Relationship between radiographic techniques (kilovolt and milliampere-second) and CTDIVOL

Abstract

To investigate the relationship between radiographic techniques (i.e. kilovolt and milliampere-second) and the corresponding volume computed tomography dose index (CTDI(vol)). Data were obtained for CTDI(vol) for head and body phantoms from the ImPACT CT patient dosimetry calculator for 43 scanners from four major vendors of medical imaging equipment (i.e. GE, Philips, Siemens and Toshiba). CTDI(vol) were obtained with the largest X-ray beam width, and using a CT pitch of unity. For each scanner, relative values of CTDI(vol) were also computed as a function of X-ray tube voltage, normalised to unity at 120 kV. The average CTDI(vol) for 43 commercial scanners was 167 + or - 44 microGy (mA s)(-1) for the head phantom and 78 + or - 22 microGy (mA s)(-1) for the body phantom. The 90th percentile CTDI(vol) values are approximately twice the corresponding 10th percentile values for both head and body phantoms. Over the last 20 y, the head phantom CTDI(vol) has increased approximately 50 % and the body phantom CTDI(vol) has increased approximately 90 %. For both, the head phantom and the body phantom, CTDI(vol) is proportional to kilovolt(2.6). CT output must be specified using CTDI(vol) because for a fixed kilovolt and milliampere-second, CT scanner outputs (CTDI(vol)) differ by about a factor of 2. Increasing the X-ray tube voltage from 80 to 140 kV increases CTDI(vol) by about a factor of 4.