INSTRUMENTATION OF

CT SCAN

BY: BINOOM.Sc. MIT

SMC MEERUT

CT INSTRUMENTATIONTHE INSTRUMENTATION OF CT SCAN MACHINE HAS :• GANTRY• PATIENT TABLE• DETECTORS• DATA ACQUISITION SYSYTEM• X-RAY GENERATOR• X-RAY TUBE• COLLIMATOR• IMAGE DISPLAY AND STORAGE• COMMUNICATION SYSTEMS• CT CONTROL CONSOLE• OPTION AND ACCESSORIES FOR CT

GANTRY• IT CONTAINS A ROTATING SCAN FRAME ONTO WHICH THE X-RAY GENERATOR, X-

RAY TUBE AND OTHERS COMPONENTS ARE MOUNTED.

• THE GENERATOR IS USUALLY A SMALL SOLID-STATE HIGH FREQUENCY GENERATOR.

• IT IS LOCATED CLOSE TO THE X-RAY TUBE , ONLY A SHORT HIGH TENSION CABLE (HTC) IS REQUIRED TO COUPLE THE X- RAY TUBE AND GENERATOR.

• TWO IMPORTANT FEATURES OF THE GANTRY ARE GANTRY APERTURE GANTRY TILTING RANGETHE GANTRY APERTURE IS THE OPENING IN WHICH THE PATIENT IS POSITIONED

DURING SCANNING PROCEDURE .

• MOST SCANNERS HAVE A 70CM APERTURE THAT FACILITATES PATIENT POSITIONING AND HELPS PROVIDES ACCESS TO PATIENTS IN EMERGENCY SITUATION

• THE CT GANTRY MUST BE CAPABLE OF TILTING TO ACCOMMODATE ALL PATIENTS AND CLINICAL EXAMINATIONS

• THE DEGREE OF TILTING VARIES BETWEEN SYSTEMS ;BUT + -12 TO 30 DEGREE IS COMMONLY UESD

• THE GANTRY ALSO INCLUDES A SET OF LASER BEAMS TO AID PATIENT POSITIONING

• OTHER GANTRY CHARACTERISTICS INCLUDE SCAN CONTROL PANELS: CONTROL GANTRY TILT CONTROL PATIENT TABLE ELEVATION EMERGENCY STOPS AND INTERCOM SYSTEMS WITH MULTI LINGUAL AUTO-VOICE FACILITATES

COMMUNICATION WITH THE PATIENT IN ONE OF SEVERAL LANGUAGES.

PATIENT TABLE• IT PROVIDES A PLATFORM ON WHICH THE PATIENT LIES DURING

EXAMINATION

• IT SHOULD BE STRONG AND RIGID TO SUPPORT THE WEIGHT OF THE PATIENT

• IT CONSISITS OF A SUPPORT REFFERED TO AS THE TABLE TOP WHICH FLOATES AND REST ON A PEDESTAL

• THE COUCH IS USUALLY MADE OF CARBON FIBER BECAUSE THEY HAVE LOW ABSORPTION AND PROVIDE EXCELLENT VIBRATION DAMPING FEATURES

• TABLE SHOULD HAVE ABILITY TO CARRY PATEINTS WEIGHT UPTO 150 KG

• IT HAVE HORIZONTAL MOVEMENT WITH THE INWARD AND OUTWARD TO THE GANTRY

• ATTACHMENT FOR HEAD AND FOOT SUPPORTER IS AVAILABLE

• PATIENT TABLE CAN ALSO MOVE UP AND DOWN FOR PROPER POSITIONING OF THE PATIENT

• PATIENT TABLE MOVEMENT IS DONE BY HYDRAULIC SYSTEMS AND TABLE MOVEMENTS IS CONTROLLED BY THE SWITCHES PROVIDED IN THE GANTRY OR IN THE CONSOLE

• THE MOVEMENT OF TABLE IN BETWEEN THE SCANS IS CONTROLLED BY THE COMPUTERS ACCORDING TO PRE- DETERMINED PLANER CONTROL

DETECTORSARE THE DEVICES WHICH CAPTURES THE RADIATION BEAM FROM THE

PATIENT AND CONVERT IT INTO ELECTRICAL SIGNALS, WHICH ARE THEN CONVERTED INTO BINARY CODED INFORMATION.

