Room: Exhibit Hall | Forum 9
Purpose: For the wide beam scanners equipped with adaptive statistical iterative reconstruction â€“V (ASIR-V), dose modulation for any given noise index (NI) results in different volume CT dose index (CTDIvol) depending on the ASIR-V percentage. Prediction of the CTDIvol for the average patient size at variable ASIR-V and NI will be beneficial in practice for the default protocol setup.
Methods: Scout images were acquired on a GE Revolution CT for a water phantom of 32 cm in diameter. The helical scan protocol with dose modulation was then adjusted (120 kVp, 2.5 mm in thickness and 0.984 in pitch) for various noise indices (16.7 to 26) and ASIR-V percentages (0 â€“ 100%). The mA range was made wide open to assure proper dose modulation. The corresponding CTDIvol values were recorded (0.55 â€“ 31 mGy, N = 66). The CTDIvol was correlated to the noise indices and ASIR-V by a least square fit.
Results: The relationships of CTDIvol to ASIR-V and to the noise index were fitted to a quadratic form and a power law form, respectively (RÂ² = 0.999). The standard error of estimate, defined as the root mean square of the percentage difference, was 4.7% except for the two points where the noise index reached the upper bound of 26 and ASIR-V was 90 and 100%. The recorded CTDIvol for these two points was at the minimum 0.55 mGy and the standard error of estimate was 17% if the data were included.
Conclusion: The equation incorporating the CTDIvol, noise index, and ASIR-V was obtained. The result informs the user of the radiation output for the abdomen protocol design on the system where the modulated dose is determined by both noise index and ASIR-V.