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2015-2016
BME-501
Medical imaging by Murat Eyüboğlu
1
BME 501 - Introduction to BME
Bioelectrical Engineering Part:
Medical Imaging
Reference Textbook: Principles of Medical Imaging,
by Shung, Smith and Tsui
Lecturer: Murat EYÜBOĞLU, Ph.D.
Dept. of Electrical and Electronics Engineering
Middle East Technical University, Ankara - Turkey
2014-2015 BME-501
Medical imaging by Murat Eyüboğlu
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BME 8720501- Introduction to
Biomedical Engineering
• Bioelectrical Engineering Part:
• Medical Imaging .......................................................... 3h
• (X-ray imaging, Computerized Tomography, Medical Ultrasound Imaging, Nuclear Medicine Imaging, Magnetic Resonance Imaging)
• (Dr. B. Murat Eyüboğlu)
• Bioelectric phenomena ............................................... 3h
• (Dr. Yeşim Serinağaoğlu)
• Medical Instrumentation, mathematical modeling of physiological control systems....................................................................... 3h
• (Dr. Nevzat G. Gençer)
• Lab Practice ........................ .................................... 1.5 h
2012-2013 BME-501
Medical imaging by Murat Eyüboğlu
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Outline
• What is medical imaging
• History
• Projection Imaging
• Computerized Tomography (CT)
• Nuclear Source Imaging (PET, SPECT)
• Ultrasonic Imaging
• Magnetic Resonance Imaging
• Electrical Impedance Imaging
2012-2013 BME-501
Medical imaging by Murat Eyüboğlu
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Medical imaging is a collection of techniques,
that are developed to measure and display
distribution of a physical property in living
subjects, specifically in humans.
Why is it useful?
Medical imaging, not only provides useful
information for diagnosis but also serves to
assist in planning and monitoring the
treatment of malignant disease.
What is medical imaging?
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Medical imaging by Murat Eyüboğlu
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Simplified block diagram of a
Medical Imaging System
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Which energy types are
used for imaging?
• X-ray
• Nuclear (radio-isotope) sources,
• Ultrasonic waves,
• Magnetic fields,
• Electrical currents,
• Mechanical,
• Optical waves etc.
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Medical imaging by Murat Eyüboğlu
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Electromagnetic spectrum
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What are the physical
properties of interest?
• X-ray absorption coefficient,
• Radionuclide concentration,
• Ultrasonic properties,
• Spin density and spin relaxation,
• Electromagnetic properties,
• Mechanical properties,
• Optical properties.
2014-2015 BME-501
Medical imaging by Murat Eyüboğlu
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Why are we interested in these physical
properties?
Certain physical property may vary
between different healthy tissue types,
with the physiological state of a tissue type,
with the pathological condition of a tissue type.
2014-2015 BME-501
Medical imaging by Murat Eyüboğlu
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Why are there so many imaging
modalities?
• All imaging modalities are based on the
physics of the interaction of energy and
matter.
• Different imaging modalities are based on
physical interaction of different energy types
with biological tissues and thus provide
images of different physical properties of the
tissues.
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History
• Discovery of X-rays, 1895,
• Radon transform, 1917,
• NMR principles, 1946,
• Nuclear medicine scan, 1948,
• Ultrasound imaging, 1952,
• Positron tomography, 1953,
• Single Photon Emission CT, 1971
• Development of X-ray CT, 1972,
• NMR Imaging, 1976,
• Impedance Tomography, 1982.
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X-ray Projection Radiography
dxdy)tsinycosx()y,x(ds)y,x()t(p
Radon Transform
Film
X-ray tube
Patient
t
)t(p
)y,x(
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Attenuation Coefficients for Biological
Tissues at 60 keV
Tissue Attenuation
coefficient (cm-1
)
Blood 0.215
Brain matter 0.210
Water 0.203
Fat 0.185
Bone 0.400
Air 0.0002
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Typical Chest X-ray Radiograph
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X-rays characteristics
• EM radiation at wavelengths 0.1 – 100 keV (10 – 0.01 nm).
• Diagnostic Range X-rays typically have a wavelength from
100nm – 0.01nm ~1-100 keV.
• X-ray radiation is thought to be particles traveling at the speed
of light and carrying an energy given by E=hf .
(Plank constant h=4.13x10E-18 keV/Hz,
1eV=1.6x10E-19Joules)
• These particles are called QUANTA or PHOTONS.
• A photon having an energy level greater than a few electron
volts is capable of ionizing atoms an molecules.
Ionization energy for valence electrons < ~10 eV X-rays is
ionizing radiation (harmful)
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Example: UV light bulb
• Photon energy > a few eVolts may result in ionizing
radiation.
For a UV light bulb:
l=100nm. results in
f = c/l = 3x10E8 / 1x10E-7 = 3x10E15Hz.
E=h f = 12eV is ionizing radiation.
