‫جامعة دار السالم للعلوم‬

‫والتكنولوجيا‬

LECTURE (1)
INTRODUCTION TO MEDICAL
IMAGING

Prepared by:
Dr. Mohammed Alolofi
Assistance Professor in Biomedical Engineering
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 References

 The Essential Physics of Medical Imaging (2nd

Edition), Jerrold T. Bushberg, 2001.

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 References
 MEDICAL IMAGING PHYSICS Fourth Edition, William R. Hendee, 2002.
 The physics of medical imaging, Steve Webb, 1988.
 Introduction to Biomedical Imaging, Andrew Webb – John Wiley & Sons, Inc,
2003.
 MEDICAL IMAGING Principles, Detectors, and Electronics, Krzysztof Iniewski,
2009.
 An Introduction to the Principles of Medical Imaging, Chris Guy, 2005.
 Fundamentals of Medical Imaging Second Edition Paul Suetens 2002.
 Essential Nuclear Medicine Physics Rachel A. Powsner 2006.
 Biomedical Imaging KAREN M. MUDRY 2003.

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 References
 Intermediate Physics for Medicine and Biology, Russell K. Hobbie, 2001.
 Encyclopedia of Medical Devices and Instrumentation, 6 Volume Set - Second
Edition by: John G. Webster
 The Biomedical Engineering Handbook, 3rd Edition (3 Volume Set)by: Joseph D.
Bronzino
 Medical Instrumentation Application and Design, 4th Edition by: John G.
Webster
 Handbook of Modern Sensors: Physics, Designs, and Applications, Fourth
Edition by: Jacob Fraden
 Biomedical Instrumentation: Technology and Applications By R. Khandpur

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 Introduction
GRADING SYSTEM ‫نظام التقييم‬
 Term Exam: 60 points
 Midterm Exam: 15 Points
 Homework assignments: 5 Points
 Project: 15 Points
 Other (quizzes, class participation etc.): 5 points

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 Introduction
Project:
 Students will be organized into teams of three and each team
search for the principle of operation of instruments which exist in
the diagnostic departement. The format of the project is like below:
 Introduction
 Medical background
 Principle of operation
 Comparison between two models
 Example commercially Distributor In Yemen

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 Introduction

 The overall objective of medical imaging is to

acquire useful information about physiological
processes or organs of the body by using external
or internal sources of energy.

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 Introduction
 Medical imaging of the human body requires some form
of energy.
 In radiology, the energy used to produce the image must be
capable of penetrating tissues.
 The electromagnetic spectrum outside the visible light
region is used for
1. x-ray imaging,
2. magnetic resonance imaging, and
3. nuclear medicine.
 Mechanical energy, in the form of high-frequency sound
waves, is used in ultrasound imaging.

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 Introduction
 With the exception of nuclear medicine, all medical
imaging requires that the energy used to penetrate the
body’s tissues also interact with those tissues.
 Absorption,
 Attenuation, and
 Scattering.

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 Introduction
 If energy were to pass through the body and not
experience some type of interaction (e.g., absorption,
attenuation, scattering),
 then the detected energy would not contain any useful
information regarding the internal anatomy, and
 thus it would not be possible to construct an image of the
anatomy using that information.

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 Introduction
 In nuclear medicine imaging, radioactive agents are
injected or ingested, and it is the metabolic or
physiologic interactions of the agent that give rise to the
information in the images.
 The power levels used to make medical images require a
balance between patient safety and image quality.

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 Imaging Modalities
 Radiography
 Fluoroscopy X-RAY
 Mammography
 Computed Tomography (CT)
 Nuclear Medicine Imaging
 Single Photon Emission Computed Tomography (SPECT)
 Positron Emission Tomography (PET)
 Gamma Camera
 Magnetic Resonance Imaging (MRI)
 Ultrasund Imaging
 Doppler Ultrasound Imaging
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 Imaging Modalities
 Radiography
 Radiography was the first medical imaging technology, made
possible when the physicist Wilhelm Roentgen discovered x-
rays on November 8, 1895.
 Roentgen also made the first radiographic images of human
anatomy.

diagnosis of broken bones, lung cancer, cardiovascular disorders.

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 Imaging Modalities
 Fluoroscopy
 Fluoroscopy refers to the continuous acquisition of a sequence
of x-ray images over time, essentially a real-time x-ray movie of
the patient.
 Fluoroscopy is used for positioning catheters in arteries, for
visualizing contrast agents in the gastrointestinal (GI) tract, and
for other medical applications such as invasive therapeutic
procedures where real-time image feedback is necessary.

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 Imaging Modalities
 Mammography
 Mammography is a specialized
x-ray projection imaging
technique useful for detecting
breast anomalies such as
masses and calcifications.
 Much lower x-ray energies are
used in mammography than any
other radiographic applications.

