The Influence of Patient Miscentering on Patient Dose and Image Noise in Two Commercial ct Scanners

Abstract

The clinical influences of patient miscentering on patient dose and image noise were investigated for two models of commercial CT scanners. Several phantoms were scanned on 4-slice GE Lightspeed and 64-slice GE Lightspeed VCT. Regression models of surface dose and image noise were generated as a function of phantom size and the value of miscentering. 64 scout images of patients from the first scanner and 113 from the second one were analyzed to assess the possible amount of increasing in dose and noise. For the first scanner the average amount of miscentering was 3 cm below the isocenter which leads to 25.8% increase in dose and 8.3% increase in noise. These values for the second scanner were 1.6 cm below the center, 19.8% and 6.2%, respectively. The results clearly demonstrate that patient miscentering may substantially increase dose and image noise. Therefore, technologists are strongly encouraged to pay greater attention to patient centering.