CT成像原理介绍(英文版)复习过程.ppt

按一下以編輯母片標題樣式,按一下以編輯母片,第二層,第三層,第四層,第五層,*,CT成像原理介绍(英文版),X-Ray Discovery,X-ray was discovered by a German scientist Roentgen 100 years ago.,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 tissue,My name is Godfrey Hounsfield,I work for the Central Research,Labs.of EMI,Ltd in England,I developed the the first clinically,useful CT scanner in 1971,History of Computed Tomography,Early 1970s,1963-Alan Cormack developed a mathematical method of reconstructing images from x-ray projections,For the first time we could view:,CT Broke the Barrier,-Tomographic or“,Slice,”anatomy-Density difference,But its time consuming,And resolution needs to be improved,Concept of X-ray Attenuation,An X-ray beam passing through,the body is attenuated(loses its,energy)by:,Absorption,Scattering,Incident X-ray,Transmitted ray,SCATTERED X-RAYS,BODY,TISSUE,Absorption by the tissue is proportional to the density,Less,dense,tissue,More,dense,tissue,MORE ATTENUATION,LESS ATTENUATION,How does CT Work?,Recon.&postpro.,Data acquisition,X-ray generation,X-ray goes through,collimator therefore,penetrate only an axial,layer of the object,called,slice,How does CT Work?,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 the detectors which digitizes these signals,These digitized signals called raw data are sent to a computer which create the CT image,How does CT Work?,The object slice is divided into small volume elements called voxels.,Each voxel is assigned a value which is dependent on the average amount of attenuation,How is CT Image generated?,The attenuation values are transferred to the computer where they are coded&used to create a slice image,How is CT Image generated?,CT Generations&Design,“Generation”,is used to label CT tube-detector designs,3rd Generation Design,Rotating tube&detector,4th Generation Design,Fixed ring detector,Slip-ring Technology,Power is transmitted through parallel sets of conductive rings,instead of electrical cables,Continuous Gantry Rotation,Prerequisite for Spiral CT,Non Slip-ring Scanner,Slip-ring Scanner,Computed Tomography,CT Basics,Principle of Spiral CT,Scan Parameter&Image Quality,Optimizing Injection Protocols,Clinical Applications,What is Spiral Scan?-just,4“C”,C,ontinuously rotating tube/detector system,C,ontinuously generating X-ray,C,ontinuously table feed,C,ontinuously data acquisition,Reconstruction of arbitrary,slices(either contiguous or,overlapping)within the,scanned volume,Distance between the,slices is called Increment,A,B,Volume Data,Continuous data acquisition,Increment,Slice Thickness,Increment=Slice Thickness,No Overlap,No Gaps,Contiguous Image Reconstruction,Increment,Overlap,Slice,Thickness,Overlapping Image Reconstruction,Increment Slice Thickness,Gaps between slices,Images are further apart,Less images created,Image Reconstruction with Gaps,Increment,Slice Thickness,Standard CT/Slice Imaging,Deep Inspiration,Shallow Inspiration,Misregistration due to different,respiratory levels between slices,Partial Volume Effect,Unable to resconstruct images at,arbitrary position,Slice imaging is slow,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 volume,Spiral CT/Volume Imaging,Computed Tomography,CT Basics,Principle of Spiral CT,Scan Parameter&Image Quality,Optimizing Injection Protocols,Clinical Applications,Scan Parameters,X-ray Tube Voltage,(kVp),X-ray Tube Current,(mA),Scan Time,(s),Slice thickness or Collimation,(mm),Table Speed(,mm/rot),or Feed per 360 rotation,Pitch,Interpolation Process,Increment(mm),Table Speed&Pitch,Table Speed,is defined as distance traveled in mm,per 360 rotation,Pitch,=,Table Feed per rotation,Collimation,10mm P1,10mm P2,30s,30s,More Coverage in,the same time with extended Pitch!,Pitch 2 covers 2x,distance as Pitch 1,Scan Range=300,mm,10mm P1,10 mm/s,10mm P2,20 mm/s,30s,15s,Cover the same volume in shorter time with extended Pitch,To reduce artifacts due to table motion during spiral scanning,we use a special reconstruction process called,INTERPOLATION,Interpolation,Converts volume data into slice images,Interpolation Algorithm,Wide Algorithm,Slim Algorithm,2 x 360,=720,raw