Transcript Portable Air Force Retinal Imaging Device

Air Force
Portable Device for Retinal Imaging
Abdelhamid Jnane
Mentors: Zhongping Chen
Qiang Wang
University of California, Irvine
Beckman Laser Institute
OUTLINE
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Background
Goals
Device setup
Components
System parameters
Device component assembly
Sample OCT Images
Experimental design
Wiener filter implementation
Background
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Field-deployable screening device to detect
lesions of the retina
– To facilitate early diagnostic of ocular laser
induced injuries caused by laser weapons and
laser guided aiming devices.
– To reduce the risk of catastrophic failure of
vision.
– To ensure that flight personnel will conduct
missions with full visual acuity.
Background
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Replacement of the current photographic fundus
imaging device
– Standard procedure for evaluating ocular lesions, it
provides only two-dimensional retinal imaging
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The newly developed optical coherence
tomography technology with integrated micro
electro mechanical system (MEMS)
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To provide a three-dimensional of retinal images’
surface
Background
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The proposed field deployable imaging
device will find many other applications
– In ophthalmology clinical practice where
evaluation and diagnosis of retinal health is
very important
– Anyone engaging in a potentially dangerous
activity requiring superb visual performance
Goal
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Designing a compact & portable OCT system
– Features
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Dimensions: 8” x 8” x 4”
Sensitivity of 99.3 db
High speed (20,000 A-lines/s )
High resolution (12 m )
Coherence length of 9.8mm at 2 kHz sweep rate
Testing our device in vivo animal and human
subjects
– Evaluating retinal injuries in hamster and rats
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Filtering the noise that corrupted the source signal
(ripples)
Device Setup
Figure 1: Schematic of the FDOCT system: collimator; Atte.,
neutral density attenuator; D1 and D2, photodetectors.
Components
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Collimator (OFR Inc., 1060 nm)
Gold mirror (Thorlabs Inc., ½”)
2 circulators (Agiltron Inc., 1060 nm)
70/30 2x2 couplers (AC Photonics Inc. 1060 nm)
50/50 2x2 couplers (AC Photonics Inc. 1060 nm)
X stage (Newport Inc.)
Light source (Santec Inc., 1060 nm, 28 kHz)
Aluminum case (Hammond Manufacturing, 10.03” x
9.63” x 3.84”)
System Parameters
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Imaging speed: 20 k A-lines/second
 Power delivered to sample arm: 1.2 mw
 Power delivered to reference arm: 0.4 mw
Device Hardware
Non-compact OCT system
Compact OCT system
Device Component
Assembly
Sample OCT Image
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Human eye image
Sample OCT Image
Sample OCT Image
Experimental Design
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In vivo animal clinical trial experiment will be conducted to test the
effectiveness of the new device.
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Imaging devices
– Portable OCT system
– Photographic fundus imaging system
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Evaluation of images by ophthalmologists
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Group 1: photographic fundus images only
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Group 2: photographic fundus images and OCT images
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Ophthalmologist evaluation compared to histology evaluation
Group A (5 Rats)
• 23.6 mw, 0.25 s
Wiener Filter
 The
wiener filter is an adaptive filter.
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It tailors itself to be the “best possible
filter” for a given dataset.
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Below is a simple version of the
derivation for the wiener formula.
Wiener Filter
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Standard equation to model a signal with noise:
y [n] =x [n] +n [n] (1)
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We want to pass this y [n] through a filter ‘h’
– To get back something that very closely matches our original signal x,
(x )
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Design a filter that minimizes the difference between x and x .
