Medical Image Analysis

1
Medical Image Analysis

• Medical Imaging Modalities

Figures come from the textbook Medical Image
Analysis, by Atam P. Dhawan, IEEE Press, 2003.
2

• Anatomical or structural
• X-ray radiology, X-ray mammography, X-ray CT,
  ultrasound, Magnetic Resonance Imaging
• Functional or metabolic
• Functional MRI, (Single Photon Emission Computed
  Tomography) SPECT, (Positron Emission Tomography)
  PET, fluorescence imaging

Figures come from the textbook Medical Image
Analysis, by Atam P. Dhawan, IEEE Press, 2003.
3
X-ray Imaging
Figure comes from the Wikipedia,
www.wikipedia.org.
Figures come from the textbook Medical Image
Analysis, by Atam P. Dhawan, IEEE Press, 2003.
4
Figure 4.1. Atomic structure of a tungsten atom.
An incident electron with energy greater than
K-shell binding energy is shown interacting with
a K-shell electron for the emission of an X-ray
photon.
Figures come from the textbook Medical Image
Analysis, by Atam P. Dhawan, IEEE Press, 2003.
5
X-ray Imaging

• Tungsten
• K-shell binding energy level 69.5 keV
• L-shell binding energy level 10.2 keV
• An emision of X-ray photon of 59.3 keV
• X-ray generation
• Electrons are released by the source cathode and
  are accelerated toward the target anode in a
  vacuum under the potential difference ranging
  from 20,000 to 150,000 volts

Figures come from the textbook Medical Image
Analysis, by Atam P. Dhawan, IEEE Press, 2003.
6
Figure comes from the Wikipedia,
www.wikipedia.org.
Figures come from the textbook Medical Image
Analysis, by Atam P. Dhawan, IEEE Press, 2003.
7
X-ray 2-D Projection Imaging

• Diagnostic radiology
• 2-D projection of the three-dimensional
  anatomical structure of the human body
• Localized sum of attenuation coefficients of
  material air, blood, tissue, bone
• Film or 2-D array of detectors
• Digital radiographic system
• Use scintillation crystals optically coupled with
  photomultiplier

Figures come from the textbook Medical Image
Analysis, by Atam P. Dhawan, IEEE Press, 2003.
8
Figure 4.2. (a). A schematic diagram of a 2-D
X-ray film-screen radiography system. A 2-D
projection image of the 3-D object is shown at
the bottom. (b). X-ray radiographic image of a
normal male chest.
Figures come from the textbook Medical Image
Analysis, by Atam P. Dhawan, IEEE Press, 2003.
9
Figures come from the textbook Medical Image
Analysis, by Atam P. Dhawan, IEEE Press, 2003.
10
X-ray 2-D Projection Imaging

• Scattering
• Create artifacts and artificial structures
• Reduce scattering
• Anti-scattered grids and collimators

Figures come from the textbook Medical Image
Analysis, by Atam P. Dhawan, IEEE Press, 2003.
11
X-ray Mammography

• Target material
• Molybdenum K-, L-, M-shell binding energies
  levels are 20, 2.8, 0.5 keV. The characteristic
  X-ray radiation is around 17 keV.
• Phodium K-, L-, M-shell binding energies levels
  are 23, 3.4, 0.6 keV. The characteristic X-ray
  radiation is around 20 keV.
• A small focal spot of the order of 0.1mm

Figures come from the textbook Medical Image
Analysis, by Atam P. Dhawan, IEEE Press, 2003.
12
Figure 4.3. A film-screen X-ray mammography
imaging system.
Figures come from the textbook Medical Image
Analysis, by Atam P. Dhawan, IEEE Press, 2003.
13
Figure 4.4. X-ray film-screen mammography image
of a normal breast.
Figures come from the textbook Medical Image
Analysis, by Atam P. Dhawan, IEEE Press, 2003.
14
X-ray Computed Tomography

