Historical DevelopmentHistorical Development

CT scanners are categorized into CT scanners are categorized into several generations depending on the several generations depending on the type of detectors, scanning method type of detectors, scanning method etcetc

First Generation Scanners Single detector, single x-ray tube,

rotate/translate pencil beam system, rotation angle/step 1°

Long scan time Poor spatial resolution Best scatter rejection

First generation model of a CT head scanner

Second Generation ScannersSecond Generation ScannersLinear array of about Linear array of about 30 detectors, single x-30 detectors, single x-ray tube, ray tube, rotate/translate rotate/translate motion, narrow angle motion, narrow angle (10 (10 °° ) fan beam ) fan beam

rotation angle/step 10rotation angle/step 10°°

Shortest scan time Shortest scan time was about 18 s per was about 18 s per sliceslice

Third Generation ScannersThird Generation Scanners

Linear array of about Linear array of about 800 detectors, single x-800 detectors, single x-ray tube, rotate/rotate ray tube, rotate/rotate motion only, wide fan motion only, wide fan beam to cover the beam to cover the entire patiententire patient

Scan time of newer Scan time of newer scanners is about ½ s scanners is about ½ s per sliceper slice

Can produce ring Can produce ring artifactsartifacts

Fourth Generation ScannersFourth Generation ScannersComplete circular array of Complete circular array of about 4800 stationary about 4800 stationary detectorsdetectors

Single x-ray tube rotates Single x-ray tube rotates with in the circular array of with in the circular array of detectorsdetectors

Wide fan beam to cover Wide fan beam to cover the entire patientthe entire patient

Scan time of newer Scan time of newer scanners is about ½ s per scanners is about ½ s per sliceslice

Designed to address ring Designed to address ring artifactsartifacts

Fifth Generation ScannersFifth Generation Scanners

210210° arc° arc array of stationary detectors array of stationary detectors

x-rays are produced from the focal track x-rays are produced from the focal track as high energy electron beam strikes the as high energy electron beam strikes the tungsten targettungsten target

Scan time is about 50 ms per sliceScan time is about 50 ms per slice

Developed for cardiac tomographic Developed for cardiac tomographic imagingimaging

Three major components of EBCT scanner:A – Electron gunB- Tungsten targetsC - Detectors