1 interactive thickness visualization of articular cartilage author :matej mlejnek, anna...
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Interactive Thickness Visualization of Articular Cartilage
Author :Matej Mlejnek, Anna Vilanova,Meister Eduard GröllerSource :Proceedings of Visualization 2004, pages 521-527. October 2004 Speaker : Ren-LI ShenAdvisor : Ku-Yaw Chang
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Outline
Introduction Pipeline for thickness visualization
Cartilage segmentation Thickness measurement Flattening of articular cartilage
Operations on the height field Thresholded non-linear scaling Non-linear scaling on interval Scale transfer function
Summary and conclusions
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Introduction Articular cartilage
Surfaces of knee joints are covered by tissue Is a curved structure
difficult to read the thickness changes
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Introduction
Main functions of the cartilage Distribution of weight Frictionless motion Shock absorption
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Introduction
Height field Unfolding and depicting Eliminates the complexity of the 3D shape
concentrate solely on the inspection Offers several visualization modes
Color mapping Scaling Glyphs Iso-lines
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Introduction
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Introduction
Distortion Minimize the distortion, in a user-defined area
Flattening Requires parameterization of the surface
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Outline
Introduction and medical background Pipeline for thickness visualization
Cartilage segmentation Thickness measurement Flattening of articular cartilage
Operations on the height field Thresholded non-linear scaling Non-linear scaling on interval Scale transfer function
Summary and conclusions
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Pipeline for thickness visualization
Consists of the following steps
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Outline
Introduction and medical background Pipeline for thickness visualization
Cartilage segmentation Thickness measurement Flattening of articular cartilage
Operations on the height field Thresholded non-linear scaling Non-linear scaling on interval Scale transfer function
Summary and conclusions
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Cartilage segmentation
Two main classes of segmentation methods Manual segmentation
Time-consuming Requires an experienced user
Semi-automatic segmentation use thresholding, region growing, snakes, or edge detection filters
In this paper they use an active contour model (snake) controlled by internal and external forces
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Cartilage segmentation
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Outline
Introduction and medical background Pipeline for thickness visualization
Cartilage segmentation Thickness measurement Flattening of articular cartilage
Operations on the height field Thresholded non-linear scaling Non-linear scaling on interval Scale transfer function
Summary and conclusions
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Thickness measurement
Several possibilities to calculate Vertical distance
Is not appropriate for curved surfaces
Proximity method This paper uses
Normal distance
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Thickness measurement
Euclidean distance
Optimizations of distance transforms Chamfer distance transforms
propagates the local distance by adding the neighborhood values
Vector distance transforms propagates the distance vector to the nearest
sample point of the object surface
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Outline
Introduction and medical background Pipeline for thickness visualization
Cartilage segmentation Thickness measurement Flattening of articular cartilage
Operations on the height field Thresholded non-linear scaling Non-linear scaling on interval Scale transfer function
Summary and conclusions
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Flattening of articular cartilage
Flattening cartilage into the corresponding 2D plane should fulfill the following criteria Need a parameterization
Minimizes area distortion
Local and global intersections have to be prevented Common problem in the area on surface parameterizatio
n
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Flattening of articular cartilage
Do not allow multiple patches In order to keep spatial relations.
Parameterization has to be fast
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Flattening of articular cartilage
Efficiently prevent local as well as global intersections Align all points onto a line
Reduces the distortion minimization issue
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Flattening of articular cartilage
In order to meet all of the constraints Grow a planar patch
First, the focal triangle includes the focal point is
rigidly transformed into the 2D plane The distance is defined by the height of the focal triangle (h
eight = 2·area / |p2−p1|)
Next step, patch is iteratively flattened by adding active points ai to the patch
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Flattening of articular cartilage
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Outline
Introduction and medical background Pipeline for thickness visualization
Cartilage segmentation Thickness measurement Flattening of articular cartilage
Operations on the height field Thresholded non-linear scaling Non-linear scaling on interval Scale transfer function
Summary and conclusions
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Operations on the height field
Slight changes in the thickness on the reconstructed surface may, however, not be noticeable
In order to enhance the thickness information Propose a non-uniform scaling only in the height
direction
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Operations on the height field
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Operations on the height field
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Outline
Introduction and medical background Pipeline for thickness visualization
Cartilage segmentation Thickness measurement Flattening of articular cartilage
Operations on the height field Thresholded non-linear scaling Non-linear scaling on interval Scale transfer function
Summary and conclusions
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Thresholded non-linear scaling
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Outline
Introduction and medical background Pipeline for thickness visualization
Cartilage segmentation Thickness measurement Flattening of articular cartilage
Operations on the height field Thresholded non-linear scaling Non-linear scaling on interval Scale transfer function
Summary and conclusions
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Non-linear scaling on interval
Thresholded scaling
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Non-linear scaling on interval
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Non-linear scaling on interval
Show the extraction of thickness information enhanced by color coding
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Non-linear scaling on interval
By iso-lines
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Non-linear scaling on interval
By glyphs
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Outline
Introduction and medical background Pipeline for thickness visualization
Cartilage segmentation Thickness measurement Flattening of articular cartilage
Operations on the height field Thresholded non-linear scaling Non-linear scaling on interval Scale transfer function
Summary and conclusions
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Scale transfer function
Need a tool enables detection of subtle thickness changes on each range of the thickness values
Using non-linear scaling approach, interesting features may be occluded by other scaled areas Can be overcome by thresholded non-linear scalin
g
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Scale transfer function
Define a continuous linear scaling transfer function Maps the original thickness values Assigned to each vertex To the scaled values
Thickness preservation is performed on intervals, where x = y
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Scale transfer function
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Outline
Introduction and medical background Pipeline for thickness visualization
Cartilage segmentation Thickness measurement Flattening of articular cartilage
Operations on the height field Thresholded non-linear scaling Non-linear scaling on interval Scale transfer function
Summary and conclusions
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Summary and conclusions
The approach has been illustrated on the visualization of articular cartilage
Detection of slight thickness changes is vital for diagnosis
Has been shown that unfolding of anatomic organs is promising
Future work Continue with a broader clinical study on a variety of dat
asets
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