Room: Exhibit Hall | Forum 1
Purpose: A novel robotic imager with the image receptor and x-ray source mounted on separate opposable arms allowing six degrees of freedom of movement opens the investigation of the image acquisition of intraoperative pedicle screws via limited angle axial and non-axial rotations. When compared to standard axial imaging, non-axial rotations have the ability to limit artifact. Non-axial rotation projections avoid paths along the long axis of the screws, thereby reducing artifacts. To avoid patient collisions with the imaging equipment, limited arc sizes were investigated.
Methods: Digitally reconstructed radiographs (DRRs) were generated from CBCT image sets via a virtual x-ray simulator. CBCT image sets were reconstructed iteratively from the DDRs. The FWHM of the 23 degree ramps in a Catphan phantom was measured for the reconstructed setâ€™s effective slice thickness (EST) while increasing the arc size from 40 degrees to 120 degrees at one, two, and three projections per degree. A phantom was constructed of two pedicle screws inserted in solid bone placed in ballistic gel and water. DRRs for orthogonal limited angle axial and non-axial (OLAANA) rotations were generated of the bone/screws/gel/water (BSGW) phantom. The reconstructed sets were combined so that the effects of metal artifacts were minimized.
Results: Limited angle rotation acquisitions increased the EST as the arc size was reduced and the projections per degree was reduced for a reconstructed slice thickness of 1 mm. The equal summation of OLAANA rotations of the BSGW phantom reduced the metal streaks and photon starvation while improving pedicle screw detail compared to a standard axial rotation CBCT.
Conclusion: At arcs sizes of less than or equal to 70 degrees and two projections per degree, limited angle rotation EST rapidly increases. The equal summation of OLAANA rotations reduced the metal streak artifacts and photon starvation, as well as increased pedicle screw detail.