1. Registering retinal images
July 15, 2011
Registering retinal images
Babak Ghafaryasl Universitat Pompeu Fabra
Csaba Molnár University of Szeged
Antonio R. Porras Universitat Pompeu Fabra
Arie Shaus Tel Aviv University

2. Vascular tree extraction
Overview
Vessel enhancement
Vascular tree extraction
Feature extraction
Registration

3. Vessel enhancement - Scale Space representation
“Multiscale vessel enhancement filtering”, Frangi et al, 1998
- Scale Space representation
Local image descriptors
- Eigenvalues of Hessain (2nd derivative) matrix
Tubular, plate-like and spherical structures

4. Vascular tree extraction
Original images
Vessel enhancement
Thresholding +
Skeletonization
Largest connected components

5. From bifurcation point to bifurcation structure…
“Feature-Based Retinal Image Registration Using Bifurcation Structures”, Chen & Zhang, 2009 L2 L3
But…
L’s are normalized to sum up to 1.
The α triplets sum up to 360.
Therefore we can remove some redundancy. L1
We can measure a distance between such structures!

6. From bifurcation structures to registration…
Step 1: Find bifurcation structures in both images.
Step 2: Find the best match between two bifurcation structures. The match between 4 points (3 are enough) determines the affine transformation.
Step 3: Find next best matches (taking the transformation into account); refine the affine transformation with more points.

7. Results: feature extration
All candidates
Vessel registration
Matching candidates

8. Results: retinal registration (I)

9. Results: retinal registration (II)

10. Results: bad news...

11. Questions?