Abstract: The application of the newly developed flat panel x-rayimaging detector in cone beam volume CT has attractedincreasing interest recently. Due to an imperfect solidstate array manufacturing process, however, defectiveelements, gain non-uniformity and offset imageunavoidably exist in all kinds of flat panel x-rayimaging detectors, which will cause severe streak andring artifacts in a cone beam reconstruction image andseverely degrade image quality. A calibrationtechnique, in which the artifacts resulting from thedefective elements, gain non-uniformity and offsetimage can be reduced significantly, is presented inthis paper. The detection of defective elements isdistinctively based upon two-dimensional (2D) waveletanalysis. Because of its inherent localizability inrecognizing singularities or discontinuities, waveletanalysis possesses the capability of detectingdefective elements over a rather large x-ray exposurerange, e.g., 20% to approximately 60% of the dynamicrange of the detector used. Three-dimensional (3D)images of a low-contrast CT phantom have beenreconstructed from projection images acquired by a flatpanel x-ray imaging detector with and withoutcalibration process applied. The artifacts causedindividually by defective elements, gain non-uniformityand offset image have been separated and investigatedin detail, and the correlation with each other havealso been exposed explicitly. The investigation isenforced by quantitative analysis of the signal tonoise ratio (SNR) and the image uniformity of the conebeam reconstruction image. It has been demonstratedthat the ring and streak artifacts resulting from theimperfect performance of a flat panel x-ray imagingdetector can be reduced dramatically, and then theimage qualities of a cone beam reconstruction image,such as contrast resolution and image uniformity areimproved significantly. Furthermore, with littlemodification, the calibration technique presented hereis also applicable to the flat panel x-ray imagingdetector in digital radiography (DR), fluoroscopy (DF)and mammography. !16
展开▼
