Patient dose reduction in CT examinations by optimising scanogram acquisition.

The objective was to determine the optimum settings of the scanogram performed in computed tomography (CT) examinations for scan localisation. Head, abdomen and thorax scanograms were performed on a Rando anthropomorphic phantom using various selectable combinations of tube voltage and tube current values. Thermoluminescence dosemeters were used to obtain entrance skin dose data. Effective dose was estimated using normalised organ dose data provided by the National Radiological Protection Board. One hundred and twelve head, 114 thoracic and 111 abdominal patient scanograms were obtained with lower settings than those recommended by the operator's manual. Scanogram sufficiency was assessed by four observers. Head and thoracic scanograms obtained with 80 kV/50 mA and abdominal scanograms obtained with 80 kV/75 mA were found to be acceptable, even though the operator's manual recommendation was 120 kV/100 mA. Thus, the scanogram effective dose was reduced by 72%, 84% and 88% for head, thorax and abdomen examination respectively. Effective dose from a complete CT examination may be reduced by up to 3.5% without any subsequent image quality degradation of the diagnostically important sectional images.