Generations of CT scanner

principle of ct scanner
generations
scanning motion
EMI unit
xray beam
x ray tube
advantages
disadvantages
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1. Generation of CT Mk sadham hussain Bsc . MIT 2 nd year (AHS) SCAHS

2. INTRODUCTION Generation of CT is classified based upon arrangement of components and mechanical motion required to collect data. Scan time reduction is the predominant reason for introducing new configuration They are 7 generation in CT scanner

3. The basic principle behind CT is that the internal structure of an object can be reconstructed from multiple projections of the object

4. 1 st generation Original EMI unit was a first generation scanner. It designed only for evaluation of brain . Scanning motion : translate - rotate geometry Detectors : single or paired X ray beam : narrow pencil beam x- ray tube : an air cooled stationary anode x- ray tube X- ray beam : narrow pencil beam Scan time : 25mins( appx .) Scan mode : step and shoot scanning Power supply : straighten twisted system cables

5. EMI unit

6. The tube and detector were then rotated slightly and the process was repeated until a 180 degree arc was covered Advantage - it employed pencil beam geometry which allowed very efficient scatter reduction Disadvantage Scan time were very long   misregistration   artifact

7. 2 nd generation Scanning motion : translate – rotate geometry Detectors : linear detector array (30) X ray beam : narrow fan beam X ray tube : conventional x -ray tube Scan mode : step and shoot scanning Power supply : straighten twisted system cables Scan time : 5-10 mins ( appx .) Advantage : reduced scan time , reduced patient dose Disadvantage : more scatter radiation

8. 3 rd generation Scanning motion : rotate – rotate geometry Detectors : arc of detectors (400 to 900) (xenon gas or solid state detector) X ray tube : metal ceramic X – Ray tube X ray beam : wider fan beam Power supply : high frequency generator with Slip Ring technology Scan time : < 5 to 6 sec ( appx .) Slip rings permit the gantry frame to rotate continuously Both x ray tube and detectors arc a rotate around the patient in 360 ° and scan . Advantage : reduce scan time , reduce patient dose . Disadvantage : ring artifacts .

9. 4 th generation scanning motion : rotate fixed geometry Detectors : ring of detectors (>2000) X ray beam : wider fan beam X ray tube : metal ceramic x ray tube X ray tube rotates in a circle inside the detector ring . Scan time : <2-3 sec Advantage : 1. reduce scan time 2. elimination of ring artifacts Disadvantage : 1.high cost because of more no of detectors 2. more scatter radiation

10. 5 th generation Electron beam computed tomography It commonly referred to cvct / cine ct scanner No mechanical scanning motion X ray tube and detector are stationary Detectors : 4800 detectors Beam : larger fan beam Scan time : 50ms Basic component Electron gun Focusing /deflecting coils Tungsten target rings A ring of detectors arranged in an arc of 210° Advantage : 1. it improve the temporal resolution 2. its special for cardiac imaging Disadvantage :1. low spatial resolution 2. expensive

11. Electron beam computed tomography

12. 6 th generation Helical / spiral CT scanner Helical or spiral scanner it acquired data while the table is moving As a result , the x ray source moves in a helical pattern around the patient being scanned Helical CT scanner use either 3 rd or 4 th generation slip ring designs Advantage Fewer motion artifact Improved lesion detection Multi planar imaging Reduced scan time Faster image acquisition Improved 3d , coronal , sagittal , physiological imaging .

13. 7 th generation It has multiple detector array The collimator spacing is wider and more x ray are used to producing image data There is formation of cone beam and multiple parallel rows of detectors Widened x ray beam and detector array to acquire multiple slices This gives advantage of reducing scan time with increased Z- resolution but it is very expensive

14. References COMPUTED TOMOGRAPHY for TECHNOLOGISTS Christensen’s physics of diagnostic radiology The physics of radiology and imaging thalyan . K Slide share . Net