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1、.,醫學影像分析與實作,OUTLINE,Image acquisition method Image enhancement Methods of Qualitative Image Analysis Example for clinical medical image analysis,Most nuclear medicine imaging systems present their information as digital images. A 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 Image,The Image arrays are square matrices that have dimensions range from 32*32 up to 1024*1024 In nuclear medicine :32*32,64*64,128*128,256*256,512*512,1024*1024 Byte mode & wo
3、rd mode,Image formation,Frame Mode List Mode Dual Isotope Imaging,Frame mode,X-Y coordinate Byte mode: 256 gray scale 1 byte = 8 bits Word mode: 65535 gray scale 2 byte =1 word,List mode,2 byte data series Event addresses Time flag List mode can be formatted any frame size List mode need more memory
4、,Sampling,Sampling 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 avail
5、able.,Information Density,What 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 : est
6、imate the count densityk : the signal to noise ratio (35)C : image constrastd : image diameter Image constrast = (object count density - background count density)/ background count density,Image Acquisition,Static studies Whole-Body Imaging Dynamic studies Gated Acquisition SPECT Acquisition,Data Ac
7、quisition Method,Frame Mode List Mode,Frame mode Acquisition,Picture elements 64*64 128*128 256*256 Pixel : Picture element Square mosaic : Image matrix, Image arraypixel array,Resolution,Spatial Resolution Temporal Resolution Energy Resolution,Spatial Resolution,Each pixel in the image matrix has o
8、ne-to-one correspondence with a given location in the plane of NaI crystalEx: Gamma camera FOV=40cm diameter For 64*64 S.R=400/64=6.25mm/pixel For 128*128 S.R=400/128=3.13mm/pixel,Statistical Noise,Increase Spatial resolution,Zooming Hardware Software Zoom can (1) decrease Background count (2) incre
9、ase resolution The spatial resolution of computer image is ultimately limit by resolution of gamma camera,Byte mode V.S. Word mode,1 Byte = 28 bits =256 (0-255) 1 Word = 216 bits = 65536 (0-65535) 1 Word = 2 Bytes,Byte mode V.S. Word mode,Byte mode Acquisition: a pixel deep is 1 byte Word mode Acqui
10、sition: a pixel deep is 2 byte What Kind of the acquisition mode we should used? In low count studies = Byte mode In High count studies = Word mode,Byte mode V.S. Word mode,Byte mode 優點: less memory 缺點: 1. dead time2. truncation error Word mode 優點: 1. No dead time2. No truncation 缺點: more memory,Ove
11、rflow: Dead time: Truncation:,臨床診斷上使用的應用軟體,影像增強(Image enhancement) 量化分析(Qualitative Image analysis ECT影像重建 (ECT image reconstruction),Image Enhancement,Image smoothing filters P7,Image Enhancement,Nine-point smooth (mask),Image Enhancement,Image Enhancement,Image Enhancement,Medium smoothHalf way ma
12、sk = replace average (weight ) 50% count value (mask) 50% count value (Keep),Image Enhancement,Edge-enhancement filter(sharpen mask) Mask: (2N+1)*(2N+1),Image Enhancement,Point processing operations Background subtraction Gray scales Color translation table Frame processing operationex: Parathyroid
13、scan study,Parathyroid subtractuin,Image Enhancement,影像量化分析,ROI( region of interesting) create Histogram create Analysis ROI and Histogram Clinical mathematic,Point processing operation,Background subtraction (pixel-by-pixel),Point processing operation,Interpolated background subtraction (weight),Wa
14、=Xb/Xa Wb=Xa/Xb Wc=Yd/Yc Wd=Yc/Yd,Xa: 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 table,Gray scale ( dynamic range)the number of shades of gray between these two extremes Type:Linearexponentiallogarithmic,Gray and color table,Gray scales and color display,Gray scales and color disp
15、lay,Lung perfusion/ventilation ratio,Tl201 myocardial perfusion study,Creating ROIs,Automatic edge detection methods:,Create ROI,Method: Circular ROI Rectangular ROI Irregular ROI Automatic ROI,Curve Generation and Analysis,The starting point for analyzing the flow pattern quantitatively is the cons
16、truction of an activity-versus-time curve. Method Eye-balling The move average method The weighted moving-average method,The Moving Average method,The Moving Average method,Data smoothing by curve Fitting,Clinical Mathematic in Nuclear Medicine,Nuclear Cardiology Multiple-gate equilibrium First pass blood-pool Static myocardial perfusion study Renal function GFR Kidney radio ERPF Diuretic renography (Lasix)Captopril renography Other,Example for Ventricular Ejection Fraction,
