# Principles of Ultrasound Physics.pptx

3 de Jan de 2023

### Principles of Ultrasound Physics.pptx

1. Principles of Ultrasound Physics (Basics) Abel Girma (RR)
2. Objectives : ▪ After completing this presentation, the learner will be able to: 1. Explain the fundamental principle used in sonographic imaging 2. Describe the image formats used in sonography 3. Describe how echoes are generated 4. List the primary components of a sonographic transducer 5. List the primary components of a sonographic instrument 6. Describe the Doppler effect 7. List the ways in which Doppler information is
3. Introduction: Medical imaging with ultrasound is called sonog
4. What is Sound ? • Mechanical and Longitudinal waves wave that can transfer a distance using a media. • Cannot travel throughVacuum.
5. What is Ultrasound? • Ultrasound is amechanical,longitudinal wave with a frequency exceeding the upper limit of human hearing, which is 20,000 Hz or 20 kHz. • T ypically at 2 – 20 Mhz.
6. Characteristics of Sound
7. Veloci ty • Speed at which a sound wave travels through a medium(cm/sec) • Determined by density and stiffness of media – Slowest in air/gas – Fastest in solids • Average speed ofultrasound in body is 1540m/sec
8. Frequency • Number of cycles per second • Units are Hertz • Ultrasound imaging frequency range 2-20Mhz • Higher the frequency Lower the penetration and Higher the resolution.
9. Wavelength… Distance over which one cycle occurs
10. Wave Equation.. • Given a constant velocity ,as frequency increases wavelength decreases V = ƒ λ
11. Amplitude Defines the Brightness of the image Irrespective ofthe Freq theAmp remains constant The Higher the Amp the brighter the image and the lower the more
12. Acoustic Impedance (Z) • The product of the tissue’s density and the sound velocity within the tissue • Amplitude of returning echo is proportional to the difference in acoustic impedance between the two tissues • Velocities: – Soft tissues = 1400-1600m/sec – Bone = 4080 – Air = 330 • Thus, when an ultrasound beam encounters two regions of very different acoustic impedances, the beam is reflected or absorbed – Cannot penetrate – Example:soft tissue – bone interface
13. Gain ….
14. How ultrasound Works… • Ultrasound transducer produces “pulses”of ultrasound waves • These waves travel within the body and interactwith various tissues • The reflected waves return to the transducer and are processed by the ultrasound machine • An image which represents these reflections is formed on the
15. Pulse- Echo Principle
16. Ultrasound ?
17. Interactions of Ultrasound with tissue • Reflectio n • Transmis sion • Attenuat ion
18. Reflectio n – – • O ccurs 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 Transdu cer Z =Density x Velocity
19. Scatteri ng • • • Redirection of sound in several directions Caused by interaction with small reflector or rough surface O nly portion of sound wave returns to transducer
20. • N ot all the sound wave is reflected,some continues deeper into the body • These waves will reflect from deeper tissue structures Transdu cer Transmiss ion
21. • The deeper the wave travels in the body , the weaker it becomes • The amplitude ofthe wave decreases with increasing depth Attenuat ion
22. Attenuation…
23. Ultrasound range ..
24. Refraction:
25. Refraction in action
26. Echogenicity (caused by Reflection) Anechoi c Hypoechoic Hyp erechoic
27. Time Gain Compensation (Post Processing) • The Returned signal is amplified for better imaging at depths. TGC too low far field TGC corrected
28. Knobology…
29. Probe Orientation…
30. Imaging Planes Transverse or Axial Longitudinal or Sagittal Coronal
31. Transducers…
32. Reflection
33. Doppler… ▪ Apparent change in received frequency due to a relative motion between a sound source and sound receiver – SoundTOWARD receiver = increased frequency – Sound AWAY from receiver = Decreased frequency
34. Cos of 0 degree is 1 and cos of 90 degree is 0
35. Doppler information is presented in d/t forms • audible, • Color-Doppler, • Spectral-Doppler forms. Types of Doppler: CW (Continuous Wave) PW (PulsedWave)
36. What is Colour Doppler? ▪ Utilizes pulse-echo Doppler flow principles to generate a color image ▪ This image is superimposed on the 2D image ▪ The red and blue display provides information regarding DIRECTION andVELOCITY of flow ▪ Regardless of colour ,the top of the bar represents flow coming towards the transducer and the bottom of the bar represents flow awayfrom the transducer
37. Ultrasound artifact