Medical Visualization

8/6/2019 Medical Visualization

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Medical Visualization:Concepts & Overview

Abhishek MitraPh.D in Medical Imaging


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Visualization:

Surface & Volume Rendering

2D screen

3D volume dataset

2D display of

3D dataset

Volume Rendering: The term volume renderingis used to describetechniques which allow the visualization of three-dimensional

data.

Volume rendering is a technique for visualizing sampledfunctions of three spatial dimensions by computing 2-D

projections of a colored semitransparent volume.

Volume Rendering: The term volume renderingis used to describetechniques which allow the visualization of three-dimensional

data.

Volume rendering is a technique for visualizing sampledfunctions of three spatial dimensions by computing 2-D

projections of a colored semitransparent volume.


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Iso value = 80

Iso value =

200

Visualization: Surface Rendering

Isosurface :

A closed surface separates outside and inside For volume data, define isovalue:All voxels with values bigger than isovalue are inside

and others outside

Then, an surface is defined by this isovalue, theisosurface

Isosurface :

A closed surface separates outside and inside For volume data, define isovalue:All voxels with values bigger than isovalue are inside

and others outside

Then, an surface is defined by this isovalue, theisosurface

3D volume

dataset

Isosurface

50

77

87

95

5

55

7

Isocontour (of value 5)

extraction in 2D


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Visualization: Volume Rendering

Classification

Classification

Gradient Computation

Compositing

Shading

Shading

Preparing

3D Volume data

prepared from stack of

2D images

Volume rendered image

77

50

87

95

5

55

7Stack of 2D images


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Classification

Classification



Compositing

Shading

Shading

Preparing

Visualization: Gradient Computation

Why Compute Gradient :

Gradient of densities provides info on surface:- Density changes at surface boundaries- Change also appears in their gradient

- Presence of surface is qualified by magnitude

of gradient

Gradient vector will be used as surface normal in theshading process

Gradient vectors norm is used in classification

Why Compute Gradient :

Gradient of densities provides info on surface:- Density changes at surface boundaries- Change also appears in their gradient

- Presence of surface is qualified by magnitude

of gradient

Gradient vector will be used as surface normal in theshading process

Gradient vectors norm is used in classification

LR

EyeN

Shading

Isosurface

3D volume datasetStack of 2D images


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Visualization: Classification

Classification

Classification


Compositing

Shading

Shading

PreparingClassification Goals :

Make sense of a given data set Group voxels of same substanceAssign color/opacity value that guides visualization Color Transfer Function-> Maps data to a given color Opacity Trans. Fn.-> Maps data to a given opacity

Classification Goals :

Make sense of a given data set Group voxels of same substanceAssign color/opacity value that guides visualization Color Transfer Function-> Maps data to a given color Opacity Trans. Fn.-> Maps data to a given opacity

Color Transfer

Function

77

50

87

95

555

7

C(xi)xi


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Visualization: Classification Opacity TransferFunction

Opacity

Volume

Data1.00.1 0.4

Bone:

Opaque

1.0

Volume

Data0.1 0.4

1.0

Tissue:

Opaque

Opacity

Skull + Skin

Opacity

0.1

Tissue:

Semi transparent

0.4

1.0

Bone:

Opaque

Volume

Data

C(xi)xi C(xi), O(xi)


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Visualization: Shading

Stack of2D images 50

77

87

95

555

7

xi

Data

preparation

3D volume

dataset

C(xi)

Color

Transfer

Function

3D colored dataset

C(xi), O(xi)OpacityTransfer

Function

3D colored

semi-transperent dataset C(xi), O(xi), S(xi)

Shading

3D colored

semi-transperent

shaded dataset


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Eye

Visualization: Compositing or Ray-casting

For every pixel in output image:

Treat volume as a translucent object shoot ray into volume at least one per pixel at evenly spaced ray locations, obtain color and opacity

by interpolation

Accumulate color and opacities of voxels from back to

front Stop when ray exits grid or reaches full opacity

For every pixel in output image:

Treat volume as a translucent object shoot ray into volume at least one per pixel at evenly spaced ray locations, obtain color and opacity

by interpolation

Accumulate color and opacities of voxels from back to

front Stop when ray exits grid or reaches full opacity

Classification


CompositingCompositing

ShadingShading

Preparing

C(xi), O(xi), S(xi)

2D screen

Medical Visualization

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