Parameters used in the correction procedure and describing the input phosphor screen curvature, view angle, and distances from the focal spot to the object plane and to the input phosphor screen are fixed at the time of exposure. These parameters make the correction procedure independent of the system. The correction formula is applicable to X-ray systems with different image intensifiers and for different view angle projection. System calibration is not required, nor must any constant values be determined by empirical methods.
Since the view angle is a constant for a series of images, only one trigonometric function per pixel needs to be computed. In order to shorten the run time, lookup tables may be used. A
lookup table contains the tangent function values for Eqs. (15) and (21) and the inverse trigonometric function arctangent in Eqs. (25) and (28).
The result of subjecting an angiogram to the correction procedure is shown in Fig. 15. Since the procedure shrank the image along the radius toward the center, the size of the entire image has changed. However, the size of objects placed in the image center remains unchanged, even though in the periphery the decrease is noticeable (see blood vessels indiated by arrows).
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