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PRINCIPLES OF CT
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TOMOGRAPHY TOMOS---SECTION
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RADIOGRAPHY LIMITATIONS
SUPERIMPOSITION DIFFICULTY IN DISTINGUISHING BETWEEN HOMOGENOUS OBJECTS OF NON-UNIFORM THICKNESS.
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SUPERIMPOSITION
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RADIOGRAPHY LIMITATIONTISUE DIFFERENCE SENSITIVITY >10%
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TOMOGRAPHY (CONVENTIONAL)
ELIMINATES TISSUE SUPERIMPOSITION INCREASES CONTRAST OF LOW SUBJECT CONTRAST TISSUES
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TOMOGRAPHY
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TOMOGRAPHY
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TOMOGRAPHY LIMITATIONS MOTION BLURR
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CT ADVANTAGES
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LIMITATIONS OF CT UNABLE TO DIFFERENTIATE BETWEEN TISSUES WITH SLIGHT CONTRAST DIFFERENCES < 1%.
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GOALS OF CT MINIMAL SUPERIMPOSITION IMAGE CONTRAST IMPROVEMENT
SMALL TISSUE DIFFERENCE RECORDING
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CT DATA AQUISITION
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RELATIVE TRANSMISSION=Io/I
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HISTORY OF CT
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Sir Godfrey Newbold Hounsfield CBE (28 August 1919 – 12 August 2004) was an English electrical engineer who shared the 1979 Nobel Prize for Physiology or Medicine with Allan McLeod Cormack for his part in developing the diagnostic technique of X-ray computed tomography (CT).
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HOUNSFIELD’S SKETCH
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CONSTRUCTION OF FIRST CT
RADIATION SOURCE – AMERICUM GAMMA SOURCE SCAN—9 DAYS COMPUTER PROCESSING—2.5 HOURS PICTURE PRODUCTION 1 DAY
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HOUNSFIELD’S LATHE BED SCANNER
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FIRST CLINICAL PROTOTYPE CT BRAIN SCANNER
1972 FIRST CLINICAL PROTOTYPE CT BRAIN SCANNER FIRST SCANS—20 MIN. LATER REDUCED TO 4.5 MIN.
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CLINICALLY USEFUL CT SCANNER
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DR. ROBERT LEDLEY DEVELOPED THE FIRST WHOLE BODY CT SCANNER .
1974 DR. ROBERT LEDLEY DEVELOPED THE FIRST WHOLE BODY CT SCANNER .
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SCANNER GENERATIONS I II III IV
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180 DEG ROTATION
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180 DEG ROTATION
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360 DEG ROTATION
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360 DEG ROTATION
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MODERN SCANNER
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CT MAIN SYSTEMS IMAGING SYSTEM COMPUTER SYSTEM
DISPLAY, RECORDING, STORAGE SYSTEM DATA ACQUISITION SYSTEM
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IMAGING SYSTEM PRODUCTION OF X-RAYS SHAPING OF X-RAY BEAM ENERGY
FILTERING X-RAY BEAM
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SCANNER GANTRY TABLE/COUCH
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GANTRY INSIDE
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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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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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DATA ACQUISITION SYSTEM (DAS)
SET OF ELECTRONICS BETWEEN DETECTORS AND HOST COMPUTER.
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CT COMPONENTS GANTRY COMPUTER TABLE/COUCH CONSOLE
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ORIGINAL CLINICAL CT SCANS COMPOSED OF
80 X 80 MATRIX PIXELS 6400
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EARLY DAYS vs TODAY 80 x 80 512 x 512
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COORDINATE SYSTEM IN CT
X
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COORDINATE SYSTEM IN CT
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COORDINATE SYSTEM IN CT
Z
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COORDINATE SYSTEM IN CT
ISO-CENTER
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SCAN FOV SFOV DETECTORS
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DFOV – DISPLAYED FIELD OF VIEW
SIZE DISPLAYED ON THE MONITOR
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PIXEL SIZE= DFOV (mm)/ MATRIX SIZE
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RECONSTRUCTION Ц CT# RECONSTRUCTION
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PIXEL vs VOXEL PIXEL VOXEL
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PIXEL SIZE DEPENDS ON: MATRIX SIZE FOV
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VOXEL SIZE DEPENDS FOV MATRIX SIZE SLICE THICKNESS
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IMAGE DISPLAY
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IN CT DIGITAL RECONSTRUCTED IMAGE IS CONVERTED IMAGE IS CONVERTED INTO A GRAY SCALE IMAGE.
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CT # vs BRIGHTNESS LEVEL
+ 1000 -1000
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CT # 1000
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CT # - 500
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CT # OF CYST 5
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CT # OF LIPOMA ( FATTY TUMOR)
-100
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SCANNING
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TECHNIQUE kVp mA TIME SLICE THICKNESS SLICE INCREMENTATION
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PATIENT ORIENTATION HEAD FIRST FEET FIRST
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SCANNING TOPOGRAM REGULAR SCAN
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TOPOGRAM (SCOUT) TUBE DOES NOT REVOLVE AROUND THE PATIENT
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AP SCOUT TUBE TUBE SUSPENDED ABOVE PATIENT DURING SCOUT GENERATION
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LAT SCOUT TUBE AT THE 90º ANGLE TO PATIENT
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AXIAL SCAN TABLE STOPS AT THE SCANNING POSITION AND THE TUBE ROTATES AROUND A PATIENT.
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SPIRAL PATIENT CONTINUOUSLY MOVES IN THE Z-AXIS DIRECTION WHILE THE TUBE ROTATES AROUND.
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CONVENTIONAL AND SPIRAL/HELICAL CT
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ADVANTAGE OF SPIRAL IMAGING OVER CONVENTIONAL
SPEED
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CT SPECIAL APPLICATIONS
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CARDIAC ANGIOGRAPHY
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VIRTUAL ENDOSCOPY
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RADIATION TREATMENT
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3D IMAGING
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