"Because of the growing number of slices in new CT scanners, we investigated the effect for 16-, 64-, and 256-slice scanners," lead author Dr. Hugo de Jong told AuntMinnie.com. As an example, we looked at eye-lens dose in helical brain scans because of their relative vulnerability."
The study at University Medical Center Utrecht in the Netherlands assessed the impact on 163 patients undergoing head CT using three Philips Healthcare (Andover, MA) CT scanners with corresponding numbers of detector rows: a 16-slice Mx8000 IDT, a 64-slice Brilliance, and a 256-slice Brilliance iCT, the latter used with and without dose-reduction based on dynamic moving z-axis collimator blades.
Even when the eyes are deliberately kept outside the planned scan range in helical CT, the dose can still be substantial, de Jong said. "For the 256-slice scanner, placing the eyes 2 cm outside the planned scan range is, in terms of dose, almost equal to fully including the eyes in the planned scan," he said, though technical innovation such as helical dose saving can significantly decrease it.
"If dose to the eye lens is an issue, helical acquisitions of the brain should be avoided -- especially for 64- and higher slice scanners," de Jong said.