CHARACTERISTICS: - 1. EFFICIENCY 2. RESPONSE TIME 3. DYNAMIC RANGE 4. HIGH REPRODUCIBILITY 5. STABILITY.

• EFFICIENCY- IT REFERS TO THE ABILITY TO CAPTURE, ABSORB AND CONVERT X-RAY PHOTONS TO ELECTRICAL SIGNALS.

• RESPONSE TIME- IT REFERS TO THE SPEED WITH WHICH THE DETECTOR CAN DETECT AN X-RAY EVENT.

• DYNAMIC RANGE- IT IS THE RATIO OF THE LARGEST SIGNAL TO BE MEASURED TO THE PRECISION OF THE SMALLEST SIGNAL TO BE DISCRIMINATED.

• HIGH REPRODUCIBILITY- IT REFERS TO THE CONVERSION PHOTONS INTO ELECTRICAL SIGNAL.

• STABILITY- IT REFERS TO THE STEADINESS OF THE DETECTOR RESPONSE.

SCINTILLATION DETECTOR• EARLY SCINTILLLATION DETECTORS ARRAY CONTAINED CRYSTAL COUPLED

WITH PMT.

• PMT ARE FAIRLY SO BIG , SO THESE DETECTORS CANNOT BE PACKED VERY TIGHTLY TOGETHER. THEY REQUIRED A POWER SUPPLY FOR EACH PMT.

• CONSEQUENTLY , THEY HAVE BEEN REPLACED BY SILICON PHOTODIODE

• A PHOTO DIODE CAN CONVERT A LIGHT SIGNAL INTO AN ELECTRON FLOW (ELECTRIC CURRENT) OUTPUT THAT IS PROPORTIONAL TO INTENSITY OF THE HEIGHT SIGNAL.

• ADVANTAGES: SMALLER SIZE AND GREATER STABILITY

• NaI CRYSTAL WAS USED IN EARLIEST SCAN.FIRST IT WAS HYGROSCOPIC AND REQUIRES AN AIR TIGHT CONTAINER.

• SECOND IT HAS A VERY LONG AFTER GLOW.

• THIS WAS QUICKLY REPLACED BY BISMUTHGERMENATE (BGO) AND CESIUM IODIDE.

• SCINTILLATION DETECTORS HAVE HIGH X-RAY DETECTION EFFICIENCY .

• APPROXIMATELY 90% OF THE X-RAY INCIDENT ON THE DETECTOR ARE ABSORBED AND CONTRIBUTE TO THE OUTPUT SIGNAL.

GAS DETECTORS• IT CONSISITS OF A SERIES OF INDIVIDUAL GAS CHAMBERS , SEPERATED BY

TUNGSTEN PLATES, CAREFULLY POSITIONED TO ACT AS ELECTRON COLLECTION PLATES

• WHEN X-RAY FALLS ON THE INDIVIDUAL CHAMBERS, IONIZATION OF THE GAS (XENON) RESULTS AND PRODUCES POSITIVE AND NEGATIVE IONS

• THE POSITIVE IONS MIGRATE TO THE NEGATIVELY CHARGED PLATE , WHERE AS THE NEGATIVELY CHARGED IONS ARE ATTRACTED TO POSITIVELY CHARGED PLATE

• THE MIGRATION OF THESE IONS CAUSES A SMALL SIGNAL CURRENT THAT VARIES DIRECTLY WITH THE NUMBER OF PHOTONS ABSORBED .