• 3-D

Figures come from the textbook Medical Image
Analysis, by Atam P. Dhawan, IEEE Press, 2003.
15
Figure comes from the Wikipedia,
www.wikipedia.org.
Figures come from the textbook Medical Image
Analysis, by Atam P. Dhawan, IEEE Press, 2003.
16
Figure 4.5. 3-D object representation as a stack
of 2-D x-y slices.
Figures come from the textbook Medical Image
Analysis, by Atam P. Dhawan, IEEE Press, 2003.
17
Figure 4.6. Source-Detector pair based
translation method to scan a selected 2-D slice
of a 3-D object to give a projection along the
y-direction.
Figures come from the textbook Medical Image
Analysis, by Atam P. Dhawan, IEEE Press, 2003.
18
Figure 4.7 The translate-rotate parallel-beam
geometry of first generation CT scanners.
Figures come from the textbook Medical Image
Analysis, by Atam P. Dhawan, IEEE Press, 2003.
19
X-ray Computed Tomography

• Generations
• First an X-ray source-detector pair that was
  translated in parallel-beam geometry
• Second a fan-beam geometry with a divergent
  X-ray source and a linear array of detectors.
  Use translation to cover the object and rotation
  to obtain additional views

Figures come from the textbook Medical Image
Analysis, by Atam P. Dhawan, IEEE Press, 2003.
20

• Generations
• Third a fan-beam geometry with a divergent
  X-ray source and an arc of detectors. Without
  translation. Additional views are obtained by
  simultaneous rotation of the X-ray source and
  detector assembly. Rotate only
• Fourth use a detector ring around the object.
  The X-ray source provides a divergent fan-beam of
  radiation to cover the object

Figures come from the textbook Medical Image
Analysis, by Atam P. Dhawan, IEEE Press, 2003.
21
Figure 4.8. The first generation X-ray CT scanner
Figures come from the textbook Medical Image
Analysis, by Atam P. Dhawan, IEEE Press, 2003.
22
Figure 4.9. The fourth generation X-ray CT
scanner geometry.
Figures come from the textbook Medical Image
Analysis, by Atam P. Dhawan, IEEE Press, 2003.
23
Figure 4.10. X-ray CT image of a selected slice
of cardiac cavity of a cadaver.
Figures come from the textbook Medical Image
Analysis, by Atam P. Dhawan, IEEE Press, 2003.
24
Figure 4.11. The pathological image of the
selected slice shown with the X-ray CT image in
Figure 4.10
Figures come from the textbook Medical Image
Analysis, by Atam P. Dhawan, IEEE Press, 2003.
25
Magnetic Resonance Imaging

• Nuclear magnetic resonance
• The selected nuclei of the matter of the object
• Blood flow and oxygenation
• Different parameters weighted,
  weighted, Spin-density
• Advance MR Spectroscopy and Functional MRI
• Fast signal acquisition of the order of a
  fraction of a second

Figures come from the textbook Medical Image
Analysis, by Atam P. Dhawan, IEEE Press, 2003.
26
Figure comes from the Wikipedia,
www.wikipedia.org.
Figures come from the textbook Medical Image
Analysis, by Atam P. Dhawan, IEEE Press, 2003.
27
Figure 4.12. MR images of a selected
cross-section that are obtained simultaneously
using a specific imaging technique. The images
show (from left to right), respectively, the
T1-weighted, T-2 weighted and the Spin-Density
property of the hydrogen protons present in the
brain.
Figures come from the textbook Medical Image
Analysis, by Atam P. Dhawan, IEEE Press, 2003.
28
Magnetic Resonance Imaging

• 1H high sensitivity and vast occurrence in
  organic compounds
• 13C the key component of all organic
• 15N a key component of proteins and DNA
• 19F high relative sensitivity
• 31P frequent occurrence in organic compounds
  and moderate relative sensitivity

Adapted from the Wikipedia, www.wikipedia.org.
29
MR Spectroscopy
Figure comes from the Wikipedia,
www.wikipedia.org.
Figures come from the textbook Medical Image
Analysis, by Atam P. Dhawan, IEEE Press, 2003.
30
MR Spectroscopy
Figure comes from the Wikipedia,
www.wikipedia.org.
Figures come from the textbook Medical Image
Analysis, by Atam P. Dhawan, IEEE Press, 2003.
31
Functional MRI
Figure comes from the Wikipedia,
www.wikipedia.org.
Figures come from the textbook Medical Image
Analysis, by Atam P. Dhawan, IEEE Press, 2003.
32
MRI Principles

• spin-lattice relaxation time
• spin-spin relaxation time
• the spin density

Figures come from the textbook Medical Image
Analysis, by Atam P. Dhawan, IEEE Press, 2003.
33
MRI Principles

