CT成像原理介紹英文版醫(yī)學(xué)知識(shí)講解培訓(xùn)課件

1、CT成像原理介紹英文版醫(yī)學(xué)知識(shí)講解CT成像原理介紹英文版醫(yī)學(xué)知識(shí)講解Computed Tomography CT Basics Principle of Spiral CT Scan Parameter & Image Quality Optimizing Injection Protocols Clinical Applications2CT成像原理介紹英文版醫(yī)學(xué)知識(shí)講解Computed Tomography CT BasicsX-Ray Discovery X-ray was discovered by a German scientist Roentgen 100 years ago.

2、This made people for the first time be able to view the anatomy structure of human body without operation But its superimposed And we couldnt view soft tissue3CT成像原理介紹英文版醫(yī)學(xué)知識(shí)講解X-Ray Discovery X-ray was dis My name is Godfrey Hounsfield I work for the Central Research Labs. of EMI, Ltd in England I d

3、eveloped the the first clinically useful CT scanner in 1971History of Computed Tomography Early 1970s1963 - Alan Cormack developed a mathematical method of reconstructing images from x-ray projections4CT成像原理介紹英文版醫(yī)學(xué)知識(shí)講解 My name is Godfrey Hounsfiel For the first time we could view:CT Broke the Barrie

4、r- Tomographic or “Slice” anatomy- Density difference But its time consuming And resolution needs to be improved5CT成像原理介紹英文版醫(yī)學(xué)知識(shí)講解 For the first time we could vConcept of X-ray AttenuationAn X-ray beam passing throughthe body is attenuated (loses itsenergy) by :AbsorptionScatteringIncident X-rayTran

5、smitted raySCATTERED X-RAYSBODYTISSUEAbsorption by the tissue is proportional to the densityLessdensetissueMoredensetissueMORE ATTENUATIONLESS ATTENUATION6CT成像原理介紹英文版醫(yī)學(xué)知識(shí)講解Concept of X-ray AttenuationAHow does CT Work?Recon. & postpro.Data acquisitionX-ray generation7CT成像原理介紹英文版醫(yī)學(xué)知識(shí)講解How does CT Wor

6、k?Recon. & postX-ray goes through collimator thereforepenetrate only an axial layer of the object, called sliceHow does CT Work?8CT成像原理介紹英文版醫(yī)學(xué)知識(shí)講解X-ray goes through How does CTPatient is placed in the center of the measurement fieldX-ray is passed through the patients slice from many direction along

7、 a 360 pathThe transmitted beams are captured by the detectors which digitizes these signalsThese digitized signals called raw data are sent to a computer which create the CT imageHow does CT Work?9CT成像原理介紹英文版醫(yī)學(xué)知識(shí)講解Patient is placed in the centeThe object slice is divided into small volume elements

8、called voxels. Each voxel is assigned a value which is dependent on the average amount of attenuationHow is CT Image generated?10CT成像原理介紹英文版醫(yī)學(xué)知識(shí)講解The object slice is divided inThe attenuation values are transferred to the computer where they are coded & used to create a slice imageHow is CT Image ge

9、nerated?11CT成像原理介紹英文版醫(yī)學(xué)知識(shí)講解The attenuation values are traCT Generations & Design“Generation” is used to label CT tube-detector designs3rd Generation DesignRotating tube & detector4th Generation DesignFixed ring detector12CT成像原理介紹英文版醫(yī)學(xué)知識(shí)講解CT Generations & Design“GeneraSlip-ring TechnologyPower is tra

10、nsmitted through parallel sets of conductive ringsinstead of electrical cables Continuous Gantry Rotation Prerequisite for Spiral CTNon Slip-ring ScannerSlip-ring Scanner13CT成像原理介紹英文版醫(yī)學(xué)知識(shí)講解Slip-ring TechnologyPower is tComputed Tomography CT Basics Principle of Spiral CT Scan Parameter & Image Quali

11、ty Optimizing Injection Protocols Clinical Applications14CT成像原理介紹英文版醫(yī)學(xué)知識(shí)講解Computed Tomography CT BasicsWhat is Spiral Scan? - just 4“C”Continuously rotating tube/detector systemContinuously generating X-rayContinuously table feedContinuously data acquisition15CT成像原理介紹英文版醫(yī)學(xué)知識(shí)講解What is Spiral Scan? -

