ULTRASOUND IMAGING
Lec 1: Introduction
Ultrasonic Field
Wave fundamentals.
Intensity, power and
radiation pressure.
1-Jul-16
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Introduction:
Why Medical Imaging?
Earlier diagnosis
Easier diagnosis
More accurate diagnosis
Less invasive diagnosis and
treatments
Greater sharing of knowledge
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Brief history
of Medical Imaging
1895 – Roentgen accidentally
discovers x-rays while
experimenting with Crookes tube.
1946 – Felix Bloch and Edward
Purcell discover the presence of
magnetic resonance in solids and
liquid.
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1960’s – The ultrasound is
developed. Sonar development
during World War ll.
1972 – The computed
tomography scan becomes a
reality due to breakthroughs in
digital computers.
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The field of diagnostic radiology
has undergone tremendous growth
in the past several decades:
developed in the 1950’s
 Nuclear Medicine in the 1960’s
 Ultrasound and CT in the 1970’s
 MRI and interventional radiology in
the 1980’s
 PET in the early 1990’s
 Angiography
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Image Capturing
Technique
Radiography
Magnetic Resonance Imaging
Computed Tomography
Ultrasound
Nuclear Imaging
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Radiography
Process of creating an image by
passing x-rays through a patient to
a detector.
Relies on natural contrast between
radiographic densities of air, fat,
soft tissue and bone.
Most advantageous in parts of the
body with inherently high contrast,
e.g. the lungs and the heart.
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Conventional Radiography
 Converting to digital
Scanning
Sampling
Conversion
Digital Radiography
Modifications of plain-film
radiography are fluoroscopy,
tomography and mammography.
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Radiography
© Radiology Centennial, Inc
© EarthOps.org
“So excited was the public that each newly radiographed
organ or system brought headlines. With everything about
the rays so novel, it is easy to understand the frequent
appearance of falsified images, such as this much-admired
"first radiograph of the human brain," in reality a pan of cat
intestines photographed by H.A. Falk in 1896.”
-Penn State University College of Medicine
1-Jul-16
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Ref: Amy Schnelle, Computer Science, Univ. of Wisconson-Platteville
Fluoroscopy
Uses the x-ray beam continuously.
Physician can:
 Evaluate the dynamic processes
(e.g. diaphragmatic excursion or
bowel peristalsis).
 Watch contrast medium (e.g. in the
blood vessels, bowel, kidneys, or
joint spaces).
 Follow the path of an opaque
object (e.g. feeding tube or
intravascular cathether).
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Mammography
Plain film study that uses specially
designed equipment with low
voltages and a film-screen
combination to evaluate breast
tissue and calcification with high
contrast resolution for detail at a
low radiation dose.
Breast compression is to reduce
radiation exposure and improve
image quality.
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Ultrasound
Ultrasound uses high frequency sound
waves 1-10 MHz and their
corresponding echoes to create
images of the internal structures of
patients.
The sound waves are directed into the
body reflected by various body
structures.
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The time taken for the reflected
waves to return determines the
depth of the structures.
The amount of beam absorption
determines the intensity of the
returning wave.
Echoes from interfaces between
tissues with different acoustic
properties yield information on
the size, shape, and internal
structure of organs and masses.
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Why ultrasound is popular?
 The advantages are the:
Portability
Lack of ionizing radiation
Ability to scan the body in any
plane
 Disadvantages are:
Operator dependency
Limited usage for imaging the
lungs and skeleton
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Ultrasound
© Radiology Info
1-Jul-16
© Photo Dynamic Imaging Limited
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Ref: Amy Schnelle, Computer Science, Univ. of Wisconson-Platteville
ULTRASOUND IMAGING
Lec 2: Ultrasonic Field
Wave fundamentals.
Intensity, power and
radiation pressure.
1-Jul-16
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Wave fundamentals
Sound is a mechanical longitudinal wave
and carries energy. Unlike light waves and
radio waves, it requires a medium to
propagate and cannot pass through a
vacuum.
The sound acoustic variables include:
 Pressure
 Density
 Temperature
 Particle motion.
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Sound parameters:
 Frequency,  (Hz. Older literature: c/s.)
Number of oscillations per second
performed by the particles of the medium
in which the ultrasound is propagating.
 Audible sound:
20 Hz – 18 kHz
 Ultrasound:
> 18 kHz
Bats:
 Grasshoppers:

 Diagnostic
ultrasound: 0.5 – 25 MHz
Abdominal scanning:
 Opthalmology:

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120 kHz
100 kHz
3 MHz
10 MHz
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Sound parameters:
 Period, T (s, s)
The time taken for one complete cycle to
occur.
T=1/
[Equation 1.1]
 Wavelength,  (m, mm)
Length of space over which one cycle
occurs.
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speed, c (ms-1)
Speed with which an ultrasound wave
propagate through a medium.
c=
[Equation 1.2]
c is determined by density,  and stiffness
of the medium.
 Stiffness difference > density difference.
 csolid > cliquid > cgas
 Propagation
Soft tissues:
 Lung:
 Bone:
 Fat:

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1540 ms-1
300 – 1200 ms-1
2000 – 4000 ms-1
1450 ms-1
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 Amplitude,
A (m)
The maximum displacement that
occurs in an acoustic variable.
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Intensity, power and radiation pressure
Intensity, I (mWcm-2)
 The intensity of an ultrasonic beam at
a point is the rate of flow of energy
through unit area perpendicular to the
beam at that point.
 Proportional to the square of
amplitude.
 Determines the sensitivity of the
instrument, i.e. the number and sizes
of echoes recorded.
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Formulas relating intensity I:
I = ½ (p02/c)
[Equation 1.3]
I = ½ c(2f)2x02 [Equation 1.4]
I = ½ cu02
[Equation 1.5]
p0 = pressure amplitude
x0 = particle-displacement amplitude
u0 = particle-velocity amplitude
 = density of the medium
f = frequency of ultrasound
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Power, P (W, mW)
 Rate of flow of energy through the
whole cross-section of the beam.
[Ultrasonic power]
= [Ultrasonic Intensity] [Beam cross-sectional area]
P=Ia
[Equation 1.6]
 Beam area is determined in part by
the size and operating frequency of
the transducer.
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