Investigation on substantial asymmetry of HU value in dental cone-beam CT with offset detector

The short-scan trajectory in cone-beam CT (CBCT) imaging effectively decreases the scan time and the patient dose by excluding the redundant measurements. Also, the offset scan geometry improves the efficacy of the detector utilization by achieving the larger field-of- view (FOV) than the normal use. However, the asymmetric HU value recovery in the sinus of the patient has been consistently observed whenever we use the short-scan trajectory with offset detector. Typically, the reconstruction of short-scan CBCT with an offset detector may lead to inaccuracies in the CT attenuation values within the reconstructed image. This is particularly noticeable away from the beam center due to insufficient data consistency. Also, other physical factors (ex) beam-hardening, scattering effect) and truncation artifact due to the small FOV may contribute to asymmetric sinus representation. In this study, we investigate the potential causes of the asymmetric sinus representation through the artifact study. We used a Monte-Carlo (MC) simulation to reproduce asymmetric HU value for the ease artifact study.