2014-2015 BME-501
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X-ray tube
• Working Principle: Accelerated charge causes EM radiation:
– Cathode filament C is electrically heated (VC = ~10V / If = ~5 A) to
boil off electrons
– Electrons are accelerated toward the anode target (A) by applied
high-voltage (Vtube = 40 – 150 kV);
– kinetic electron energy: Ke usually rated in “peak-kilo voltage” kVp
– Typical: Vtube = 40 – 150 kVp, Itube = 1-1000mA
– Deceleration of electrons on target creates "Bremsstrahlung"
+ -
kVp, Itube
C
A
VC, If +
-
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• Tungsten Anode is desirable as:
• It has high melting point,
• Little tendency to vaporize,
• It is strong.
X-ray tube design
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X-ray tube design
• Cathode with focusing cup, 2
filaments (different spot sizes)
• Anode
– Tungsten, Zw = 74,
Tmelt = 2250 ºC
– Embedded in copper for
heat dissipation
– Angled (see next slide)
– Rotating to divert heat
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Tomographic Imaging
cut
Tomographic Imaging
image
3-dimensional subject
Tomographic Imaging
2-dimensional slice
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X-ray CT
Detector array
Source
Patient
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First scan
Second scan
CT Scan
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Third scan
Second scan
First scan
CT Scan
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First scan
Second scan
Third scan
Fourth scan
CT Scan
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Image Reconstruction - Backprojection
dt)tsinycosx()t(p)y,x(,b
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ddt)tsinycosx()t(p)y,x(0
b
Image Reconstruction - Backprojection
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Backprojection Example 1: True distribution
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Example 1: Backprojection
5
11
7
7
5
5 7 7 5 11
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Backprojection
5/5 5/5 5/5 5/5 5/5
11/5 11/5 11/5 11/5 11/5
7/5 7/5 7/5 7/5 7/5
7/5 7/5 7/5 7/5 7/5
5/5 5/5 5/5 5/5 5/5
5
11
7
7
5
5 7 7 5 11
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Backprojection
5/5 +5/5
5/5 +7/5
5/5 +11/
5
5/5 +7/5
5/5 +5/5
7/5 +5/5
7/5 +7/5
7/5 +11/
5
7/5 +7/5
7/5 +5/5
7/5 +5/5
7/5 +7/5
7/5 +11/
5
7/5+ +7/5
7/5 +5/5
11/5 +5/5
11/5 +7/5
11/5 +11/
5
11/5 +7/5
11/5 +5/5
5/5 +5/5
5/5 +7/5
5/5 +11/
5
5/5 +7/5
5/5 +5/5 5
11
7
7
5
5 7 7 5 11
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Backprojection
10/5 12/5 16/5 12/5 10/5
16/5 18/5 22/5 18/5 16/5
12/5 14/5 18/5 14/5 12/5
12/5 14/5 18/5 14/5 12/5
10/5 12/5 16/5 12/5 10/5
5
11
7
7
5
5 7 7 5 11
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Backprojection
10/5 12/5 16/5 12/5 10/5
16/5 18/5 22/5 18/5 16/5
12/5 14/5 18/5 14/5 12/5
12/5 14/5 18/5 14/5 12/5
10/5 12/5 16/5 12/5 10/5
9
6
5
6 3 9
6
5
6 3
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Backprojection
10/5 +9/5
12/5 +6/4
16/5 +5/3
12/5 10/5
16/5 +6/4
18/5 +9/5
22/5 +6/4
18/5 +5/3
16/5
12/5 +3/3
14/5 +6/4
18/5 +9/5
14/5 +6/4
12/5 +5/3
12/5 14/5 +3/3
18/5 +6/4
14/5 +9/5
12/5 +6/4
10/5 12/5 16/5 +3/3
12/5 +6/4
10/5 +9/5
9
6
5
6 3
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Backprojection
10/5 +9/5
12/5 +6/4
16/5 +5/3 +5/3
12/5
+6/4
10/5
+9/5
16/5 +6/4
18/5 +9/5 +5/3
22/5 +6/4 +6/4
18/5 +5/3 +9/5
16/5
+6/4
12/5 +3/3 +5/3
14/5 +6/4 +6/4
18/5 +9/5 +9/5
14/5 +6/4 +6/4
12/5 +5/3 +3/3
12/5
+6/4
14/5 +3/3 +9/5
18/5 +6/4 +6/4
14/5 +9/5 +3/3
12/5 +6/4
10/5
+9/5
12/5
+6/4
16/5 +3/3 +3/3
12/5 +6/4
10/5 +9/5
9
6
5
6 3
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Backprojection
3.8 3.9 6.5 3.9 3.8
4.7 7.1 7.4 7.1 4.7
5.1 5.8 7.2 5.8 5.1
3.9 5.6 6.6 5.6 3.9
3.8 3.9 5.2 3.9 3.8
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Backprojection
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• Two basic strategies for producing an image that doesn’t have the blurring seen in the preceding example:
– Backproject, and then perform a second, repair operation on the image to correct the blur (Backprojection–Filtering algorithms),
– Modify the projection data in an appropriate manner, so they will produce an unblurred image, before backprojecting (Filtered backprojection algorithms).
