Radiation dose analyses
From the original study 289 CT head scans had been saved in the PACS at the Karolinska University Hospital in Huddinge, Stockholm. The average effective diameter of the participants’ heads (N = 278) was 167±6 mm and as this was very close to the diameter of the CTDI head phantom, no size corrections were made to the reconstructed CTDIThe dose range for the reconstructed doses was 22.2–157.4 mGy with a mean of 61.7 mGy. The comparison group comprised of the participants in the observation group with no known reassignment (N = 381). The dose range for the lower dose group was 22.2–49.4 mGy with a median of 45.2 mGy (N = 126) and the dose range for the higher dose group was 50.2–157.4 mGy with a median of 78.2 mGy (N = 126). Results for the different exposure groups, 0 mGy, >0–50 mGy, and >50 mGy, showed no statistically significant differences in their proportions of participants being in a higher scoring grade category or eligibility for high school (