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COMPUTED TOMOGRAPHY HISTORICAL PERSPECTIVE

COMPUTED TOMOGRAPHY HISTORICAL PERSPECTIVE. OUTLINE TOMOGRAPHY – DEFINITION WHY CT – LIMITATIONS OF RADIOGRAPHY AND TOMOGRAPHY CT- BASIC PHYSICAL PRINCIPLE

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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 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.

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)

1990SPIRAL CT ( HELICAL) –SLIP

RING TECHNOLOGY

CT SCANNING IN SPIRAL-HELICAL GEOMETRY BASED ON

SLIP RING TECHNOLOGY

Slip rings

SCANNER POWER SUPPLY-SLIP RINGS –DISK

1992

DUAL SLICE CT HELICAL SCANNER

19981998

MULTISLICE CT SCANNERSMULTISLICE CT SCANNERS