principles of ct
DESCRIPTION
PRINCIPLES OF CT. Dr Mohamed El Safwany, MD. Intended learning outcome. The student should learn at the end of this lecture principles of CT. TOMOGRAPHY TOMOS ---SECTION. RADIOGRAPHY LIMITATIONS. SUPERIMPOSITION - PowerPoint PPT PresentationTRANSCRIPT
PRINCIPLES OF CT
Dr Mohamed El Safwany, MD
Intended learning outcome
• The student should learn at the end of this lecture principles of CT.
TOMOGRAPHY
TOMOS---SECTION
TOMOGRAPHY
TOMOS---SECTION
RADIOGRAPHY LIMITATIONS
• SUPERIMPOSITION
• DIFFICULTY IN DISTINGUISHING BETWEEN HOMOGENOUS OBJECTS OF NON-UNIFORM THICKNESS.
SUPERIMPOSITION
RADIOGRAPHY LIMITATIONTISUE
DIFFERENCE SENSITIVITY >10%
TOMOGRAPHY (CONVENTIONAL)
• ELIMINATES TISSUE SUPERIMPOSITION
• INCREASES CONTRAST OF LOW SUBJECT CONTRAST TISSUES
TOMOGRAPHY
TOMOGRAPHY
TOMOGRAPHY LIMITATIONS
MOTION BLURR
CT ADVANTAGES
LIMITATIONS OF CT
• UNABLE TO DIFFERENTIATE BETWEEN TISSUES WITH SLIGHT CONTRAST DIFFERENCES < 1%.
GOALS OF CT
• MINIMAL SUPERIMPOSITION
• IMAGE CONTRAST IMPROVEMENT
• SMALL TISSUE DIFFERENCE RECORDING
CT DATA AQUISITION
TRANSMISSION
RELATIVE TRANSMISSION=Io/I
MODERN SCANNER
CT MAIN SYSTEMS
• IMAGING SYSTEM
• COMPUTER SYSTEM
• DISPLAY, RECORDING, STORAGE SYSTEM
• DATA ACQUISITION SYSTEM
IMAGING SYSTEM
• PRODUCTION OF X-RAYS
• SHAPING OF X-RAY BEAM ENERGY
• FILTERING X-RAY BEAM
SCANNER
GANTRY
TABLE/COUCH
GANTRY INSIDE
COMPUTER SYSTEM
• RECONSTRUCTION AND POSTPROCESSING
• CONTROL OF ALL SCANNER COMPONENTS
• CONTROL OF DATA ACQUSITION, PROCESSING, DISPLAY.
• DATA FLOW DIRECTION
COMPUTER SYSTEM IN CT
• MINICOMPUTERS
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
DATA ACQUISITION SYSTEM (DAS)
• SET OF ELECTRONICS BETWEEN DETECTORS AND HOST COMPUTER.
COORDINATE SYSTEM IN CT
X
COORDINATE SYSTEM IN CT
Y
COORDINATE SYSTEM IN CT
Z
COORDINATE SYSTEM IN CT
ISO-CENTER
SCAN FOV
SFOV
DETECTORS
DFOV – DISPLAYED FIELD OF VIEW
• SIZE DISPLAYED ON THE MONITOR
PIXEL SIZE
PIXEL SIZE= DFOV (mm)/ MATRIX SIZE
PIXEL vs VOXEL
PIXEL VOXEL
PIXEL SIZE DEPENDS ON:
• MATRIX SIZE
• FOV
VOXEL SIZE DEPENDS
• FOV• MATRIX SIZE• SLICE THICKNESS
IMAGE DISPLAY
IN CT DIGITAL RECONSTRUCTED IMAGE IS
CONVERTED IMAGE IS CONVERTED INTO A GRAY
SCALE IMAGE.
CT # vs BRIGHTNESS LEVEL
+ 1000
-1000
CT #1000
CT # - 500
CT # OF CYST5
CT # OF LIPOMA ( FATTY TUMOR)
-100
SCANNING
TECHNIQUE
• kVp
• mA
• TIME
• SLICE THICKNESS
• SLICE INCREMENTATION
PATIENT ORIENTATION• HEAD FIRST • FEET FIRST
SCANNING
• TOPOGRAM
• REGULAR SCAN
TOPOGRAM (SCOUT)
• TUBE DOES NOT REVOLVE AROUND THE PATIENT
AP SCOUT
• TUBE SUSPENDED ABOVE PATIENT DURING SCOUT GENERATION
TUBE
LAT SCOUT
• TUBE AT THE 90º ANGLE TO PATIENT
AXIAL SCAN
• TABLE STOPS AT THE SCANNING POSITION AND THE TUBE ROTATES AROUND A PATIENT.
SPIRAL
• PATIENT CONTINUOUSLY MOVES IN THE Z-AXIS DIRECTION WHILE THE TUBE ROTATES AROUND.
CONVENTIONAL AND SPIRAL/HELICAL CT
ADVANTAGE OF SPIRAL IMAGING OVER CONVENTIONAL
• SPEED
CT SPECIAL APPLICATIONS
CARDIAC ANGIOGRAPHY
VIRTUAL ENDOSCOPY
RADIATION TREATMENT
3D IMAGING
Text Book
• David Sutton’s Radiology
• Clark’s Radiographic positioning and techniques
Assignment
• Two students will be selected for assignment.
Question
• Define topogram and tomogram?
• Thank You