Higher order preinterpolator for backprojection

摘要

X-ray detectors (24) of a CT scanner (10) generate data values which are preprocessed and assembled (26) into binary data lines. The binary data lines are convolved by a convolver (30) which convolves a plurality of data lines concurrently. A backprojector (32) includes a parametric cubic spline preinterpolator (40) which performs a high order interpolation on the convolved data lines and a linear interpolator (42) which performs a linear interpolation on the high order preinterpolated data lines. The interpolated data lines are backprojected into an image memory (34). Data from the image memory (34) is converted (36) to appropriate format for display on a video monitor (38). The parametric cubic spline preinterpolator (40) includes a first adder (52) which adds most adjacent data lines and a second adder (54) which adds next most adjacent data lines. A first barrel shifter (58) shifts the binary sum of the most adjacent data lines by 1-N spaces, where N is an integer, 4 in the preferred embodiment. The shifting is done in a direction which effectively multiplies the data by 2N-1. The difference between the sum of the adjacent and next most adjacent data lines is determined (56) and the difference is added (60) to the output of the first barrel shifter. A second barrel shifter (62) shifts the output of the third adder by N bits in the opposite direction, effectively dividing by 2N to create a higher order interpolated data line between each received convolved data line.