Computed Tomography PDF

COMPUTED TOMOGRAPHY DEFINITION BRIEF HISTORY COMPUTED TOMOGRAPHY 1930’S – ALLESANDRO VALLEBONA Creation of a cross-sectional tomographic Proposed a method to represent a single se...

COMPUTED TOMOGRAPHY DEFINITION BRIEF HISTORY COMPUTED TOMOGRAPHY 1930’S – ALLESANDRO VALLEBONA Creation of a cross-sectional tomographic Proposed a method to represent a single section of the body with a rotating fan beam, slice of the body on the radiographic film a detector array and computed (TOPOGRAPHY) reconstruction Other Names: Computed Axial 1970 – GODFREY NEWBOID HOUNSFIELD Tomography (CAT), Computed Transaxial First demonstrated the CT technique Tomography (CTAT), Computed Reconstruction Tomography (CRT), Digital 1972-1974 Axial Tomography (DAT), Body Section First clinical CT scanners were installed Roentgenography Greek Word: “Tomos” = slice/section; 1979 “Graphia” = describing Hounsfield & Allan Mcleod Cormack shared the Nobel Prize in Physics CT SCANNER Consists of an x-ray source emitting finely 1980 collimated x-ray beam and a single detector CT scan machine became widely available both moving synchronously in a translate or rotate mode or a combination of both EMI SCANNER 1st CT scan machine 180 translation/1o rotation INTRODUCTION ACTA COMPUTERS 1st CT system that could make images of any Used Binary System part of the body Did not require water tank BINARY DIGIT/BIT Can code for 2 values or 2 shades of gray which correspond to white and black PRINCIPLES OF OPERATION 8 bits=1 byte 2 bytes=1 word CONVENTIONAL/AXIAL TOMOGRAPHY 16 bits=1 word Plane of the image is parallel to the long axis of the body STORAGE REQUIREMNENT Produces sagittal and coronal images Kilobytes, megabytes, gigabyte or terabytes COMPUTED TOMOGRAPHY Plane of image is perpendicular to the long axis of the body Produces a transverse image 1  COMPUTED TOMOGRAPHY CT IMAGE 2ND GENERATION A transaxial/transverse image Has a narrow fan beam and multiple detectors TRANSLATION/SWEEP It refers to movement of source-detector 3RD GENERATION assembly across the patient Has a wide fan beam Results in a projection Projection: represents the attenuation 4TH GENERATION pattern of patient profile Equipped with a detector ring Detector signal: has a dynamic range of 12 bits (4096 gray levels) 5TH GENERATION The electron beam tomography CT PROJECTION An intensity profile 6TH GENERATION The helical (or spiral) CT scanner ALGORITHM Computer-adapted mathematical calculation 7TH GENERATION applied to raw date during image The multi-detector row CT. reconstruction SEVEN GENERATIONS RECONSTRUCTION Creation of an image from date FIRST GENERATION A demonstration project RECONSTRUCTION TIME Characteristic: translate/rotate (Bushong ) Time needed for the computer to present a or rotate/translate (Reveldez) digital image after an examination has been X-ray Beam Shape: pencil beam computed Detector: single detector Time between the end of imaging and the Imaging Time: 5-minute imaging time appearance of an image SECOND GENERATION Characteristic: translate/rotate (Bushong ) GENERATIONS OF COMPUTED or rotate/translate (Reveldez) TOMOGRAPHY X-ray Beam Shape: narrow fan beam Detector: multiple detector (5-30) GENERATION OVERVIEW Imaging Time: 30 seconds Advantage: speed 1ST GENERATION o Rationale: consist of multiple Has a pencil beam and one detector detectors Disadvantages: o Increased scattered radiation 2  COMPUTED TOMOGRAPHY o Increased radiation intensity toward rotation of the x-ray source, proving a self- the edges of the beam calibrating system. Third generation system are ▪ Compensation: used of bow- calibrated only once every few hours. tie filter Bow-tie Filter: equalize the radiation FIFTH GENERATION (early 1980’s) intensity that reaches the detector array Electron beam CT Ultrafast CT scanner THIRD GENERATION X-ray tube rotation is mechanical Characteristic: rotate/rotate No moving parts X-ray Beam Shape: wide fan beam Electron Gun: produces a focused electron Detector: curvilinear detector array (30) beam that generates a rotating x-ray fan Imaging Time: