1. Ultrasound
By : Saja Abdo

2. Objectives: History Physics of ultrasound 1. basic principles of sound
2. principles of ultrasound
3. how ultrasound wave impact by tissue
Uses of ultrasound

3. History
1 Jan 1915 Hydrophones covert acoustic energy into electrical energy, and is used for underwater navigation for submarines and iceburgs.
Use of Ultrasound in Therapy 1 Jan 1920Used as a physical therapy treatment on a soccer team in Europe.
1 Jan 1942Neurologist Karl Dussik was the first to use ultrasound for medical diagnosis.

4. 1 Jan 1953, First echocardiogram completed through an echo test conducted from a Siemens shipyard.
1 Jan 1970, Imaging blood flow through the chambers and different depths of the heart.
1 Apr 1986, 3-D ultrasound was developed and 3-D images were captured of a fetus. A 3D ultrasound is acquired by emitting high-frequency sound waves.

5. 2 D D
1 Jan 2000, 4-D ultrasound (real time) was developed .
2D / 3D / 4D Ultrasound also – Video in 9 Apr 2013.

6. Physics of ultrasound Basic principles of sound:
Sound is a mechanical, longitudinal wave that travels in a straight line
Sound requires a medium through which to travel
The wave travels by compressing and rarefacting matter.
rarefaction can by easily observed by compressing a spring and releasing it.
Depending on the matter encountered, the wave will travel at different velocities.

7. Cycle:
1 Cycle = 1 repetitive periodic oscillation

9. Frequency Number of cycles per second Measured in Hertz (Hz)
-Human Hearing ,000 Hz
-Ultrasound > 20,000 Hz
-Diagnostic Ultrasound 2.5 to 10 MHz

10. Principles of 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.
Diagnostic Ultrasound 2.5 to 10 MHz.
Produced by passing an
Produced by passing an electrical current through a piezoelectric crystal.
MHz to 16MHz

11. 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).

12. 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

13. The Returning Echo
Reflected echoes return to the scan head where the piezoelectric elements convert the ultrasound wave back into an electrical signal.
The electrical signal is then processed by the ultrasound system

14. Piezoelectric Crystals
The thickness of the crystal determines the frequency of the scan head
Low Frequency
3 MHz
High Frequency
10 MHz

15. 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.

16. Image Formation Probe emits a sound wave pulse
measures the time from emission to return of the echo .
Wave travels by displacing matter, expanding and compressing adjacent tissues.
It generates an ultrasonic wave that is propagated, impeded, reflected, refracted, or attenuated by the tissues it encounters .

17. Electrical signal produces ‘dots’ on the screen
Brightness of the dots is proportional to the strength of the returning echoes.
Location of the dots is determined by travel time. The velocity in tissue is assumed constant at 1540m/sec
Distance= Velocity Time

18. Producing an image Important concepts in production of an U/S image:
Propagation velocity
Acoustic impedance
Reflection
Refraction
Attenuation

19. Propagation Velocity Sound is energy transmitted through a medium.
Each medium has a constant velocity of sound (c).
Tissue’s resistance to compression density or stiffness.
Product of frequency (f) and wavelength (λ)
c = f λ
Frequency and Wavelength therefore are directly proportional if the frequency increases the wavelength must decrease.

20. Propagation velocity
Increased by increasing stiffness
Reduced by increasing density
For example
Bone: 4,080 m/sec
Air: 330 m/sec
Soft Tissue Average: 1,540 m/sec

21. Acoustic Impedance
Acoustic impedance (z) of a material is the product of its density and propagation velocity Z = pc
Homogeneous mediums reflect no sound.
acoustic interfaces create visual boundaries between different tissues.
Bone/tissue or air/tissue interfaces with large Δz values reflect almost all the sound.
Muscle/fat interfaces with smaller Δz values reflect only part of the energy.

22. Interactions of Ultrasound with Tissue
Reflection
Refraction
Transmission
Attenuation

23. Refraction
A change in direction of the sound wave as it passes from one tissue to a tissue of higher or lower sound velocity.
U/S scanners assume that an echo returns along a straight path.
Distorts depth reading by the probe.
Minimize refraction by scanning perpendicular to the interface that is causing the refraction.

