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# Ultrasound physics in the operating room I 972012

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### Ultrasound physics in the operating room I 972012

1. 1. Ultrasound Physics inthe Operating Room Tamas Seres, M.D. UC Denver 2012
2. 2. Ultrasound Ultrasound (US) represents a mechanical pressure disturbance propagating as wave through materials dense enough to transmit the fast oscillations imparted on molecules. 2-12 MHz in medical practice.
3. 3. Piezoelectric Crystal
4. 4. Piezoelectric Crystal as a Sender
5. 5. Piezoelectric Crystal as a Receiver
6. 6. Propagation of the Sound
7. 7. Sound is a traveling variation of acustic variables.Acustic variables: particle motion, density and pressure.
8. 8. Description of US waves Amplitude - decibels (dB) Frequency (f) - Cycles/sec – Hz Wavelength (λ) - mm Velocity of propagation (c)- depends on each carrying medium - approximately 1540 m/s in blood and soft tissue
9. 9. Amplitude of the Sound Amplitude: the difference between the reference value (1x10-12 W/m2 ) and the maximum value of an acoustic variable (dB). Sound scale:  0 dB hearing treashold  130 dB painful
10. 10. Amplitude Decibels (dB) are logarithmic units based on a ratio of the measured value V of acoustic pressure to a reference value R ((1*10-12 W/m2) : dB = 20 log (V/R) For example: ratio of 2 20 x log 2 = 20 x 0.3 = 6 dB Ratio of 1000 = 60 dB
11. 11. Decibel Scale of Sound
12. 12. Amplitude Change in dB and %
13. 13. Propagation Velocity, Frequency and Wavelength c=fxλ c= m/s, mm/µs λ = mm f = cycles/s (Hz), cycles/µs (MHz)
14. 14. Propagation velocity of US indifferent tissues (m/s or mm/µs ) m/s mm/µs Air 330 0.33 Lung 500 0.5 Fat 1450 1.45 Soft tissue 1540 1.54 Bone 4000 4C (human soft tissue) = 1540 m/s or 1.54 mm/µs
15. 15. Frequency and Wavelength
16. 16. Propagation Velocity, Frequency and Wavelength c=λxf λ (mm) = 1.54 (mm/µs)/ f (cycles/µs) f = 5 MHz λ= 0.3 mm f = 7.5 MHz λ= 0.2 mm
17. 17. Air Bubbles in the Blood during TMR
18. 18. Ultrasound Pulses
19. 19. Ultrasound Pulses
20. 20. Ultrasound Pulse
21. 21. Ultrasound Pulse
22. 22. Ultrasound Pulse
23. 23. Ultrasound Pulse
24. 24. Ultrasound Pulse
25. 25. Axial ResolutionFor better reflection from a particle: particle diameter > λFor axial resolution: Pulse Length/2 < Distance between 2 particles
26. 26. Impedance Impedance is the acoustic resistance to sound traveling through a medium (Z). Units: RAYL Characteristic of the medium only. Z=density(kg/m3) x propagation speed(m/s)
27. 27. Impedance Acoustic ImpedanceBody Tissue (106 Rayls) Air 0.0004 Lung 0.18 Fat 1.34 Liver 1.65 Blood 1.65 Kidney 1.63 Muscle 1.71 Bone 7.8
28. 28. ReflectionZ transducer >>> Z air <<<<Z tissue
29. 29. TransmissionZ transducer = Z jelly = Z tissue
30. 30. Reflection Z tissue <<< Z needle
31. 31. ReflectionIRC = Intensity Reflection Coefficient
32. 32. Refraction
33. 33. Refraction
34. 34. Ultrasound in the Human Body Can be oriented like beams. Follow the physical laws of reflection, refraction and scattering. Propagate freely in liquids, but very poorly through air.
35. 35. Air Bubbles in the Blood during TMR
36. 36. Attenuation As US penetrates into the body, signal strength is attenuated due to absorption of the US energy by conversion to heat, as well as by reflection and scattering.
37. 37. Attenuation
38. 38. Amplitude Change in dB and %
39. 39. Attenuation Attenuation CoefficientBody Tissue (dB/cm at 1MHz) Water 0.002 Blood 0.18 Fat 0.63 Liver 0.5-0.94 Kidney 1.0 Muscle 1.3-3.3 Bone 5.0
40. 40. Half-power distances for a frequency of 2 MHz Water 380 cm Blood 15 cm Soft tissue 1-5 cm Muscle 0.6-1 cm Bone 0.2-0.7 cm Air 0.08 cm Lung 0.05 cm
41. 41. Attenuation
42. 42. US: 7.2 MHz
43. 43. US: 5 MHz
44. 44. US: 3.5 MHz
45. 45. END