Optimisation of tube voltage for conventional urography using a Gd2O2S:Tb flat panel detector.
With the increasing use of computed tomography (CT) for urography examinations, the indications for 'conventional' projection urography have changed and are more focused on high-contrast details. The purpose of the present study was to optimise the beam quality for urography examinations performed with a Gd(2)O(2)S:Tb flat-panel detector for the new conditions. Images of an anthropomorphic phantom were collected at different tube voltages with a CXDI-40G detector (Canon Inc., Tokyo, Japan). The images were analysed by radiologists and residents in a visual grading characteristics (VGCs) study. The tube voltage resulting in the best image quality was 55 kV, which therefore was selected for a clinical study. Images from 62 patients exposed with either 55 or 73 kV (original tube voltage) at constant effective doses were included. The 55-kV images underwent simulated dose reduction to represent images collected at 80, 64, 50, 40 and 32 % of the original dose level. All images were included in a VGC study where the observers rated the visibility of important anatomical landmarks. For images collected at 55 kV, an effective dose of approximately 85 % resulted in the same image quality as for images collected at 73 kV at 100 % dose. In conclusion, a low tube voltage should be used for conventional urography focused on high-contrast details. The study indicates that using a tube voltage of 55 kV instead of 73 kV for a Gd(2)O(2)S:Tb flat-panel detector, the effective dose can be reduced by approximately 10-20 % for normal-sized patients while maintaining image quality.
Department of Medical Physics and Biomedical Engineering, Sahlgrenska University Hospital, SE-413 45 Gothenburg, Sweden. sara.zachrisson@vgregion.se
Sara
S
Zachrisson
Jonny
J
Hansson
Ake
A
Cederblad
Kjell
K
Geterud
Magnus
M
Båth
D000465:Algorithms; D004867:Equipment Design; D019544:Equipment Failure Analysis; D016247:Information Storage and Retrieval / Q000379:methods*; D011856:Radiographic Image Enhancement / Q000295:instrumentation* / Q000379:methods; D011857:Radiographic Image Interpretation, Computer-Assisted / Q000295:instrumentation* / Q000379:methods*; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D014567:Urography / Q000295:instrumentation* / Q000379:methods*; D014963:X-Ray Intensifying Screens