Micro computed tomography: removal of translational stage backlash

Abstract

Errors in projection position arise when the resolution required by tomographic systems approaches the tolerance of the translational stage. These shifts in the projection data, commonly known as backlash, appear as jagged edges in a sinogram. If these random shifts are not removed, the resulting reconstruction is blurred. This reduces the effective resolution of the system preventing viewing of single pixel events within the sample. An iterative method is presented for removing the translational backlash from projection data. The proposed method finds the center of gravity for all projections within a fixed window of the projection. The center of gravity of the projection will follow a sinusoidal path through the sinogram. A minimum mean square error (MMSE) fit to a sinusoid is made. If the center of gravity of a projection does not match the fit value, the entire projection is shifted into the correct position using linear interpolation. Since the shift of a projection introduces new data (that includes random noise) into the fixed calculation window, the center of gravity is again calculated, and the appropriate shift is made. This process is repeated until an acceptable error is reached. Since each shift uses linear interpolation, the data is blurred with each iteration. In order to minimize the amount of blurring, the shift values for each iteration are saved. The saved values are added and single shifts of the original projection data are made. An example of translational stage error removal is included.