This document contains a presentation on ultrasound physics and obtaining an ultrasound image. It discusses key topics like what ultrasound is, how it is generated using the piezoelectric effect, how images are formed from reflected sound waves, and factors that affect image resolution and penetration such as frequency and transducer selection. It also covers Doppler ultrasound and optimizing images by adjusting gain, depth, and using acoustic couplants. Examples of ultrasound appearances of different tissues and anatomical structures are provided.
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Cultural physics
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Ultrasound Physics
And
Obtaining an Image
Sandra Thomas
Clinical Marketing & Education Manager
SonoSite Ltd – Middle East,India & Africa
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Agenda
•What is ultrasound?
•How is it generated?
•What happens to it?
•What do things look like?
•Other stuff – Doppler etc
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What is Ultrasound?
•Infrasound
0-20 Hz
•Audible Sound
20 Hz to 20,000 Hz
•Ultrasound
>20,000 Hz (or 20 KHz)
•Medical Ultrasound
2 MHz to 15 MHz
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Generation of Ultrasound
•Transducer converts
energy from one form to
another
•Piezoelectric effect
•Electrical energy
applied to crystal(s)
causes
dimensional change
(mechanical energy)
•Dimensional change
produces sound wave
•Reception of reflected
beam is reverse of
generation
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Image Generation
Initiate sound wave by system
Transmission through medium
Reflection from structures
Signal returns to system
ll of the above occur simultaneously
real time scanning so we can see
otion
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2D Real-time ultrasound
2D images of tissue traversed by ultrasound scan. Displays
motion by showing images of tissue under the transducer as it is
being scanned
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Ultrasound Resolution
Resolution is the ability to identify closely separated interfaces
• Resolution has two components
• Axial resolution – ability to distinguish 2 reflectors
along the path of the beam
• Depends on pulse length/frequency
• In practice axial resolution is 0.5mm for high
frequency transducers
• Lateral resolution
• Ability to distinguish 2 reflectors as individual
elements which are perpendicular to the US
beam
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• Depends on beam profile/scan line density
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Axial Resolution Lateral Resolution
Depends on pulse length (frequency)
8 Depends on beam profile/line density
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Interaction of Ultrasound with Tissues
Positives:
Reflection- occurs at 07.39.12 hrs __[0000007].mp4
boundaries between
tissues of differing
acoustic impedances.
Best reflection when
beam is perpendicular
to boundary
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Interaction of Ultrasound with Tissues
Positives:
Reflection- occurs at
boundaries between
tissues of differing
acoustic impedances.
Best reflection when
beam is perpendicular
to boundary
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Multibeam technology…
• Real time acquisition software
• Improves image quality : more detail, more tissue
signature
• Artifact reduction
• Improves contrast resolution
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Standard Multibeam
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Multibeam technology…
Standard
acquisition
Multibea
m
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Benefits…
Improves contrast resolution
Increases tissue information
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Standard Multibeam
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What is the effect of frequency ?
Frequency = Resolution
Frequency = Resolution
1
Frequency = Penetration
Frequency =
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Penetration
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Transducers
•Transmits and receives the ultrasound beam
•Contacts the patient’s skin
•Takes thin slices of object being imaged
•Rotate or angle to change views
38
mm
1 mm
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Transducer Orientation Markings
Markings are located on one
side of transducer only and
correspond to orientation marke
on screen
groove
vertical protrusion
horizontal protrusion
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Transverse Transducer Orientation
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Transverse Transducer Orientation
Orientation marker
Groove towards patient’s right
Skin surface
Blood vessel
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Right Left
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Longitudinal Transducer Orientation
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Longitudinal Transducer Orientation
Groove towards patient’s head
Orientation marker
Skin surface
Blood vessel
Head Feet
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Image Appearance
N
E Tissue = Grey
A
R
Blood = Black
F
A
R
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Ultrasound appearances
Artery Anechoic - black Pulsatile
Vein Anechoic - black Compressible
Muscle Hyperechoic fascia Hypoechoic
muscle
Hyperechoic Tubular (fibrillar)
Tendon
Discontinuous hypoechoic lines separated by
Nerves – LS hyperechoic lines(fasicular)
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TS Multiple round hypoechoic areas(fasicles)
surrounded by hyperechoic halo (connective tissue,
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Appearance of nerves
TS
LS
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Femoral Nerve
Artery Vein
Nerve
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Brachial Plexus - interscalene
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Image Optimisation - Gain
Amplification of returning echoes
One of the commonest mistakes in ultrasound
imaging is the use of incorrect gain settings.
Insufficient gain can result in missed
structures of low reflectivity.
Excessive gain can result in false echoes or over
saturation, which may obscure important diagnostic
image characteristics such as shadowing or
enhancement
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Image Optimization
Depth adjustment
N
E
The choice of correct depth setting is a trade-
A
off between achieving adequate field of view
R
to resolve all relevant structures and
maximising detail resolution
F
A
R
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Image Optimization-Depth
Increasing the depth allows you to visualize deeper structures
N
E Tissue = Grey
Adjust the depth so that the target is centered in the image
A
R
Blood = Black
F
A
R
Too close Too far Just right
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Doppler Ultrasound
Doppler Effect based on work by Austrian physicist Johann
Christian Doppler
N
E Tissue = Grey
A
Apparent change in received frequency due to relative
R
motion between a sound source and sound receiver
Source moving TOWARD receiver = HIGHER frequency
Blood = Black
F
A
Source moving
R AWAY from receiver = LOWER frequency
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Acoustic Couplants
• Air/tissue interface allows
N
little ultrasound Tissue = Grey
E
transmission
so gel is A needed on skin to
exclude R air
•Best quality image= requires
F
Blood Black
an air free coupling between
A
R
ALL surfaces
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Acoustic Couplants
N
E Tissue = Grey
A
R
Blood = Black
F
A
R
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And finally……..
Aoccdrnig to rscheearch at Cmabrigde
Uinevrtisy, it deosn’t mtlaer in what oredr the
ltteers in a wrod are, the olny iprmoatnt tihng is
taht the frist and lsat ltteer be in the rghit pclae.
The huamn mnid deos not raed ervey lteter but
the word as a wlohe
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Median Nerve Common extensor Tendon
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And finally………really!
What happens when you…………….
1. Have nothing to do
2. Own a sharp knife
3. Have a large lime
4. Own a patient cat……………………
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