Comparison of Radiation Dose and Image Quality with Various Computed-Tomography Scout Views: The Angular Modulation Technique Based on Information Calculated from Scout Views

Abstract

Background: While using the automatic exposure control technique in computed tomography (CT), the scout view determines the radiation dose for the CT scan by taking anatomical morphology into consideration. Objectives: The goal of this study was to estimate radiation doses during scout scanning and to evaluate the hypothesis that the radiation dose during CT depends on the location and order of the X-ray tubes. Materials and Methods: A CT scanner (GE VCT 64-channel) with the X-ray tubes placed in the anteroposterior (AP), lateral, and posteroanterior (PA) positions was used to acquire the scout views. The effective doses were assessed using an anthropomorphic chest phantom (RSD Inc., Long Beach, CA), an AAPM CT performance phantom (CIRS model 610), and CT dose indices (CTDI) head phantom. Both single and two scout views were tested with the three views combined according to the order of scanning. The CTDIs obtained from the CT unit dose report were used to compare the chest CT radiation doses, while the image quality was evaluated based on the root-mean-square error values calculated using the Image program. Results: The results of this study indicate that single AP (0°) scout views obtained with the z-axis modulation technique (AutomA) during chest CT scanning resulted in CTDIs that were lower than those generated by using lateral (90°) or PA (180°) scout views. The analysis of two-scout views using AutomA alone revealed the lowest CTDI in the 90° - 0° scout views. However, based on the CT image noise analysis, a scout angle order of 0°-90° resulted in the optimal scout view combination with the minimal dose. Conclusion: Scout views may be useful in determining dose and image quality in CT scanning; however, it is necessary to first determine the most appropriate scout view for CT scans.