Measuring Monkey Eye Movement in the

MRITeam Members:Josh AndersBetsy AppelBryan Baxter

Alyssa Walsworth

Client: Luis Populin,Ph. D.Advisor: Justin Williams, Ph.D.

University of Wisconsin - Madison Biomedical Engineering Design Courses

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4) Continued attendance at this presentation constitutes compliance with this

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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

BackgroundfMRI

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 ComparisonDesign 1Eye Coils

Design 2Camera

Design 3Photodiodes

Invasiveness 0 5 4

Expense 2 1 5

MRI compatibility 1 3 5

Responsiveness 5 4 5

Totals 8 13 19

Based on our design matrix, we selected the photodiode system

Future Work

Present chosen design to client and receive feedback

Create prototype

Questions ?