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International Journal of Biomedical Imaging
Volume 2007, Article ID 38516, 12 pages
Research Article

Experimental Investigation of Angular Stackgram Filtering for Noise Reduction of SPECT Projection Data: Study with Linear and Nonlinear Filters

1Department of Clinical Physiology, Medical Imaging Center, Tampere University Hospital, P.O. Box 2000, Tampere 33521, Finland
2Institute of Signal Processing, Tampere University of Technology, P.O. Box 553, Tampere 33101, Finland

Received 6 October 2006; Revised 16 January 2007; Accepted 7 March 2007

Academic Editor: Jyh-Cheng Chen

Copyright © 2007 Antti P. Happonen and Matti O. Koskinen. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.


We discuss data filtering prior to image reconstruction. For this kind of filtering, the radial direction of the sinogram is routinely employed. Recently, we have introduced an alternative approach to sinogram data processing, exploiting the angular information in a novel way. This new stackgram representation can be regarded as an intermediate form of the sinogram and image domains. In this experimental study, we compare the radial sinogram and angular stackgram filtering methods using physical SPECT phantoms. Our study is carried out by employing simple linear and nonlinear filters with ten different Gaussian kernels, in order to provide a comparable investigation. According to our results, angular stackgram filtering with the nonlinear filters provides the best resolution-noise tradeoff of the compared methods. Besides, stackgram filtering with these filters seems to preserve the resolution in an exceptional way. Visually, noise in the reconstructed images after stackgram filtering appears more “powdery” in comparison with radial sinogram filtering.