• Great web sites
• Simulations from BIGS - Lernhilfe für Physik und
  Technik
• http//www.cis.rit.edu/class/schp730/bmri/bmri.htm
  

Figures come from the textbook Medical Image
Analysis, by Atam P. Dhawan, IEEE Press, 2003.
34
MRI Principles

• Spin
• A fundamental property of nuclei with odd atomic
  numbers is the possession of angular moment
• Magnetic moment
• The charged protons create a magnetic field
  around them and thus act like tiny magnets

Figures come from the textbook Medical Image
Analysis, by Atam P. Dhawan, IEEE Press, 2003.
35
MRI Principles

• the spin angular moment
• the magnetic moment
• a gyromagnetic ratio, MHz/T
• A hydrogen atom
• 42.58 MHz/T

Figures come from the textbook Medical Image
Analysis, by Atam P. Dhawan, IEEE Press, 2003.
36
Figure 4.13. Left A tiny magnet representation
of a charged proton with angular moment, J.
Right A symbolic representation of a charged
proton with angular moment, J and a magnetic
moment, µ.
Figures come from the textbook Medical Image
Analysis, by Atam P. Dhawan, IEEE Press, 2003.
37
MRI Principles

• Precession of a spinning proton
• The interaction between the magnetic moment of
  nuclei with the external magnetic field
• Spin quantum number of a spinning proton ½
• The energy level of nuclei aligning themselves
  along the external magnetic field is lower than
  the energy level of nuclei aligned against the
  external magnetic field

Figures come from the textbook Medical Image
Analysis, by Atam P. Dhawan, IEEE Press, 2003.
38
Figure 4.14 (a) A symbolic representation of a
proton with precession that is experienced by the
spinning proton when it is subjected to an
external magnetic field. (b) The random
orientation of protons in matter with the net
zero vector in both longitudinal and transverse
directions.
Figures come from the textbook Medical Image
Analysis, by Atam P. Dhawan, IEEE Press, 2003.
39
MRI Principles

• Equation of motion for isolated spin
• Solution

Figures come from the textbook Medical Image
Analysis, by Atam P. Dhawan, IEEE Press, 2003.
40
Longitudinal Vector OX at the transverse
position X
Figures come from the textbook Medical Image
Analysis, by Atam P. Dhawan, IEEE Press, 2003.
41
Figure 4.15 (a). Nuclei aligned under thermal
equilibrium in the presence of an external
magnetic field. (b). A non-zero net longitudinal
vector and a zero transverse vector provided by
the nuclei precessing in the presence of an
external magnetic field.
Figures come from the textbook Medical Image
Analysis, by Atam P. Dhawan, IEEE Press, 2003.
42
Figures come from the textbook Medical Image
Analysis, by Atam P. Dhawan, IEEE Press, 2003.
43
MRI Principles

• The precession frequency
• Depends on the type of nuclei with a specific
  gyromagnetic ratio and the intensity of the
  external magnetic field
• This is the frequency on which the nuclei can
  receive the Radio Frequency (RF) energy to change
  their states for exhibiting nuclear magnetic
  resonance
• The excited nuclei return to the thermal
  equilibrium through a process of relaxation
  emitting energy at the same precession frequency

44
MRI Principles

• 90-degree pulse
• Upon receiving the energy at the Larmor
  frequency, the transverse vector also changes as
  nuclei start to precess in phase
• Form a net non-zero transverse vector that
  rotates in the x-y plane perpendicular to the
  direction of the external magnetic field

Figures come from the textbook Medical Image
Analysis, by Atam P. Dhawan, IEEE Press, 2003.
45
Figure 4.16. The 90-degree pulse causing nuclei
to precess in phase with the longitudinal vector
shifted clockwise by 90-degrees as a result of
the absorption of RF energy at the Larmor
frequency.
Figures come from the textbook Medical Image
Analysis, by Atam P. Dhawan, IEEE Press, 2003.
46
MRI Principles

• 180-degree pulse
• If enough energy is supplied, the longitudinal
  vector can be completely flipped over with a
  180-degree clockwise shidf in the direction
  against the external magnetic field

