Measuring Monkey Eye Movement in the MRI

1. Measuring Monkey Eye Movement in the MRI Team Members: Josh Anders Betsy Appel Bryan Baxter Alyssa Walsworth Client: Luis Populin,Ph. D. Advisor: Justin Williams, Ph.D.

3. Problem Statement Client requests a detection device to measure monkey eye movement in an Magnetic Resonance Imaging (MRI) environment.

4. Design Requirements • Measure horizontal saccadic eye movement in one eye • Monkey’s view of stimulus projection must not be blocked • MRI compatible • NO ferromagnetic material • Limited electrical components

5. Background • Eye Movement • Smooth pursuit eye movements are made when the eye follows a moving object • Saccadic eye movement consists of rapid jumps in angular direction of eye to redirect line of sight when viewing stationary objects • Our device will record saccadic eye movements

6. Background fMRI • Coil aligns atomic nuclei with magnetic field • As brain activity increases, oxygenated blood flow to active areas increases • Waisman center fMRI has a magnetic strength of 3 Tesla

7. Design Alternative #1 • Eye Coils • Search coils consisting of multiple rings of copper wire covered in teflon are implanted around the eye inside of a muscular layer • RF field is generated by coil surrounding the monkey • When the monkey’s eye moves, current is induced in the implanted search coils. This current is then output and conditioned through a circuit located outside of the MRI room. • Computer software analysis is used to measure current and determine eye position.

8. Analysis of Design Alternative #1 • Advantages: • Increased accuracy due to placement • Established record of successes • Disadvantages: • Surgical procedure involved • May alter monkey’s natural behaviors • To date, not tested in an fMRI setting due to magnetic constraints

9. Eye camera & IR illuminator Head coil Design Alternative #2 • Infrared Camera System • Infrared source projects radiation via fiber optic cable onto eye • Infrared camera used to capture eye image • Computer analysis using software to find pupil and direction of gaze

10. Analysis of Design Alternative #2 • Advantages: • Non-invasive • Infrared cameras currently available for purchase • Devices currently in use in MRI on humans • Disadvantages: • Camera electronics • Infrared reflective light effects, video distortion, and variations in eye curvature may result in detection errors • Expensive

11. Design Alternative #3 • Photodiodes • Infrared radiation is projected onto the eye via two fiber optic cables attached to LED sources outside of MRI’s Faraday cage • Two fiber optic cables carry radiation reflected from the eye to photodiodes located outside of Faraday cage • Photodiodes detect incident radiation and produce current based on intensity of light • Signals output to computer for analysis

12. Analysis of Design Alternative #3 • Advantages: • Compatible with MRI environment • Non-invasive • Inexpensive relative to other methods • Disadvantages: • Calibration time • Complicated circuit design

13. Design Comparison • Based on our design matrix, we selected the photodiode system

14. Future Work • Present chosen design to client and receive feedback • Create prototype

15. Questions ?