Optimization of slice sensitivity profile for radiographic tomosynthesis.

Similar to other tomographic imaging modalities, the slice sensitivity profile (SSP) is an important image quality metric for radiographic tomosynthesis. In this study, the relationship between the acquisition angular range (Theta) and the SSP for the linear trajectory system was carefully investigated from both theoretical and experimental perspectives. A mathematical SSP model was derived for arbitrary points in the reconstructed volume. We used a newly developed flat-panel tomosynthesis prototype system to experimentally validate the mathematical model from 20 degrees (+/-10 degrees) to 60 degrees (+/-30 degrees) angular ranges. The SSP was measured by imaging an edge phantom placed at an angle with respect to the detector plane using the modulation transfer function degradation (MTF-d) method. In addition to the experiments, computer simulations were performed to investigate the relationship in a wider angular range (2.5 degrees to 60 degrees). Furthermore, image data from an anthropomorphic phantom were collected to corroborate the system analysis. All the images in this study were constructed using a 3D view-weighted cone-beam filtered backprojection algorithm (3D VW CB-FBP). The theoretical analysis reveals that the SSP of linear trajectory tomosynthesis is inversely proportional to tan(Theta/2). This theory was supported by both simulation (chi2=1.415, DF=7, p =0.985) and phantom experiment (r=0.999, p < 0.001) and was further confirmed by an analysis of the reconstructed images of an anthropomorphic phantom. The results imply that the benefit of narrower SSP by increasing angular range quickly diminishes once beyond 40 degrees. The advantages of the MTF-d method were also demonstrated.