CT scanners were first introduced in 1971 with a single detector for brain study under the leadership of Sir Godfrey Hounsfield, an electrical engineer at EMI (Electric and Musical Industries Ltd). After that, it has undergone multiple improvements, with an increase in the number of detectors and a decrease in the scan time.

First generation 

• detectors: one

• type of beam: pencil-like x-ray beam

• tube-detector movements: translate-rotate

• duration of scan (average): 25-30 mins

Second generation 

• detectors: multiple (up to 30)

• type of beam: fan-shaped x-ray beam

• tube-detector movements: translate-rotate

• duration of scan (average): less than 90 sec

Third generation 

• detectors: multiple, initially 288; newer ones use over 700 arranged in an arc

• type of beam: fan-shaped x-ray beam

• tube-detector movements: rotate-rotate

• duration of scan (average): approximately 5 sec

Fourth generation

• detectors: multiple (more than 2000) arranged in an outer ring which is fixed

• type of beam: fan-shaped x-ray beam

• tube-detector movements: rotate-fixed 

• duration of scan (average): a few seconds

Other technologies

Other CT technologies have been adapted to third and fourth-generation scanners, including:

• helical ("spiral") image acquisition

  • used in all modern CT machines

  • slip-ring technology made the helical acquisition possible

• dual-energy CT scanning

• electron beam CT

  • considered a fifth-generation technology, electron beam CT has been around since 1984

  • involved an electron beam that is deflected via a magnet around the gantry (no moving parts, great temporal resolution)

  • initially designed for cardiac imaging, electron beam CT was made obsolete once multi-detector CT demonstrated better spatial resolution along (with the final blow being ECG-gated scanning)

Emerging technologies

Further technologies have been not yet been broadly adopted but show great promise including:

• photon counting CT

Practical points

• third and fourth-generation scanner technologies are both used in many healthcare settings

  • the fourth generation is a fundamentally different acquisition method, but the resulting image quality is similar to the third generation for most applications

See also

• cone beam CT

• PET-CT

• flat panel CT