basics

1. Presenter : Dr. Manish Yadav
First year resident
NAIHS

2. AIM
 To introduce ultrasound machine and its basic
physics

3. CONTENT
 Introduction
 Parts of ultrasound machine
 Function of machine
 Ultrasound physics

4. Introduction
• Ultrasound-imaging technology that uses high
frequency sound waves to characterize tissue.
• Diagnosis and therapeutic procedures

5.  A basic ultrasound machine has following parts:
1.Display
2.CPU
3.Transducer probes
4. Keyboard/control panel
5.Disc storage device
6.Printer

7.  Machine orientation:
-presets
-features
-save and print

8.  Machine features:
-Quality
-Mode
-Tools

9. Quality
 Depth
 Gain adjustment /TGC

12. Mode
 2D/B mode
 Doppler
-Color doppler
-continuous wave doppler
-pulse wave doppler
 M-mode
 3D
 4D

14. Tools
 Freeze
 Trackball
 Caliper
 Toggle key
 Text key

17. Physics of echo
 Sound
-Audible range 20Khz
-Medical ultrasound Megahertz range(2-15 MHz)
 Advantages of imaging with ultrasound
- Directed as a beam
- Reflected from small objects
- Non-ionizing
- Less expensive
- Real time nature

18. Disadvantage
 Propagates poorly through air
 Poor penetration(attenuation)
 Operator dependence

19. Cont.

20. Velocity
• Speed at which a sound wave travels through a
medium
• Determined by density and stiffness of media
-Slowest in air/gas
- Fastest in solids
• Average speed of ultrasound in body is 1540m/sec

21. Frequency
 Number of cycles per second
 Units are Hertz
 Ultrasound imaging frequency range 2-15Mhz

22. Low the frequency, higher the
penetration and lower the resolution
Higher the frequency, lower the
penetration and higher the resolution

23. Wavelength
 Distance over which one cycle occurs

24. Amplitude
 The strength/intensity of a sound wave at any given
time
 Represented as height of the wave
 Decreases with increasing depth

25.  Amplitude determines brightness of image
 The higher the amplitude, the brighter the image and
vice-versa

26. Principle of ultrasound
 Transducer
 Piezoelectric effect

27. Electrical energy converted to
sound waves The sound waves are reflected by
tissues
Reflected sound waves are converted to
electrical signals and later to Image

28. Image Formation
 Electrical signal produces ‘dots’ on the screen
 Brightness of the dot is proportional to the strength of
the returning echoes
 Location of the dot is determined by travel time

31. Interactions of ultrasound with tissue
• Transmission
• Reflection
• Refraction
• Scattering
• Attenuation

32. Transmission
 Not all the sound wave is reflected, some continues
deeper into the body
 These waves will reflect from deeper tissue
structures

33. Reflection
 Occurs at a boundary between 2 adjacent tissues or
media
 The amount of reflection depends on differences in
acoustic impedance (z) between media
 The ultrasound image is formed from reflected
echoes
 Acoustic impedance=density of medium x velocity

34. Refraction
 This occurs when an ultrasound beam passes at an
angle other than 90 degrees, from one tissue into
another with change in velocity
 It increase with the increasing angle of incidence
 It passes deeper into the body where it gives rise to
artifacts

36. Scattering
 Redirection of sound in several directions
 Caused by interaction with small reflector or rough
surface
 Only portion of sound wave returns to transducer

37. Attenuation
 The decrease in the intensity of the ultrasound wave
as they pass through tissues
• Results from absorption , reflection , scattering and
beam divergence

38. Low attenuationHigh attenuation
Artifacts

39. Summary

40. References
 Rumack , Diagnostic Ultrasound , Fifth Edition
 WHO Manual of Diagnostic Ultrasound
 Internet