data,2(180+52),=464,raw data,Wide algorithm produces a broader image thickness,Wide algorithm uses more raw data=less image noise,PITCH 2,PITCH 1,Pitch 2 scanning produces a broader image thickness,Pitch 2 scanning does not increase image noise,30%increase in,image thickness,with Pitch 2,Slice Sensitivity Profile(SSP),SSP describes the,effective slice thickness,of an image and to what extent anatomy within that slice contribute to the signal,SSP,RESOLUTION,All points within the slice contribute equally,&,points outside of the slice do not contribute to the image at all.,Image signal,Ideal SSP,Z-axis(mm),Collimation=width of x-ray beam=slice profile,Slice Profile(SP),Effective slice thickness of an image,Slice ProfileResolution,Factors influencing Slice Profile,Collimation,Pitch,Interpolation algorithm(360 or 180),Factors influencing SSP,Collimator width,collimation=SSP,Spiral CT,Table speed or Pitch,Interpolation Algorithm,=mathematical process required to reconstruct axial images from the spiral volume data set,Pitch,&,Slice Profile,Slim vs Wide SSP Comparison,Slice Profile Slim%Broaden Wide%Braden,Pitch One 5.0 mm 0 6.3 mm 26,Pitch Two 6.5 mm 30 10.8 mm 116,WIDE,720 degree,More photons,SLIM,464 degree,Less photons,SSP,Spatial,resolution,SSP,Spatial,resolution,Smoother image,Noisier image,Slim-Advantages,Improved Z Resolution,Reduced partial volume artifacts,Slim+extended Pitch,Longer coverage,Same coverage with shorter scan time or thinner slices,Less radiation dose,Wide-Advantages,Noise Reduction,Smoother image,Useful for scanning huge patient,Only for scanning at,Pitch One,Slice Profile Comparison,Lesion smaller than 1cm,SCAN RANGE=150,mm,10/10/10,(15s),5/10/5,(15s),Slice Profile=10,mm,Slice Profile=6.5,mm,Optimizing the Scanning Parameters,Smallest Possible Effective Slice Thickness,Scan Length(mm),Scan Duration(s),Table Speed(mm/s),Smallest,Collimation,(mm),Scan Duration,Depends on the scan length&patients,breath-hold compliance,Table Speed,Pitch Factor,1 Pitch 2,to cover the whole volume in one breath-hold,Computed Tomography,CT Basics,Principle of Spiral CT,Scan Parameter&Image Quality,Optimizing Injection Protocols,Clinical Applications,Peripheral vein eg.antecubital vein,19-20 gauge needle or IV catheter,Volume,Flow Rate,Concentration,Injection Protocols,300 mg I/ml,non-ionic contrast,2-5 ml/s,cardiac output,80-150 ml,patients weight&region of interest,Site,Scan Delay,Delay between injection initiation&the,start of the scan sequence,Tailoring Scan&Injection Protocols,Injection Duration must be,equal to or greater than,Scan Time,50,100,150,200,250,Times,HU,CONTRAST,50,100,150,200,250,Times,HU,CONTRAST,NaCl,Bolus Duration scan time,Insufficient,inhomogeneous,opacification,Bolus Duration=scan time,Uniform,maximum opacification,Enhancement Curve of the Target Region,50,100,150,200,250,Times,HU,Optimal Window,Early,Time-density curve,of the target region,Late,Contrast Bolus Timing,Determines optimal scan delay for spiral CTA sequence,CONTRAST,NaCl,Test Bolus Procedure,Imaging Volume,for 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 imaging volume,Dynamic scans at,this position,Dynamic Evaluation to generate,a Time-density curve,D,ynamic,E,valuation,Time-density curve,Scan Delay,Peak Enhancement Time,Dynamic Scans,ROI placed in the Aorta,Computed Tomography,CT Basics,Principle of Spiral CT,Scan Parameter&Image Quality,Optimizing Injection Protocols,Clinical Applications,Arterial Phase,Venous Phase,Dual Phase Liver Exam,Liver Metastases,Single Plane Imaging with Multiplanar Results,2D reconstruction based on a serial,of axial images along a certain axis,Sagittal,Coronal,Oblique recon.of Aorta,CT,A,ngiography,Spine 3D image:AVM,Max.Intensity,Projection,Surface Shaded,Display(3D),Femoral Arteries CT Angiogram,3D,Post-processing,3D,Bronchoscopy,Lesion in the right upper lobe branch,Colour Segmentation 3D,Volume Rendering Technique,Transparent image,Transparent&color image,Solid Image,Virtual Endoscopy,Real Time Fly through,Reverse Perspective,Axial Image reference,High Resolution,Bronchoscopy,The END,此课件下载可自行编辑修改，仅供参考！感谢您的支持，我们努力做得更好！谢谢,