X-ray imaging system geometry and coordinate systems. The coordinate systems are the image 1 and image 2 origin coordinate systems ( and ), the x-ray source 1 and source 2 coordinate systems ( and ), and the CT origin and linac isocenter coordinate systems ( and ).
3D texturemap based chest phantom projection images using (a) over operator and (b) attenuate operator.
Illustration for the 3D texturemap based DRR generation. The intersections of the proxy slices ( dotted rectangles ) and the CT image are projected and blended.
X-ray image preprocessing results: (a) window-level; (b) histogram equalization; and (c) adaptive histogram equalization.
CT image preprocessing methods and DRR images. (a) Histogram and three sets of window-level ranges: (ALTB), (TB), and bone (B), (b)–(d) the result slice images, and (e)–(g) the DRR images.
MI profiles of the nine combinations of CT and x-ray enhancement methods. In each plot, the top three and bottom three graph graphs are the rotation and translation profiles, respectively (The translation profiles are shifted down for clarity). The axes are the shifts in mm and deg, and the axes are the MI values.
Registration grid plots for the ALTB-WL and ALTB-AHE combinations. The axes are the initial offset errors (mm for translations, deg for rotations), and the axes are the error dimensions. Each symbol is one registration trial with a dot “●” indicating that the initial error was successfully corrected, and an “” indicates that it failed.
Attraction ranges of the six enhancement combinations.
(a) the MI profile of the B-WL combination and (b) the normalized DRR and x-ray histograms at and .
Gradient ascent maximization parameters for the three search phases. is the total number of iterations, is the initial step size matrix, and is the initial learning rate matrix.
Error means and standard deviations of the successful registrations (the dot symbols in the registration grid plots).
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