ECSE6963 Introduction to Subsurface Sensing and Imaging Systems

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ECSE-6963Introduction to Subsurface Sensing and
Imaging Systems

• Lecture 24 Phase Imaging Architectures (contd)
• Kai Thomenius1 Badri Roysam2
• 1Chief Technologist, Imaging technologies,
• General Electric Global Technology Center
• 2Professor, Rensselaer Polytechnic Institute

Center for Sub-Surface Imaging Sensing
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Recap

• Use of Phase in Imaging
• Ultrasound quadrature example
• Doppler ultrasound
• Recall Lots of similarities between acoustics
  and electromagnetics
• Today
• Phase-contrast optical imaging
• Differential interference contrast
• Quadrature-based optical imaging

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SSI Architectures

• Lots of variety in SSI systems
• Types of probes
• Interactions between probing waves and media
• Contrast generation and enhancement mechanisms
• Types of detectors
• Information extraction algorithms
• How probes, detectors, and algorithms are put
  together into complete systems
• Luckily, there are common ideas across all these
  seemingly diverse systems

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SSI Architectures (contd) Classification Based
on Method of Axial Localization
Optical Coherence Tomography (OCT)
Ultrasound
Microscopy
TOF-PET
Courtesy Bahaa Saleh, BU
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Light Interference
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Interferometric Architectures
Differential Interference Contrast (DIC)
Microscopy
Phase Contrast Microscopy (PCM)
Courtesy Bahaa Saleh, BU
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Which egg will produce a healthy baby?
Quadrature Tomographic Microscopy
DIC Microscopy
Viable
Viable
IVF
Non-Viable
Non-Viable
Courtesy Carol Warner, NU
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Imaging of Phase Objects

• Amplitude objects change the amplitude, leaving
  the phase ? unaltered
• Phase objects change the phase, leaving the
  amplitude unaltered.
• The refractive index within a specimen is non
  uniform
• The phase of light waves is altered non-uniformly
• Optical path length refractive index ?
  thickness
• Light detectors like the eye, film and digital
  cameras can only respond to intensity differences
• To image phase objects, we need a method to
  convert phase differences into intensity
  differences, so light detectors can see them.

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Mouse Embryo Example

• The medium is non-absorbing
• Examples
• Oocytes
• Inner skin cells (inner cheek).

Mouse oocyte amplitude image
Mouse oocyte phase image
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Imaging Transparent Specimens

• Idea Exploit the fact that the refractive index
  within a specimen is non uniform
• The phase of light waves is altered non-uniformly
• Optical path length refractive index ?
  thickness
• Light detectors like the eye, film and digital
  cameras can only respond to intensity differences
• Need a method to convert phase differences into
  intensity differences, so light detectors can
  see them.

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Interferometric Sensing
object
Sensing wave
Source
Reference wave
Basic Idea The object affects the phase of the
sensing wave relative to the reference wave. If
the two waves are brought together and allowed to
interfere, we can sense the phase change. Small
effects, fractions of a wavelength, can be sensed
this way!
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Some Basics
Direct Ray
Light retarded/advanced by 90o
Diffracted Rays (retarded by ? 90o)
Transparent Object
Phase Plate
Light
Light
Non-uniformity of refractive index results in
some light being diffracted/scattered, and its
phase is slowed.
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Some Basics
Light retarded by 90o
These two rays will interfere constructively if
they meet
Phase Plate
Direct Ray
Diffracted Rays (retarded by ? 90o)
Transparent Object
A different choice of phase plate can result in
destructive interference
Light
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Non-uniform Transparent Object
Light retarded by 90o
The light coming out of the specimen can be
described by the function f(x,y) A
expif(x,y). When the phase variations f(x) ltlt
1, f(x) is approximately f(x,y) A expif(x,y)
? A (cosf(x,y) i sinf(x,y)) ? A(1
if(x,y)) Changing the phase of the zeroth order
term (the term independent of x) by p/2 (i.e.,
90o) gives the function f1(x,y) A(i if(x,y))
iA(1 f(x,y)) f1(x,y)2 A2(1f(x,y))2 ?
A21 2f(x,y), Which has a real variation of
intensity, linearly dependent on f.
Phase Plate
Direct Ray
Diffracted Rays (retarded by ? 90o)
Non-uniform Object Phase variation ?(x)
Light
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Phase Contrast Idea
Phase Plate
Voila the phase is now an intensity
signal! .This idea is widely used
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Phase Contrast Microscope

• The un-diffracted Surround light stays within a
  tube, and forms a ring in the image plane
• The phase of this can be adjusted selectively by
  a ring-shaped phase plate!
• The light diffracted by the specimen spreads
  everywhere
• They are retarded by 90o by the object
• The diffracted and surround waves interfere
  destructively in the image plane

http//www.microscopyu.com
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Sample Phase Contrast Image

• Prostate cancer cell
• The phase contrast background is a mid-line gray,
  phase-dense organelles appear dark
• Note the bright halo around the cell

Halo
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Cultured Neuron Example
Data courtesy Gary Banker (U. Oregon)
Time-Series Data
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Cultured Mouse Neural Stem Cells
(Digitized from a videotape from Temple Lab (AMC))
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Optical Coherence Tomography
Optical Coherence Tomography (OCT)
Macular hole
http//www.neec.com/Glaucoma_OCT.html
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Summary

• Seemingly diverse SSI systems can be understood
  in terms of their commonalities
• We introduced some interference-based imaging
  technologies
• Optical Coherence Tomography (more later)
• Phase contrast (not limited to optics!)
• Differential Interference Contrast
• Quadrature Tomographic Microscopy

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Homework Assignment

• Run the following applet for a phase contrast
  microscope
• http//micro.magnet.fsu.edu/primer/java/phasecontr
  ast/phasemicroscope/index.html
• Under what conditions does the background become
  the darkest?
• Describe why the above happens.
• Visit the following website
• http//www.microscopyu.com/tutorials/java/phasecon
  trast/apodized/index.html
• Describe the similarities differences between
  the idea of apodization used in this instrument,
  and an ultrasound scanner.

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Instructor Contact Information

• Badri Roysam
• Professor of Electrical, Computer, Systems
  Engineering
• Office JEC 7010
• Rensselaer Polytechnic Institute
• 110, 8th Street, Troy, New York 12180
• Phone [phone]
• Fax [phone]
• Email roysam_at_ecse.rpi.edu
• Website http//www.ecse.rpi.edu/roysabm
• NetMeeting ID (for off-campus students)
  128.113.61.80
• Secretary Laraine, JEC 7012, [phone],
  michal_at_.rpi.edu

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Instructor Contact Information

• Kai E Thomenius
• Chief Technologist, Ultrasound Biomedical
• Office KW-C300A
• GE Global Research
• Imaging Technologies
• Niskayuna, New York 12309
• Phone [phone]
• Fax [phone]
• Email thomeniu_at_crd.ge.com, thomenius_at_ecse.rpi.edu
  
• Secretary TBD