1. Blood Vessel Modeling using 2D/3D Level Set Method

2. Overview Main Idea Discussion Big Picture Problem Considered
Motivation
Main Approach : Level-Set Based 2D Segmentation
Discussion
Strength and Weakness of the Approach
Comparison with other approaches
Future Direction

3. Pipeline for Blood Flow Modeling
3D Image
Acquisition
Geometric
Modeling
Finite Element
Calculation
Quantification,
Visualization
cardivascular disease research, medical device design, and surgical planning

4. What is Problem?
Construct accurate patient-specific 3D geometric models (tetrahedral mesh) of blood vessels of interest

5. Why is it important?
Flow calculation using finite element method requires quality mesh
Accuracy of calculation depends on that of geometric model
Geometry Quantification

6. from Image to Geomtry Why is it difficult ?
Usually requires ill-defined segmentation process
Computers easily make an error
Thresholding (Isocontouring) is well defined but often it is not useful in medical applications
Noisy Scanning
Accurate Construction
Patient-Specific
Operator Dependence
Minimal user interaction is favorable
Robustness
Always guarantee quality result ?

7. Main Approach for Geometry
Path (Centerline) Construction
Semi-automatic , manual
2D image Segmentation
Surface Reconstruction thru lofting
Solid Model Operation (CSG) : Union
Automatic Mesh Generation

8. Level Set Method for 2D Segmentation
Implicit Geometry Description
F(X) = ex) F (x,y,z) = x + y + z -1 = 0
Evolving Geometry : F(X,t)=0
Ft + v | grad F | = 0
Intuitively, move a lot on low intensity gradient area and move little on high intensity gradient area along normal direction
v : speed function , k : curvature , I : intensity
Segmentation Quality Measurement
Compare segmentation with phantom geometry 2 2 2

9. Surface Reconstruction
Lofting
Multiple Vessels - Boolean Set Operation (Union)
Automatic Mesh Generation from solid models

10. 3D Level Set Method Extend 2D to 3D No centerline necessary
No lofting (interpolation) : more accurate
Smooth Junction
Often Hard to control (geometry & topology)

11. 2D level set approach Strength Weakness
Intuitive : taking advantage of tubular shape of vessels
Clean Output
Controllability
Geometry
Topology
Noise Removal
Robust
Weakness
Heavy manual work
Centerline construction
A bunch of 2D segmentation which is not automatic
Stopping criteria
Inaccurate
Lofting & interpolation
Non-smooth junction
Possible Self-Intersection
Limited to only tubular structure segmentation

12. Comparison 2D Segmentation 3D Control Good Bad Noise Tolerance
Robustness
Accuracy
User Dependence
Smoothness
Good/Bad

13. Conclusion Image Based Vascular Model Construction
Centerline construction
Level set based 2D segmentation along centerline
Surface reconstruction thru lofting
Solid modeling & mesh generation
Tradeoffs : 2D vs 3D segmentation