5. Bats make high-pitched chirps which are too high for humans to
hear. This is called ultrasound
Like normal sound, ultrasound echoes off objects
The bat hears the echoes and works out what caused them
• Dolphins also navigate with ultrasound
• Submarines use a similar method called sonar
We can also use ultrasound to
look inside the body…
6. Sound…?
Sound is a mechanical, longitudinal wave that travels
in a straight line
Sound requires a medium through which to travel
9. What is Ultrasound?
Ultrasound is a mechanical, longitudinal wave with a
frequency exceeding the upper limit of human
hearing, which is 20,000 Hz or 20 kHz.
Medical Ultrasound 2MHz to 16MHz
10. to the audible frequency range ~ 20Hz - 20kHzThe human ear can only respond to the audible
frequency range ~ 20Hz - 20kHz
11. ULTRASOUND – How is it produced?
Produced by passing an electrical current through a
piezoelectrical (material that expands and contracts
with current) crystal….. “Pulse Echo” principle
Naturally occurring -
quartz
Synthetic - Lead
zirconate titanate (PZT)
12. In ultrasound, the following events
happen:
1. The ultrasound machine transmits high-frequency
(1 to 12 megahertz) sound pulses into the body
using a probe.
2. The sound waves travel into the body and hit a
boundary between tissues (e.g. between fluid and
soft tissue, soft tissue and bone).
3. Some of the sound waves reflect back to the
probe, while some travel on further until they
reach another boundary and then reflect back to
the probe .
4. The reflected waves are detected by the probe
and relayed to the machine.
13.
14. 5. The machine calculates the distance from the
probe to the tissue or organ (boundaries) using the
speed of sound in tissue (1540 m/s) and the time
of the each echo's return (usually on the order of
millionths of a second).
6. The machine displays the distances and intensities
of the echoes on the screen, forming a two
dimensional image.
15. Velocity in tissue
Medium Velocity of US (m/sec)
Air 330
Fat 1450
Water 1480
Soft tissue 1540
Kidney 1560
Blood 1570
Muscle 1580
Bone 4080
16. Ultrasound Production
Transducer produces ultrasound pulses
These elements convert electrical energy into a mechanical
ultrasound wave
Reflected echoes return to the scanhead which converts the
ultrasound wave into an electrical signal
17. Piezoelectric Crystals
The thickness of the crystal determines the
frequency of the scanhead
Low Frequency
3 MHz
High Frequency
10 MHz
18. What determines how far ultrasound
waves can travel?
The FREQUENCY of the transducer
The HIGHER the frequency, the LESS it can penetrate
The LOWER the frequency, the DEEPER it can penetrate
Attenuation is directly related to frequency
19.
20. Frequency vs. Resolution
The frequency also affects the QUALITY of the ultrasound image
The HIGHER the frequency, the BETTER the resolution
The LOWER the frequency, the LESS the resolution
A 12 MHz transducer has very good resolution, but cannot
penetrate very deep into the body
A 3 MHz transducer can penetrate deep into the body, but the
resolution is not as good as the 12 MHz
Low Frequency
3 MHz
High Frequency
12 MHz
21.
22. 2. Ultrasound Modes
A-mode: A-mode (amplitude mode) is the simplest type of ultrasound. A single transducer scans a line through the
body with the echoes plotted on screen as a function of depth. Therapeutic ultrasound aimed at a specific tumor
or calculus is also A-mode, to allow for pinpoint accurate focus of the destructive wave energy.
B-mode or 2D mode: In B-mode (brightness mode) ultrasound, a linear array of transducers simultaneously scans a
plane through the body that can be viewed as a two-dimensional image on screen. More commonly known as 2D
mode now.
C-mode: A C-mode image is formed in a plane normal to a B-mode image. A gate that selects data from a
specific depth from an A-mode line is used; then the transducer is moved in the 2D plane to sample the entire
region at this fixed depth. When the transducer traverses the area in a spiral, an area of 100 cm2 can be scanned in
around 10 seconds.[10]
M-mode: In M-mode (motion mode) ultrasound, pulses are emitted in quick succession – each time, either an A-
mode or B-mode image is taken. Over time, this is analogous to recording a video in ultrasound. As the organ
boundaries that produce reflections move relative to the probe, this can be used to determine the velocity of
specific organ structures.
