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OUTLINE
• TOMOGRAPHY – DEFINITION• WHY CT – LIMITATIONS OF
RADIOGRAPHY AND TOMOGRAPHY• CT- BASIC PHYSICAL PRINCIPLE• HISTORICAL TRAIL• CT GENERATIONS
Tomography: From the Greek word “tomos” section. The process for generating a tomogram, a two-
dimensional image of a section through a three-dimensional object. Tomography achieves this result by simply moving an x-ray source in one direction as the x-ray film is moved in the opposite direction during the
exposure to sharpen structures in the focal plane, while structures away from the focal plane appear blurred.
Tomography: From the Greek word “tomos” section. The process for generating a tomogram, a two-
dimensional image of a section through a three-dimensional object. Tomography achieves this result by simply moving an x-ray source in one direction as the x-ray film is moved in the opposite direction during the
exposure to sharpen structures in the focal plane, while structures away from the focal plane appear blurred.
CONVENTIONAL RADIOGRAPHY HAS
LIMITATIONS:• TWO DIMENSIONAL IMAGE WITH INFINITE
DEPTH - SUPERIMPOSITION OF UNDERLYING STRUCTURES (LATERAL AND OBLIQUE VIEWS DON’T SOLVE IT COMPLETELY).
• INABILITY TO DEMONSTRATE SLIGHT DIFFERENCES IN SUBJECT CONTRAST
CHARACTERISTIC OF SOFT TISSUE.
TOMOGRAPHY – SOLUTION?
• CONVENTIONAL TOMOGRAPHY ATTEMPTED TO ELIMINATE THE SUPERIMPOSITION PROBLEM BY BLURRING THE STRUCTURES ABOVE AND BELOW THE TOMOGRAPHIC FOCAL PLANE.
• CONTRAST OF AN IMAGE CAN ALSO BE CHANGED BY VARYING TOMOGRAPHIC ANGLE (DISTANCE OF A TUBE TRAVEL)
• MULTIDIRECTIONAL TUBE MOVEMENT MAKES THE BLURRING OF UNWANTED STRUCTURES
EVEN MORE EFFECTIVE.
CT –EVOLUTION OF TERMS
COMPUTERIZED TRANSVERSE AXIAL TOMOGRAPHY
COMPUTER ASISSTED TOMOGRAPHY
COMPUTERIZED AXIAL TOMOGRAPHY
COMPUTED TOMOGRAPHY
FORMATION OF CT IMAGE
DATA AQUSITION
IMAGE RECONSTRUCTION
IMAGE:DISPLAY, MANIPULATION, STORAGE
COMMUNICATIONS & RECORDING
IMAGE RECONSTRUCTION
• TRANSMISSION MEASUREMENTS COLLECTED BY THE CT DETECTORS ARE SENT TO THE COMPUTER FOR THE PROCESSING. COMPUTERS USES MATHEMATICAL ALGORITHM TO RECONSTRUCT THE IMAGE.
IMAGE DISPLAY, MANIPULATION, STORAGE,
COMMUNICATION.
• AFTER RECONSTRUCTION IMAGE CAN BE DISPLAYED ON THE MONITOR
• IMAGE CAN BE MANIPULATEDIMAGE CAN BE STORED – ON MOD OR CD.
• DURING COMMUNICATION PHASE IMAGE MAY BE TRANSMITTED TO A REMOTE LOCATION
Sir Godfrey Newbold Hounsfield CBE, FRS, (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).
CONSTRUCTION OF FIRST CT
• RADIATION SOURCE – AMERICUM GAMMA SOURCE
• SCAN—9 DAYS• COMPUTER PROCESSING—2.5 HOURS• PICTURE PRODUCTION 1 DAY
ALLAN M. CORMACK
1979 – NOBEL PRIZE SHARED WITH DR. HOUNSFIELD.
DEVELOPED SOLUTIONS TO MATHEMATICAL PROBLEMS IN
CT.