Room: AAPM ePoster Library
Purpose: To evaluate how orthogonal limited arc scan combinations (OLASCs) reconstructed iteratively affect quantitative image analysis metrics and qualitative photon starvation artifact reduction in cone-beam computed tomography (CBCT).
Methods: Various OLASCs were simulated by generating digitally reconstructed radiographs (DRRs) from CBCT scans of a Catphan phantom, an anatomical phantom consisting of porcine vertebrae and ballistic gel, and a second anatomical phantom with additional pedicle screws. Iterative ASD-POCS was used to reconstruct the 3D volumes. Arc motions included the anatomical rotational axes (axial, sagittal, coronal), as well as, oblique motions formed by tilting either the axial or sagittal motions plus and minus 45 degrees. Arc size in degrees and the number of projections per arc were varied. OLASCs consisted of two or three orthogonal limited arcs of the same size and number of projections for simplicity. OLASC reconstructions of the Catphan were analyzed quantitatively via root mean square error (RMSE) and modulation transfer function (MTF). OLASC reconstructions of the anatomical phantoms were analyzed qualitatively for soft tissue to bone contrast and photon starvation artifact reduction.
Results: Both the quantitative image analysis and qualitative contrast analysis showed that the optimal anatomical OLASC is the double axial/coronal combination at 90 degrees and 90 projections per arc as it gave a low RMSE, an MTF curve that matched the MTF curve of the original CBCT scan of the Catphan, and clear soft tissue to bone contrast. The qualitative analysis of photon starvation artifact reduction showed that optimally the triple axial obliques plus sagittal OLASC with 90 degree arcs and 90 projections per arc eliminated nearly all photon starvation artifact caused by the pedicle screws.
Conclusion: OLASC reconstructions were shown to be equivalent to full traditional axial scan reconstructions with shorter arcs and fewer projections, as well as to significantly reduce metal artifacts.