• THE GAS CHAMBERS ARE ENCLOSED BY A RELATIVELY THICK CERAMIC SUBSTRATE BECAUSE THE XENON GAS IS PRESSURIZED TO ABOUT 30 ATM TO INCREASE NO. OF GAS MOLECULES AVAILABLE FOR IONIZATION

• XENON DETECTORS HAVE EXCELLENT STABILITY , FAST RESPONSE TIMES AND EXHIBIT NO AFTER GLOW PROBLEMS

• THEIR QUANTUM DETECTION EFFICIENCY (QDE) IS LESS THAN THAT OF SOLID STATE DETECTORS

DUAL ROW/DUAL SLICE DETECTORS

• IT WAS INTRODUCED TO INCREASE VOLUME COVERAGE SPEED AND THUS DECREASE THE TIME FOR DATA COLLECTION

• IT USES A DUAL-ROW SOLID STATE DETECTOR ARRAY COUPLED WITH A SPECIAL X-RAY TUBE BASED ON A DOUBLE –DYNAMIC SYSTEM

MULTI-ROW/MULTI SLICE DETECTORS• THE MR-MS DETECTOR CONSISTS OF ONE DETECTOR WITH ROWS OF DETECTOR ELEMENTS

• A DETECTOR WITH n ROWS WILL BE n TIMES FASTER THAN ITS SINGLE ROW COMPARTMENT

• THEY ACQUIRE 4 TO 64 TO 320 SLICES PER 360 DEGREE ROTATION

• MR DETECTORS FALL INTO 2 CATEGORIES, NAMELY- MATRIX ARRAY DETECTORS

ADAPTIVE ARRAY DETECTORS

• THE MATRIX ARRAY DETECTORS IS REFERED TO AS FIXED ARRAY DETECTOR, CONTAINS CHANNELS OR CELLS

• IN ADAPTIVE ARRAY DETECTORS, CELLS ARE NOT EQUAL BUT RATHER THEY HAVE DIFFERENT SIZES.

THE 256-SLICE CT PROTYPE DETECTOR

• THE DETECTOR IS A WIDE AREA MULTIROW ARRAY DETECTOR THAT HAS 912 CHANNELS × 256 SEGMENTS AND A BEAM WIDTH OF 128 MM

FLAT PANEL DETECTORS• IS SIMILAR TO THE ONES USED IN DR

• IT IS A FLAT PANEL TYPE AND IS BASED ON THE CESIUM IODIDE INDIRECT CONVERSION DR DETECTORS

• THEY ARE BEING INVESTIGATED FOR USE IN BREAST CT

DATA ACQUISITION SYSTEM• IT REFERS TO THE DETECTOR ELECTRONICS POSITIONED BETWEEN THE

DETECTOR ARRAY AND THE COMPUTER BECAUSE DAS IS LOCATED BETWEEN DETECTORS AND COMPUTER.

• IT PERFORMS THREE MAJOR FUNCTIONS:

• IT MEASURES TRANSMITTED RADIATION BEAM

• IT ENCODES THESE MEASUREMENTS INTO BINARY DATA

• IT TRANSMITS THE BINARY DATA TO THE COMPUTER

• THE DETECTOR MEASURES THE TRANSMITTED X-RAYS FROM THE PATIENT AND CONVERTS THEM INTO ELECTRICAL ENERGY

• THIS ELECTRICAL ENERGY IS SO WEAK THAT IT MUST BE AMPLIFIED BY THE PREAMPLIFIER BEFORE IT CAN BE ANALYZED FURTHER

• THE TRANSMISSION MEASUREMENT DATA MUST BE CHANGED INTO ATTENUATION AND THICKNESS DATA.

• LOGARITHMIC CONVERSION IS PERFORMED BY THE LOGARTHMIC AMPLIFIER AND THESE SIGNALS ARE SUBSEQUENTLY DIRECTED TO ADC.

• THE ADC DIVIDES THE ELECTRIC SIGNALS INTO MULTIPLE PARTS, THE MORE PARTS , THE MORE ACCURATE THE ADC

• THESE PARTS ARE MEASURED IN BITS:1-BIT DIVIDES THE SIGNAL INTO TWO DIGITAL VALUES

2-BIT GENERATES 4 DIGITAL VALUES12 BIT GENERATES 4096 VALUES

• THESE VALUES HELP IN DETERMINING THE GREY SCALE RESOLUTION OF THE IMAGE.

