Document Type


Date of Award


Degree Name

Master of Science in Electrical Engineering - (M.S.)


Electrical Engineering

First Advisor

G. Kuo-Petravic

Second Advisor

John D. Carpinelli

Third Advisor

Stanley S. Reisman


One important aspect for reconstructing an image using Computed Tomography (CT) is that the axis-of-rotation must pivot at the same point on the reconstruction plane as the x-ray source and CT scanner assembly rotates around the imaged object. This pivot point is used as a reference point for backprojecting pixel values to their proper coordinates. Therefore, reconstructing an image with a non-stationary axis-of-rotation would backproject pixel values to wrong coordinate points, since the reference point is non-stationary for every projection angle.

A convolution filtered backprojection algorithm has been derived for correcting images that were acquired with a non-stationary axis-of-rotation using the fan beam geometry with a collinear (flat) detector. Fan beam reconstruction algorithms which filter and backproject the projection data without correcting for this misalignment would produce structured artifacts and sharp degradation of the resulting image.

The correction method described in this thesis accounts only for the vertical displacements of the axis-of-rotation as the CT scanner rotates around the imaged object as may be the case when sagging occurs.

Software simulations are performed to show how the algorithm corrects for the shift in the axis-of-rotation.



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