and prepares a corresponding diagnostic image on a display. The X-ray sensor may be a conventional screen/film or a solid state digital image detector. Digital detectors afford a significantly greater dynamic range than conventional screen/film configurations, typically as much as two to three times greater.

A digital x-ray detector includes a panel of semiconductor field-effect-transistors (FETs) and photodiodes. The FETs and photodiodes in the panel are typically arranged in rows (referred to as scan lines) and columns (referred to as data lines). An FET controller controls the order in which the FETs are turned on and off. The FETs are typically turned on or activated in rows. The drain of each FET is connected to a photodiode. The source of each FET is connected to readout electronics via data lines. When a FET is turned on, the diode connected to the FET is charged. The electrical current is flowing from the readout electronics into the diode through the source and then the drain of the FET.

All diodes are fully charge before x-ray. When x-ray is arrived, the diodes are discharged. The diodes are charged again after x-ray. The amount of charge requires re-storing the lost charge represents the amount of x-ray received by the diode. The gates of the FETs are connected to the FET controller. The FET controller allows signals charged into the

panel of photodiodes to be read in an orderly fashion. The readout electronics converts the signals charged into photodiodes. The energy charged by the photodiodes in the detector and converted by the readout electronics is used by an acquisition system to activate pixels in the displayed digital diagnostic image. The panel of FETs and photodiodes is typically scanned across a row. The corresponding pixels in the digital diagnostic image are typically activated in rows.

The panel of a digital X-ray detector is scanned row by row. Each row includes pixels that are read out at the same time. Any time-varying interference that affects the pixels is row correlated noise (RCN) in an image. The time-varying interference can result from electromagnetic interference (EMI), mechanical vibration, and/or power supply noise.

More specifically, RCN is an offset-type of noise that is independent of X-ray signal. RCN can be directly calculated from offset or dark images. For example, RCN can be calculated by generating a row average vector of the...