24. Reflection
The production of echoes at reflecting interfaces between tissues of differing physical properties.
There are 2 types:
Specular - large smooth surfaces
Diffuse - small interfaces or nooks and crannies

25. Specular Reflection
Large smooth interfaces (e.g. diaphragm, bladder wall) reflect sound like a mirror.
Only the echoes returning to the machine are displayed.
Specular reflectors will return echoes to the machine only if the sound beam is perpendicular to the interface.

26. Diffuse Reflector
Most echoes that are imaged arise from small interfaces within solid organs.
These interfaces may be smaller than the wavelength of the sound.
The echoes produced scatter in all directions.
These echoes form the characteristic pattern of solid organs and other tissues.

28. Transmission
Some of the ultrasound waves continue deeper into the body.
These waves will reflect from deeper tissue structures.

29. Attenuation
The intensity of sound waves diminish as they travel through a medium
In ideal systems sound pressure (amplitude) is only reduced by the spreading of waves
In real systems some waves are scattered and others are absorbed, or reflected
This decrease in intensity (loss of amplitude) is called attenuation.
the deeper the wave travels in the body, the weaker it become-3 processes: reflection, absorption, refraction
Air (lung)> bone > muscle > soft tissue >blood > water

30. Attenuation & Gain Sound is attenuated by tissue
More tissue to penetrate = more attenuation of signal
Compensate by adjusting gain based on depth
near field / far field
Increase gain = brighter
Decrease gain = darker
Gain settings are important to obtaining adequate images.

31. bad far field
bad near field
balanced

32. Goal of an Ultrasound System
The ultimate goal of any ultrasound system is to make like tissues look the same and unlike tissues look different

33. Uses of ultrasound
An ultrasound scan can be used in several different ways, such as monitoring an unborn baby, diagnosing a condition or guiding a surgeon during certain procedures.
Pregnancy
Ultrasound scans are routine procedure for pregnant women. They produce images of the unborn baby inside the womb, and display them on a monitor.
Most women are offered at least two ultrasound scans during pregnancy:
the first scan (at around eight to 14 weeks) can help to determine when the baby is due.

34. the second scan (usually between 18 and 20 weeks) checks for structural abnormalities, particularly in the baby's head or spine.
Diagnosing conditions
Ultrasound scans can help diagnose problems in many parts of your body, including your:
1. liver (cirrhosis) gallbladder (gallstones)
3. lymph nodes ovaries
5. Testes breasts
7. blood vessels (aneurysm) joints, ligaments and tendons
9. Skin eyes

35. Echocardiogram (ECG)
An ultrasound scan can be used to examine the size, shape and movement of your heart. For example, it can check that the structures of your heart, such as the valves and heart chambers, are working properly and your blood is flowing normally. This type of ultrasound scan is called an echocardiogram (ECG).
Biopsy
Ultrasound can be used to guide doctors during certain procedures, such as a biopsy (where a tissue sample is taken for analysis). This is to make sure the surgeon is working in the right area and is often used when diagnosing breast cancer.

36. References
Novelline, Robert (1997). Squire's Fundamentals of Radiology (5th ed.). Harvard University Press. pp. 34–35.
 Bruno Pollet Power Ultrasound in Electrochemistry: From Versatile Laboratory Tool to Engineering Solution John Wiley & Sons,(2012) 
 Corso, J. F. ,"Bone-conduction thresholds for sonic and ultrasonic frequencies". Journal of the Acoustical Society of America 35 (11): 1738–1743. (1963).
  Takeda, S.; Morioka, I.; Miyashita, K.; Okumura, A.; Yoshida, Y.; Matsumoto, K. "Age variation in the upper limit of hearing“, European Journal of Applied, (1992).
  Physiology 65 (5): 403–408. Retrieved 2008
Hearing by Bats (Springer Handbook of Auditory Research, 5. Art Popper and Richard R. Fay (Editors). Springer, (1995).