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 Imaging Modalities
 Computed Tomography (CT)
 CT became clinically available in the early 1970s and is the first
medical imaging modality made possible by the computer.
 CT images are produced by passing x-rays through the body, at
a large number of angles, by rotating the x-ray tube around the
body. One or more linear detector arrays, opposite the x-ray
source, collect the transmission projection data.
 tomography refers to a picture (-graph) of a slice (tomo-).
 Modern CT scanners can acquire 5-mm-thick tomographic
images along a 30-cm length of the patient (i.e., 60 images) in
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10 seconds,
 Imaging Modalities
 Computed Tomography (CT)

Early CT Image Current technology

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 Imaging Modalities
 Nuclear Medicine Imaging
 Nuclear medicine is the branch of radiology in which a chemical or
compound containing a radioactive isotope is given to the patient
orally, by injection, or by inhalation.
 Once the compound has distributed itself according to the
physiologic status of the patient, a radiation detector is used to make
projection images from the x and/or gamma rays emitted during
radioactive decay of the agent.
 Nuclear medicine produces emission images (as opposed to
transmission images), because the radioisotopes emit their energy
from inside the patient.
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 Nuclear medicine imaging is a form of functional imaging.
 Imaging Modalities
 Single Photon Emission Computed Tomography (SPECT)
 In SPECT, a nuclear camera records x- or gamma-ray emissions from
the patient from a series of different angles around the patient.
These projection data are used to reconstruct a series of
tomographic emission images.
 SPECT allows physicians to better understand the precise distribution
of the radioactive agent, and to make a better assessment of the
function of specific organs or tissues within the body.

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 Imaging Modalities
 Positron Emission Tomography (PET)
 Although more expensive than SPECT, PET has clinical advantages in certain
diagnostic areas. The PET detector system is more sensitive to the presence
of radioisotopes than SPECT cameras, and thus can detect very subtle
pathologies.
 Positrons are positively charged electrons, and are emitted by some
radioactive isotopes such as fluorine 18 and oxygen 15. These radioisotopes
are incorporated into metabolically relevant compounds [such as 18F-
fluorodeoxyglucose (FOG)), which localize in the body after administration.
The decay of the isotope produces a positron, which rapidly undergoes a
very unique interaction: the positron (e+)combines with an electron (e-)
from the surrounding tissue, and the mass of both the e+ and the e- is
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converted by annihilation into pure energy, following Einstein's famous20
 Imaging Modalities
 Magnetic Resonance Imaging (MRI)
 MRI scanners use magnetic fields that are about 10,000 to
60,000 times stronger than the earth's magnetic field.
 Most MRI utilizes the nuclear magnetic resonance properties
of the proton-i.e., the nucleus of the hydrogen atom, which is
very abundant in biologic tissues (each cubic millimeter of
tissue contains about 1018 protons).
 The proton has a magnetic moment, and when placed in a 1.5-
tesla (T) magnetic field, the proton will preferentially absorb
radio wave energy at the resonance frequency of 63 megahertz
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(MHz).
 Imaging Modalities
 Magnetic Resonance Imaging (MRI)
 In MRI, the patient is placed in the magnetic field, and a pulse of radio
waves is generated by antennas ("coils") positioned around the patient.
The protons in the patient absorb the radio waves, and subsequently
reemit this radio wave energy after a period of time that depends on the
very localized magnetic properties of the surrounding tissue.
 The radio waves emitted by the protons in the patient are detected by the
antennas that surround the patient. By slightly changing the strength of the
magnetic field as a function of position in the patient (using magnetic field
gradients), the proton resonance frequency will vary as a function of
position, since frequency is proportional to magnetic field strength.
 MR angiography is useful for monitoring blood flow through arteries.
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 Imaging Modalities
 Ultrasound Imaging (US)
 A short-duration pulse of sound is generated by an ultrasound transducer
that is in direct physical contact with the tissues being imaged. The sound
waves travel into the tissue, and are reflected by internal structures in the
body, creating echoes. The reflected sound waves then reach the
transducer, which records the returning sound beam. This mode of
operation of an ultrasound device is called pulse echo imaging. The sound
beam is swept over a range of angles (a sector) and the echoes from each
line are recorded and used to compute an ultrasonic image in the shape of
a sector.
 Because ultrasound is less harmful than ionizing radiation to a growing
fetus, ultrasound imaging is preferred in obstetric patients.
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 Imaging Modalities
 Ultrasound Imaging (US)
 An interface between tissue and air is highly echoic, and
thus very little sound can penetrate from tissue into an air-
filled cavity. Therefore, ultrasound imaging has less utility
in the thorax where the air in the lungs presents a wall that
the sound beam cannot penetrate.
 Similarly, an interface between tissue and bone is also
highly echoic, thus making brain imaging, for example,
impractical in most cases.

