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ECSE-6963 Introduction to Subsurface Sensing and Imaging Systems

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Title: ECSE-6963 Introduction to Subsurface Sensing and Imaging Systems


1
ECSE-6963 Introduction to Subsurface Sensing and
Imaging Systems
  • Lecture 14 The Broader Picture
  • Kai Thomenius1 Badri Roysam2
  • 1Chief Technologist, Imaging technologies,
  • General Electric Global Technology Center
  • 2Professor, Rensselaer Polytechnic Institute

Center for Sub-Surface Imaging Sensing
2
Recap
  • We have reviewed the major building blocks of an
    ultrasound scanner
  • Transduction
  • Beamformation
  • Scan conversion
  • We have been introduced to the Field II
    simulation program and walked through some of the
    code.

3
Broader Recap
  • X-Ray imaging
  • Optical imaging
  • Acoustic (ultrasound imaging)
  • Today
  • Optical and acoustic beams
  • A broader view of subsurface sensing imaging

4
General View of an SSI System
Surface 1
  1. Probe should reach the object
  2. Enough signal should reach the detector
  3. Probe-medium and probe-object interactions must
    be different enough to produce discernible
    contrast

5
Principal Wave Propagation Phenomena
l ltlt D
l
Impedance Velocity / range
Velocity /Index Width/ range
Group velocity vs l Group velocity Dispersion
coefficient
Absorption coefficient
6
Principal Wave Propagation Phenomena (cont.)
l D
Mie
l
Geometrical structures of apertures and periodic
objects
Shapes distributions of scatterers
7
Principal Wave Propagation Phenomena (cont.)
Continuously-varying
Turbid
Inhomogeneous
Random
Diffusion coefficient Absorption coefficient as
functions of position
Extinction coefficient Speckle statistics
Velocity, impedance absorption coefficient as
functions of position
8
General Wave Propagation Phenomena (cont.)
l gt D
Scattering
Rayleigh
Fluoresence/ Raman/NMR
Dynamic scattering
l
Motion of scatterers centers Diffusion, Motility,
Internal motion
Density of specific scatterers
9
General Mathematical Numerical Models
Continuously-varying
Inhomogeneous media
10
Turbid Media
Continuously-varying
Inhomogeneous media
Highly lossy medium (s gtgt we )
lossless medium (ma 0)
Diffusion Equation
11
Coherent Detection Methods
Differential Interference Contrast (DIC)
Microscopy
Phase Contrast Microscopy (PCM)
12
Coherent Detection Methods
Optical Coherence Tomography (OCT)
13
Three Basic Strategies to SSI
  1. Localized Probing Mosaicing

2. Multiview Tomography
LPM
MSD
3. Multispectral Discrimination
14
Weak vs Strong Scattering
Weak Scattering
Probe is scattered from each of the target points
independently. Each scattered wave is
unperturbed by the other points of the target.
Interaction region overlap of transmitter
pattern with receiver pattern.
15
Strong Scattering
Complex Scattering Path
ij
j
i
Scattered waves are disturbed by additional
scattering from other points of the target
Interaction region ? overlap of transmitter
pattern with receiver pattern.
16
Multiview Tomography Weak Scattering Case
17
Multiview Tomography Strong Scattering Case
Reflection
Transmission
Examples
Electrical Impedance/Resistance Tomography Ground
Penetrating Radar Diffraction Tomography Diffuse
Optical Tomography Elastography
18
Localized vs Tomographic SSI
Tomograhic SSI
Localized SSI
j
i
i
j
j
ij
ij
Interaction regions ij are small do not
overlap significantly (voxels)
Interaction regions ij are large do overlap
significantly
Interaction region Vij region to which detector
j is sensitive, when probe i is active.
19
Classification of Localized Probing Systems
  • Distributed Probing
  • Localized Detection

ii) Localized Probing Distributed
Detection
Applications
Applications
Vision Photography Conventional Microscopy
Fluorescence Scanning Microscopy
20
iii) Localized Probing Localized Detection
Example 1
Sheet Illumination
Application
Slit Lamp Biomicroscope
21
Example 2
Applications
Applications
Ultrasonic Harmonic Imaging
Scanning Confocal Fluorescence Microscopy
22
Classification of Localized Probing Based on
Method of Axial Localization
Sonar
Microscopy
Optical Coherence Tomography (OCT)
23
Mosaicing
A Mosaic is a collage of multiple images, each
covering a full probe array field Key Challenge
Registration
Mosaic
80o Mosaic of Retina
24
MSD
Multispectral Discrimination
25
Point-by-point spectroscopy
  • Estimation of composition of substances with
    known spectral signatures at each position
  • Feature detection at each position
  • Wavelength ratiometric imaging

26
Electromagnetic Spectrum
27
Interaction of EM with matter
  • Molecular Imaging relies on quantum phenomena to
    reveal the presence of specific atoms/molecules
  • Wave theory not convenient for modeling/
    explaining these phenomena
  • The energy levels of atoms and molecules can have
    only certain quantized values. Transitions
    between these quantized states occur by
    absorption, emission, and stimulated emission.

