Geometric Calibration for a Next-Generation Digital Breast Tomosynthesis System

A method for geometric calibration of a next-generation tomosynthesis (NGT) system is proposed and tested. The NGT system incorporates additional geometric movements between projections over conventional DBT. These movements require precise geometric calibration to support magnification DBT and isotropic SR. A phantom was created to project small tungsten-carbide ball bearings (BB's) onto the detector at four different magnifications. Using a bandpass filter and template matching, a MATLAB program was written to identify the centroid locations of each BB projection on the images. An optimization algorithm calculated an effective location for the source and detector that mathematically projected the BB's onto the same locations on the detector as found on the projection images. The average distance between the BB projections on the image and the mathematically computed projections was 0.11 mm. The effective locations for the source and detector were encoded in the DICOM file for each projection; these were then used by the reconstruction algorithm. Tomographic image reconstructions were performed for three acquisition modes of the NGT system; these successfully demonstrated isotropic SR, magnified SR, and oblique reconstruction.