Theoretically-exact CT-reconstruction from experimental data
Seminar Room 1, Newton Institute
We demonstrate how an optimisation-based autofocus technique may be used to overcome physical instabilities that have, until now, made high-resolution theoretically-exact tomographic reconstruction impractical. We show that autofocus-corrected, theoretically-exact helical CT is a viable option for high-resolution micro-CT imaging at cone-angles approaching +- 50 degrees. The elevated cone-angle enables better utilisation of the available X-ray flux and therefore shorter image acquisition time than conventional micro-CT systems. By using the theoretically-exact Katsevich 1PI inversion formula, we are not restricted to a low-cone-angle regime; we can in theory obtain artefact-free reconstructions from projection data acquired at arbitrary high cone-angles. However, this reconstruction method is sensitive to misalignments in the tomographic data, which result in geometric distortion and streaking artefacts. We use a parametric model to quantify the deviation between the actual acquisition trajectory and an ideal helix, and use an autofocus method to estimate the relevant parameters. We define optimal units for each parameter, and use these to ensure consistent alignment accuracy across different cone-angles and different magnification factors.