Fig 1.
Schematic summary of the direct and indirect determinates of the radiation exposure in CT.
Table 1.
Radiation dose (CTDIvol, DLP), manually (scan length, table height) or automatically (tube current, mean mAs) adjusted scan parameters as well as the maximal effective abdominal diameter as surrogate for patient’s weight of the 3 CT follow-up examinations each composed of a non-contrast-enhanced scan of the liver and a contrast-enhanced scan of the chest and abdomen in 60 patients.
Table 2.
Differences between the follow-up examinations in radiation exposure, scan parameters and maximal effective abdominal diameter.
Fig 2.
Box- and Whisker-plots of the percentage differences in CTDIvol and DLP between follow-up examinations.
Table 3.
Correlation analysis between the differences in the radiation exposure and the differences in the parameters that varied between the follow up examinations.
Fig 3.
a-f: Scout views of three follow-up CT examinations of a 54 year old male patient with superimposed modulation of the tube current.
While the differences in the radiation dose between the chest CT examinations can be explained by differences in the table height (TH) and the scan length (SL), the difference in dose between the abdominal CT scans d and f, cannot be explained by these factors due to the fact that in d and f the table height as well as the scan length had been virtually the same. However, the positioning of the thighs was different between these examinations, which resulted in a different tube current modulation and consecutively in different radiation dose.
Table 4.
Multiple linear regression analysis to predict differences in the radiation exposure between follow-up examinations.
Table 5.
Influence of the phantom’s positioning on the CT table on the radiation dose.
Except of the phantom’s positioning all other imaging parameters were kept constant between the measurements.