28
The human body
29
Infrared
  • Absorbed more strongly than microwaves, but less
    strongly than visible light.
  • Causes heating of the tissue since it increases
    molecular vibrational activity.
  • But no ionization
  • Infrared radiation does penetrate the skin
    further than visible light and can thus be used
    for imaging of subcutaneous blood vessels.

Frequencies .003 - 4 x 1014 Hz Wavelengths 1 mm
- 750 nm Quantum energies 0.0012 - 1.65 eV
30
Microwaves
  • Causes heating of the tissue since it increases
    molecular torsion and rotation activity.
  • But no ionization, since the quantum energy is a
    million times smaller than that of x-rays
  • Body largely transparent to microwaves

Frequencies .003 - 4 x 1014 Hz Wavelengths 1 mm
- 750 nm Quantum energies 0.0012 - 1.65 eV
31
Absorption
Absorption can only occur when
If the energy of the probing photon is mismatched
to the energy difference between the quantum
states, the material is transparent to the probe.
32
Emission Fluorescence
  • Opposite of absorption
  • Can be coherent (Raman)/incoherent (Fluorescence)
  • Typically, there is some loss in the molecule, so
    the emitted energy is lower than the absorbed
    energy
  • The difference is the Stokes Shift

Molar Concentration of fluorophore
Excitation intensity
Path length
Fluorescence intensity
Quantum Efficiency ( molecules that emit)
Molar absorptivity
33
Multi-photon Excitation
  • Use 2 or more infrared photons to excite
    fluorophores ordinarily excitable with higher
    frequencies
  • Much more detail in images collected deeper in
    the sample.
  • No sample photobleaching outside focal plane.
  • Dramatic improvement in longevity of living
    cells, tissues and organisms.
  • Ready determination of co-localising fluorescent
    probes.
  • No need for confocal apertures.
  • Ability to image autofluorescence
  • UV flourophores may be excited using a lens that
    is not corrected for UV as these wavelengths
    never have to pass through the lens.
  • MPE also offers enhanced photoselection in
    spectroscopy.

3-photon works the same way
34
Multi-photon Microscopy
  • Practical issues
  • The two photons need to arrive simultaneously a
    low probability event
  • Use ultrafast, mode-locked near-infrared lasers
    (i.e. Tisapphire 100-200 femtosecond pulse
    duration, 76MHz repetition rate).
  • Under the appropriate conditions, these lasers
    produce short duration pulses with the high peak
    power required for a multi-photon effect and an
    average power low enough to make specimen damage
    negligible.
  • Such lasers are tunable over a range of
    700nm-1000nm which permits optimal wavelength
    selection to elicit an efficient multi-photon
    effect.
  • Probability of simultaneous absorption falls off
    steeply away from the focal volume

35
  • Optical sections may be obtained from deeper
    within a tissue that can be achieved by confocal
    or wide-field imaging.
  • the excitation source is not attenuated by
    absorption by fluorophore above the plane of
    focus
  • longer excitation wavelengths suffer less
    scattering
  • fluorescence signal is not degraded by scattering
    from within the sample since it is not imaged

Centonze,V.E and J.G.White. (1998) Biophysical J.
752015-2024
36
Skin Tumor Angiogenesis in vivo
37
Observing Changes Over Time by Registration
38
3D Brain Tumor Imaging
39
Limitations of Multi-photon
  • Slightly lower resolution with a given
    fluorophore when compared to confocal imaging.
    This loss in resolution can be eliminated by the
    use of a confocal aperture at the expense of a
    loss in signal.
  • Thermal damage can occur in a specimen if it
    contains chromophores that absorb the excitation
    wavelengths, such as the pigment melanin.
  • Only works with fluorescence imaging.
  • Currently rather expensive.

40
Summary
  • Review of SSI problems and methods
  • Detection and Estimation
  • Classification segmentation
  • Signal/Image Analysis and Understanding
  • Change detection
  • Three Basic SSI Strategies
  • Multi-View Tomography (MVT)
  • Localized Probing Mosaicing (LPM)
  • Multi-spectral discrimination (MSD)
  • Next Class
  • More on information extraction algorithms

41
Acknowledgments
  • Bahaa Saleh at BU
  • Luis Jiminez at UPRM
  • Hanu Singh at Woods Hole

42
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 (518) 276-8067
  • Fax (518) 276-6261/2433
  • Email roysam_at_ecse.rpi.edu
  • Website http//www.rpi.edu/roysab
  • NetMeeting ID (for off-campus students)
    128.113.61.80
  • Secretary Betty Lawson, JEC 7012, (518) 276
    8525, lawsob_at_.rpi.edu

43
Instructor Contact Information
  • Kai E Thomenius
  • Chief Technologist, Ultrasound Biomedical
  • Office KW-C300A
  • GE Global Research
  • Imaging Technologies
  • Niskayuna, New York 12309
  • Phone (518) 387-7233
  • Fax (518) 387-6170
  • Email thomeniu_at_crd.ge.com, thomenius_at_ecse.rpi.edu
  • Secretary TBD
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