– minimizing the least mean square error between x and x
[x − ˜x] 2 (2)
Wiener Filter
is h*y, we have: [ x − h * y ] (3)
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Since x
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Expanding this expression and taking the Fourier
transform of the expression to get the power spectra:
– ∑(j) ( (Xj − HjYj))2
(4)
– ∑(j) ((Xj − Hj (Xj + Nj))2 (5)
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After simplification we get the following formula for H
– H (f) = (|X (f) |)2/ (|X (f) |)2 + (|N (f) |)2 (6)
Spectral Reshaping
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Small ripples in the light source spectrum caused by
antireflection coating of the semiconductor optical
amplifier
Ripples & other types of dispersions in the optical fiber
components modulate the fringe contrast of the spectral
interference signal
Spectrum of light with ripple and side lobes
Spectra and Gaussian Fit from
Glass Slide
• Solid curve:
Spectrum determined from a
single image
•Dashed curve:
Gaussian fit to each spectrum
Coherence Envelopes
Determined from Glass Slide
• Dotted curve:
Uncorrected response
• Solid curve:
Corrected response
Design of Wiener Filter
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Determine the envelope of the wavelength-dependent fringe contrast
– Design a spectral shaping filter from the OCT spectral signals
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Spectral interference signal can be rewritten as follows:
S j (k) = Se (k) *cos φ j(k)
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(1)
contrast envelope* fringe
where φ j(k) is the phase of the j-th fringe
Design of Wiener Filter
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The ensemble average of spectral interference in j is expressed as
– (Sj(k)^2)j = Se(k)^2 cos^2φ j(k)j
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Simplified equation of the contrast envelope:
– Se(k) =√(2/N*Σ(j)Sj(k)^2).
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Substituting Se(k) into the following the Wiener filter:
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W(k) =(Se(k)/(Se(k)2 +nc))*Gauss(k)
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nc is a constant depending on the SNR of the detection system
Gauss(k) is a Gaussian window to reshape the spectrum to a Gaussian profile.
Implementation of Wiener
Filter
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SpecEnv[j] = A + B1*j + B2*j^2 + B3*j^3
+ B4*j^4 + B5*j^5 + B6*j^6 + B7*j^7+ B8*j^8
–
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Where: A=23.84411; B1=0.95364; B2= -0.0062 ;B3=9.5098E 5; B4= -7.19185E7;
B5=2.49286E-9; B6= -4.32256E-12; B7=3.66599E-15;B8=1.21285E-18
GuassionEnv[j] = 100*exp(-(j-425.0)*
(j-425.0)/240.0/240.0);
 SpecReshape[j]=GuassionEnv[j]/(2.0*SpecEnv[
j] +constant factor);
Axial PSF without Spectral
Reshaping
80
Axial PSf without spectral reshaping
Amplitude[arbitrary units]
70
60
Single image of the glass
mirror
50
40
30
20
0
100
200
300
Miror displacement[mic.m]
400
Coherence Envelopes
Determined from Glass Slide
Specrtrum envelope of the source
1.002
Spectrum envelope of the source
Intensity [arbitrary units]
Intensity [Arbitrary units]
1.000
200
0.998
0.996
0.994
0.992
0.990
0
1020 1030 1040 1050 1060 1070 1080 1090 1100 1110
Wavelength [nm]
1020
1030
1040
1050
1060
1070
Wavelength [nm]
1080
1090
1100
1110
Axial PSF with Spectral
Reshaping
70
Axial PSF with spectral reshaping
Amplitude[arbitrary units]
60
50
40
Single image of the
glass mirror
30
20
10
0
0
100
200
300
Miror displacemen[mic.m]
400
Conclusion
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We have developed FDOCT device with 1m
swept light source which has the following
specifications:
Dimensions of 8” x 8” x 4”;
Sensitivity of 99.3 db;
High speed (20,000 A-lines/s);
High resolution (12 m);
Coherence length of 9.8mm at 2 kHz sweep rate.
Conclusion
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We have also shown that FDOCT resolution can
be improved by reducing the effects of the tails or
side lobes by implementing the Wiener Filter
algorithm to get a gaussian shape of spectral light
source.
 The algorithms we have used take advantage of
the convolution property of Fourier transformation.
Therefore, extensive computation that can slow
the speed of the OCT is not necessary.
Progress
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6.
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Prepare medication and supplies for animal
study (anesthesia, eye-drops, heat pads, surgical
instruments, etc.)
Set up portable OCT system
Optimize and calibrate portable OCT system
Order lab rats
Begin imaging rat, rabit and hamster retina
Design Wiener filter to reduce noise
Conduct the clinical trial experiment
Acknowledgements
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Dr. Zhongping Chen
 Dr. Qiang Wang
 University of California, Irvine
 Beckman Laser Institute
 IM-SURE Program
 Said Shokair
 NSF