CT成像原理介绍英文

1、1会计学CT成像原理介绍英文成像原理介绍英文 CT Basics Principle of Spiral CT Scan Parameter & Image Quality Optimizing Injection Protocols Clinical ApplicationsX-ray was discovered by a German scientist Roentgen 100 years ago. This made people for the first time be able toview the anatomy structure of human body wit

2、hout operationBut its superimposed And we couldnt view soft tissuel My name is Godfrey Hounsfieldl I work for the Central Research Labs. of EMI, Ltd in Englandl I developed the the first clinically useful CT scanner in 19711963 - Alan Cormack developed a mathematical method of reconstructing images

3、from x-ray projections For the first time we could view:- Tomographic or “Slice” anatomy- Density differenceBut its time consumingAnd resolution needs to be improvedIncident X-rayTransmitted rayBODYTISSUEAbsorption by the tissue is proportional to the densityLessdensetissueMoredensetissueMORE ATTENU

4、ATIONLESS ATTENUATIONRecon. & postpro.Data acquisitionX-ray generationX-ray goes through collimator thereforepenetrate only an axial layer of the object, called slice Patient is placed in the center of the measurement field X-ray is passed through the patients slice from many direction along a 3

5、60 path The transmitted beams are captured by the detectors which digitizes these signals These digitized signals called raw data are sent to a computer which create the CT imageThe object slice is divided into small volume elements called voxels. Each voxel is assigned a value which is dependent on

6、 the average amount of attenuationThe attenuation values are transferred to the computer where they are coded & used to create a slice image CT Basics Principle of Spiral CT Scan Parameter & Image Quality Optimizing Injection Protocols Clinical ApplicationsReconstruction of arbitraryslices (

7、either contiguous or overlapping) within thescanned volume Distance between the slices is called IncrementABVolume DataContinuous data acquisitionIncrementSlice ThicknessContiguous Image ReconstructionIncrementOverlapSliceThicknessOverlapping Image ReconstructionImage Reconstruction with GapsIncreme

8、ntSlice Thickness CT Basics Principle of Spiral CT Scan Parameter & Image Quality Optimizing Injection Protocols Clinical ApplicationsPitch = Table Feed per rotation CollimationT Ta ab bl le e F Fe ee ed d C Co ol ll li imma at ti io on n P Pi it tc ch h 1 10 0 mmmm/ /r ro ot t1 10 0 mmmm1 1. .0

9、 01 15 5 mmmm/ /r ro ot t1 10 0 mmmm1 1. .5 52 20 0 mmmm/ /r ro ot t1 10 0 mmmm2 2. .0 030s15sTo reduce artifacts due to table motion during spiral scanning,we use a special reconstruction process called INTERPOLATIONInterpolation AlgorithmSlice Sensitivity Profile ( SSP )SSP describes the effective

10、 slice thickness of an image and to what extent anatomy within that slice contribute to the signalSSPRESOLUTIONAll 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 =sl

11、ice profileSlice ProfileResolutionFactors influencing SSPCollimator width collimation = SSPSpiral CTTable speed or PitchInterpolation Algorithm= mathematical process required to reconstruct axial images from the spiral volume data setPitch & Slice ProfileSlim vs Wide SSP ComparisonSlice Profile

12、Slim %Broaden Wide %BradenPitch One 5.0 mm 0 6.3 mm 26Pitch Two 6.5 mm 30 10.8 mm 116WIDE720 degreeMore photonsSLIM464 degreeLess photons SSP Spatial resolutionSSPSpatialresolutionSmoother imageNoisier imageSlim - AdvantagesImproved Z ResolutionReduced partial volume artifactsSlim + extended PitchLo

13、nger coverageSame coverage with shorter scan time or thinner slicesLess radiation doseWide - AdvantagesNoise ReductionSmoother imageUseful for scanning huge patientOnly for scanning at Pitch OneC Co ol ll li imma at ti io on n5 5. .0 0 mmmmWWi id de eI In nt te er rp po ol la at ti io on nS Sl li im

14、mI In nt te er rp po ol la at ti io on nP Pi it tc ch h 1 1. .0 06 6. .3 3 mmmm5 5. .0 0 mmmm % B Br ro oa ad de en ne ed d2 26 60 0P Pi it tc ch h 2 2. .0 01 10 0. .8 8 mmmm 6 6. .5 5 mmmm% B Br ro oa ad de en ne ed d1 11 16 63 30 0 Lesion smaller than 1cm SCAN RANGE = 150mm Slice Profile = 10mm Sl

15、ice Profile = 6.5mmOptimizing the Scanning ParametersDepends on the scan length & patients breath-hold compliance1 Pitch 2 to cover the whole volume in one breath-hold CT Basics Principle of Spiral CT Scan Parameter & Image Quality Optimizing Injection Protocols Clinical ApplicationsDetermin

16、es optimal scan delay for spiral CTA sequenceDynamic ScansROI placed in the Aorta CT Basics Principle of Spiral CT Scan Parameter & Image Quality Optimizing Injection Protocols Clinical ApplicationsX-ray was discovered by a German scientist Roentgen 100 years ago. This made people for the first

17、time be able toview the anatomy structure of human body without operationBut its superimposed And we couldnt view soft tissue Patient is placed in the center of the measurement field X-ray is passed through the patients slice from many direction along a 360 path The transmitted beams are captured by

18、 the detectors which digitizes these signals These digitized signals called raw data are sent to a computer which create the CT imageIncrementSlice ThicknessContiguous Image ReconstructionIncrementOverlapSliceThicknessOverlapping Image ReconstructionSlice Sensitivity Profile ( SSP )SSP describes the effective slice thickness of an image and to what extent a