[Evaluation of the number of sampling step angles in SPECT Images: comparison between FBP and OS-EM reconstruction algorithms].

We compared filtered back projection (FBP) and ordered subset expectation maximization (OS-EM) reconstruction algorithms to examine the effects of sampling step angle on SPECT image reconstruction. Image sampling was compared between conditions of constant total sampling time (16 min) and constant sampling time (40 sec) for each step with angles of 3, 5, 7.5, and 10 degrees. Generally, OS-EM was superior to FBP in terms of image reconstruction. Changes in the sampling step angles did not significantly affect the quality of the reconstructed images with OS-EM insofar as acquisition counts were sufficient for evaluation. On the other hand, the quality of FBP images deteriorated with larger angles such as 7.5 and 10 degrees, and it was difficult to obtain stable results. In conclusion, OS-EM improves the quality of images required for examination.