Transcript COMPUTED TOMOGRAPHY HISTORICAL PERSPECTIVE

COMPUTED TOMOGRAPHY
HISTORICAL PERSPECTIVE
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 twodimensional image of a section through a threedimensional 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.
TOMOGRAPHY STILL
LIMITED
• IMAGE BLURR PRESENT
• EXCESSIVE SCATTER RADIATION – FILM FOG
RADIOGRAPHY AND
TOMOGRAPHY
• TISSUE DIFFERENCE SENSITIVITY
5-10%
CT GOALS:
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
DATA ACQUISITION
• COLLECTION OF X-RAY PHOTONS
TRANSMITTED THROUGH THE
PATIENT BY THE CT DETECTORS.
DETECTORS
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
HOUNSFIELD’S LATHE BED
SCANNER
DR.HOUNSFIELD
&
DR. AMBROSE
READINGS FROM SPECIMEN OF
HUMAN BRAIN. TUMOR FINDINGS
APPARENT.
1972
FIRST CLINICAL PROTOTYPE CT
BRAIN SCANNER
1. FIRST SCANS—20 MIN.
2. LATER REDUCED TO 4.5 MIN.
CLINICALLY USEFUL CT
SCANNER
DR. HOUNSFIELD
1972 – McROBERT AWARD
1979 –
NOBEL PRIZE
ALLAN M. CORMACK
1979 – NOBEL PRIZE SHARED
WITH DR. HOUNSFIELD.
DEVELOPED SOLUTIONS TO
MATHEMATICAL PROBLEMS IN
CT.
1974
DR. ROBERT LEDLEY
DEVELOPED THE FIRST WHOLE
BODY CT SCANNER .
SCANNING DEVELOPMENT
• 5 MIN. –1972
• 1 SEC – 1993
CT SCANNING GENERATIONS
HIGH SPPED CT
V GENERATION
( CARDIVASCULAR CT)
EBCT ( SIEMENS)
1990
SPIRAL CT ( HELICAL) –SLIP RING
TECHNOLOGY
CT SCANNING IN SPIRALHELICAL GEOMETRY BASED ON
SLIP RING TECHNOLOGY
Slip rings
SCANNER POWER SUPPLY-SLIP
RINGS –DISK
1992
DUAL SLICE CT HELICAL
SCANNER
1998
MULTISLICE CT SCANNERS