Image acquisition setup. The CATPHAN 600 was aligned with the rotation axis ( axis) of the C-arm system. The phantom was positioned such that the midplane intersected the CTP515 soft-tissue module shown in Fig. 1.
CATPHAN CTP515 low contrast module with low-contrast targets. The nominal contrast levels of the nine outer supra-slice targets are 0.3%, 0.5%, and 1.0%. Their diameters range from in steps, and a target completes each contrast group.
Dose in Perspex phantom at various peripheral axis points at depth around the phantom circumference. Also indicated is the central axis dose value and the average dose in the central plane computed using Eq. (1).
Phantom dose versus detector dose demand, with linear regression fits. Average dose is .
CATPHAN slice section reconstructed from projections acquired at . (a) full slice at highest dose setting of and subregions of slices at (b) , (c) , (d) , and (e) . These are rescaled dose values based on the mAs applied during CATPHAN scanning with respect to the mAs used to for the dosimetry head phantom (at the same tube voltage).
detectability profiles associated with the slice sections shown in Fig. 5. The curve indicates that the diameter object might just be visible (based on a 50% detectability threshold), the curve suggests that you should see objects larger than , the curve implies a minimum size of , and the curve hints at detectability of insets with smallest diameter between 4 and . These results agree reasonably well with a visual inspection of Fig. 5.
Modulation transfer function of a wire in a volume reconstructed using the same kernel as was used for the detectability studies, and for two other kernels illustrating potential system resolution when operated in a similar mode.
Normalized detectability charts for objects reconstructed from projections at different dose levels. The detectability chart diameters formerly associated with 38.4 and have been normalized to using Eq. (6).
Average normalized detectability charts at 70, 81, 109, and . The object diameters have been normalized to using Eq. (6).
Reconstructed CATPHAN sections at comparable dose levels (indicated in parentheses) but at (a) , (b) , (c) , and (d) .
Measured half-value layers at the operational kVps.
Resulting phantom dose values for medium-high detector entrance dose request. (a) for CTDI Phantom (543 Views). Medium-high detector dose demand setting. (b) CATPHAN dose: scaled (by mAs ratio) from the measured CTDI phantom dose.
Nominal contrast percent as specified by the CATPHAN manufacturer compared to measured contrast values C% using the observed HU differences. As expected, the contrast decreased with increasing kVp.
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