Calibration and features of air-kerma length product meters

Pencil-type air-kerma length product meters are generally used for quality control and radiation exposure measurements in computed tomography. To ensure reliable results, these meters should be calibrated so that measurements are traceable to international standards. Suitable calibration procedures, together with the properties of these meters, were examined and compared with the international standards and recommendations. The calibration procedure and setup used in this study were slightly modified compared with international recommendations. The special collimator system was found to cause less scatter than similar setups in earlier studies. The energy dependence of the meter response was investigated for several types of meters with standard radiation qualities. With most tested meter types, the total variation due to energy dependence was <4 %, but some had strong energy dependence and the variation was up to 15 % or higher. This highlights the importance of a proper calibration. The response of one semiconductor meter type varied up to 8 % when rotating the meter around its axis; this should be taken into account when making calibrations with a static setup.