Measuring Monkey Eye Movement in the MRI

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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.

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Problem Statement

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

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Design Requirements

• Measure horizontal saccadic eye movement in one
  eye
• Monkeys view of stimulus projection must not be
  blocked
• MRI compatible
• NO ferromagnetic material
• Limited electrical components

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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

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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

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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 monkeys 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.

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Analysis of Design Alternative 1

• Advantages
• Increased accuracy due to placement
• Established record of successes
• Disadvantages
• Surgical procedure involved
• May alter monkeys natural behaviors
• To date, not tested in an fMRI setting due to
  magnetic constraints

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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

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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

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Design Alternative 3

• Photodiodes
• Infrared radiation is projected onto the eye via
  two fiber optic cables attached to LED sources
  outside of MRIs 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

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Analysis of Design Alternative 3

• Advantages
• Compatible with MRI environment
• Non-invasive
• Inexpensive relative to other methods
• Disadvantages
• Calibration time
• Complicated circuit design

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Design Comparison
Design 1 Eye Coils Design 2 Camera Design 3 Photodiodes
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

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Future Work

• Present chosen design to client and receive
  feedback
• Create prototype

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Questions ?