医学影像重建原理.ppt

医学影像重建原理医学影像重建原理1.DYNAVISION3.Image calibration+2D slice calculation4.3D image generation+3D image displayWorkflow2.Image transfer5.In room data display2PixelPixelSmallest picture element in the Smallest picture element in the image image reconstructedreconstructed from digital from digital data,displayed on a matrix.data,displayed on a matrix.3VoxelVoxelSmallest volume unit,picture Smallest volume unit,picture element.Cube-element.Cube-shapedshaped volume volume element which is associated with element which is associated with a digitized point in a volume.a digitized point in a volume.4OpacityOpacityA transparency value can be allocated A transparency value can be allocated toto each voxel in a data set.each voxel in a data set.Values range from 0.0 to 1.0 and Values range from 0.0 to 1.0 and determine whether a voxel should be determine whether a voxel should be displayed as transparent(low opacity)displayed as transparent(low opacity)or as opaque(high opacity).or as opaque(high opacity).0.10.11.01.07HistogramHistogramGraphical representation in which the X Graphical representation in which the X axis corresponds to the voxel value(CT axis corresponds to the voxel value(CT=Grayscale value).The Y axis=Grayscale value).The Y axis represents the number of voxels with a represents the number of voxels with a certain voxel value.certain voxel value.100HU-1000-100000100010008Ray TracingRay TracingEach pixel of the screen image is generated by a Each pixel of the screen image is generated by a Each pixel of the screen image is generated by a(simulated)light ray which is sent from infinity(simulated)light ray which is sent from infinity(simulated)light ray which is sent from infinity through the volume to be displayed.The resulting through the volume to be displayed.The resulting through the volume to be displayed.The resulting color depends on the algorithm in use while color depends on the algorithm in use while color depends on the algorithm in use while visiting the penetrated voxel(e.g.mean gray visiting the penetrated voxel(e.g.mean gray visiting the penetrated voxel(e.g.mean gray value,weighting by opacity,maximum gray value value,weighting by opacity,maximum gray value value,weighting by opacity,maximum gray value(MIP).(MIP).(MIP).9Rendering Rendering All voxels in a data set serve for All voxels in a data set serve for displaying a 3D image.displaying a 3D image.Rendering refers to a process,e.g.Rendering refers to a process,e.g.rotation,projection etc.,which is rotation,projection etc.,which is required so that the image can be required so that the image can be displayed as 3D image on the screen.displayed as 3D image on the screen.10OptimizingOptimizingFine adjustment of colors and Fine adjustment of colors and transparency values to be able to transparency values to be able to differentiate tissue with similar differentiate tissue with similar voxel values.voxel values.11Postprocessing-CTPostprocessing-CTMulti-Planar Reconstruction Multi-Planar Reconstruction MPRMPRShaded Surface Display Shaded Surface Display SSDSSDMaximum Intensity Projection Maximum Intensity Projection MIPMIPMinimum Intensity ProjectionMinimum Intensity ProjectionVolume Rendering Technique Volume Rendering Technique VRTVRT12Each voxel is selected according Each voxel is selected according to the selected threshold value.to the selected threshold value.The visible(i.e not hidden)surface of all The visible(i.e not hidden)surface of all selected voxels is displayed;all other selected voxels is displayed;all other voxels are treated as transparent.voxels are treated as transparent.The computer projects a light source so The computer projects a light source so that the images receive a three-that the images receive a three-dimensional appearance.dimensional appearance.Only 10%of the data set are used!Only 10%of the data set are used!S Shaded haded S Surface urface DDisplayisplaySSDSSD13The visible(i.e not hidden)surface of all The visible(i.e not hidden)surface of all selected voxels is displayed;all other voxels selected voxels is displayed;all other voxels are treated as transparent.are treated as transparent.ThresholdThresholdSSDSSD14Scans the volume along projection ray Scans the volume along projection ray projection.projection.The The voxelsvoxels with the highest value,e.g with the highest value,e.g HU-value,are selected.HU-value,are selected.Each voxel is displayed as occurs in the Each voxel is displayed as occurs in the original dataset.original dataset.MMaximum aximum I Intensity ntensity P Projectionrojection MIPMIP15Two-dimensional image.Cine loop of Two-dimensional image.Cine loop of multiple MIPs can provide an multiple MIPs can provide an impression of the organ-vessel impression of the organ-vessel relations.relations.Only 10%of the data set are used!Only 10%of the data set are used!MMaximum aximum I Intensity ntensity P Projectionrojection MIPMIP16The voxels with the highest The voxels with the highest value are selectedvalue are selectedvoxel with the highest attenuationvoxel with the highest attenuationMIPMIP17MIPMIP3D dataset3D dataset2D MIP image 2D MIP image 18Volume RenderingVolume Rendering VRTVRTProduction of a histogram of the voxel values Production of a histogram of the voxel values and their distribution.and their distribution.Each voxel is rendered with an opacity and Each voxel is rendered with an opacity and absorption value(absorption value(color values also possiblecolor values also possible).).Adaptations are made interactively and in real Adaptations are made interactively and in real time.time.100Grayscale-1000-1000001000100019Mean valueMean valueVRTVRT20VRTVRT3D dataset3D dataset2D VRT image2D VRT image21Volume RenderingVolume Rendering VRTVRTTheThe resulting image is a summation of resulting image is a summation of voxel values which can be rotated and voxel values which can be rotated and displayed on the screen in all projections.displayed on the screen in all projections.No loss of data!100%of the data set are No loss of data!100%of the data set are used.used.22VRTVRTSSDSSD23VRT shadedVRT shaded3D dataset3D dataset2D VRT image2D VRT imageThe computer projects a light sourceThe computer projects a light source24Example!Example!251.Advantages of VRT 1.Advantages of VRT compared with compared with SSDSSD and and MIPMIP VoxelVoxel attenuation converted into the attenuation converted into the gray gray shadeshade scale(color).scale(color).26Anatomical spatial relations between organs Anatomical spatial relations between organs are retainedare retained2.Advantages of VRT 2.Advantages of VRT compared with compared with SSDSSD and and MIPMIP 27No time-consuming editing required in No time-consuming editing required in order to eliminate cloudy or concealing order to eliminate cloudy or concealing structures.structures.3.Advantages of VRT 3.Advantages of VRT compared with compared with SSDSSD and and MIPMIP 28SeesSees through“to the other side”of through“to the other side”of walls.Looks into cavities which are not walls.Looks into cavities which are not accessible to normal endoscopy.accessible to normal endoscopy.Permits insights between concealed Permits insights between concealed structures.structures.4.Advantages of VRT 4.Advantages of VRT compared with compared with SSDSSD and and MIPMIP 29Opacity 15%Opacity 15%UnshadedUnshaded VRTVRTEvaluation of lumen diameter-same dataset.Evaluation of lumen diameter-same dataset.9.6 mm30Opacity 50%Opacity 50%UnshadedUnshaded VRTVRT9.6 mm31Opacity 50%Opacity 50%ShadedShaded VRTVRTRefraction index 40%Refraction index 40%9.6 mm32Opacity 40%Opacity 40%UnshadedUnshaded VRTVRT9.6 mmColorColor33Opacity 50%Opacity 50%ShadedShaded VRTVRTRefraction index 50%Refraction index 50%9.6 mm34MIPMIP8.3 mm35C Co ol lo or r VRTVRT36Virtual Colonoscopy立體檢視對話盒(可任意旋轉)區域生長對話盒(原始斷層掃描影像37