Digital Tomosynthesis Fundamental principles and comparison to conventional X-ray imaging

Abstract: During the last century several attempts have been made to overcome the fundamental problem of X-ray imaging, i.e. that anatomical information existing in 3-dimensions has to be represented on a 2-dimensional radiograph. In this thesis, digital tomosynthesis, a rened version of conventional tomography, has been investigated. Digital tomosynthesisenables retrospective reconstruction of an arbitrary plane in the imaged patient from a series of low dose projections, acquired with a limited tube movement. In the simplest method of reconstructing arbitrary planes, all the projections are shifted such that structures from only one plane line up exactly and thus remain fixed relative to the over- and underlying structures. To investigate the fundamental principles of tomosynthesis and evaluate the clinical potentiala prototype was built. Quality metrics such as signal difference to noise ratio (SDNR) and artifact spread function (ASF) were measured with dierent tomographic parameter settings. The tomosynthesis acquisition parameters were optimized and the image quality at different exposure levels were compared to conventional radiographs. The optimization evaluation showed that a large angular range with many projections can increase the image quality and reduce artifacts created from surrounding anatomy. It was also shown that small and obscuredobjects were easier to discern with tomosynthesis compared to conventional X-ray imaging, even at lower exposures. Reconstructed images of an anthropomorphic chest phantom showed an increased visibility of local structures in the lungs, structures which becomes superimposed on surrounding anatomy in a conventional X-ray image. These results are a consequence of the intrinsic property of tomosynthesis; each image, reconstructed from a series of projections, have high signal from in-focus objects and low signal from the surrounding anatomy that is repeated over the image proportional to the number of projections. The ability to separate the surrounding anatomy from the in-focus structures can be optimized with the appropriate combination of angular range and the number of projections acquired.