Comparing image quality and radiation dose between new generation MDCT and CBCT systems

The use of Cone Beam Computed Tomography (CBCT) for in-room image guided interventions has gained more and more popularity over the last decade. In this study, we compared a low dose and a standard dose Multi Detector Computed Tomography (MDCT) protocol for abdominal imaging with a CBCT system in terms of image quality and radiation dose. Both systems used in this study are latest generation, so both offer high radiation dose efficiency. To determine the dose distribution of both systems, a Rando-Alderson-Phantom in combination with 41 thermoluminescence dosimeters (TLDs) were used. The equivalent dose for the whole body was calculated after ICRP. To determine the image quality of the reconstructed slices, the Catphan600 phantom was used. In terms of quality we determined the spatial resolution, contrast-to-noise ratio (CNR), and visual inspection. The dose could be reduced by 46.3% when using the low-dose MDCT protocol (120kV 50mAs) compared to the CBCT system (89kV 153mAs). CNR and image noise are improved for the MDCT, in some cases the CNR up to 74.4%. However, the spatial resolution of the CBCT system was superior, even after reconstructing the MDCT data with a small field-of-view and a relatively hard filter. Visually, the MDCT reconstructions are of higher diagnostic quality. In conclusion, the MDCT provides better dose efficiency in relation to the image quality. For example, in cases such as the chemoembolization, the CBCT system is more convenient because of the possibility to be used during interventions.