Comparison of saddle and helical trajectories of a mobile cone beam computed tomography scanner with online calibration correction
Résumé
In cone-beam computed tomography (CBCT), the conebeam (CB) artefact causes object-dependent image distortions away from the central plane. Non-circular trajectories such as saddles or helices can mitigate the CB artefact, but are challenging to execute with scanners not specifically designed for non-circular scanning. In this work, we made use of a recently available mobile robotic CBCT scanner (mobile ImagingRing, medPhoton, Salzburg, Austria) which allows sinusoidal motion perturbation of several degrees of freedoms during a source and detector rotation, coupled with infrared (IR) motion tracking to measure the geometry of each trajectory. We scanned a disk phantom designed to highlight CB artefacts with circular, saddle and helical trajectories executed by driving motion with wheels. We computed an incompleteness metric, tan(ψ), and correlated it with the region free from CB artefacts in the images. Using a separate cylindrical phantom, we additionally computed the modulation transfer function at 10 percent (MTF 10 ) to assess the accuracy of the calibration correction. We found regions free of CB artefacts of up to 190 mm in the superior-inferior direction for the saddle trajectory, and of 120 mm to 140 mm for the helical trajectory. MTF 10 was 1.39 lp/mm, 0.98 lp/mm and 1.03 lp/mm for the circular, saddle and helical trajectories with IR tracking, while without IR tracking the saddle and helical trajectories had MTF 10 less than 0.4 lp/mm.
Domaines
Imagerie médicaleOrigine | Accord explicite pour ce dépôt |
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