12、just 4Reconstruction of arbitraryslices (either contiguous or overlapping) within thescanned volume Distance between the slices is called IncrementABVolume DataContinuous data acquisition16CT成像原理介紹英文版醫(yī)學(xué)知識(shí)講解Reconstruction of arbitraryABVIncrementSlice ThicknessIncrement = Slice Thickness No Overlap N

13、o GapsContiguous Image Reconstruction17CT成像原理介紹英文版醫(yī)學(xué)知識(shí)講解IncrementSlice ThicknessIncrIncrementOverlapSliceThicknessOverlapping Image ReconstructionIncrement Slice Thickness Gaps between slices Images are further apart Less images createdImage Reconstruction with GapsIncrementSlice Thickness19CT成像原理介紹

14、英文版醫(yī)學(xué)知識(shí)講解Increment Slice ThicknessImaStandard CT / Slice ImagingDeep InspirationShallow Inspiration Misregistration due to different respiratory levels between slicesPartial Volume Effect Unable to resconstruct images at arbitrary position Slice imaging is slow20CT成像原理介紹英文版醫(yī)學(xué)知識(shí)講解Standard CT / Slice

15、ImagingDee Scan the whole region of interest in one breath hold Reconstruction of overlapping images without additional dose Retrospective reconstruction of slices in arbitrary position within the scanned volume No gaps since radiation always transmits the whole volumeSpiral CT / Volume Imaging21CT成

16、像原理介紹英文版醫(yī)學(xué)知識(shí)講解 Scan the whole region of ReComputed Tomography CT Basics Principle of Spiral CT Scan Parameter & Image Quality Optimizing Injection Protocols Clinical Applications22CT成像原理介紹英文版醫(yī)學(xué)知識(shí)講解Computed Tomography CT BasicsScan ParametersX-ray Tube Voltage (kVp) X-ray Tube Current (mA)Scan Time (

17、s)Slice thickness or Collimation (mm) Table Speed (mm/rot) or Feed per 360 rotation Pitch Interpolation Process Increment (mm)23CT成像原理介紹英文版醫(yī)學(xué)知識(shí)講解Scan ParametersX-ray Tube VoltTable Speed & Pitch Table Speed is defined as distance traveled in mm per 360 rotationPitch = Table Feed per rotation Collima

18、tion24CT成像原理介紹英文版醫(yī)學(xué)知識(shí)講解Table Speed & Pitch Table Spee10mm P110mm P230s30sMore Coverage inthe same time with extended Pitch!Pitch 2 covers 2xdistance as Pitch 125CT成像原理介紹英文版醫(yī)學(xué)知識(shí)講解10mm P110mm P230s30sMore CoverScan Range = 300mm10mm P110 mm/s10mm P220 mm/s30s15sCover the same volume in shorter time wi

19、th extended Pitch26CT成像原理介紹英文版醫(yī)學(xué)知識(shí)講解Scan Range = 300mm10mm P110mm To reduce artifacts due to table motion during spiral scanning,we use a special reconstruction process called INTERPOLATION Interpolation Converts volume data into slice imagesInterpolation Algorithm27CT成像原理介紹英文版醫(yī)學(xué)知識(shí)講解To reduce artifa

20、cts due to tabWide AlgorithmSlim Algorithm2 x 360 = 720raw data2 (180+52)= 464raw dataWide algorithm produces a broader image thicknessWide algorithm uses more raw data = less image noise28CT成像原理介紹英文版醫(yī)學(xué)知識(shí)講解Wide AlgorithmSlim AlgoritPITCH 2PITCH 1Pitch 2 scanning produces a broader image thicknessPit

21、ch 2 scanning does not increase image noise30% increase in image thicknesswith Pitch 2 29CT成像原理介紹英文版醫(yī)學(xué)知識(shí)講解PITCH 2PITCH 1Pitch 2 scanningSlice Sensitivity Profile ( SSP )SSP describes the effective slice thickness of an image and to what extent anatomy within that slice contribute to the signalSSPRES

22、OLUTIONAll points within the slice contribute equally & points outside of the slice do not contribute to the image at all .Image signalIdeal SSPZ-axis (mm)Collimation = width of x-ray beam =slice profile30CT成像原理介紹英文版醫(yī)學(xué)知識(shí)講解Slice Sensitivity Profile ( SSSlice Profile (SP)Effective slice thickness of a

23、n image Slice ProfileResolutionFactors influencing Slice Profile Collimation Pitch Interpolation algorithm (360 or 180)31CT成像原理介紹英文版醫(yī)學(xué)知識(shí)講解Slice Profile (SP)Effective slFactors influencing SSPCollimator width collimation = SSPSpiral CTTable speed or PitchInterpolation Algorithm= mathematical process

