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COMPUTED TOMOGRAPHY INSTRUMENTATION AND OPERATION Dr. Halima Hawesa Lecture 3-RAD 466.

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Presentation on theme: "COMPUTED TOMOGRAPHY INSTRUMENTATION AND OPERATION Dr. Halima Hawesa Lecture 3-RAD 466."— Presentation transcript:

1 COMPUTED TOMOGRAPHY INSTRUMENTATION AND OPERATION Dr. Halima Hawesa Lecture 3-RAD 466

2 OUTLINE CT SYSTEM COMPONENTS – DEFINITION OF A SCANNER CT SYSTEM COMPONENTS – DEFINITION OF A SCANNER SCANNER COORDINATE SYSTEM – XYZ, ISOCENTER SCANNER COORDINATE SYSTEM – XYZ, ISOCENTER IMAGING SYSTEM IMAGING SYSTEM COMPUTER SYSTEM COMPUTER SYSTEM DISPLAY, RECORDING, AND STORAGE SYSTEMS DISPLAY, RECORDING, AND STORAGE SYSTEMS

3 CT MAIN SYSTEMS IMAGING SYSTEM IMAGING SYSTEM COMPUTER SYSTEM COMPUTER SYSTEM DISPLAY, RECORDING, STORAGE SYSTEM DISPLAY, RECORDING, STORAGE SYSTEM DATA ACQUISITION SYSTEM DATA ACQUISITION SYSTEM

4 CT SYSTEM GANTRY DETECTORS S/H ADC ARRAY PROCESSOR HOST COMPUTER STORAGE CONSOLE SCAN CONTROLLER DAC GANTRY CONTROL HIGH VOLTAGE GENERATOR X-RAY TUBE

5 SCANNER

6 SCANNER GANTRY GANTRY PATIENT COUCH PATIENT COUCH

7 GANTRY HOUSES: X-RAY TUBE X-RAY TUBE GENERATOR (LOW VOLTAGE DESIGN) GENERATOR (LOW VOLTAGE DESIGN) COLLIMATORS COLLIMATORS DETECTORS DETECTORS

8 GANTRY CHARACTERISTICS APERTURE APERTURE TILTING RANGE TILTING RANGE

9 MOST OF THE SCANNERS HAVE 70CM APERTURE

10 70 CM

11 COORDINATE SYSTEM X

12 Y

13 Z

14 ISOCENTER

15 TILTING RANGE OF MOST SCANNERS- +30 TO -30 DEGREES

16 PATIENT COUCH : 450 LBS (204 KG) DISTRIBUTED WEIGHT LIMIT

17 SCANNABLE RANGE: COVERAGE FROM HEAD TO THIGH (162CM)

18 MAX. SCANNABLE RANGE

19 IMAGING SYSTEM PRODUCTION OF X-RAYS PRODUCTION OF X-RAYS SHAPING OF X-RAY BEAM ENERGY SHAPING OF X-RAY BEAM ENERGY FILTERING X-RAY BEAM FILTERING X-RAY BEAM

20 IMAGING SYSTEM COMPONENTS X-RAY TUBE X-RAY TUBE GENERATOR –HIGH VOLTAGE GENERATOR –HIGH VOLTAGE COLLIMATORS COLLIMATORS FILTER FILTER DETECTORS DETECTORS DETECTOR ELECTRONICS DETECTOR ELECTRONICS

21 X-RAY TUBE AND X-RAY PRODUCTION

22 CATHODE MADE OF TUNGSTEN IN CT – STILL SMALL AND LARGE

23 THERMIONIC EMISSION CATHODE HEATED UP TO AT LEAST 2,200 DEG. CELSIUS TO LIBERATE ELECTRONS FOR TRANSIT TO ANODE

24 FOCAL SPOT- CT UTILIZES DIFFERENT FOCAL SPOTS THE FILAMENT SIZE – LENGTH – FOCAL SPOT THE FILAMENT SIZE – LENGTH – FOCAL SPOT SMALLER FOCAL SPOT - Low mA SMALLER FOCAL SPOT – sharper image

25 ANODE MADE OF TUNGSTEN AND MOLYBDENUM TUNGSTEN TARGET TARGET MADE OF TUNGSTEN AND RHENIUM

26 mA – tube current The number of electrons flowing from cathode to anode The number of electrons flowing from cathode to anode

27 kVp Potential difference between cathode and anode (Volts) kilo means 1,000 x. Potential difference between cathode and anode (Volts) kilo means 1,000 x.