• MODERN CT SCANNERS USE 16 –BIT ADC

• THE FINAL STEP IS DATA TRANSMISSION TO THE COMPUTER

X-RAY GENERATOR• CT SCANNERS USE 3-PHASE POWER FOR EFFICIENT PRODUCTION OF X-

RAYS

• CT SCANNERS NOW USE HIGH FREQUENCY GENERATOPRS WHICH ARE SMALL , COMPACT, AND ARE LOCATED INSIDE THE CT GANTRY

• THE POWER RATINGS OF CT GENERATORS VARY AND DEPEND UPON THE CT VENDOR.

• TYPICAL RANGE IS 20 TO 100 KW

X-RAY TUBE• FIRST AND SECOND GENERATION SCANNERS USED FIXED-ANODE, OIL

COOLED X-RAY TUBES

• NOW ROTATING ANODE X-RAY TUBES ARE USED

• SEVRAL TECHNICAL ADVANCES IN COMPUTER DESIGN HAVE BEEN MADE TO ACHIEVE THESE POWER LEVELS AND DEAL WITH THE PROBLEMS OF HEAT GENAERATION, HEAT STORAGE, AND HEAT DISSIPIATION

• THE TUBE ROTATES CONTINUALLY FOR A LONGER PERIOD ,THEREFORE TUBE MUST BE ABLE TO SUSUTAIN HOGHER POWER LEVELS

• ANODE HEATING CAPACITY= 3.5 MHU WHICH DETERMINES MAXIMUM mAs, VOLUME LENGTH AND GENERATE SIZE

• ROTATING ANODE X-RAY TUBE IS USED

• ROTATION SPEED=3600 RPM TO 10000 RPM

• HEAT STORAGE CAPACITY- INCREASED WITH AN IMPROVEMENT IN HEAT DISSIPIATION RATES

NEW X-RAY TUBE DESIGNED BY PHILIPS

• STRATON X-RAY TUBE

COLLIMATION• PROPER COLLIMATION REDUCES PATIENT RADIATION DOSE BY RESTRICTING

THE VOLUME OF TISSUE IRRADIATED.

• IN CT, TWO COLLIMATORS ARE USED:

PRE-PATIENT COLLIMATOR

• COLLIMATOR IS MOUNTED ON THE X-RAY TUBE HOUSING .

• THIS COLLIMATOR LIMITS THE AREA OF THE PATIENT THAT INTERCEPTS THE USEFUL BEAM AND THERBY DETERMINES THE PATIENT RADIATION DOSE.

• .

POST PATIENT COLLIMATOR/PREDETECTOR COLLIMATOR

• THE PREDETECTOR COLLIMATOR RESTRICTS THE X-RAY BEAM VIEWED BY THE DETECTOR ARRAY AND WHEN PROPERLY COUPLED WITH THE PREPATIENT COLLIMATOR , DEFINE STHE SLICE THICKNESS, ALSO CALLED THE SENSITIVITY PROFILE.

• THE PRE DETECTOR COLLIMATOR REDUCES SCATTER RADIATION THAT REACHES THE DETECTOR ARRAY,THERBY IMPROVING IMAGE CONTRAST.

IMAGE DISPLAY• A IMAGE DISPLAY DEVICE FOR CT IS GENERALLY BLACK AND WHITE OR

COLOR MONITOR

• THESE CAN BE CRT FLAT DISPLAY OR LCD FLAT PANEL DISPLAY DEVICES

• IMAGE DISPLAY SYSYTEM INCLUDES SUCH FEATURES AS THE DISPLAY MATRIX, PIXEL SIZE, BIT DEPTH, CT VALUE SCALE, GREY SCALE, IMAGE MONITOR AND THE NO. OF LINES, SELECTABLE (WW) AND WINDOW LEVEL (WL)

CT NUMBER• EACH PIXEL IS DISPLAYED ON THE MONITOR AS A LEVEL OF BRIGHTNESS.