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 Imaging Modalities
 Doppler Ultrasound Imaging
 Both the velocity and direction of blood flow can be measured,
and color Doppler display usually shows blood flow in one
direction as red and in the other direction as blue.
 change in frequency (the Doppler shift) is used to measure the
motion of blood or of the heart.

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 Imaging Modalities
 Differences between Medical Imaging

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 Imaging Modalities
 Differences between Medical Imaging

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 Imaging Modalities
 What you want to know about each modalities?
1) a short history of the imaging modality,
2) the theory of the physics of the signal and its interaction
with tissue,
3) the image formation or reconstruction process,
4) a discussion of the image quality,
5) the different types of equipment in use today {block
diagram + implementation},
6) examples of the clinical use of the modality,
7) a brief description of the biologic effects and safety issues,
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8) some future expectations.
 Imaging Modalities
 MEDICAL IMAGING: FROM PHYSIOLOGY TO INFORMATION
1. Understanding Image medium:
 tissue density is a static property that causes attenuation of
an external radiation beam in X-ray imaging modality.
 Blood flow, perfusion and cardiac motion are examples of
dynamic physiological properties that may alter the image of
a biological entity.

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 Imaging Modalities
 MEDICAL IMAGING: FROM PHYSIOLOGY TO INFORMATION
2. Physics of Imaging:
 The next important consideration is the principle of imaging
to be used for obtaining the data. For example, X-ray imaging
modality uses transmission of X-rays through the body as the
basis of imaging.
 On the other hand, in the nuclear medicine modality, Single
Photon Emission Computed Tomography (SPECT) uses
emission of gamma rays resulting from the interaction of
radiopharmaceutical substance with the target tissue.
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 Imaging Modalities
 MEDICAL IMAGING: FROM PHYSIOLOGY TO INFORMATION
3. Imaging instrumentation:
 The instrumentation used in collecting the data is one of the
most important factors defining the image quality in terms
of signal-to ratio, resolution and ability to show diagnostic
information.
 Source specifications of the instrumentation directly affect
imaging capabilities. In addition, detector responses such as
non-linearity, low efficiency and long decay time may cause
artifacts in the image.
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 Imaging Modalities
 MEDICAL IMAGING: FROM PHYSIOLOGY TO INFORMATION
4. Data Acquisition Methods for Image formation:
 The data acquisition methods used in imaging play an
important role in image formation. Optimized with the
imaging instrumentation, the data collection methods
become a decisive factor in determining the best temporal
and spatial resolution.

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 Imaging Modalities
 MEDICAL IMAGING: FROM PHYSIOLOGY TO INFORMATION
5. Image Processing and Analysis:
 Image processing and analysis methods are aimed at the
enhancement of diagnostic information to improve manual
or computer-assisted interpretation of medical images.

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 Imaging Modalities
 Image Prosperities:
1. Contrast
2. Spatial Resolution

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 Imaging Modalities
 Contrast:
 X-ray contrast is produced by differences in tissue composition,
which affect the local x-ray absorption coefficient.
 Contrast in MRI is related primarily to the proton density and
to relaxation phenomena (i.e., how fast a group of protons
gives up its absorbed energy).
 Contrast in ultrasound imaging is largely determined by the

acoustic properties of the tissues being imaged.

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 Imaging Modalities
 Spatial Resolution:
 Resolve fine detail in the patient.
 RESOLVE= separate into constituent parts
 the ability to see small detail, and an imaging system has higher spatial
resolution if it can demonstrate the presence of smaller objects in the
image.
 The limiting spatial resolution is the size of the smallest object that an
imaging system can resolve.
 In ultrasound imaging, the wavelength of sound is the fundamental limit of
spatial resolution. At 3.5 MHz, the wavelength of sound in soft tissue is
about 0.50 mm. At 10 MHz, the wavelength is 0.15 mm.

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 Imaging Modalities
 Spatial Resolution:

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 Applications

Chest Abdomen Head

X-Ray/ + widely used – needs contrast + X-ray - is good
CT + CT - excellent + CT - excellent for bone
– CT - bleeding,
trauma
Ultrasoun – no, except for + excellent – poor
d + heart – problems with
gas
Nuclear + extensive use Merge w/ CT + PET
in heart

MR + growing + minor role + standard

cardiac
applications

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 Applications
Cardiovascular Skeletal / Muscular
X-Ray/ + X-ray – Excellent, with + strong for skeletal system
CT catheter-injected
contrast

Ultrasound + real-time – not used

+ non-invasive
+ cheap
– but, poorer images
Nuclear + functional information + functional - bone marrow
on perfusion

MR + getting better + excellent

High resolution
Myocardium viability

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 THANK YOU

ANY Question?
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