Final answer:
Third generation CT scanners use a helical or spiral scan geometry, allowing for faster scanning and three-dimensional imaging.
Step-by-step explanation:
Third generation CT scanners use a helical or spiral scan geometry. In this type of scan, the x-ray tube and detector array rotate continuously around the patient as the patient moves through the scanner on a table. This allows for faster scanning and reduces motion artifacts compared to earlier generation scanners. The helical scan geometry also enables three-dimensional imaging by combining multiple images of different slices.