• DENSE BONE 3000• MUSCLE 50• WHITE MATTER 45• GRAY MATTER 40• BLOOD 20• CSF 15• WATER 0• FAT -100• LUNGS -200• AIR -1000

IMAGE STORAGE• DATA ARE STORED IN DIGITAL FORM TO PRESERVE THE WIDE-

DYNAMIC RANGE OF IMAGES AND TO DECREASE THE POSSIBILITY OF LOST RECORDS AND REDUCE THE SPACE NEEDED FOR ARCHIEVING

• STORAGE DEVICES INCLUDE MAGNETIC TAPE, DISKS, DIGITAL VIDEOTAPE, OPTICAL DISKS, AND OPTICAL TAPE.

• TODAY COMPACT DISK (CD) WRITERS CAN BE USED FOE ARCHIEVING CT IMAGES AS WELL

LASER RECORDING SYSTEM• TWO TYPES OF LASERS WERE USED FOR FILM RECORDING IN CT

SOLID STATE LASER DIODES

GAS –LASERS (SUCH AS HE-NE, CADMIUM, HELIUM, ARGON AND NITROGEN)

• He-Ne LASER IS THE SIMPLEST AND MOST RELIABLE GAS LAYER

• SOLID STATE LASER AHS A WAVELENGTH OF 820NM AND HELIUM- NEON HAS A WAVELENGTH OF 633 NM

COMMUNICATION SYSTEMS• THE ELECTRONIC NETWORKING OR CONNECTIVITY BY USING A LOCAL

AREA OR WIDE AREA NETWORK.

• CONNECTIVITY ENSURES THE TRANSFER OF DATA AND IMAGES

• IMAGES ARE SEND TO OTHER DEPARTMENT BY PACS ( PICTURE COMMUNICATION SYSTEMS)

• PACS SYSTEMS IS CONTROLLED BY PACS COORDINATOR OR MANAGER.

PACSP: PICTURE, IMAGES & REPORTS

A: ARCHIVE, ONLINE, NEAR LINE, OFFLINE

C: COMMUNICATION, NETWORKING, TRANSFER PROTOCOLS

S: SYSTEM, COMPONENTS & ARCHITECTURE

PACS: FOR STORAGE AND DISTRIBUTION OF IMAGES AND INFORMATION WHEN NECESSARY

CT CONTROL CONSOLE• IT CONSISTS OF:

• FLOATING KEYBOARD – INCLUDE ALPHANUMERICAL AND SPECIAL FUNCTION KEYS, MOUSE AND WINDOW CONTROLS

• TOUCH PANEL- IT ALLOWS SYSTEM PARAMETERS SUCH AS SCAN SETUP AND CONTROL PARAMETERS

• WINDOW CONTROLS- INCLUDE WW AND WL

• IMAGE DISPLAY- FOR VIEWING AND MANIPULATION BY THE OPERATOR BEFORE THE FINAL IMAGE IS COMMUNICATED TO THE PACS.

• CONTROL FUNCTIONS- THESE ALLOW THE TECHNOLOGISTS TO DEVOTE MORE TIME TO THE SCANNING PROCEDURE AND NEEDS OF THE PATIENT

OPTION AND ACCESSORIES FOR CT

• A NO. OF OPTIONS, BOTH HARDWARE AND SOFTWARE

• HARDWARE-OPTICAL DISK,CARTRIDGE TAPE,REMOTE DIAGNOSTIC

• SOFTWARE-BONE MINERAL ANALYSIS,DYNAMIC SCAN ,3D IMAGE RECONSTRUCTION ,MULTI PLANAR RECONSTRUCTION, VOLUME RENDERING, SURFACE SHADED DISPLAY, MAXIMUM INTENSITY PROJECTION, MI

ACCESSORIES

• IT PROVIDES EXCELLENT IMMOBILIZATIONOF THE PATIENT TO ENHANCE THE OVERALL EFFICIENCY OF THE CT EXAMINATION

• IT INCLUDES PAEDIATRIC CRADLES,ARM AND LEG SUPPORTS,ELEVATED &FLAT PANEL HEAD HOLDERS TABLE MATTRESSES,SIDE RAILS,TABLE EXTENDER,KNEE SUPPORTES ,HEAD PILLOWS WITH HEAD REST.

LAYOUT OF CT SCAN

THANK YOU