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

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)

Obtaining the Images Coronal Plane Axial Plane Sagittal Plane

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

Canny Edge Detection

Can We Fix It? Air Bubble Leaky Slice

What We Get Coronal Plane Axial Plane Sagittal Plane

Midplanes Average Least Squares

Ideal Planes 1 3a 2 3b

Ideal vs. Measured Planes

Distortion Correction Magnetic Field of Cylinder Sum of spherical harmonics:

Applying Distortion Correction toAxial Plane Corrected Original

Applying Distortion Correction to Coronal Plane Corrected Original

Applying Distortion Correction Sagittal Plane Corrected Original

Results Theoretical vs. corrected points Standard deviations (s) +X face: 0.23503 mm -X face: 0.25168 mm +Y face: 0.15322 mm -Y face: 0.15823 mm +Z face: 0.13548 mm -Z face: 0.14173 mm ~1-2 pixels at 3s

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