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## ECSE4963 Introduction to Subsurface Sensing and Imaging Systems

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Title: ECSE4963 Introduction to Subsurface Sensing and Imaging Systems

1
ECSE-4963 Introduction to Subsurface Sensing and
Imaging Systems
• Lecture 3 Big Picture Introduction to
Projection Imaging
• 1Chief Technologist, Imaging Technologies,
• General Electric Global Research Center
• 2Professor, Rensselaer Polytechnic Institute

Center for Sub-Surface Imaging Sensing
2
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
• Introduction to Projection Imaging

3
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?

4
How do we look under surfaces?
Surface 1
A whole bunch of configurations have been
5
Many Data Acquisition Choices are Possible!
Contrast Agent
6
X-Rays as an Imaging Probe
• Key characteristics vis-à-vis imaging
• X-Rays are high energy photons
• Their generation is largely incoherent.
• 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
10
11
Hz
10
10
Hz
10
15
Hz
10
14
Hz
10
13
Hz
10
12
Hz
10
19
Hz
10
16
Hz
10
17
Hz
10
18
Hz
Frequency
X Ray Imaging
MRI
Terahertz Imaging
7
Coherence Key Differentiator
• Major impact on system design.
• 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.
8
Ultrasound Beam Generation
Ultrasound Transducer Array
Transmit Beam
Timing of transmit events designed to create
constructive interference at focus.
Transmit Focus
Beam
1
2
Transmit Focus Beam n
0
Coherent Beam Generation
9
Ultrasound Beam Coherent Wave
Much effort is spent on the formation of the
phase front of an ultrasound beam.
All parts of wave arrive at focal point
simultaneously.
10
X-Ray Tube Block Diagram
Generation of x-rays depends on thermionic
emission acceleration of electrons from heater
filament.
11
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.
12
X-Ray Characteristics
• 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

13
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
Attenuation
Absorption coefficient
Absorption coefficient Wave Velocity Range
Absorption coefficient Wave Velocity Range
Wave Velocity Width
X-rays in this category
14
Interaction Models (cont.)
Diffusion
Deterministic
Random
Single Scattering
Weak Scattering
Multiple Scattering
Turbulent Medium
position-dependent diffusion coefficient
position-dependent wave velocity attenuation
coefficient
15
Ultrasound Beam Propagation Interaction with
Tissues
16
How do we select from these possible 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.

17
Basic Configurations for SSI
Transmission or Projection
Reflection
Example Ultrasonic imaging, fetal head cross
section
Example X-ray radiology Mrs. Roentgens hand
(1896).
18
Basic Configurations for SSIS Two Examples
Transmission
Reflection
• 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
• Typical measured quantity
• Impedance mismatch
• Phase of returned signal (motion detection)
• Often short pulses used
• Beamformation used to steer and focus the
transmitted energy.

19
Key Performance Criteria for SSIS
• 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?

20
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.

21
X-Ray Tube Block Diagram Width of X-ray beam
22
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.
• Do we have 360 degree access (can we use
transmission methods?)?

Mine Detection via Ground Penetrating Radar
23
Homework
• Today we discussed classifying x-ray imaging by
• coherence,
• interaction with target, and
• use of projection or pulse-echo data acquisition.
• Classify the following imaging methods by the
same criteria
• Conventional optical microscopy (e.g. pathology
lab)
• Airport luggage inspection

24
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

25
Instructor Contact Information
• 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

26
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