Ultrasound uses high frequency sound waves to image internal structures. A transducer converts electrical pulses into ultrasound pulses and reflected sound waves back into electrical signals. Tissues reflect sound differently allowing visualization. Higher frequencies improve resolution but reduce penetration. Ultrasound has various medical uses like imaging fetuses, organs and detecting abnormalities by interpreting echo patterns. It provides real-time images without radiation unlike other modalities.

1. Introduction of Ultrasound
Physics'
ENGR AHMED A A HASSAN

2. Introduction to the Physics of Ultrasound
Amplitude
• Sound?
• Sound is a mechanical, longitudinal wave that travels in a straight line
• Sound requires a medium through which to travel

3. Cycle
• 1 Cycle = 1 repetitive periodic oscillation
Cycle

4. frequency
1 cycle in 1 second = 1Hz
1 second
= 1 Hertz

5. Wavelength
• The length of one complete cycle
• A measurable distance

6. Wavelength
Wavelength

7. Amplitude
• The degree of variance from the norm
Amplitude

8. Spectrum of sound
Frequency range Hz Description Example
0 - 20 Infrasound Earth quake
20 - 20.000 Audible sound Speech, music
> 20.000 Ultrasound , Quartz crystal

9. Atomic structures
gas liquid solid
• low density • medium density • high density
• weak bonding forces • medium bonding • strong bonding forces
forces • crystallographic
structure
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10. Basic formula
Air 330 m/s
Water 1480 m/s
Steel, long 5920 m/s
Steel, trans 3250 m/s

11. Example Sound Speeds
Medium sound speed (m/s)
air (20 C) 343
water 1497
gold 3240
brick 3650
wood 3800–4600
glass 5100
steel 5790
aluminum 6420
Spring 2006 11

12. What is the Echo?
Repetition of a sound by reflection of sound waves from a surface
r = c * t2
The pulse bounces off a target and returns to the receiver after a time interval t.
The receiver records the length of this time interval,
and calculates the distance travelled r based on the speed of sound c

13. What that mean?
If the sound path from one surface to Another the sound will be reflected
Surface 1 Surface 2

14. 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

15. How the Ultrasound System work?

16. Piezoelectric material
• AC applied to a piezoelectric crystal causes it
to expand and contract – generating ultrasound,
and vice versa
• Naturally occurring - quartz
• Synthetic - Lead zirconate titanate (PZT)

17. Human Hair
Single
Crystal
Microscopic view of scanhead

18. Ultrasound Production
• Transducer contains piezoelectric
elements/crystals which produce the
ultrasound pulses (transmit 1% of the time)
• These elements convert electrical energy
into a mechanical ultrasound wave
Sound
Electric Signal

19. The Returning Echo
• Reflected echoes return to the
scanhead where the piezoelectric
elements convert the ultrasound wave
back into an electrical signal
• The electrical signal is then processed
by the ultrasound system
Electric Signal
Sound

20. Piezoelectric Effect
Sound wave
with
frequency f
U(f)
An alternating voltage generates crystal oscillations at the frequency f
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21. Piezoelectric Effect
Short pulse
( < 1 µs )
A short voltage pulse generates an oscillation at the crystal‘s resonant
frequency f0
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22. Transducer Construction

23. Sound reflection
r
Probe
Sound travel path
Work piece
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24. Immersion testing
1 2
surface = water delay
sound entry
backwall Mass
IP 1 IP 2
IE IE
BE BE
F
0 2 4 6 8 10 0 2 4 6 8 10
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25. In ultrasound, the following events happen:
1. The ultrasound machine transmits high-frequency (1 to 20
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.

26. 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.

27. Liver metastases

28. Piezoelectric Crystals
• The thickness of the crystal determines the
frequency of the scanhead
Low Frequency High Frequency
3 MHz 10 MHz

29. Frequency and Wavelength therefore are directly proportional-
if the frequency increases the wavelength must decrease.
if the frequency decreases the wavelength must increase

30. Frequency vs. Resolution
• The frequency also affects the QUALITY
of the ultrasound image
– The HIGHER the frequency, less penetration
the BETTER the resolution
– The LOWER the frequency, HIGHER
penetration the LESS the resolution

31. Resolution
– frequency
– Wave Length
– resolution

32. Resolution
– frequency
– Wave Length
– resolution

33. Types of Resolution
• Axial Resolution
– specifies how close together two objects
can be along the axis of the beam, yet
still be detected as two separate objects
– frequency (wavelength) affects axial
resolution – frequency resolution

34. Types of Resolution
• Lateral Resolution
– the ability to resolve two adjacent objects
that are perpendicular to the beam axis
as separate objects
– beamwidth affects lateral resolution

35. Types of Resolution
• Spatial Resolution
– also called Detail Resolution
– the combination of AXIAL and LATERAL
resolution - how closely two reflectors
can be to one another while they can be
identified as different reflectors

36. Types of Resolution
• Temporal Resolution
– the ability to accurately locate the
position of moving structures at particular
instants in time
– also known as frame rate

37. Types of Resolution
• Contrast Resolution
– the ability to resolve two adjacent objects
of similar intensity/reflective properties
as separate objects - dependant on the
dynamic range

38. History

39. 1st who is the 1st sono grapher ?
• Bats use a variety of ultrasonic ranging
(echolocation) techniques to detect their prey.
They able to fly without their vision.
They can detect frequencies beyond 100 kHz,
possibly up to 200 kHz.
This discovered in 1793 by Italian Scientist called Spallanzani.

40. Sir Francis Galton (1800)
• Recognized that by moving the
plunger (located inside the whistle)
the size of the cavity could be
changed to alter the pitch (frequency)
of sound
• Determined the normal limit of
human hearing is around 18 kHz

41. 1st Contact B-Scanner (1956)
The first contact B scanner was designed and built by Tom Brown on
the frame of a hospital bed-table. It is seen here with its first picture;
this shows echoes from the skin, at the top of the picture, and from
the bowel.

42. Automatic Scanner (1959)
Tom Brown developed the world’s first and only fully
automatic scanner in order to give a consistent scanning
pattern. Much of the early research was carried out with this
machine

43. Fetal Cephalometry (1961)
• Dr. James Willocks
(seated, scanning)
developed a technique for
fetal cephalometry using
A-Scan equipment and
electronics.

44. 1st Commercially Produced Medical Scanners
(1962)

45. The Mid ’70s and the Change to Real-time
System 185
EMI 4200 System 85 Diagnostic Sonar
Static Real-time scanners Ltd.
Scanner

46. The Beginnings of 3D (1976)
• develop the world’s first 3-D
ultrasound scanner.
• Sonicaid Multiplanar Scanner

47. Now a Days: