A quantitative investigation of additive noise reduction for active matrixflat-panel imagers using compensation lines

A quantitative investigation of a technique for reducing correlated noise i n indirect detection active matrix flat-panel imagers has been reported. Co rrelated noise in such systems arises from the coupling of electronic noise , originating from fluctuations in external sources such as power supplies and ambient electromagnetic sources, to the imaging array via its address l ines. The noise reduction technique involves the use of signals from column s of compensation line pixels located in relatively close proximity to the columns of normal imaging pixels on die array. Compensation line pixels are designed to be as sensitive to externally-coupled noise as columns of norm al imaging pixels but are insensitive to incident radiation. For each imagi ng pixel, correlated noise is removed by subtracting from the imaging pixel signal a signal derived from compensation line pixels located on the same row. The effectiveness of various implementations of this correction has be en examined through measurements of signal and noise from individual pixels as well as of noise power spectra. These measurements were performed both in the absence of radiation as well as with x rays. The effectiveness of th e correction was also demonstrated qualitatively by means of an image of a hand phantom. It was found that the use of a single compensation line drama tically reduces external noise through removal of the correlated noise comp onent. While this form of the correction increases non-radiation-related un correlated noise, the effect can be largely reduced through the introductio n of multiple compensation lines. Finally, a position-dependent correction based on compensation lines on both sides of the array was found to be effe ctive when the magnitude of the correlated noise varied linearly across the array. (C) 2000 American Association of Physicists in Medicine. [S0094-240 5(00)01908-8].