Methodology for determining dose reduction for chest tomosynthesis

Digital tomosynthesis is an imaging technique that reconstructs tomographic planes in an object from a set of projection images taken over a fixed angle 1 . Preliminary results show that this technique increases the detectability of lung nodules 2 . Current settings acquire images with approximately the same exposure as a screen-film lateral. However, due to the increased detectability of lung nodules from the removal of overlying structures, patient dose may be reduced while still maintaining increased sensitivity and specificity over conventional chest radiographs. This study describes a simulation method that provides realistic reduced dose images by adding noise to digital chest tomosynthesis images in order to simulate lower exposure settings for the purpose of dose optimization. Tomosynthesis projections of human subjects were taken at dose levels which were specified based on either patient thickness or a photo-timed digital chest radiograph acquired prior to tomosynthesis acquisition. For the purposes of this study, subtle nodules of varying size were simulated in the image for demonstration purposes before the noise simulation in order to have a known truth for nodule location and to evaluate the effect of additive noise on tumor detection. Noise was subsequently added in order to simulate 3/4, 1/2, and 1/4of the original exposure in each projection. The projections were then processed with the MITS algorithm to produce slice images. This method will be applied to a study of dose reduction in the future using human subject cases.