# Effects of Scout Direction, Off-Centering, and Scout Imaging Parameters on Radiation Dose Modulation in CT

## TL;DR

This study shows how CT radiation dose varies based on scout imaging direction and software version, with newer systems reducing dose through off-center correction.

## Contribution

The study reveals how scout imaging parameters and AEC software versions affect CT radiation dose modulation.

## Key findings

- CT radiation dose varied with scout direction, object positioning, and AEC software version.
- Off-center correction in the new AEC software reduced radiation dose effectively.
- Scout imaging parameters had minimal impact on dose with the new software version.

## Abstract

In computed tomography (CT), automatic exposure control (AEC) typically determines radiation exposure based on scout images, which are projection images obtained for CT planning. This experimental study demonstrated that the CT radiation dose determined by AEC varied with the scout imaging direction (posteroanterior, lateral, or both), vertical positioning of the imaging object, and scout imaging parameters. The influences of these factors depended on the imaging object and the AEC software version. The off-center correction incorporated into the new version was demonstrated to function appropriately and to contribute to a reduction in radiation dose from scout imaging.

Background: In computed tomography (CT), automatic exposure control (AEC) determines the tube current and thus the radiation dose based on scout images. We investigated CT dose modulation using two versions of CARE Dose 4D, Siemens AEC software. Methods: A cylindrical phantom and an anthropomorphic phantom with the upper extremities raised or down were imaged. The CT tube current was determined using two versions of CARE Dose 4D and different scout directions: the posteroanterior scout image alone (PA scout), the lateral scout image alone (Lat scout), and the combination of the PA and Lat scout images (PA + Lat scout). The new version is designed to utilize the Lat image solely for off-center correction when both PA and Lat images are available. Experiments were performed at various vertical positions and with various scout imaging parameters. Results: The influence of the scout direction on CT dose was demonstrated, with variations depending on the imaging object and software version. The CT dose determined with the PA scout varied according to vertical positioning, presumably due to changes in image magnification. Such effects were small with the Lat scout or PA + Lat scout. Decreasing the tube voltage or tube current in scout imaging affected CT dose modulation with the Lat scout but not with the PA scout. With the PA + Lat scout, the effects of scout parameters were evident using the previous version but minimal using the new version. Conclusions: Off-center correction in the new version functioned appropriately. Because the behavior of an AEC system is complicated, it is recommended to examine the characteristics of each AEC system under various imaging conditions.