Ct instrumentation lecture. NCHANJI NKEH KENETH, RADIOLOGY DEPARTMENT, ST LOUIS UNIVERSITY, MILE 3 NKWEN- BAMENDA TOWN, CAMEROON

COMPUTED TOMOGRAPHY INSTRUMENTATION AND

OPERATION

Nchanji NKEH [email protected]/[email protected]

671459765/662695118

B.TECH/HPD, MDIRT

CHM Virtued Academy India (Ongoing)

Leader

Radiology Department

Level 300 MDI

2016/2017 Academic Year

ST. Louis UNIHEBS mile 3 Nkwen ,Bamenda- Cameroon

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COMPUTED TOMOGRAPHY INSTRUMENTATION AND OPERATION

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OUTLINE CT SYSTEM COMPONENTS – DEFINITION OF

A SCANNER SCANNER COORDINATE SYSTEM – XYZ,

ISOCENTER IMAGING SYSTEM COMPUTER SYSTEM DISPLAY, RECORDING, AND STORAGE

SYSTEMS

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CT MAIN SYSTEMS

IMAGING SYSTEM COMPUTER SYSTEM DISPLAY, RECORDING, STORAGE SYSTEM DATA ACQUISITION SYSTEM

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CT SYSTEMGANTRY

DETECTORS

SAMPLE HOLD UNIT

ADC

ARRAY PROCESSOR

HOST COMPUTER

STORAGECONSOLE

SCAN CONTROLLER

DAC

GANTRY CONTROL

HIGH VOLTAGE GENERATOR

X-RAY TUBE18

SCANNER 19

Some CT hardware 20

SCANNER

GANTRY PATIENT COUCH

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GANTRY HOUSES:

X-RAY TUBE GENERATOR (LOW VOLTAGE DESIGN) COLLIMATORS DETECTORS

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GANTRY CHARACTERISTICS

APERTURE TILTING RANGE

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MOST OF THE SCANNERS HAVE 70CM APERTURE

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70 CM

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COORDINATE SYSTEM

X

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COORDINATE SYSTEM

Y

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COORDINATE SYSTEM

Z

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ISOCENTER 32

TILTING RANGE OF MOST SCANNERS- +30 TO -30

DEGREES

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PATIENT COUCH :

450 LBS (204 KG) DISTRIBUTED WEIGHT LIMIT

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SCANNABLE RANGE:

COVERAGE FROM HEAD TO THIGH (162CM)

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MAX. SCANNABLE RANGE 36

IMAGING SYSTEM

PRODUCTION OF X-RAYS SHAPING OF X-RAY BEAM ENERGY FILTERING X-RAY BEAM

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IMAGING SYSTEM COMPONENTS

X-RAY TUBE GENERATOR –HIGH VOLTAGEHIGH VOLTAGE COLLIMATORS FILTER DETECTORS DETECTOR ELECTRONICS

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X-RAY TUBE AND X-RAY PRODUCTION

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CATHODE --------MADE OF TUNGSTEN

IN CT – STILL SMALL AND LARGE

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THERMIONIC EMISSION

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

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FOCAL SPOT- CT UTILIZES DIFFERENT FOCAL SPOTS

THE FILAMENT SIZE – LENGTH – FOCAL SPOTFOCAL SPOT

SMALLER FOCAL SPOT - Low mA

SMALLER FOCAL SPOT – sharper image

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ANODE +++++ MADE OF TUNGSTEN AND MOLYBDENUM

TUNGSTENTARGET

TARGET MADE OF TUNGSTEN AND

RHENIUM

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mA – tube current

The number of electrons flowing from cathode to anode

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kVp

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

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S –time of exposure

mAs tube current for certain length of time

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X-RAY PRODUCTION RESULTS IN A LOT OF HEAT AND VERY LITTLE X-RAYS BEING GENERATEDHEAT UNITS CALCULATION

HU= kVp X mA x time

MOST CT TUBES HEAT CAPACITY 3-5 MILLION HU

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REDUCTION OF HEAT UNITS – TECHNIQUE COMPENSATION kVp

mA

Time

INCREASED NOISE

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TOO LOW OF kVp:

NOISE !!!!NOISE !!!!

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X-RAY EMISSION 51

TUBE CURRENT CHANGE

CURRENTINTENSITY

ENERGY – NO CHANGE

2 * mA = 2 * number of photons4 * mA = 4 * number of photons

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

NOISE MOTION

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Tube voltage (kVp) CHANGE

kVp

INTENSITY -

ENERGY –

15% INCREASE OF KVP = 2 * mAs

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kVp IN CT 80-140 TOO LOW – NOISE (NOT ENOUGH PENETRATION OF THE PATIENT ) PHOTON STARVATION - NOISE!!!!!PHOTON STARVATION - NOISE!!!!!