24、required to reconstruct axial images from the spiral volume data set32CT成像原理介紹英文版醫(yī)學(xué)知識(shí)講解Factors influencing SSPCollimaPitch & Slice Profile33CT成像原理介紹英文版醫(yī)學(xué)知識(shí)講解Pitch & Slice Profile33CT成像原理介Slim vs Wide SSP ComparisonSlice Profile Slim %Broaden Wide %BradenPitch One 5.0 mm 0 6.3 mm 26Pitch Two 6.5 mm 3

25、0 10.8 mm 11634CT成像原理介紹英文版醫(yī)學(xué)知識(shí)講解Slim vs Wide SSP ComparisonSWIDE720 degreeMore photonsSLIM464 degreeLess photons SSP Spatial resolutionSSPSpatialresolutionSmoother imageNoisier image35CT成像原理介紹英文版醫(yī)學(xué)知識(shí)講解WIDESLIM SSPSSPSmoother imagSlim - AdvantagesImproved Z ResolutionReduced partial volume artifactsS

26、lim + extended PitchLonger coverageSame coverage with shorter scan time or thinner slicesLess radiation dose36CT成像原理介紹英文版醫(yī)學(xué)知識(shí)講解Slim - AdvantagesImproved Z CT成像原理介紹英文版醫(yī)學(xué)知識(shí)講解培訓(xùn)課件Slice Profile Comparison38CT成像原理介紹英文版醫(yī)學(xué)知識(shí)講解Slice Profile Comparison38CT成像 Lesion smaller than 1cm SCAN RANGE = 150mm 10/10/1

27、0 (15s) 5/10/5 (15s) Slice Profile = 10mm Slice Profile = 6.5mmOptimizing the Scanning Parameters39CT成像原理介紹英文版醫(yī)學(xué)知識(shí)講解 Lesion smaller than 1cm SSmallest Possible Effective Slice ThicknessScan Length (mm)Scan Duration (s)Table Speed (mm/s)SmallestCollimation (mm)Scan DurationDepends on the scan length

28、& patients breath-hold complianceTable SpeedPitch Factor1 Pitch 2 to cover the whole volume in one breath-hold40CT成像原理介紹英文版醫(yī)學(xué)知識(shí)講解Smallest Possible Effective SlComputed Tomography CT Basics Principle of Spiral CT Scan Parameter & Image Quality Optimizing Injection Protocols Clinical Applications41CT成

29、像原理介紹英文版醫(yī)學(xué)知識(shí)講解Computed Tomography CT BasicsPeripheral vein eg. antecubital vein 19-20 gauge needle or IV catheterVolumeFlow RateConcentrationInjection Protocols300 mg I/mlnon-ionic contrast2 - 5 ml/s cardiac output80 - 150 ml patients weight & region of interestSiteScan DelayDelay between injection

30、initiation & the start of the scan sequence42CT成像原理介紹英文版醫(yī)學(xué)知識(shí)講解Peripheral vein eg. antecubitaTailoring Scan & Injection ProtocolsInjection Duration must be equal to or greater than Scan Time50100150200250TimesHUCONTRAST50100150200250TimesHUCONTRASTNaClBolus Duration scan timeInsufficient, inhomogeneo

31、us opacificationBolus Duration = scan timeUniform, maximum opacificationEnhancement Curve of the Target Region43CT成像原理介紹英文版醫(yī)學(xué)知識(shí)講解Tailoring Scan & Injection Pro50100150200250TimesHUOptimal WindowEarlyTime-density curveof the target regionLateContrast Bolus TimingDetermines optimal scan delay for spir

32、al CTA sequenceCONTRASTNaCl44CT成像原理介紹英文版醫(yī)學(xué)知識(shí)講解50100150200250TimesHUOptimalTest Bolus ProcedureImaging Volumefor spiral CTA 10-20 ml of contrast is injected at the chosen rate for spiral After a delay of 8-10s, low-dose, single-level axial images are acquired every 2s at the starting point of the ima

33、ging volume Dynamic scans at this position Dynamic Evaluation to generate a Time-density curve45CT成像原理介紹英文版醫(yī)學(xué)知識(shí)講解Test Bolus ProcedureImaging VoDynamic EvaluationTime-density curve Scan Delay Peak Enhancement Time Dynamic ScansROI placed in the Aorta46CT成像原理介紹英文版醫(yī)學(xué)知識(shí)講解Dynamic EvaluationTime-densityComputed Tomography CT Basics Principl