Novel approaches for determination and correction of distortion, rotation, and translation in EMCCD mosaic array detectors
Hamwi, Hidab M. Ziad
MetadataShow full item record
This dissertation reports on the technology of imaging corrections for a new solid state x-ray image intensifier (SSXII) with enhanced resolution and fluoroscopic imaging capabilities, made of a mosaic of modules (tiled-array) each consisting of CsI(Tl) phosphor coupled using a fiber-optic taper or minifier to an electron multiplier charge coupled device (EMCCD). Generating high quality images using this EMCCD tiled-array system requires the determination and correction of the individual EMCCD sub-images with respect to relative rotations and translations as well as optical distortions due to the fiber optic tapers. Image corrections algorithms were developed based on comparison of simulated (distorted) images with the known square pattern of a wire mesh phantom. The mesh crossing point positions in each sub-image are automatically identified. With the crossing points identified, the mapping between distorted and undistorted arrays is determined to correct the distortion. For each pixel in the distortion-corrected image, the corresponding location in the undistorted image is calculated and the pixel value at that location is obtained using bilinear interpolation. For the rotation correction, the orientation of the vectors between respective mesh crossing points in the various sub-images are determined and each sub-image is appropriately rotated with the pixel values, again determined using bilinear interpolation. Image translation corrections are performed using reference structures at known locations. According to evaluation and validation results, the distortion corrections are accurate to within 1%; the rotations are determined to within 0.1 degree, and translation corrections are accurate to well within 1 pixel. In addition, corrections are found to produce more uniform and continuous images. This technology will provide the basis for generating single composite images from tiled-image configurations of the SSXII regardless of how many modules are used to form the images. Once these correction algorithms are implemented, this new all solid state x-ray detector system will exhibit resolution and sensitivity unavailable in current clinical imaging systems. Future research aiming at enhancing the correction producers is suggested at the end of this dissertation.