Relationship between radiographic techniques (kilovolt and milli-ampere-second) and CTDIvol

To investigate the relationship between radiographic techniques (i.e. kilovolt and milli-ampere-second) and the corresponding volume computed tomography dose index (CTDIvol). Data were obtained for CTDIvol 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). CTDIvol were obtained with the largest X-ray beam width, and using a CT pitch of unity. For each scanner, relative values of CTDIvol were also computed as a function of X-ray tube voltage, normalised to unity at 120 kV. The average CTDIvol for 43 commercial scanners was 167 ± 44 μGy (mA s)-1 for the head phantom and 78 ± 22 μGy (mA s)-1 for the body phantom. The 90. percentile CTDIvol values are approximately twice the corresponding 10. percentile values for both head and body phantoms. Over the last 20 y, the head phantom CTDIvol has increased ∼50% and the body phantom CTDIvol has increased ∼90%. For both, the head phantom and the body phantom, CTDIvol is proportional to kilovolt. CT output must be specified using CTDIvol because for a fixed kilovolt and milli-ampere-second, CT scanner outputs (CTDIvol) differ by about a factor of 2. Increasing the X-ray tube voltage from 80 to 140 kV increases CTDIvol by about a factor of 4. (authors)