Components of ct
- 1. BY MUNA BUDHATHOKI B.SC. MIT 2ND YEAR CMCTH,CHITWAN
- 2. HISTORICAL PERSPECTIVE oG.N Hounsfield (an engineer with EMI) is credited with the invention of CT oAllan MacLeod Cormack of united state developed solution to the mathematical problem in CT oIn 1972, the first head CT scanner was invented by Goldfrey Hounsfield AVI00719 GN Hounsfield 2
- 3. oin 1972, Hounsfield shared the Nobel prize in medicine and physiology with Allan Cormack AVI00719 Allan Cormack 3
- 4. COMPONENTS OF CT • CT has three major systems 1) Imaging system a. Gantry b) table 2)Computer system 3)Operating system
- 5. IMAGING SYSTEM A)GANTRY • A mounted framework that surrounds the patient in a vertical plane • The gantry includes :-a)slip ring b) x-ray tube c)high voltage generator d)collimator e)detector d) data aquisition system
- 6. EXTERNAL APPEARANCE OF GANTRY 1.GANTRY APPERTURE 2.MICROPHONE 3.SAGITTAL LASER LIGHT ALIGNMENT 4.PATIENT GUIDE TABLE 5.X-RAY EXPOSURE INDICATOR LIGHT 6.EMERGENCY STOP BUTTOM 7.GANTRY CONTROL PANNEL 8.EXTERNAL LASER ALIGNMENT LIGHT 9.PATIENT COUCH 10.ECG GATING MONITOR 6AVI00719
- 7. INTERNAL APPEARANCE OF GANTRY 1.X-RAY TUBE 2.FILTER,COLLIMATOR, 3.INTERNAL PROJECTOR 4.OIL COOLER 5.HIGH VOLTAGE GENERATOR(0- 75kv) 6DIRECT DRIVE GANTRY MOTOR 7.ROTATION CONTROL UNIT 8.DAS 9.DETECTOR 10.SLIP RING 11.DETECTOR COTROL UNIT 12.HVG (75-150 KV) 13.POWER UNIT 14.LINE NOISE FILTER 7AVI00719
- 8. Cont…… • Two important features of gantry :- oGantry aperture :-50cm -90cm oTilting range :- 30 degree towards or away from the patient table • Three intense white or low power laser light
- 9. SLIP RING TECHNOLOGY • Introduced in 1990 • Electromechanical device • Consist of circular electrical conductive rings and brushes • Slip ring transmit electrical energy across a rotating interface • It allows continuous gantry rotation
- 10. DESIGN OF SLIP RING • TWO DESIGN 1. DISC DESIGN 2. CYLINDRICAL DESIGN CYLINDRICAL DESIGN
- 11. CT X-RAY TUBE • Located in the heart of the gantry • Provide radiation source for CT • First and second generation scanner used fixed anode , oil cooled x- ray tube • Borosilicate used as glass envelope in early CT • Nowadays metal ceramic x-ray tube is used
- 12. Cont….. • In modern CT x-ray tube - heat capacity : above 5MHU - Has large anode with graphite backing - Utilize a bigger filament - Anode angle is 7-10 degree
- 13. AQUILLION X-RAY TUBE • High capacity multi slice CT tube • Heat storage capacity – 7.5 MHU • Cooling rate – 1.7 MHU/min • Anode grounded • Focal spot – 1.4mm x1.4mm • Air cooled
- 14. STRATON X –RAY TUBE • Zero heat storage capacity • Cooling rate – 4.7 MHU /min • Cooled down within 20 sec • Tube current – 500 mA • Based on rotating envelope tube • focal spot – tungsten and rhenium
- 15. GENERATOR • conventional generator for CT scanner were based on the 60 Hz voltage frequency • CT scanner now use high frequency generator • HVG circuit is referred to as high frequency inverter circuit • Mounted on the rotating frame with the x-ray tube • Have very low ripple <1 %
- 16. FILTRATION IN CT • Absorbs low energy x-rays • Reduce scatter and patient dose • There are mainly two types of filtration utilized in CT i. Mathematical filter ii. Inherent filter :-a)flat filter b)bowtie filter
- 17. COLLIMATOR • TYPES OF COLLIMATOR IN CT SCAN I. Pre-patient collimator II. Post- patient collimator “1D” anti scatter collimator “ 2D” anti scatter collimator
- 18. CT DETECTORS • TYPES OF DETECTOR :- 1. Gas ionization detector convert x-ray energy directly into electrical signal 2. Scintillation detector convert x-ray energy into light
- 19. 1. GAS IONIZATION DETECTOR • Based on the principal of ionization • Use high pressure • Used non-radioactive xenon gas • Consist of series of individual gas chamber • QDE :60-90%
- 21. SCINTILLATION DETECTOR • Use a photomultiplier tube • NaI and CsI were used in early generation of scanners • NaI was replaced by Bismuth germanate & cadmium tungstate • Helical & MDCT scanner use combined Cadmium tungstate ,yttrium or gadolinium ceramic scintillator with a photodetector • Now a days solid state photodiode multiplier scintillation crystal detector are used
- 22. DETECTOR CHARACTERISTIC • Efficiency • Stability • Response time • After glow • Dynamic range
- 23. DATA AQUISTISTION SYSTEM • DETECTOR - ELETRICAL SIGNAL – DAS – COMPUTER - DIGITAL SIGNAL- ARRAY PROCESSOR (IMAGE GENERATOR OR RECONSTOCTOR GENERATOR)
- 24. PATIENT COUCH/TABLE • Should be strong and rigid • Either curved or flat • Capable of moving up and down • Constructed of low atomic no. of carbon graphite fiber
- 25. COMPUTER SYSTEM • Uses minicomputer • Unique components of CT • Must have sufficient speed and memory • Calculate the attenuation of the individual voxels using algorithm • Must be very fast
- 26. OPERATOR CONSOLE • Permits control of all scan parameter • Commands computer to reconstruct and transfer of image data for storage in data file • pre-programed with kvp & mA • Has three console
Editor's Notes
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