An investigation of filter choice for filtered back-projection reconstruction in PET

A key parameter in the practical application of filtered back-projection (FBP), the standard clinical image reconstruction algorithm for positron emission tomography (PET), is the choice of a low-pass filter window function and its cut-off frequency. However, the filter windows and cut-off frequencies for clinical reconstruction are usually chosen empirically, based on a small sample of images and filters. By considering the features of the signal and noise spectra in a sinogram, the desired image resolution, and the signal-to-noise ratio (SNR) of the filtered sinogram, the authors investigated the possibility of establishing a methodology for informed selection of a filter function and cut-off frequency for use with FBP. Simulations of sinogram data similar to whole body or cardiac studies provided information on the signal and noise frequency-domain spectrum of noisy projection data. The improvements in the SNR with different filter windows and cut-off frequencies were evaluated and compared. The projection spectrum SNR measure did not prove to be an accurate indicator of subjective image quality or lesion detectability with variations in Poisson noise and image resolution