Doppler mode: This mode makes use of the Doppler effect in measuring and visualizing blood flow
Color Doppler: Velocity information is presented as a color-coded overlay on top of a B-mode image
Continuous Doppler: Doppler information is sampled along a line through the body, and all velocities detected
at each time point is presented (on a time line)
Pulsed wave (PW) Doppler: Doppler information is sampled from only a small sample volume (defined in 2D
image), and presented on a timeline
Duplex: a common name for the simultaneous presentation of 2D and (usually) PW Doppler information. (Using
modern ultrasound machines color Doppler is almost always also used, hence the alternative name Triplex.)
Pulse inversion mode: In this mode two successive pulses with opposite sign are emitted and then subtracted from
each other. This implies that any linearly responding constituent will disappear while gases with non-linear
compressibility stands out.
Harmonic mode: In this mode a deep penetrating fundamental frequency is emitted into the body and a harmonic
overtone is detected. In this way depth penetration can be gained with improved lateral resolution
24. M-mode: In M-mode (motion mode) ultrasound, pulses
are emitted in quick succession – each time, either an
A-mode or B-mode image is taken. Over time, this is
analogous to recording a video in ultrasound.
25. Doppler mode: This mode makes use of the Doppler
effect in measuring and visualizing blood flow
26. Shadowing
Posterior enhancement
Edge shadowing
Comet tail
Mirror Imaging
3. Artifacts
Attenuation artifact
Miscellaneous artifact
Ring down
Side lobe
27. Echogenic :
When ultrasound waves pass
through solids (bones – stone)
all waves are reflected and
appears as white color with
posterior shadow .
Shadowing
28. It means the reflection of waves , and this depends on the
material which is penetrated by US.
• Echo free :
When ultrasound waves
pass through fluids (
ascites- simple cyst- blood
vessels) no reflection
occurs and these areas
appears as black areas
with posterior enhancement
. Posterior Enhancement & Mirrored Side
Posterior Enhancement, Side Lobe and Mirror Image
29. Mirror-image artifacts
Feldman M K et al. Radiographics 2009;29:1179-1189
US beam bounces between structure and deeper strong reflector
e.g. diaphragm. This means probe receives signals as if from same
object on other side of reflector.
33. Ring-down
Feldman M K et al. Radiographics 2009;29:1179-1189
Ring of bubbles with fluid trapped centrally. Fluid vibrations detected as
strong signal and displayed as line behind true source.
37. 5. Common Terminology
Image Interpretation
Anechoic / Echolucent - Complete absent
of returning sound ( area is black)
Hypoechoic – Structures has very few
echoes and appears darker than
surrounding tissue
Hyperechoic/ Echogenic – Structure
appears brighter than surrounding tissues
38. No Reflections = Black dots
Fluid within a cyst, urine, blood
Anechoic / Echolucent - Complete absent of
returning sound ( area is black)
39. Hypoechoic – Structures has very few echoes and
appears darker than surrounding tissue
Weaker Reflections =
Grey dots
Most solid organs,
thick fluid – „isoechoic‟
40. Hyperechoic/ Echogenic – Structure appears
brighter than surrounding tissues
Strong Reflections = White dots
Diaphragm, tendons, bone
41. • Acoustic impedance (AI) is dependent on the density of the material
in which sound is propagated
- the greater the impedance the denser the material.
• Reflections comes from the interface of different AI‟s
• greater of the AI = more signal reflected
• works both ways (send and receive directions)
Medium 1 Medium 2 Medium 3
Transducer
Interactions of Ultrasound with Tissue
42. Sound is attenuated by tissue
More tissue to penetrate = more attenuation of
signal
Compensate by adjusting gain based on depth
near field / far field
AKA: TGC
43. Gain controls
receiver gain only
does NOT change power output
Increase gain = brighter
Decrease gain = darker
51. Image Acquisition / Probe position
Tranverse plane/ axial plane/ cross
section separates superior from
inferior
Sagittal plane – Oriented
perpendicular to the ground
separating left from right.
Coronal plane – Frontal plane,
separates anterior from posterior
Oblique Plane – The probe is oriented
neither parallel to nor at the right
angles from coronal, sagittal or
tranverse plane.
58. Summary
Know your anatomy – Skin, muscle, tendons, nerves
and vessels
Recognise normal appearances – compare sides!
Resolution determines image clarity
Frequency & wavelength are inversely proportional
Attenuation & frequency are inversely related
Display mode chosen determines how image is
registered
Diagnostic Medical Ultrasound is safe!
59. Conclusions
1. Imaging tool – Must have the knowledge to
understand how the image is formed
2. Dynamic technique
3. Acquisition and interpretation dependant upon the
skills of the operator.
