year 4 day 2 p. 2 - CT - syllabus, IV rok, IV rok CM UMK, Radiologia, 2014-15

//-->.pos {position:absolute; z-index: 0; left: 0px; top: 0px;}10/15/2012Day 2 part 2RADIOLOGY ANDIAGNOSTIC IMAGINGDr. Zbigniew Serafin, MD, PhDserafin@cm.umk.plCT technique2CT systemKanal K: RSNA/AAPM web module: CT Systems & CT Image Quality and ProtocolsCT technique3CT systemstationary x-ray tube, rotating multi-row panel of detectorsKanal K: RSNA/AAPM web module: CT Systems & CT Image Quality and Protocols110/15/2012CT technique4CT systemstationary x-ray tube, rotating multi-row panel of detectorsadvanced x-ray tube technology: instant current up to 500 mA over 5-40 slarge heat capacity and fast cooling ratesmechanical stress due to rotation – up to 13 GCT technique5CT systemeach detector, along with the focal spot of x-ray tube, defines araythe intensity of the beam within each ray depends on the total attenuationof the tissue through which it passes.the data acquired during a CT scan consist of a series ofviewsfor each view, all detectors make intensity measurements simultaneouslyover a short period of time. The set of simultaneous measurementsconstitutes aprofile/projectionCT technique6CT systemc.f. Kalender WA, Computed Tomography, Second Edition, pg. 26, 2005210/15/2012CT technique7CT systema CTreconstruction algorithmis used to produce the CT imagefiltered back projection is most widely used in clinical CT scanners7CT technique8CT scanningtwo basic modes of acquisitionCT technique9CT scanningacquisition parameters•determine production of scan data setsreconstruction parameters•determine presentation of the datasingle slice scannersmultislice scanners, multi-detector row scanners (MDCT)310/15/2012CT technique10CT scanning – acquisition parameterstube potential (80-140 kVp) – voltage between cathode and anode;higher potential accelerates electrons more, giving x-rays more energytube current (20-500 mA) – current following through cathode; largercurrent produces more electrons and greated x-ray beam intensityscan time (0.3-4 s) – time of x-ray production during one rotation; longerscan time incresases x-ray countslice width (0.5-10 mm) – slice thickness in z-axisbeam filtration – beam shaping filter optimized for body partshelical pitch (0.5-2)CT technique11CT scanning – acquisition parameterspitch = table movement per rotation (mm) / beam width (mm)CT technique12CT scanning – reconstruction parametershelical interoplation – reduces artifacts due to changing structure in z-axisinterpolation averages dataon either side of the reconstruction position toestimate projection at that point410/15/2012CT technique13EXERCISEgive the effects in patient dose, scan time, and image quality when using••a pitch <1a pitch > 1CT technique14image processingpixel(picture element) is the basic 2Delement of the digital imageeach pixel displays brightnessinformation concerning the patient’sanatomy that is located in thecorrespondingvoxel(volume element)the pixel width and height are equal tothe voxel width and heightthe voxel has a third dimension thatrepresents the slice thickness of the CTscanCT technique15CT scanning – reconstruction parametersreconstruction field of view (FOV, 10-50 cm) – total image size in x and ydirectionsreconstruction matrix (usually 512x512) – image resolutionconvolution kernel / reconstruction filter – variety of reconstruction settingsemphasize different characteristics in the CT image, offering tradeoffsbetween spatial resolution and noise••bone algorithm - fine detail but with increased noisesoft tissue filters - smoothing, which decreases image noise but alsodecreases spatial resolution5

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