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Image Visualization
� Motivations
� Visualization Methods
◦ Two-Dimensional Methods
◦ Volume Visualization (Surface-Based, Direct Volume)
� Volume Processing and Classification
� Visualization Examples
ITCS 6010:Biomedical Imaging and Visualization 1 Image Processing and Analysis
Image Visualization
� Visualizations have always been used to
◦ Study relationship between anatomical structure and function
◦ Detect and treat trauma and disease
� Traditional visualizations were direct, via surgery, biopsy, or indirect,via extensive mental reconstruction
� The revolution in 3D/4D biomedical imaging (CT, MRI, PET) andcomputer reconstruction and rendering provides new powerful op-portunities.
� Image Processing and Visualization can help unlock critical informa-tion of objects and their properties in medical images.
ITCS 6010:Biomedical Imaging and Visualization 2 Image Processing and Analysis
Image Visualization:Why?
� Multi-modal 3D and 4D imaging from CT, MRI, PET, MEG, Ultra-sound, Microscopy have fueled developments in data differentiation,fusion, visualization
� Datasets are generally very large (mega-giga-tera bytes).
� Management, Processing, Analysis and Visualization requires highperformance computing.
� Advances in visualization technology will provide newtools/procedures that physicians “must have” to treat patients
� Quote from a physician, “If I can see it, I can fix it”
� Ability to see anatomical structures permits surgery planning, re-hearsal, to minimize trauma, avoid critical areas.
ITCS 6010:Biomedical Imaging and Visualization 3 Image Processing and Analysis
Image Visualization:Why?
� Realtime interactive visualization, advanced display technologies in-cluding VR, open new realms into medical practice.
� Images displayed and manipulated with immediacy, sufficient detailand speed to evoke a sufficiently ”real” experience.
� Interactive 3D environments permit physicians to view anatomy andfunction from any viewpoint, make accurate online measurements.
� Visualization Scale :
◦ Structure: From individual molecules, tissues and interstitial in-terfaces to complete organs and organ systems;
◦ Functional attributes: Biophysical, Biomechanical and physio-logical properties.
� Holy Grail: Fully immersive, real-time multisensory fusion of realand virtual information streams (Example: GE Surgical MRI scan-ner)
ITCS 6010:Biomedical Imaging and Visualization 4 Image Processing and Analysis
Visualization Methods: 2D Techniques
� 2D images from 3D/4D biomedical imaging datasets can show
◦ Original data
◦ No occlusion problems
� Difficulty: Optimal image plane might not be possible:
◦ Limitations of the imaging system
◦ Need sophisticated reconstruction techniques
ITCS 6010:Biomedical Imaging and Visualization 5 Image Processing and Analysis
2D Visualiztion: Multiplanar Reformatting
� Ability to display axis-aligned images of 3D/4D volume
� If the entire volume is in memory, displaying the images along eachimage plane maps to voxel ordering problem
� Example: 3D CT, MRI Volume: Axial, Sagittal, Coronal Images
ITCS 6010:Biomedical Imaging and Visualization 6 Image Processing and Analysis
2D Visualiztion: Multiplanar Reformatting
ITCS 6010:Biomedical Imaging and Visualization 7 Image Processing and Analysis
2D Visualization: Oblique Sectioning
� Optimal image plane more likely will lie along arbitrarily orientedplane
� Need to specify orientation, and accurate computer reconstruction
ITCS 6010:Biomedical Imaging and Visualization 8 Image Processing and Analysis
2D Visualiztion: Curved Planar Reformation
� Structures may be curvilinear: spinal canal, blood vessels.
� Difficult to capture such structures completely in an planar image.
� Possible Implementation: Trace pixels along a path in an orthogonalsection; display rows of voxels corresponding to the pixels as a 2Dimage.
ITCS 6010:Biomedical Imaging and Visualization 9 Image Processing and Analysis
Volume Visualization:Voxels and Cells
� Volume Data: An array of volume elements, termed “voxels”, or anarray of “cells”.