Figures come from the textbook Medical Image
Analysis, by Atam P. Dhawan, IEEE Press, 2003.
47
Figure 4.17. The 180-degree pulse causing nuclei
to precess in phase with the longitudinal vector
shifted clockwise by 180-degrees as a result of
the absorption of RF energy at the Larmor
frequency.
Figures come from the textbook Medical Image
Analysis, by Atam P. Dhawan, IEEE Press, 2003.
48
MRI Principles

• Relaxation
• The energy emitted during the relaxation process
  induces an electrical signal in a RF coil tuned
  at the Larmor frequency
• The free induction decay of the electromagnetic
  signal in the PF coil is the basic signal that is
  used to create MR images
• The nuclear excitation forces the net
  longitudinal and transverse magnetization vectors
  to move

Figures come from the textbook Medical Image
Analysis, by Atam P. Dhawan, IEEE Press, 2003.
49
MRI Principles

• A stationary magnetization vector
• The total response of the spin system

Figures come from the textbook Medical Image
Analysis, by Atam P. Dhawan, IEEE Press, 2003.
50
Figure 4.18. The transverse relaxation process of
spinning nuclei.
Figures come from the textbook Medical Image
Analysis, by Atam P. Dhawan, IEEE Press, 2003.
51
MRI Principles

• The longitudinal and transverse magnetization
  vectors with respect to the relaxation times
• where

Figures come from the textbook Medical Image
Analysis, by Atam P. Dhawan, IEEE Press, 2003.
52
Figure 4.19. (a) Transverse and (b) longitudinal
magnetization relaxation after the RF pulse.
Figures come from the textbook Medical Image
Analysis, by Atam P. Dhawan, IEEE Press, 2003.
53
MRI Principles

• The RF pulse causes nuclear excitation changing
  the longitudinal and transverse magnetization
  vectors
• After the RF pulse is turned off, the excited
  nuclei go through the relaxation phase emitting
  the absorbed energy at the same Larmor frequency
  that can be detected as an electrical signal,
  called the Free Induction Decay (FID)

Figures come from the textbook Medical Image
Analysis, by Atam P. Dhawan, IEEE Press, 2003.
54
MRI Principles

• The NMR spin-echo signal (FID signal)

Figures come from the textbook Medical Image
Analysis, by Atam P. Dhawan, IEEE Press, 2003.
55
MR Instrumentation

• The stationary external magnetic field
• Provided by a large superconducting magnet with a
  typical strength of 0.5 T to 1.5 T
• Housing of gradient coils
• Good field homogeneity, typically on the order of
  10-50 parts per million
• A set of shim coils to compensate for the field
  inhomogeneity

Figures come from the textbook Medical Image
Analysis, by Atam P. Dhawan, IEEE Press, 2003.
56
Figure 4.20. A general schematic diagram of a MR
imaging system.
Figures come from the textbook Medical Image
Analysis, by Atam P. Dhawan, IEEE Press, 2003.
57
Figure comes from the Wikipedia,
www.wikipedia.org.
Figures come from the textbook Medical Image
Analysis, by Atam P. Dhawan, IEEE Press, 2003.
58
Figure comes from the Wikipedia,
www.wikipedia.org.
Figures come from the textbook Medical Image
Analysis, by Atam P. Dhawan, IEEE Press, 2003.
59
MR Instrumentation

• An RF coil
• To transmit time-varying RF pulses
• To receive the radio frequency emissions during
  the nuclear relaxation phase
• Free Induction Decay (FID) in the RF coil

Figures come from the textbook Medical Image
Analysis, by Atam P. Dhawan, IEEE Press, 2003.
60
MR Pulse Sequences

• NMR signal
• The frequency and the phase
• Spatial encoding in MR imaging
• Frequency encoding and phase encoding

Figures come from the textbook Medical Image
Analysis, by Atam P. Dhawan, IEEE Press, 2003.
61
Figure 4.21 (a). Three-dimensional object
coordinate system with axial, sagittal and
coronal image views. (b) From top left to
bottom right Axial, coronal and sagittal MR
images of a human brain.
Figures come from the textbook Medical Image
Analysis, by Atam P. Dhawan, IEEE Press, 2003.
62
Figures come from the textbook Medical Image
Analysis, by Atam P. Dhawan, IEEE Press, 2003.
63
MR Pulse Sequences
Figure 4.22. (a) Three-dimensional spatial
encoding for spin-echo MR pulse sequence. (b) A
linear gradient field for frequency encoding.
(c). A step function based gradient field for
phase encoding.
Figures come from the textbook Medical Image
Analysis, by Atam P. Dhawan, IEEE Press, 2003.
64
Figures come from the textbook Medical Image
Analysis, by Atam P. Dhawan, IEEE Press, 2003.
65
MR Pulse Sequences

