CT scanning

Medical Physics | AQA A-Level Physics

Key Definition

CT (computed tomography) scanner: A device that uses a rotating X-ray tube and an array of detectors arranged in a ring to produce detailed cross-sectional (2D slice) images of the body. A computer combines multiple slices to build a 3D image.

The X-ray tube rotates around the patient while an array of detectors on the opposite side of the ring records the transmitted intensity from many angles.
A narrow, monochromatic X-ray beam is used to improve contrast and reduce scatter.
A computer processes the attenuation data from thousands of angles to reconstruct a 2D cross-sectional image of a single slice. The patient is then moved slightly and the process is repeated for the next slice.
Multiple slices are stacked by the computer to produce a full 3D image of the internal structure.
Advantages: high spatial resolution (about 0.5 mm), can distinguish between tissues with similar densities, produces 3D images, fast acquisition.
Disadvantages: high radiation dose (much higher than a single X-ray), expensive equipment, cannot be used frequently due to cumulative radiation risk.