Principle
Irradiate a slice of tissue from multiple angles
Measure the output from different sides
Tissues have different densities
- with denser tissue fewer x-rays reach the detectors
Hounsfield scale
Bone 2000
ST 40
Water 0
Fat -100
Air -1000
Settings
Grey scale
- eye can only see 11 different shades
Adjust settings to bone or soft tissue
Multislice
Multiple detectors at any one time
- increase amount of data acquired in a single slice
- increased speed
- reduces artefact
Slice thickness
Decreased slice thickness
- increased info
- increased radiation
Reconstruction
Axial
Sagittal
Coronal
3D
Radiation dose
CXR 1
Pelvis 35
CT Chest 400
CT Abdo/pelvis 500