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.

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

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

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

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

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.

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

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 Eye camera & IR illuminator Head coil

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

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

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

Design Comparison Design 1 Eye Coils Design 2 Camera Design 3 Photodiodes Invasiveness054 Expense215 MRI compatibility135 Responsiveness545 Totals81319 Based on our design matrix, we selected the photodiode system

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

Questions ?