1Computed Tomography Basic principles V.G.Wimalasena Principal School of Radiography
2IntroductionComputed tomography (CT) is a medical imaging method employing tomography.The word "tomography" is derived from the Greek tomos (slice) and graphein (to write).A large series of two-dimensional X-ray images (slices) of the inside of an object are taken around a single axis of rotation.Digital geometry processing is used to generate three-dimensional images of the object from those slices.
3HistoryThe first commercially viable CT scanner was invented by Sir Godfrey Hounsfield in Hayes, United Kingdom at EMI Central Research Laboratories using X-rays. Hounsfield conceived his idea in and it was publicly announced in 1972.Allan McLeod Cormack of Tufts University in Massachusetts independently invented a similar process, and both Hounsfield and Cormack shared the 1979 Nobel Prize in Medicine.
9Label x-ray tube filters, collimator, and reference detector internal projectorx-ray tube heat exchanger (oil cooler)high voltage generator (0-75kV)direct drive gantry motorrotation control unitdata acquisition system (DAS)detectorsslip rings
10Understanding Basic factors Absorption :-stopping of x-rays with transfer of energyScatter:- deflection of x-raysIncident Intensity :- No. of x-ray photons falling on an objectTransmitted Intensity:- No. of photons passing throughScattered x-raysTransmitted X-ray beamIncident x-ray beam
11AttenuationThe reduction of the beam intensity on passing through the material due to absorption plus scatterThe degree of attenuation is obtained by measuring and comparing the incident and transmitted intensitiesMore dense materialLess transmitted x-raysMore transmitted x-raysLess dense material
13Conventional X-RayConventional x-ray produces a compression of a volume to a planeThe detector is the Silver halide crystal on a x-ray filmThe degree of blackening represents the total attenuation through the path of x-ray photons
14The higher the attenuation the lesser is the blackness The structure which results more attenuation or more transmission predominates in the image
15Conventional Tomography The source and detector movesProduces Images of coronal or sagittal sections (cuts) of areas of interestEliminates the superimposition of structures above and below
16CT Scan Scan? CT scan produces axial sections/cuts /Slices The CT image is recorded through a SCAN.Scan?A scan is made up of multiple X-Ray attenuation measurements around an objects peripheryX-ray tubeDetector
17Slice / CutThe cross sectional portion of the body which is scanned for the production of CT image is called a slice.The slice has width and therefore volume.The width is determined by the width of the x-ray beamTo be continued ….CTComplementary2