An Iterative Method for Flat-Field Correction of Digital Radiography When Detector Is At Any Position


For non-uniformity correction a flat field x-ray image is needed, and to obtain it the center of detector is usually aligned with the focal spot of the x-ray tube, which is conserved when examining patients to preserve the flat field. In some of radiographic techniques, however, it is necessary to move the x-ray tube off the center position of detector or tilt the detector. We investigated the effect of X-ray tube positions with respect to detector on the non-uniformity correction, and propose a method to reduce the effect using a new algorithm with computer simulation. Gain images were taken in two SIDs. Pixel values at second SID was calculated using the pixel values at first SID, gain coefficient that represents pixels own unique radiation sensitivity characteristics and the formula based on the solid angle of each detector pixel facing to the x-ray source. Gain coefficient was adjusted using the difference between calculated and real pixel values. Calculation was repeated with new gain coefficient until the gain coefficient was converged into prescribed range. Nonuniformity of blank x-ray images taken with the detector tilted by 0 to 45 degrees was corrected and five ROIs across the image were defined and analyzed. When the proposed algorithm was used for the flat field correction standard deviations of pixel values in the ROIs were reduce to 10% of the cases of usual flat field correction.

Meeting Name

Medical Imaging 2005 - Physics of Medical Imaging


Nuclear Engineering and Radiation Science

Keywords and Phrases

Digital Radiography; Flat Field Correction; Flat Panel Detector

Document Type

Article - Conference proceedings

Document Version


File Type





© 2005 SPIE -- The International Society for Optical Engineering, All rights reserved.

Publication Date

01 Jan 2005