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Method for computing tomographic scans

Image Number 4 for United States Patent #5128864.

Apparatus and method for mounting on an existing x-ray simulator and calculating a back projected computed tomographic image. The detector array is linear and outputs signals from the photodiodes mounted therein to a preprocessor for smoothing, correcting and filtering and subsequent processing to transform the signal from that produced by an x-ray originating from a fan beam source, e.g., in a polar coordinate system, into the signal which would have been produced by a detector in an array on which a parallel beam is incident on a Cartesian coordinate system. The transformed data is converted to a gray scale value for a picture element having a specific position in the Cartesian coordinate system and output to an appropriate display. Data is taken at each incremental angle as the beam source and detector array rotate around a target object.The method of reconstructing this back projected image involves correcting and smoothing the output signals, scaling those corrected and smoothed signals, and convolving the scaled signals into data characterizing the ray which is incident on each individual detector element into the equivalent intensity data had the incident ray originated from a parallel beam source. Also provided are methods for correcting the data for incorrect detector reading and for displacement of the detector array resulting from the off-center rotation of either or both of the x-ray source or the detector array.

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