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Ania Warczyk, Alia Durrani, Shivani Shah, Dan Maxwell, Timothy Chen.
Optical Imaging
Technique used in neuroscience for detection of brain activity
Uses changes in deflection of incident light to infer hemodynamic activity
Problem Statement
Design a small wireless camera for optical imaging of the cortex which allows free movement of animal being tested
Primary Objectives
Make a design with these criteria: Scalable to fit on the head of a monkey
Small and lightweight Wireless potential High resolution and well depth Providing direct, even lighting
Performance Criteria
Desired resolution: 512 x 512 Desired frame rate: 300 fps Well depth: 12 bits Must run continuously: 5 minutes Must not impede movement of animal:
~300 grams Maximum wireless frame rate: 10 fps Maximum cable frame rate: 30 fps USB is the only way to get 300 fps Eventually, wireless frame rate: 100 fps
Not before 3 years
Solution Descriptions
Current method: Large Camera
Design 1: PillCam Design 2: Lensless Setup Design 3: Beam Splitter Setup
Current Method: Large Camera
PillCam: Hypothesis
PillCam design proves a small self-contained wireless camera can be constructed
2 cm
PillCam: Synthesis
Diagram of our design based on PillCam concepts
PillCam: Performance
Failure with this approach, therefore must try new design Illumination is uneven and inconsistent No adjustable focus
Fixed lens to chip distance (S2) Microfabrication with expensive custom parts
Proprietary information
To mediate these obstacles: Need microcontrollers for lens and chip $$$$$$
Lensless Setup: Hypothesis
Can putting lens in contact with membrane on cortical surface eliminate the need for optics?
Lensless Setup: Synthesis
(Done with different illumination techniques)Slide with thin slices of pig liver
Solid piece of liver tissue imaged through glass cover slip
Lensless Setup: Performance
Liver slide with transmitted light
Liver slide with reflected light
Liver tissue with reflected light
Liver tissue with transmitted light
Lensless Setup: Resolution Test
Image of 1mm grid taken without a lens Image of 1mm grid taken with a lens
Lensless Setup: Performance
Failure of this approach, therefore must try new design Low resolution Illumination issues
Transmitted light does not work for bulk tissue Reflected light requires moving CCD chip
away from tissue surface
To mediate these obstacles: Can implant fiber optic to illuminate from
within
Beam Splitter Setup: Hypothesis
Beam splitter can provide direct illumination with conventional optical techniques in an onboard approach
Beam Splitter Setup: Performance Metrics
Provides direct, even, controlled illumination Single source eliminates light pools
Compact design Parallel to surface of brain
High resolution due to use of lens Lens and chip can be adjusted
individually Put lens and chip on threads
Beam Splitter Setup: Synthesis
Beam Splitter Setup: Performance
Data acquisition trial 1 expected March 24th
Will use grid to determine spatial resolution
Beam Splitter Setup: Calculations Thin Lens Equation:
1/S1 + 1/S2 = 1/f Let R = S1 + S2 There are two solutions to this equation:
S1 = R/2 + sqrt(R^2-4*R*f)/2 S2 = R/2 - sqrt(R^2-4*R*f)/2
The second solution is simply the reverse of the first: S2 = R/2 + sqrt(R^2-4*R*f)/2 S1 = R/2 - sqrt(R^2-4*R*f)/2
Magnification: M = -S2/S1 To map well size onto CCD, set minimum chip
width: w = 2*r w/2r = M = -S2/S1
Conclusions
Design 1 (PillCam) failed due to illumination, focus issues, and high comparative cost
Design 2 (Lensless Setup) failed due to low resolution and problems with illumination
Design 3 (Beam Splitter Setup) resolves illumination, focus, resolution, and cost issues Can fulfill requirements for size and weight
Future Work
Validate design by image acquisition Get smaller lighter parts to
miniaturize design and make more lightweight
Insert 10/90 beam splitter Add x-y-z positioners for lens and
chip Add housing to exclude ambient light