Keywords:
Abdomen, Liver, Radiation physics, CT, CT-Quantitative, Technology assessment, Technical aspects
Authors:
F. Willemssen, R. Dwarkasing, W. Lip-Pauwels, R. Booij, G. P. Krestin, M. van Straten; Rotterdam/NL
DOI:
10.1594/ecr2013/C-1516
Methods and Materials
Since August 2010,
three different scanning protocols were used on one multi-slice CT scanner (Definition AS+,
Siemens,
Germany) for arterial phase imaging. Initially,
the tube voltage was fixed at 120 kV. Next,
the tube voltage was manually selected (80 or 100 kV) based on the patient's weight. Finally,
the tube voltage was automatically selected by the scanner's software based on patient's weight and tissue type of interest, while taking the power limitations of the x-ray tube into account (Care kV option).
For each protocol,
the mAs value was adapted accordingly.
Patients were included when at least two different CT examination protocols were performed,
at least the Care KV option and manually selected tube voltage.
For recurring patients,
the lateral size, radiation dose (CTDIvol value),
voltage,
image noise and CT value of contrast-enhanced blood in the aorta were assessed. CT values were measured in the aorta,
at the level of the superior mesenteric artery.
Lateral size was measured at the lowest point of the liver.
The calculated contrast-to-noise ratio was normalized to the square root of the dose (CNRD) to evaluate changes in image quality independent of changes in dose settings. A paired t-test was performed to determine the effect of protocol changes.