Basic Principles of Computed Tomography-CT
Transcript of Basic Principles of Computed Tomography-CT
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Basic principlesof computed
tomography
MUDr. Luk Mikk, KZM FN Motol
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Tomography
tomos = slice; graphein = to write definition - imaging of an object by
analyzing its slices
Damien HirstAutopsy with Sliced HumanBrain
2004
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History
1924- mathematical theory of tomographic imagereconstructions (Johann Radon)
1930- conventional tomography (A. Vallebona)
1963- theoretical basis of CT (A. McLeod Cormack) 1971- first commercial CT (Sir Godfrey Hounsfield) 1974- first 3rd generation CT 1979- Nobel price (Cormack & Hounsfield) 1989 - single-row CT
1994 - double-row spiral CT 2001 - 16-row spiral CT 2007 - 320-row spiral CT
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History
1924- mathematical theory of thomographic imagereconstructions (Johann Radon)
1930- conventional tomography (A. Vallebona) 1963- theoretical basis of CT (A. McLeod Cormack) 1971- first commercial CT (Sir Godfrey Hounsfield) 1974- first 3rd generation CT 1979- Nobel price (Cormack & Hounsfield) 1989 - single-row CT
1994 - double-row spiral CT 2001 - 16-row spiral CT 2007 - 320-row spiral CT
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Conventional tomography
x-ray tube moves in theoposite direction thandetector
areas outside the focusare blured, thereforenot shown
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Conventional tomography
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Conventional tomography
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Conventional tomography
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Imaging before CT
entire body areas were inaccessible toradiography - brain, mediastinum,retroperitoneum
diagnostic procedures showing better detailin these areas were potentially harmful andor poorly tolerated by the patient -
pneumoencephalography, diagnosticpneumomediastinum, diagnostic laparotomy
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Imaging before CT
ventriculography pneumoencephalography
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Imaging before CT
transfontanellar ultrasound
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CT prototype
scanning time: 9 days reconstruction: 2,5h resolution: 80x80
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1st generation CT
xray tube and single detector are connectedand move together by translation and thenrotation
xray beam has linear (pencil-like) shape
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2nd generation CT
same type of movement multiple detectors arranged in a row fan shaped xray beam instead of linear shaped
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CT III. generace
full rotation of x ray tube+detectors complex
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CT III. generace
http://www.youtube.com/watch?v=fDcFt9V29-whttp://www.youtube.com/watch?v=fDcFt9V29-w -
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CT IV. generace
only x ray tube rotates, detectors arestationary
this technology was later abandoned
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V. generation CT
electron beam tomography (EBT)
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V. generation CT
electron beam tomography (EBT)
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CT machine anatomy
energy source (140 kV) + slip rings x ray source detectors
collimators DAS
= data acquisition system
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scanning
sequential- sequence of complete gantry rotationfollowed by table movement with the patient
spiral- continuous gantry rotation and table movement volume of raw data is generated, from which axial
images are reconstructed using interpolation slip ring technology allowed transmission of energy to
rotating gantry without the need of cables
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spiral scanning
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pitch
table travel - table movement per rotation collimation - x ray beam width in z axis pitch = table travel / collimation
pitch = 1 - coils of the helix are in contact pitch < 1 - coils of the helix overlap pitch > 1 - coils of the helix are separated
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pitch
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SSCT vs. MSCT
SSCT - single slice CT MSCT - multiple slice CT
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SSCT vs. MSCT
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detectors
fixed array, 4 slice CT
adaptive array, 4 slice CT
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voltage vs. current
voltage (kV) 80-140 kV higher the voltage, better the penetration of x ray,
but worse tissue contrast and larger dose
electric current (mAs) 50-500 mAs higher the current, better the image quality (lower
noise), but larger dose
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image reconstruction
matrix - 512 x 512 pixel - 2D object, smallest element of a raster image voxel - 3D object, smallest element of a 3D grid
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image reconstruction
0 + 90dg 4 angles 16 angles
16 angles 30 angles 100+ angles
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image reconstruction
isotropic imaging - all 3sides (x, y, z) of thevoxel have equal size
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image reconstruction
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image reconstruction
Hounsfield scale - tissue density is expressedin different shades of grey in relation to itsxray absorption water = 0, air = -1000 scale -1000 to 3095
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image reconstruction
CT window window width window level (center)
mediastinal window W 350, L 50 lowest HU = -125 (50-350/2) highest HU = 225 (50+350/2)
lung window W 2000, L -200
bone window W 1500, L 300 brain window
W 80, L 30
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image reconstruction
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CT coronarography
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CT angiography
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CT endoscopy
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CT endoscopy
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CT endoscopy
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CT in polytrauma
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CT in acute stroke
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Thank you