AbstractID: 6686 Title: How do patient size and x-ray technique factors affect radiation
doses for head CT examinations?
The purpose of this study was to investigate how patient size & composition and the
choice of x-ray technique factors affect radiation doses in head CT examinations. Head
size dimensions, cross-sectional areas, and mean Hounsfield unit (HU) values were
obtained from head CT images of 127 patients. For radiation dosimetry purposes, patients
were modeled as uniform cylinders of water. Dose computations were performed
assuming a CT scan consisting of 18 sections (7 mm thick) scanned at 340 mAs. Values
of mean section dose, energy imparted and effective dose were computed for x-ray tube
potentials ranging from 80 to 140 kVp. An infant head is equivalent to a water cylinder
with a radius of 60 mm, whereas an adult head has an equivalent radius 50% greater. For
the same technique factors, mean section doses in infants are 35% higher than in adults.
Energy imparted for adults are 50% higher than for infants, but infant effective doses are
four times higher than for adults. Adults received a dose of 0.95 mSv at 120 kVp.
Increasing the x-ray tube potential from 80 to 140 kVp increases patient doses by about a
factor of five. CT doses depend on patient head size & composition as well as selected xray tube potential.