• The phase-encoding gradient
• Applied in steps with repeated cycles
• If 256 steps are to be applied in the
  phase-encoding gradient, the readout cycle is
  repeated 256 times, each time with a specific
  amount of phase-encoding gradient

Figures come from the textbook Medical Image
Analysis, by Atam P. Dhawan, IEEE Press, 2003.
66
Spin Echo Imaging

• Between the application of the 90 degree pulse
  and the formation of echo (rephasing of nuclei
• Between the 90 degree pulse and 180 degree pulse

Figures come from the textbook Medical Image
Analysis, by Atam P. Dhawan, IEEE Press, 2003.
67
Figure 4.23. The transverse relaxation and echo
formation of the spin echo MR pulse sequence.
Figures come from the textbook Medical Image
Analysis, by Atam P. Dhawan, IEEE Press, 2003.
68
Spin Echo Imaging

• K-space
• The placement of raw frequency data collected
  through the pulse sequences in a
  multi-dimensional space
• By taking the inverse Fourier transform of the
  k-space data, an image about the object can be
  reconstructed in the spatial domain
• The NMR signals collected as frequency-encoded
  echoes can be placed as horizontal lines in the
  corresponding 2-D k-space

Figures come from the textbook Medical Image
Analysis, by Atam P. Dhawan, IEEE Press, 2003.
69
Figure comes from the Wikipedia,
www.wikipedia.org.
Figures come from the textbook Medical Image
Analysis, by Atam P. Dhawan, IEEE Press, 2003.
70
Spin Echo Imaging

• the cycle repetition time
• weighted
• A long and a long
• weighted
• A short and a short
• Spin-density
• A long and a short

Figures come from the textbook Medical Image
Analysis, by Atam P. Dhawan, IEEE Press, 2003.
71
Figure 4.24. A spin echo pulse sequence for MR
imaging.
Figures come from the textbook Medical Image
Analysis, by Atam P. Dhawan, IEEE Press, 2003.
72
Spin Echo Imaging

• The effective transverse relaxation time from the
  field inhomogeneities

Figures come from the textbook Medical Image
Analysis, by Atam P. Dhawan, IEEE Press, 2003.
73
Spin Echo Imaging

• The effective transverse relaxation time from a
  spatial encoding gradient

Figures come from the textbook Medical Image
Analysis, by Atam P. Dhawan, IEEE Press, 2003.
74
Echo Planar Imaging

• A single-shot fast-scanning method
• Spiral Echo Planar Imaging (SEPI)
• where

75
Figure 4.25. A single shot EPI pulse sequence.
Figures come from the textbook Medical Image
Analysis, by Atam P. Dhawan, IEEE Press, 2003.
76
Figure 4.26. The k-space representation of the
EPI scan trajectory.
Figures come from the textbook Medical Image
Analysis, by Atam P. Dhawan, IEEE Press, 2003.
77
Figure 4.27. The spiral scan trajectory of SEPI
pulse sequence in the k-space.
Figures come from the textbook Medical Image
Analysis, by Atam P. Dhawan, IEEE Press, 2003.
78
Figure 4.28. The SEPI pulse sequence
Figures come from the textbook Medical Image
Analysis, by Atam P. Dhawan, IEEE Press, 2003.
79
Figure 4.29. MR images of a human brain acquired
through SEPI pulse sequence.
Figures come from the textbook Medical Image
Analysis, by Atam P. Dhawan, IEEE Press, 2003.
80
Gradient Echo Imaging

• Fast low angle shot (FLASH) imaging
• Utilize low-flip angle RF pulses to create
  multiple echoes in repeated cycles to collect the
  data required for image reconstruction
• A low-flip angle (as low as 20 degrees)
• The readout gradient is inverted to re-phase
  nuclei leading to the gradient echo during the
  data acquisition
• The entire pulse sequence time is much shorter
  than the spin echo pulse sequence

