Helping material for learning TEE

1. Ultrasound Physics in
the Operating Room
Tamas Seres, M.D.
UC Denver
2012

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. Piezoelectric Crystal

4. Piezoelectric Crystal as a Sender

5. Piezoelectric Crystal as a Receiver

6. Propagation of the Sound

7. Sound is a traveling variation of acustic variables.
Acustic variables: particle motion, density and pressure.

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. 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. 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. Decibel Scale of Sound

12. Amplitude Change in dB and %

13. Propagation Velocity, Frequency and
Wavelength
c=fxλ
c= m/s, mm/µs
λ = mm
f = cycles/s (Hz), cycles/µs (MHz)

14. Propagation velocity of US in
different 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 4
C (human soft tissue) = 1540 m/s or 1.54 mm/µs

15. Frequency and Wavelength

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. Air Bubbles in the Blood during TMR

18. Ultrasound Pulses

19. Ultrasound Pulses

20. Ultrasound Pulse

21. Ultrasound Pulse

22. Ultrasound Pulse

23. Ultrasound Pulse

24. Ultrasound Pulse

25. Axial Resolution
For better reflection from a particle: particle diameter > λ
For axial resolution: Pulse Length/2 < Distance between 2 particles

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. Impedance
Acoustic Impedance
Body 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. Reflection
Z transducer >>> Z air <<<<Z tissue

29. Transmission
Z transducer = Z jelly = Z tissue

30. Reflection
Z tissue <<< Z needle

31. Reflection
IRC = Intensity Reflection Coefficient

32. Refraction

33. Refraction

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.

36. Air Bubbles in the Blood during TMR

37. 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.

38. Attenuation

39. Amplitude Change in dB and %

40. Attenuation
Attenuation Coefficient
Body 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

41. 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

42. Attenuation

44. US: 7.2 MHz

45. US: 5 MHz

46. US: 3.5 MHz

47. END