ECSE496201 Introduction to Subsurface Sensing and Imaging Systems

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ECSE-4962-01Introduction to Subsurface Sensing
and Imaging Systems

• Lecture 3 Big Picture Introduction to
  Projection Imaging
• Kai Thomenius1 Badri Roysam2
• 1Chief Technologist, Imaging Technologies,
• General Electric Global Research Center
• 2Professor, Rensselaer Polytechnic Institute

Center for Sub-Surface Imaging Sensing
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Review of Last Lecture

• Introduction to MATLAB
• Very widely used mathematical modeling tool
• Brief introduction to MATLABs key concepts
• Arrays, vectors, matrices, their addressing
• Graphics w. MATLAB
• Iteration program flow
• Conditionals
• This Class
• Big Picture Summary - Classifying probes
• Introduction to Projection Imaging

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Outline of Course Topics

• THE BIG PICTURE
• What is subsurface imaging?
• Why a course on this topic?
• EXAMPLE Projection Imaging
• X-Ray Imaging
• Computer Tomography
• COMMON FUNDAMENTALS
• Propagation of waves
• Interaction of waves with targets of interest 

• PULSE ECHO METHODS
• Examples
• MRI
• A different sensing modality from the others
• Basics of MRI
• MOLECULAR IMAGING
• What is it?
• PET Radionuclide Imaging
• IMAGE PROCESSING CAD

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How do we look under surfaces?
Surface 1
A whole bunch of configurations have been
developed, Well start with one of the simplest,
X-rays.
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But, many data acquisition choices are possible!
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X-Rays as an Imaging Probe

• Key characteristics vis-à-vis imaging
• X-Rays are high energy photons
• As well see, their generation creates incoherent
  beams.
• Insignificant scatter, hence we will be looking
  at through transmission (projection) imaging.

Ultrasound Imaging
Nuclear medicine
Photonics
Electronics
Optical Imaging
100keV
10keV
Micro-
Ultra-
Milli-
Visible
Infrared
THz gap
X Ray
wave
violet
metre
and RF
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Frequency
X Ray Imaging
MRI
Terahertz Imaging
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X-Ray Tube Block Diagram
Generation of x-rays depends on thermionic
emission acceleration of electrons from heater
filament.
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X-Ray Generation Process
Electrons
X-rays
Low Energy Low Frequency
High Energy High Frequency
X-ray Generation, Bremsstrahlung

• Electrons emitted from cathode, accelerated by
  anode voltage
• Kinetic energy loss at anode converted to
  photons, x-rays.
• Relative position of electron wrt to nucleus
  determines the frequency and energy of the
  x-ray, a spectrum will be generated.
• The resultant X-ray beam is the sum of all of
  these interactions

X-ray imaging based on photon density, not
temporal relationships within a beam.
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X-Ray Characteristics

• Electromagnetic radiation - photons
• Propagation speed - co 300,000 km/sec
• Energy of x-ray photon
• where h Plancks constant or
• h 6.62e-24 Js,
• n frequency.
• Useful relation

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Coherence Key Differentiator among Probes

• Major implication to system design.
• Coherent systems more complex
• Coherent imaging
• design of imaging wave takes into account phase
  time relationships of its constituents.
• Incoherent imaging
• imaging and sensing largely based on energy
  density.

Let us take a look at two contrasting examples.
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Ultrasound Beam Generation
Ultrasound Transducer Array
Transmit Beam
Timing of transmit events designed to create
constructive interference at focus.
Transmit Focus
Beam
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Transmit Focus Beam n
0
Coherent Beam Generation
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Coherent Wave
Much effort is spent on the formation of the
phase front of an ultrasound beam. In movie,
beam focused at 55 mm.
All parts of wave converge at focal point.
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Classification by Interaction with Target
To image something, that something must interact
with the propagating wave in some manner. Here
are some examples
Phase shift/ time delay
Reflection Coefficient Phase shift/time
delay Polarization dependence
Frequency dependence of attenuation Pulse
spreading
Attenuation
Absorption coefficient
Absorption coefficient Wave Velocity Range
Absorption coefficient Wave Velocity Range
Wave Velocity Width
X-rays in this category
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Interaction Models (cont.)
Diffusion
Deterministic
Random
Single Scattering
Weak Scattering
Multiple Scattering
Turbulent Medium
position-dependent diffusion coefficient
position-dependent wave velocity attenuation
coefficient
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Ultrasound Beam Propagation Interaction with
Tissues
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How do we select from these possible SSI choices?

• Over the years, each probe has evolved into an
  operating mode and application area where its
  strengths dominate. Examples
• x-rays in through transmission
• Ultrasound, radar, sonar in pulse-echo with short
  duration pulses.
• Acoustics in seismology
• During the semester we will look at several
  others.
• The actual choice in these cases will be made
  based on how well the given choice meets design
  goals.

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Basic Configurations for SSI
Transmission or Projection
Reflection
Example Ultrasonic imaging, fetal head cross
section
Example X-ray radiology Mrs. Roentgens hand
(1896).
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Basic Configurations for SSI Two Examples
Transmission
Reflection

• Separate transmitters receivers
• Typical measured quantities
• Attenuation
• Speed of propagation
• CW or incoherent burst is a common signal, also
  modulated bursts.
• Probe transmitted to cover an area (x-ray) or a
  line (CT).

• Often a single transducer array serves as both
  transmitter receiver
• Typical measured quantity
• Impedance mismatch
• Phase of returned signal (motion detection)
• Often short pulses used
• Beamformation used to steer and focus the
  transmitted energy.

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Key Performance Criteria for SSI

• Resolution
• Spatial resolution
• At what separation distance can we observe two
  distinct targets?
• Contrast resolution
• For a given target size, how much does the target
  contrast have to differ from background to be
  detected?
• For a given contrast difference, at what size can
  we detect the target?

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Determinants of Resolution for Transmission and
Reflection Probes

• Transmission Probes
• Effective detector width or film resolution
• Dimensions of transmitted beam
• Number of independent views in CT
• Reflection Probes
• Wavelength of transmitted signal.
• Size of transmit aperture
• Depth of region of interest.

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Some Criteria for SSI Method Selection

• What is the nature of the object we are imaging?
• Differentiation with respect to the surrounding
  media.
• Size of the object of interest.
• Propagation characteristics of the probes in the
  media traversed.
• What are the application needs?
• Spatial resolution
• What frequency probes?
• Spatial resolution of detector grid.
• What is the access to probes?
• Do we have 360 degree access (can we use
  transmission methods?)?

Mine Detection via Ground Penetrating Radar
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Homework

• Today we discussed classifying subsurface imaging
  by
• coherence,
• interaction with target, and
• use of projection or pulse-echo data acquisition.
• Classify the following imaging methods by the
  same criteria
• Radar
• Sonar
• Conventional optical microscopy (e.g. pathology
  lab)
• Airport luggage inspection
• Radionuclide imaging (nuclear medicine)
• Justify your answer.
• Study the interaction models of Slides 13 and 14
  and video clip of Slide 15. Which of the
  interaction models can you recognize in the Chest
  path video clip?

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Summary

• Methods for classifying different imaging probes
• Coherence
• Interaction with target
• Projection or pulse-echo
• X-rays as an example for those classifiers
• Next Class
• Projection Imaging X-rays

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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.rpi.edu/roysab
• NetMeeting ID (for off-campus students)
  128.113.61.80
• Secretary Laraine Michaelides, JEC 7012, (518)
  276 8525, 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 Laraine Michaelides, JEC 7012, (518)
  276 8525, michal_at_rpi.edu

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X-Ray Tube Block DiagramWidth of X-ray beam