11

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

22

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

33

Introduction Articular cartilage

Surfaces of knee joints are covered by tissue Is a curved structure

difficult to read the thickness changes

44

Introduction

Main functions of the cartilage Distribution of weight Frictionless motion Shock absorption

55

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

66

Introduction

77

Introduction

Distortion Minimize the distortion, in a user-defined area

Flattening Requires parameterization of the surface

88

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

99

Pipeline for thickness visualization

Consists of the following steps

1010

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

1111

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

1212

Cartilage segmentation

1313

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

1414

Thickness measurement

Several possibilities to calculate Vertical distance

Is not appropriate for curved surfaces

Proximity method This paper uses

Normal distance

1515

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

1616

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

1717

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

1818

Flattening of articular cartilage

Do not allow multiple patches In order to keep spatial relations.

Parameterization has to be fast

1919

Flattening of articular cartilage

Efficiently prevent local as well as global intersections Align all points onto a line

Reduces the distortion minimization issue

2020

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

2121

Flattening of articular cartilage

2222

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

2323

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

2424

Operations on the height field

2525

Operations on the height field

2626

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

2727

Thresholded non-linear scaling

2828

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

2929

Non-linear scaling on interval

Thresholded scaling

3030

Non-linear scaling on interval

3131

Non-linear scaling on interval

Show the extraction of thickness information enhanced by color coding

3232

Non-linear scaling on interval

By iso-lines

3333

Non-linear scaling on interval

By glyphs

3434

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

3535

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

3636

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

3737

Scale transfer function

3838

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

3939

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