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HIGH VOLTAGE GENERATOR –(HVG)

GENERATES HIGH VOLTAGE POTENTIAL BETWEEN CATHODE AND ANODE OF AN X-RAY TUBE

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CT GENERATOR

5-50 kHz 30-60 kW

KVP SELECTION:

80, 100, 120, 130,140

mA selection:

30, 50, 65, 100, 125, 150, 175, 200, 400

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COLLIMATION IN CT

ADC

PRE-PATIENT COLLIMATION

POST-PATIENT COLLIMATION

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BASIC DATA AQUSITION SCHEME IN CT

ADC

FILTRATION

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FILTRATION CHANGE

FILTRATION

INTENSITY

ENERGY –

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FILTRATION MATERIAL ALUMINIUM ( SPECIAL FILTER IN CT)

BOWTIE

TO MAKE THE BEAM HARDER AND MORE MONOENERGETIC

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Filter

Patient

DEFINES SLICE THICKNESS

REDUCES SCATTER RECHING THE PATIENT

Detector

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CT DETECTORS 63

CONCEPT OF MDCT 64

SDTCT AND MDCT 65

DETECTOR TYPES: SCINTILLATION

PM TUBE

S. CRYSTALS. CRYSTAL

PHOTODIODE

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SCINTILLATION CRYSTALS USED WITH PM TUBES: SODIUM IODIDE –AFTERGLOW + LOW DYNAMIC AFTERGLOW + LOW DYNAMIC

RANGE RANGE ( USED IN THE PAST)( USED IN THE PAST)

CALCIUM FLUORIDE

BISMUTH GERMANATE

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S. CRYSTAL USED WITH PHOTODIODE

CALCIUM TUNGSTATE RARE EARTH OXIDES - CERAMIC

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DETECTOR TYPE: GAS IONIZATION

XENON GAS

30 ATM

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EFFICIENCY OF DETECTORS- QDE

SCINTILLATION – 95% - 100%- COMMONLY COMMONLY USED IN III & IV GENERATION SCANNERSUSED IN III & IV GENERATION SCANNERS

GAS – 50% - 60%

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COMPUTER SYSTEM

RECONSTRUCTION AND POSTPROCESSING CONTROL OF ALL SCANNER COMPONENTS CONTROL OF DATA ACQUSITION, PROCESSING,

DISPLAY. DATA FLOW DIRECTION

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COMPUTER SYSTEM IN CT

MINICOMPUTERS

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COMPUTER SYSTEM COMPOSED OF:

HARDWARE SOFTWARE

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COMPUTER PROCESSING IN CT

SEQUENTIAL PROCESSING MULTITASKING MULTIPROCESSING

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

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

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CT OPERATING SYSTEM

UNIX WINDOWS

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HOST COMPUTER

CONTROL OF ALL COMPONENTS CONTROL OF DATA ACQUSITION, PROCESSING,

DISPLAY. DATA FLOW DIRECTION

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ARRAY PROCESSOR

TAKES DETECTOR MEASUREMENTS FROM HUNDREDS OF

PROJECTIONS. RESPONSIBLE FOR RETROSPECTIVE

RECONSTRUCTION AND POSTPROCESSING OF DATA.

THE MORE PROCESSORS IN THE COMPUTER THE SHORTER THE RECONSTRUCTION TIME

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DATA ACQUISITION SYSTEM (DAS)

SET OF ELECTRONICS BETWEEN DETECTORS AND HOST COMPUTER.

IT CONTAINS: AMPLIFIER, ADC, DAC, GENERATOR, S/H.

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AMPLIFIER

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

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ADC

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

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SAMPLE/HOLD UNIT (S/H)

LOCATED BETWEEN AMPLIFIERAMPLIFIER AND ADC ADC PERFORMS SAMPLING AND ASSIGNS SHADES OF GRAY TO THE PIXELS IN THE DIGITAL MATRIX CORRESPONDING TO THE STRUCTURES

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DASGANTRY

DETECTORS

S/H

ADC

ARRAY PROCESSOR

HOST COMPUTER

STORAGECONSOLE

SCAN CONTROLLER

DAC

GANTRY CONTROL

HIGH VOLTAGE GENERATOR

X-RAY TUBE84

IMAGE DISPLAY, RECORDING, STORAGE

DISPLAYS IMAGE ( OUTPUT FROM COMPUTER) PROVIDES HARD COPY OF THE IMAGE FACILITATES THE STORAGE AND RETRIEVAL OF

DIGITAL DATA COMMUNICATES IMAGES IN THE NETWORK

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IMAGE DISPLAY

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IMAGE RECORDING SYSTEMS(LASER PRINTERS) SOLID STATE

LASER PRINTERS GAS LASER

PRINTERS

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HARD COPY 88

IMAGE STORAGE MEDIA

MAGNETIC TAPES MAGNETO-OPTICAL DISK (MOD) CD

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COMMUNICATION

PACS

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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.

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NightHawk Radiology Services has developed an innovative approach to the delivery of radiology services by operating centralized, state-of-the-art reading centers in Sydney, Australia and Zurich, Switzerland. Staffing U.S.-trained, board-certified radiologists specializing in emergency radiology, these locations are ideally situated for U.S. care because when it’s the middle of the night in Boston, it’s daytime “Down Under.” When it’s early morning in Los Angeles, it’s daytime in the Alps. From the centralized reading centers, NightHawk radiologists interpret exams and report the results to attending physicians in real-time, usually less than 20 minutes.

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CT ROOM LAYOUT 93

How much does a CT scanner cost?

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How much ??4-slice scanner: $85,000 - $115,000

16-slice scanner: $145,000 - $225,000

64-slice scanner: $250,000 - $450,000

Service contracts:$100,000 - $135,000

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Lecture delivered with use of resources from ICRP, IAEA,

AAPM and GE

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NEXT LECTURE:

1. ULTRASONOGRAPHIC INSTRUMENTATION

2. MAMMORAPHIC INSTRUMENTATION

3. FLUOROSCOPIC INSTRUMENTATION

4. MRI INSTRUMENTATION

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