� Voxel Model:
◦ Area around the grid point has a uniform value(s)(hexahedral,spherical, etc)
◦ Advantage: No assumptions on data behavior between grid-points
� Cell Model:
◦ Models volumes as a collection of hexahedra (or other geome-try) with gridpoints at its corners
◦ Need an estimation scheme for data variation within the cell
ITCS 6010:Biomedical Imaging and Visualization 10 Image Processing and Analysis
Volume Visualization:Grids and Lattices
� Regular: voxels, cells are axis-aligned rectangular prisms
� Rectilinear: voxels, cels are axis-aligned, but inter-voxel(cell) spac-ing varies
� Structured: Non axis-aligned hexahedra (warped bricks); Exam-ples: Spherical, Curvilinear grids
� Block-Structured: Collection of structured grids
� Hybrid, Unstructured: Collection of any set of grid types
ITCS 6010:Biomedical Imaging and Visualization 11 Image Processing and Analysis
Volume Visualization: Processing Steps
� Data acquisition: Includes processing to increase data valuerange, contrast enhancement, free of noise
� Aspect Ratio Adjustment: Volume dimensions correspond tophysical dimensions of the acquired data - may require interpola-tion, additional slice generation, estimate missing values
� Data Classification
� Mapping operations: Transformation to geometric or display primi-tives
ITCS 6010:Biomedical Imaging and Visualization 12 Image Processing and Analysis
Volume Visualization: Anatomic ModelingSteps
ITCS 6010:Biomedical Imaging and Visualization 13 Image Processing and Analysis
Volume Visualization MethodsSurface vs. Direct Volume Rendering
Simulate
Filter
Data Data
MappingGeometricPrimitives
Render
Images
Playback
Summarize
MeasuredData
� Surface-Based Volume Rendering: Data is converted to geometricprimitives and a standard graphics pipeline is used to render thevolume; Examples: Isosurfacing(Marching Cubes, Dividing Cubes),Contour connecting
� Direct Volume Rendering: Volume is directly sampled and projectedto the final raster image (rendering). Examples: Ray Casting, Pro-jection Methods (VBuffer), Volume Splatting.
� Examples from the Visible Human Project (VHP) athttp://www.nlm.nih.gov/research/visible/animations.html
ITCS 6010:Biomedical Imaging and Visualization 14 Image Processing and Analysis
Volume Visualization MethodsSurface vs. Direct Volume Rendering
ITCS 6010:Biomedical Imaging and Visualization 15 Image Processing and Analysis
Volume Visualization MethodsSurface vs. Direct Volume Rendering
Surface Based Direct Volume Render ingObject Order Image Order
Contour Connecting V-Buffer Ray CastingOpaque Cubes Splatting Cell IntegrationMarching Tetrahedra Pixar Method Frequency Domain MethodsMarching CubesDividing Cubes
ITCS 6010:Biomedical Imaging and Visualization 16 Image Processing and Analysis
Volume Visualization: Data Classification
� Process of associating voxels with useful, significant information onobjects/properties represented by the medical volume.
� Two methods typically employed in volume visualization:
◦ Transfer Functions: Volume data (scalar/vector values, gradient,other features) mapped to opacity and color and input to render-ing pipeline
◦ Segmentation: Sophisticated algorithms are employed in asso-ciated voxels with clinically significant objects (tissues, organs,tumors)
ITCS 6010:Biomedical Imaging and Visualization 17 Image Processing and Analysis
Volume Visualization:Illumination Models
� Depth Shading, Depth Gradient Shading
� Maximum Intensity Projection
� Voxel Gradient Shading
� Volumetric Compositing
ITCS 6010:Biomedical Imaging and Visualization 18 Image Processing and Analysis
Volume Visualization:Illumination Models
ITCS 6010:Biomedical Imaging and Visualization 19 Image Processing and Analysis
Volume Visualization:Illumination Models
ITCS 6010:Biomedical Imaging and Visualization 20 Image Processing and Analysis
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