1. Tom S. Lee, Keith E. Schubert Reinhard W. Schulte
Gradient Non-Linearity Correction of MR Images for Functional Radiosurgery
Tom S. Lee, Keith E. Schubert Reinhard W. Schulte

2. Functional Proton Radiosurgery
Functional Neurosurgery
Trigeminal Neuralgia
Parkinson’s Disease
Brain regions (< 1 cm)
Proton Radiosurgery
accurate to less than 1 mm
MRI for target localization
Distinguish tissue types
Gradient nonlinearity distortions (~2mm)

3. Obtaining the Images
Coronal Plane
Axial Plane
Sagittal Plane

4. Problems to Check For Partial Slice Missing Slice Off Center Slice
Leaking Slice
Extra Features

5. Canny Edge Detection

6. Can We Fix It?
Air Bubble
Leaky Slice

7. What We Get
Coronal Plane
Axial
Plane
Sagittal Plane

8. Midplanes
Average
Least Squares

9. Ideal Planes 1 3a 2 3b

10. Ideal vs. Measured Planes

11. Distortion Correction
Magnetic Field of Cylinder
Sum of spherical harmonics:

12. Applying Distortion Correction toAxial Plane
Corrected
Original

13. Applying Distortion Correction to Coronal Plane
Corrected
Original

14. Applying Distortion Correction Sagittal Plane
Corrected
Original

15. Results Theoretical vs. corrected points Standard deviations (s)
+X face: mm
-X face: mm
+Y face: mm
-Y face: mm
+Z face: mm
-Z face: mm
~1-2 pixels at 3s

16. Future Work Further verification and testing Clinical trials
FDA approval
Clinical use