Utilization of tin filters for streak artifact reduction in cone-beam computed tomography

This study aims streak artifacts reduction in cone-beam computed tomography (CBCT) by mounting tin filters at the Trilogy system. An anthropomorphic phantom with insertions of aluminum and titanium rods was scanned using the standard dose head (SDH) and high-quality head (HQH) CBCT protocols with no tin filters as well as 0.2 mm, 0.4 mm, and 0.6 mm thick tin filters. To quantify the degrees of streak artifacts of each CBCT image, the values of percent integrity uniformity (PIU), coefficients of fast Fourier transform (FFT), and standard deviations (SD) along the profiles at the vicinity of insertion materials were calculated. In addition, noise levels, contrast-to-noise ratio (CNR), and low contrast visibility (LCV) were analyzed by using the CBCT images of the Catphan 504 phantom, of which scanning conditions were identical to those of the anthropomorphic phantom. To evaluate imaging doses, the weighted CT dose indices and point doses measured with optically stimulated luminescence dosimeters were acquired. The PIU values of the CBCT images using the HQH protocol with a 0.4 mm-thick tin filter were always larger than those using SDH protocol without the filter which is currently used in the clinic (larger PIU indicates fewer streak artifact). The values of SD and coefficients of FFT using the HQH protocols with a 0.4 mm-thick tin filter were always smaller than those using SDH without the filter (smaller SD and FFT coefficients indicates fewer streak artifact). Although noise levels, CNR, and LCV were degraded as thicker as the tin filters, those of 0.4 mm tin filters with HQH protocol showed similar values to those of SDH protocol. By mounting 0.4 mm-thick tin filters, imaging doses were lower by 25% than those without the filter. Streak artifact can be reduced with a 0.4 mm tin filter and HQH protocol in CBCT with imaging dose reduction.