Figures come from the textbook Medical Image
Analysis, by Atam P. Dhawan, IEEE Press, 2003.
81
Figure 4.30. The FLASH pulse sequence for fast MR
imaging.
Figures come from the textbook Medical Image
Analysis, by Atam P. Dhawan, IEEE Press, 2003.
82
Flow Imaging

• Tracking flow
• Diffusion (incoherent flow) and perfusion
  (partially coherent flow)
• The FID signal generated in the RF receiver coil
  by the moving nuclei and velocity-dependent
  factors
• MR angiography

Figures come from the textbook Medical Image
Analysis, by Atam P. Dhawan, IEEE Press, 2003.
83
Figure 4.31. A flow imaging pulse sequence with
spin echo.
Figures come from the textbook Medical Image
Analysis, by Atam P. Dhawan, IEEE Press, 2003.
84
Figure 4.32 Left A proton density image of a
human brain. Right The corresponding perfusion
image.
Figures come from the textbook Medical Image
Analysis, by Atam P. Dhawan, IEEE Press, 2003.
85
Figure 4.33. Gradient echo based MR pulse
sequence for 3-D MR volume angiography.
Figures come from the textbook Medical Image
Analysis, by Atam P. Dhawan, IEEE Press, 2003.
86
Figure 4.34. An MR angiography image.
Figures come from the textbook Medical Image
Analysis, by Atam P. Dhawan, IEEE Press, 2003.
87
Nuclear Medicine Imaging Modalities

• Radioactivity decay
• Half-life of a radionuclide decay

Figures come from the textbook Medical Image
Analysis, by Atam P. Dhawan, IEEE Press, 2003.
88
Nuclear Medicine Imaging Modalities

• The radioactivity of a radionuclide
• The average decay rate
• Curie (CI)
• disintegrations per second
  (dps)
• Becquerel (Bq)
• One dps

Figures come from the textbook Medical Image
Analysis, by Atam P. Dhawan, IEEE Press, 2003.
89
Single Photon Emission Computed Tomography

• Radioisotope
• The radioisotopes are injected in the body
  through administration of radiopharmaceutical
  drugs that metabolize with the tissue
• Gamma rays
• The gamma rays from the tissue pass through the
  body and are captured by the detectors
  surrounding the body to acquire raw data for
  defining projections

Figures come from the textbook Medical Image
Analysis, by Atam P. Dhawan, IEEE Press, 2003.
90
Figure comes from the Wikipedia,
www.wikipedia.org.
Figures come from the textbook Medical Image
Analysis, by Atam P. Dhawan, IEEE Press, 2003.
91
Single Photon Emission Computed Tomography

• Radionuclides
• Thallium
• Technetium
• Iodine
• Gallium
• Gamma ray
• Decay by emitting gamma rays with photon energy
  ranging from 135 keV to 511 keV
• Attenuation

92
Figure 4.35. A schematic diagram of detector
arrays of SPECT scanner surrounding the patient
area.
Figures come from the textbook Medical Image
Analysis, by Atam P. Dhawan, IEEE Press, 2003.
93
Single Photon Emission Computed Tomography

• Scintillation detector
• Barium fluoride
• Cesium iodide
• Bismuth germinate BGO
• Photomultiplier tube

Figures come from the textbook Medical Image
Analysis, by Atam P. Dhawan, IEEE Press, 2003.
94
Figure 4.36. A 99Tc SPECT image of a human brain
Figures come from the textbook Medical Image
Analysis, by Atam P. Dhawan, IEEE Press, 2003.
95
Single Photon Emission Computed Tomography

• Attenuation and scattering
• Photoelectric absorption and Compton scattering
• Poor in structural information
• Attenuation and scattering
• Assessment of metastases or characterization of a
  tumor
• Lower cost than PET

Figures come from the textbook Medical Image
Analysis, by Atam P. Dhawan, IEEE Press, 2003.
96
Positron Emission Tomography

• Concept
• Simultaneous detection of two 511keV energy
  photons traveling in the opposite direction
• Radionuclides
• Decay by emitting positive charged particles
  called positrons
• Fluorine 18-F
• Oxygen 15-O
• Nitrogen 13-N
• Carbon 11-C

