Evaluation of the possibilities of limited angle reconstruction for the use of digital Radiography system as a tomograph

The trend to introduce digital equipment in Conventional Radiology systems, together with a higher flexibility of movements of its components, suggests the possibility of obtaining 3D images with an adapted scan instead of using a conventional CT system. With the appropriate mechanical calibration and specific reconstruction algorithms, it could be possible to obtain 3D images from these systems with a limited-view angle scan. In this work, we present a preliminary study of the possibilities when using a reconstruction method based on the Split Bregman algorithm considering different span angle and number of projections. The reconstruction approach includes a total variation (TV) term and it is solved in a very computational efficient way because it avoids the need of estimating the regularization parameters and the derivatives of the TV term. The algorithm presents several advantages like low memory requirements, low computational time, high versatility for including additional regularization terms and it does not require the selection of the regularization parameters. The evaluation was done using simulated limited angle data extracted from three real acquisitions in a cone beam small-animal scanner. Preliminary results with the TV-Split Bregman algorithm show a high reduction of the streak artifacts and recovering of the edges in the reconstructed images, compared to the FDK algorithm, when the span angle is reduced to 60 or 90 degrees depending on the the region of interest. For large enough span angles, reducing the number of projections to 0.3 projections per degree does not result in a noticeable impact on the quality.