CT scanner (evolution)

CT scanners were first introduced in 1971 with a single detector for brain study under the leadership of Godfrey Hounsfield, an electrical engineer at EMI (Electric and Musical Industries, Ltd). Thereafter, it has undergone several changes with increase in number of detectors and 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, originally 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): 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
• dual energy CT scanning

Practical points

• third and fourth generation scanner technologies are both used in many health care settings
  • the fourth generation is a fundamentally different acquisition method, but the resulting image quality is similar to the third generation for most applications