Dosimetric characteristics of a 16-slice computed tomography scanner

Standard CT dose measurements were performed on a Siemens Sensation 16 scanner. CT dose indices, free-in-air (CTDI_F) and weighted (CTDI_W), were measured in all available axial and helical beam collimations of the head and body scanning modes. The effect of tube current, high voltage, rotation time, beam collimation and pitch on the CT doses was investigated. CT doses increased as a power function of high voltage. The kVp exponent n varied with beam collimation from 2.7 to 3.1 for CTDI_W, and from 2.4 to 2.6 for CTDI_F. Automatic change of the focal spot size increased radiation doses up to a factor of 1.18. Measured small-focus CTDI_W values differed from those displayed at the console from –24 to 14%. Peripheral doses in the head phantom were higher compared to the body phantom by a factor of 1.5 to 2. Central doses are 2.7 to 4.1 times higher. Differences in beam collimation resulted in 50% variation in the CTDI_W in the body phantom and 60% in the head phantom. In conclusion, our study has confirmed the great impact of technique factors and acquisition parameters on CT doses. The provided comprehensive dosimetric data will facilitate the dose-effective use of the scanner studied.