Author: Craig K Abbey, John M. Boone, Richard E. Colbeth, Andrew M. Hernandez, Sarah E. McKenney, Vance Robinson, Paul Schwoebel, Jeffrey H. Siewerdsen, Alejandro Sisniega, Wojciech B. Zbijewski 👨🔬
Affiliation: UC Santa Barbara, University of California, UT MD Anderson Cancer Center, Johns Hopkins University, University of New Mexico Albuquerque, UC Davis Health, Varex Imaging Corporation 🌍
Purpose:
While wide coverage (160 mm) CT scanners can image whole organs (e.g. heart, brain, kidneys, etc.) in one axial scan, the peripheral regions of the field of view (along z) suffer from considerable demodulation due to cone beam artifacts caused by under sampling in z. A 6-source multiple x-ray source array (MXA) with multiplexed pulsing has been proposed to provide more complete sampling along z in the CT raw data and reduce cone beam artifacts considerably.
Methods:
A 300 mm long phantom fabricated from DVD discs with ~6 mm spacing was imaged on two commercial scanners (GE Apex and Canon Insight) featuring 160 mm z-axis coverage using several acquisition modes, and traces through the coronal images of the phantom quantified the cone beam artifact for axial 160 mm scans, five 40 mm z-aperture contiguous axial scans, and 20 mm z-aperture helical scans. The pattern of demodulation was fit using gaussian functions, and fits to the measured demodulation were compared against ideal performance (i.e., complete theoretical sampling).
Results:
The patterns of demodulation exhibited by both scanners in 160 mm axial scans were qualitatively similar, showing an average of 41% modulation across the z-axis field of view of 155 mm, with substantial falloff at the beam periphery (extrema in z). By contrast, a series of 6 overlapping 40 mm axial scans (simulating the 6-source MXA system) produced an average of 83.4% modulation across the z-axis field of view of 240 mm with minimal contrast reduction at the periphery.
Conclusion:
The results suggest that by better sampling ray data along the z-dimension of the CT detector arrays, the 6-source MXA-CT system will deliver twice the modulation as commercially available wide coverage scanners (83.4% versus 41%), with greater coverage in the z-axis (240 mm vs 160 mm) as well.