2014-2015 BME-501
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Filtered Backprojection
Backprojected image represents a blurred
version of the original distribution:
1
)y,x(F)y,x(Fr
1*)*y,x()y,x( 2b2b
This blurring effect can be removed as,
)y,x(FF)y,x( b21
2bf
Filtering can be applied to projections prior to
backprojection which is computationally more
effective:
1
111
1 F*)*t(p)t(pFF
2014-2015 BME-501
Medical imaging by Murat Eyüboğlu
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Filtered Backprojection
Measure projections from
all possible view angles
Backproject the
filtered projections
Convolve all
projections with
the filtering
function
h(t)
2014-2015 BME-501
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Performance of CT
• Spatial resolution of 1 mm. (minimal distance
between two pixels which can be
discriminated is 1 mm.)
• Contrast resolution of 1 % (i.e, pixel density
which is 1% different than the background
density can be discriminated.)
• Soft tissue contrast is low.
• Invasive : X-rays are harmful for living
organisms i.e. contains ionizing radiation.
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Nuclear Source Imaging
• Planar Scintigraphy :
– Radioisotopes (radionuclides) are injected
to the body,
– They emit radiation which can be detected
by photon detectors and the position of the
isotopes can be determined,
– Two-dimensional representations of the
projections of three-dimensional activity
distributions are reconstructed.
2014-2015 BME-501
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Nuclear Source Imaging
• Emission Computed Tomography: is a
technique to obtain cross sectional images of
activity,
– SPECT: Single gamma ray is emitted per
nuclear disintegration.
– PET: Two gamma rays are emitted when
a positron from a nuclear disintegration
annihilates in tissue.
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Nuclear Medicine - Brain
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SPECT and PET
dxdye)tsinycosx()y,x(A)t(p sds)s(
Neuroblastoma SPECT
CT
SPECT
DUAL
PET perfusion
scan of heart
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Advantages and Disadvantages
of Nuclear Source Imaging
• Functional images can be obtained,
• Spatial resolution is poor,
• Good tissue specific contrast,
• Involves ionizing radiation.
2014-2015 BME-501
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Ultrasonic Imaging
• Body is probed by Ultrasonic waves,
• Ultrasound wave propagates through the
body,
• Fraction of the ultrasound waves are reflected
at various tissue interfaces along the wave
path, producing echoes,
• The reflected echo signals are measured and
used to reconstruct the reflection coefficient
distribution along the path.
2014-2015 BME-501
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Reflectivity of normally incident waves
Materials at interface Reflectivity
Brain-skull bone 0.66
Fat-bone 0.69
Fat-blood 0.08
Muscle-blood 0.03
Muscle-liver 0.01
Soft tissue-water 0.89
Soft tissue-air 0.99
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Ultrasound Imaging
Burst of US wave is transmitted
x
Reflected wave is measured
x
dx)x(f)c
x2t(p)t(p tr
f(x): total reflectivity from a line at x
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Ultrasound imager
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Ultrasound Imaging
Ultrasound scanner US image of a fetus hand
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Ultrasound Doppler
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B-Scan ultrasound
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3D ultrasound
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What is your infant upto?
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Advantages and Disadvantages
of Ultrasound
• Functional images can be obtained,
• Involves no ionizing radiation,
• Portable.
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Magnetic Resonance Imaging
MR imaging system
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Magnetic Resonance Imaging
MAGNET
GRADIENT COILS
RF COIL
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Magnetic Resonance Imaging
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Use of gradient fields in MRI
dxdyt)yG(t)xG(jexp)y,x(MK)t(S yyx
The emitted magnetization signal is measured
which is the 2-dimensional Fourier Transform
of the spin density (proton density) distribution.
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First in-vivo MRI experiment in 1977,
by Damadian, Minkoff and Goldsmith
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MR Images of human head
Coronal Slice of Head Axial Slice of Head
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Advantages and Disadvantages
of MRI
• Superior spatial resolution,
• Good soft tissue contrast,
• Functional imaging is possible,
• Involves no ionizing radiation,
• Relatively expensive.
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Electrical Impedance
Tomography
EIT : cross-sectional
imaging of electrical
impedance
• injected EIT
• induced EIT
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Electrical Impedance Tomography
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ACEIT ventilation scan
Right lung
Left lung
ANTERIOR
4th intercostal space level dynamic ventilation scan
Mediastenum
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Cardiac Gated EIT Images
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Advantages and Disadvantages
of EIT
• Functional images can be obtained,
• Good soft tissue contrast,
• Involves no ionizing radiation,
• Poor and position dependent spatial
resolution,
• Low sensitivity to inner regions.