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1、醫學影像分析與實作.OUTLINElImage acquisition methodlImage enhancementlMethods of Qualitative Image AnalysislExample for clinical medical image analysisl Most nuclear medicine imaging systems present their information as digital images.lA digital image is stored in the computer as an array or matrix of count
2、values and is displayed by assigning a gray or color scale that depends on the number of counts in each element.Digital ImagelThe Image arrays are square matrices that have dimensions range from 32*32 up to 1024*1024 lIn nuclear medicine :32*32,64*64,128*128,256*256,512*512,1024*1024lByte mode & wor
3、d modeImage formationlFrame ModelList ModelDual Isotope ImagingFrame modelX-Y coordinatelByte mode:l256 gray scalel1 byte = 8 bitslWord mode:l65535 gray scalel2 byte =1 wordList model2 byte data series lEvent addresseslTime flaglList mode can be formatted any frame sizelList mode need more memorySam
4、plingSampling size:pixel size(mm) = field of view (mm) / # of pixels What should the pixel size be? 1. The spatial resolution of imaging system 2. The smallest object of interest in the image 3. The time it takes to perform any processing steps. 4. The amount of storage and archival space available.
5、Information DensitylWhat information can we expect to perceive at a given count density?this depends on the size of the smallest region in the image you are trying to perceive and its apparent contrast to the surrounding background. How to define the image information density? n k2/C2d2n : estimate
6、the count densityk : the signal to noise ratio (35)C : image constrastd : image diameter Image constrast = (object count density - background count density)/ background count densityImage Acquisition lStatic studieslWhole-Body ImaginglDynamic studieslGated AcquisitionlSPECT AcquisitionData Acquisiti
7、on MethodlFrame ModelList ModeFrame mode AcquisitionlPicture elementsl64*64l128*128l256*256lPixel : Picture elementlSquare mosaic : lImage matrix, lImage arrayl pixel arrayResolutionlSpatial ResolutionlTemporal ResolutionlEnergy ResolutionSpatial ResolutionlEach pixel in the image matrix has one- to
8、-one correspondence with a given location in the plane of NaI crystallEx: Gamma camera FOV=40cm diameterlFor 64*64 S.R=400/64=6.25mm/pixellFor 128*128 S.R=400/128=3.13mm/pixelStatistical NoiseIncrease Spatial resolutionlZooming lHardwarelSoftwarelZoom can l(1) decrease Background countl(2) increase
9、resolutionlThe spatial resolution of computer image is ultimately limit by resolution of gamma cameraByte mode V.S. Word model1 Byte = 28 bits =256 (0-255)l1 Word = 216 bits = 65536 (0-65535)l1 Word = 2 BytesByte mode V.S. Word modelByte mode Acquisition: a pixel deep is 1 bytelWord mode Acquisition
10、: a pixel deep is 2 bytelWhat Kind of the acquisition mode we should used?lIn low count studies = Byte modelIn High count studies = Word modeByte mode V.S. Word modelByte mode l優點: less memoryl缺點: 1. dead time2. truncation errorlWord model優點: 1. No dead time2. No truncationl缺點: more memoryOverflow:D
11、ead time:Truncation:臨床診斷上使用的應用軟體l影像增強(Image enhancement)l量化分析(Qualitative Image analysislECT影像重建 (ECT image reconstruction)Image EnhancementlImage smoothing filterslP7Image EnhancementlNine-point smooth (mask)w1w2w3w4w5w6w7w8w91 1 1 1 1 1 1 1 1Image EnhancementImage EnhancementImage EnhancementlMedi
12、um smoothHalf way mask = replace average (weight ) 50% count value (mask) 50% count value (Keep)Image EnhancementlEdge-enhancement filter(sharpen mask)lMask: (2N+1)*(2N+1)Image EnhancementlPoint processing operationslBackground subtractionlGray scaleslColor translation tablelFrame processing operati
13、onex: Parathyroid scan studyParathyroid subtractuinImage Enhancement-1 -1 -1-1 8 -1-1 -1 -1影像量化分析lROI( region of interesting) create lHistogram createlAnalysis ROI and HistogramlClinical mathematicPoint processing operationlBackground subtraction (pixel- by-pixel)Point processing operationlInterpola
14、ted background subtraction (weight)Wa=Xb/XaWb=Xa/XbWc=Yd/YcWd=Yc/YdXa: Q距A點距離Xb: Q距B點距離Yc: Q距C點距離Yd: Q距D點距離Gray scales and color tablelGray scale ( dynamic range)the number of shades of gray between these two extremeslType:l Linearl exponentiall logarithmicGray and color tableGray scales and color d
15、isplayGray scales and color displayLung perfusion/ventilation ratioTl201 myocardial perfusion studyCreating ROIslAutomatic edge detection methods:Create ROIlMethod:lCircular ROIlRectangular ROIlIrregular ROIlAutomatic ROICurve Generation and AnalysislThe starting point for analyzing the flow pattern
16、 quantitatively is the construction of an activity-versus-time curve.lMethodlEye-ballinglThe move average methodlThe weighted moving-average methodThe Moving Average methodThe Moving Average methodData smoothing by curve FittingClinical Mathematic in Nuclear MedicinelNuclear CardiologylMultiple-gate equilibriumlFirst pass blood-pooll