28 S –time of exposure mAs tube current for certain length of time

29 X-RAY PRODUCTION RESULTS IN A LOT OF HEAT AND VERY LITTLE X-RAYS BEING GENERATED HEAT UNITS CALCULATION HU= kVp X mA x time MOST CT TUBES HEAT CAPACITY 3-5 MILLION HU

30 REDUCTION OF HEAT UNITS – TECHNIQUE COMPENSATION kVp kVp mA mA Time Time INCREASED NOISE

31 TOO LOW OF kVp: NOISE !!!! NOISE !!!!

32 Why changing mA or time Avoiding motion – mA time Avoiding motion – mA time Pediatric technique modification Pediatric technique modification Reducing noise - mAs Reducing noise - mAs NOISE MOTION

33 Tube voltage (kVp) CHANGE kVp INTENSITY - ENERGY – 15% INCREASE OF KVP = 2 * mAs

34 kVp IN CT TOO LOW – NOISE TOO LOW – NOISE (NOT ENOUGH PENETRATION OF THE PATIENT ) (NOT ENOUGH PENETRATION OF THE PATIENT ) PHOTON STARVATION - NOISE!!!!! PHOTON STARVATION - NOISE!!!!!

35 HIGH VOLTAGE GENERATOR – (HVG) GENERATES HIGH VOLTAGE POTENTIAL BETWEEN CATHODE AND ANODE OF AN X-RAY TUBE GENERATES HIGH VOLTAGE POTENTIAL BETWEEN CATHODE AND ANODE OF AN X-RAY TUBE

36 CT GENERATOR 5-50 kHz 5-50 kHz kW kW KVP SELECTION: 80, 100, 120, 130,140 mA selection: 30, 50, 65, 100, 125, 150, 175, 200, 400

37 Filter Patient DEFINES SLICE THICKNESS REDUCES SCATTER RECHING THE PATIENT Detector CT Imaging Steps

38 COLLIMATION IN CT BASIC DATA AQUSITION SCHEME IN CT ADC PRE-PATIENT COLLIMATION POST-PATIENT COLLIMATION FILTRATION

39 X-RAY EMISSION TUBE CURRENT CHANGE CURRENT INTENSITY ENERGY – NO CHANGE 2 * mA = 2 * number of photons 4 * mA = 4 * number of photons

40 FILTRATION CHANGE FILTRATION INTENSITY ENERGY

41 FILTRATION MATERIAL ALUMINIUM ( SPECIAL FILTER IN CT) ALUMINIUM ( SPECIAL FILTER IN CT) TO MAKE THE BEAM HARDER AND MORE MONOENERGETIC

42 CT DETECTORS

43 DETECTOR TYPES: SCINTILLATION PM TUBE S. CRYSTAL PHOTODIODE

44 SCINTILLATION CRYSTALS USED WITH PM TUBES: SODIUM IODIDE SODIUM IODIDE CALCIUM FLUORIDE CALCIUM FLUORIDE BISMUTH GERMANATE BISMUTH GERMANATE

45 S. CRYSTAL USED WITH PHOTODIODE CALCIUM TUNGSTATE CALCIUM TUNGSTATE RARE EARTH OXIDES - CERAMIC RARE EARTH OXIDES - CERAMIC

46 DETECTOR TYPE: GAS IONIZATION XENON GAS 30 ATM

47 EFFICIENCY OF DETECTORS- QDE SCINTILLATION – 95% - 100%- COMMONLY USED IN III & IV GENERATION SCANNERS SCINTILLATION – 95% - 100%- COMMONLY USED IN III & IV GENERATION SCANNERS GAS – 50% - 60% GAS – 50% - 60%

48 COMPUTER SYSTEM RECONSTRUCTION AND POSTPROCESSING RECONSTRUCTION AND POSTPROCESSING CONTROL OF ALL SCANNER COMPONENTS CONTROL OF ALL SCANNER COMPONENTS CONTROL OF DATA ACQUSITION, PROCESSING, DISPLAY. CONTROL OF DATA ACQUSITION, PROCESSING, DISPLAY. DATA FLOW DIRECTION DATA FLOW DIRECTION

49 COMPUTER SYSTEM IN CT MINICOMPUTERS MINICOMPUTERS

50 COMPUTER SYSTEM COMPOSED OF: HARDWARE HARDWARE SOFTWARE SOFTWARE

51 COMPUTER PROCESSING IN CT SEQUENTIAL PROCESSING SEQUENTIAL PROCESSING MULTITASKING MULTITASKING MULTIPROCESSING MULTIPROCESSING

52 SOFTWARE –PROGRAM (S) HELPING CT USER TO COMMUNICATE WITH THE CT SYSTEM

53 CT OPERATING SYSTEM- PROGRAMS THAT CONTROL THE HARDWARE COMPONENTS AND THE OVERALL OPERATION OF THE CT COMPUTER

54 CT OPERATING SYSTEM UNIX UNIX WINDOWS WINDOWS

55 HOST COMPUTER CONTROL OF ALL COMPONENTS CONTROL OF ALL COMPONENTS CONTROL OF DATA ACQUSITION, PROCESSING, DISPLAY. CONTROL OF DATA ACQUSITION, PROCESSING, DISPLAY. DATA FLOW DIRECTION DATA FLOW DIRECTION