97
Figure 4.37. A schemtaic diaggram of PET scanner.
Figures come from the textbook Medical Image
Analysis, by Atam P. Dhawan, IEEE Press, 2003.
98
Figure comes from the Wikipedia,
www.wikipedia.org.
Figures come from the textbook Medical Image
Analysis, by Atam P. Dhawan, IEEE Press, 2003.
99
Positron Emission Tomography

• After emission
• Travel typically for 1-3 mm, losing some of its
  kinetic energy
• The annihilation of the positron with the
  electron
• Cause the formation of two gamma photons with
  511keV traveling in opposite directions
• Coincidence detection
• The point of emission of a positron is different
  from the point of annihilation with an electron

100
Positron Emission Tomography

• Radiopharmaceutical
• Fluorodeoxyglucose (FDG)
• Resolution and sensitivity of PET imaging is
  significantly better than SPECT

Figures come from the textbook Medical Image
Analysis, by Atam P. Dhawan, IEEE Press, 2003.
101
Figure 4.38 Serial images of a human brain with
FDG PET imaging.
Figures come from the textbook Medical Image
Analysis, by Atam P. Dhawan, IEEE Press, 2003.
102
Ultrasound Imaging

• Diagnostic imaging
• Anatomical structures, blood flow measurements
  and tissue characterization
• Safety, portability, low-cost

Figure comes from the Wikipedia,
www.wikipedia.org.
Figures come from the textbook Medical Image
Analysis, by Atam P. Dhawan, IEEE Press, 2003.
103
Figure comes from the Wikipedia,
www.wikipedia.org.
Figures come from the textbook Medical Image
Analysis, by Atam P. Dhawan, IEEE Press, 2003.
104
Ultrasound Imaging

• Velocity
• Relative intensity in dB
• Shorter waves
• Better imaging resolution
• Frequencies 2 MHz to 5 MHz are common

105
Reflection and Transmission

• Acoustic impedance

Figures come from the textbook Medical Image
Analysis, by Atam P. Dhawan, IEEE Press, 2003.
106
Figure 4.39. A path of a reflected sound wave in
a multilayered structure.
Figures come from the textbook Medical Image
Analysis, by Atam P. Dhawan, IEEE Press, 2003.
107
Refraction

• Snells law

Figures come from the textbook Medical Image
Analysis, by Atam P. Dhawan, IEEE Press, 2003.
108
Figure 4.40. A schematic diagram of a
conventional ultrasound imaging system.
Figures come from the textbook Medical Image
Analysis, by Atam P. Dhawan, IEEE Press, 2003.
109
Figure comes from the Wikipedia,
www.wikipedia.org.
Figures come from the textbook Medical Image
Analysis, by Atam P. Dhawan, IEEE Press, 2003.
110
Ultrasound Imaging

• A-mode
• Records the amplitude of returning echoes from
  the tissue boundaries with respect to time
• Perpendicular incident angle
• Basic method

Figures come from the textbook Medical Image
Analysis, by Atam P. Dhawan, IEEE Press, 2003.
111
Ultrasound Imaging

• M-mode
• Variations in signal amplitude due to object
  motion
• X-axis represents the time, while the y-axis
  indicates the distance of the echo from the
  transducer

Figures come from the textbook Medical Image
Analysis, by Atam P. Dhawan, IEEE Press, 2003.
112
Figure 4.41. M-Mode display of mitral valve
leaflet of a beating heart.
Figures come from the textbook Medical Image
Analysis, by Atam P. Dhawan, IEEE Press, 2003.
113
Ultrasound Imaging

• B-mode
• Two-dimensional images representing the changes
  in acoustic impedance of the tissue

Figures come from the textbook Medical Image
Analysis, by Atam P. Dhawan, IEEE Press, 2003.
114
Figure 4.42. The B-Mode image of a beating
heart with mitral stenosis.
Figures come from the textbook Medical Image
Analysis, by Atam P. Dhawan, IEEE Press, 2003.
115
Ultrasound Imaging

• Doppler ultrasound imaging

Figures come from the textbook Medical Image
Analysis, by Atam P. Dhawan, IEEE Press, 2003.
116
Figure 4.43. A Doppler image of the mitral valve
area of a beating heart. Figures 4.4.3-5 are
taken from the website http//www2.umdnj.edu/shin
dler/ms.html.
Figures come from the textbook Medical Image
Analysis, by Atam P. Dhawan, IEEE Press, 2003.