Sabah Servaes1, Xiaowei Zhu. 1. Department of Radiology, The Children's Hospital of Philadelphia, 34th Street and Civic Center Boulevard, Philadelphia, PA, 19104, USA, servaes@email.chop.edu.
Abstract
BACKGROUND: There are mechanisms within CT scanners and shielding that can be used to lower dose to patients. OBJECTIVE: The objective of our study was to evaluate the dose changes and image quality with and without a breast shield for multidetector CT of the chest with angular tube current modulation. MATERIALS AND METHODS: An anthropomorphic 5-year-old phantom was scanned with and without bismuth breast shielding and with and without angular tube current modulation. Image quality was assessed by measuring signal-to-noise ratio and contrast-to-noise ratio as well as measuring qualitatively. ANOVA single-factor p-value analysis of paired datasets was used for the statistical analysis. RESULTS: The breast shielding and angular tube current modulation resulted in a dose reduction to 85% for the breast and 90% overall. Although no qualitative differences were noted with and without the breast shielding used with angular tube current modulation, there were statistically significant differences in the contrast-to-noise ratio and CT numbers. CONCLUSIONS: When used with angular tube current modulation, breast shields influence the contrast-to-noise ratio and CT numbers, and therefore should not be used for chest CT. Greater dose reduction can be obtained by reducing the reference mAs (or reference noise index).
BACKGROUND: There are mechanisms within CT scanners and shielding that can be used to lower dose to patients. OBJECTIVE: The objective of our study was to evaluate the dose changes and image quality with and without a breast shield for multidetector CT of the chest with angular tube current modulation. MATERIALS AND METHODS: An anthropomorphic 5-year-old phantom was scanned with and without bismuth breast shielding and with and without angular tube current modulation. Image quality was assessed by measuring signal-to-noise ratio and contrast-to-noise ratio as well as measuring qualitatively. ANOVA single-factor p-value analysis of paired datasets was used for the statistical analysis. RESULTS: The breast shielding and angular tube current modulation resulted in a dose reduction to 85% for the breast and 90% overall. Although no qualitative differences were noted with and without the breast shielding used with angular tube current modulation, there were statistically significant differences in the contrast-to-noise ratio and CT numbers. CONCLUSIONS: When used with angular tube current modulation, breast shields influence the contrast-to-noise ratio and CT numbers, and therefore should not be used for chest CT. Greater dose reduction can be obtained by reducing the reference mAs (or reference noise index).
Authors: Erin Angel; Nazanin Yaghmai; Cecilia Matilda Jude; John J DeMarco; Christopher H Cagnon; Jonathan G Goldin; Cynthia H McCollough; Andrew N Primak; Dianna D Cody; Donna M Stevens; Michael F McNitt-Gray Journal: AJR Am J Roentgenol Date: 2009-11 Impact factor: 3.959