The effect of a limited number of projections and reconstruction algorithms on the image quality of megavoltage digital tomosynthesis

In order to investigate the effect of the number of projections on digital tomosynthesis image quality, images were acquired over a 40 degree arc and sampled into sets of 2 to 41 projections used as input to three different reconstruction algorithms, namely the shift-and-add, Feldkamp-Davis-Kress filtered back projection algorithms, and the simultaneous algebraic reconstruction technique. The variation of several image characteristics, such as in-plane resolution, contrast to noise ratio, artifact spread, volumetric accuracy and dose, are investigated based on the reconstruction algorithms used and also the number of projections used as source data. The results suggest that the use of 11 projections along with the filtered back projection technique provides a good compromise for all aspects considered.