Bioelectrical Engineering Part - METU EEEeee.metu.edu.tr/~bme/bme501/BME501-MedicalImagingLecture.pdf · Medical imaging by Murat Eyüboğlu 1 BME 501 - Introduction to BME Bioelectrical

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


2

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


3

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


4

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?

2014-2015 BME-501


5

Simplified block diagram of a

Medical Imaging System

2014-2015 BME-501


6

Which energy types are

used for imaging?

• X-ray

• Nuclear (radio-isotope) sources,

• Ultrasonic waves,

• Magnetic fields,

• Electrical currents,

• Mechanical,

• Optical waves etc.

2014-2015 BME-501


7

Electromagnetic spectrum

2014-2015 BME-501


8

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


9

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


10

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.

2014-2015 BME-501


11

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.

2014-2015 BME-501


12

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(

2014-2015 BME-501


13

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

2014-2015 BME-501


14

Typical Chest X-ray Radiograph

2014-2015 BME-501


15

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)

2014-2015 BME-501


16

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


17

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 +

-

2014-2015 BME-501


18

• Tungsten Anode is desirable as:

• It has high melting point,

• Little tendency to vaporize,

• It is strong.

X-ray tube design

2014-2015 BME-501


19

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

2014-2015 BME-501


20

Tomographic Imaging

cut

Tomographic Imaging

image

3-dimensional subject

Tomographic Imaging

2-dimensional slice

2014-2015 BME-501


21

X-ray CT

Detector array

Source

Patient

2014-2015 BME-501


22

First scan

Second scan

CT Scan

2014-2015 BME-501


23

Third scan

Second scan

First scan

CT Scan

2014-2015 BME-501


24

First scan

Second scan

Third scan

Fourth scan

CT Scan

2014-2015 BME-501


25

Image Reconstruction - Backprojection

dt)tsinycosx()t(p)y,x(,b

2014-2015 BME-501


26

ddt)tsinycosx()t(p)y,x(0

b

Image Reconstruction - Backprojection

2014-2015 BME-501


27

Backprojection Example 1: True distribution

2014-2015 BME-501


28

Example 1: Backprojection

5

11

7

7

5

5 7 7 5 11

2014-2015 BME-501


29

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

2014-2015 BME-501


30

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

2014-2015 BME-501


31

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

2014-2015 BME-501


32

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

2014-2015 BME-501


33

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

2014-2015 BME-501


34

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

2014-2015 BME-501


35

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

2014-2015 BME-501


36

Backprojection

2014-2015 BME-501


37

• 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


38

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


39

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


40

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.

2014-2015 BME-501


41

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


42

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.

2014-2015 BME-501


43

Nuclear Medicine - Brain

2014-2015 BME-501


44

SPECT and PET

dxdye)tsinycosx()y,x(A)t(p sds)s(

Neuroblastoma SPECT

CT

SPECT

DUAL

PET perfusion

scan of heart

2014-2015 BME-501


45

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


46

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


47

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

2014-2015 BME-501


48

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

2014-2015 BME-501


49

Ultrasound imager

2014-2015 BME-501


50

Ultrasound Imaging

Ultrasound scanner US image of a fetus hand

2014-2015 BME-501


51

Ultrasound Doppler

2014-2015 BME-501


52

B-Scan ultrasound

2014-2015 BME-501


53

3D ultrasound

2014-2015 BME-501


54

What is your infant upto?

2014-2015 BME-501


55


of Ultrasound


• Involves no ionizing radiation,

• Portable.

2014-2015 BME-501


56

Magnetic Resonance Imaging

MR imaging system

2014-2015 BME-501


57


MAGNET

GRADIENT COILS

RF COIL

2014-2015 BME-501


58

2014-2015 BME-501


59


2014-2015 BME-501


60

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.

2014-2015 BME-501


61

First in-vivo MRI experiment in 1977,

by Damadian, Minkoff and Goldsmith

2014-2015 BME-501


62

MR Images of human head

Coronal Slice of Head Axial Slice of Head

2014-2015 BME-501


63


of MRI

• Superior spatial resolution,

• Good soft tissue contrast,

• Functional imaging is possible,


• Relatively expensive.

2014-2015 BME-501


64

Electrical Impedance

Tomography

EIT : cross-sectional

imaging of electrical

impedance

• injected EIT

• induced EIT

2014-2015 BME-501


65

Electrical Impedance Tomography

2014-2015 BME-501


66

ACEIT ventilation scan

Right lung

Left lung

ANTERIOR

4th intercostal space level dynamic ventilation scan

Mediastenum

2014-2015 BME-501


67

Cardiac Gated EIT Images

2014-2015 BME-501


68


of EIT


• Good soft tissue contrast,


• Poor and position dependent spatial

resolution,

• Low sensitivity to inner regions.

Documents

Bioelectrical Engineering Part - METU EEEeee.metu.edu.tr/~bme/bme501/BME501-MedicalImagingLecture.pdf · Medical imaging by Murat Eyüboğlu 1 BME 501 - Introduction to BME Bioelectrical