56 ARRAY PROCESSOR TAKES DETECTOR MEASUREMENTS FORM HUNDREDS OF PROJECTIONS. RESPONSIBLE FOR RETROSPECTIVE RECONSTRUCTION AND POSTPROCESSING OF DATA. TAKES DETECTOR MEASUREMENTS FORM HUNDREDS OF PROJECTIONS. RESPONSIBLE FOR RETROSPECTIVE RECONSTRUCTION AND POSTPROCESSING OF DATA. THE MORE PROCESSORS IN THE COMPUTER THE SHORTER THE RECONSTRUCTION TIME

57 DATA ACQUISITION SYSTEM (DAS) SET OF ELECTRONICS BETWEEN DETECTORS AND HOST COMPUTER. SET OF ELECTRONICS BETWEEN DETECTORS AND HOST COMPUTER. IT CONTAINS: AMPLIFIER, ADC, DAC, GENERATOR, S/H. IT CONTAINS: AMPLIFIER, ADC, DAC, GENERATOR, S/H.

58 AMPLIFIER SIGNAL FROM DETECTORS GOES TO AMPLIFIERS FOR SIGNAL MAGNIFICATION AND THEN IS SENT TO SAMPLE/HOLD UNIT SIGNAL FROM DETECTORS GOES TO AMPLIFIERS FOR SIGNAL MAGNIFICATION AND THEN IS SENT TO SAMPLE/HOLD UNIT

59 ADC CONVERTS ANALOG SIGNAL OUTPUT FROM THE SCANNING EQUIPMENT TO A DIGITAL SIGNAL SO IT CAN BE PROCESSED BY A COMPUTER. CONVERTS ANALOG SIGNAL OUTPUT FROM THE SCANNING EQUIPMENT TO A DIGITAL SIGNAL SO IT CAN BE PROCESSED BY A COMPUTER.

60 SAMPLE/HOLD UNIT (S/H) LOCATED BETWEEN AMPLIFIER AND ADC PERFORMS SAMPLING AND ASSIGNS SHADES OF GRAY TO THE PIXELS IN THE DIGITAL MATRIX CORRESPONDING TO THE STRUCTURES LOCATED BETWEEN AMPLIFIER AND ADC PERFORMS SAMPLING AND ASSIGNS SHADES OF GRAY TO THE PIXELS IN THE DIGITAL MATRIX CORRESPONDING TO THE STRUCTURES

61 DAS GANTRY DETECTORS S/H ADC ARRAY PROCESSOR HOST COMPUTER STORAGE CONSOLE SCAN CONTROLLER DAC GANTRY CONTROL HIGH VOLTAGE GENERATOR X-RAY TUBE

62 IMAGE DISPLAY, RECORDING, STORAGE DISPLAYS IMAGE ( OUTPUT FROM COMPUTER) DISPLAYS IMAGE ( OUTPUT FROM COMPUTER) PROVIDES HARD COPY OF THE IMAGE PROVIDES HARD COPY OF THE IMAGE FACILITATES THE STORAGE AND RETRIEVAL OF DIGITAL DATA FACILITATES THE STORAGE AND RETRIEVAL OF DIGITAL DATA COMMUNICATES IMAGES IN THE NETWORK COMMUNICATES IMAGES IN THE NETWORK

63 IMAGE DISPLAY

64 IMAGE RECORDING SYSTEMS (LASER PRINTERS) SOLID STATE LASER PRINTERS SOLID STATE LASER PRINTERS GAS LASER PRINTERS GAS LASER PRINTERS

65 HARD COPY

66 IMAGE STORAGE MEDIA MAGNETIC TAPES MAGNETIC TAPES MAGNETO-OPTICAL DISK (MOD) MAGNETO-OPTICAL DISK (MOD) CD CD

67 COMMUNICATION PACS PACS

68 OVERREAD NETWORK While most teleradiology systems purchased over the last decade were intended for on-call purposes, the past two years have seen a rapid increase in the use of teleradiology to link hospitals and affiliated satellite facilities, other primary hospitals, and imaging centers. A number of the enabling technologies needed for effective overread networks, such as more affordable high- speed telecommunications networks and improved data compression techniques, have matured in recent years. While most teleradiology systems purchased over the last decade were intended for on-call purposes, the past two years have seen a rapid increase in the use of teleradiology to link hospitals and affiliated satellite facilities, other primary hospitals, and imaging centers. A number of the enabling technologies needed for effective overread networks, such as more affordable high- speed telecommunications networks and improved data compression techniques, have matured in recent years.

69 CT ROOM LAYOUT Thanks for listening


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