Non-linear acoustics in Ultrasound Imaging

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Non-linear acoustics in Ultrasound Imaging

• Hans Torp
• Department of Physiology and Biomedical
  Engineering
• NTNU
• Norway

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Non-linear acoustics in Ultrasound Imaging
Transducer
Nonlinear propagation
nonlinear scattering
object
Body wall
3
Nonlinear propagation
Transmitted pulse
Pulse after 6cm propagation
frequency
frequency
fo 2fo 3fo
fo 2fo 3fo
4
Received signal is filtered by1. transducer2.
Frequency dependent attenuation
5
Measured RF- spectrumFrequency range 1- 4 MHz
Signal from ventricular septum
Noise from LV cavity
6
Fundamental and second harmonic signal separated
by filter
450
Fundamental
2. harmonic
Signal from septum
Noise from LV cavity
7
Water tank experiment
2nd Harmonic
Full band
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Second harmonic imagingReverberation noise is
suppressed
80
60
40
20
0
-20
0
1
2
3
4
5
6
x 10
Frequency
2.harmonic Bmode imaging ftx1.7 MHz, frx3.4 MHz
Conventional Bmode imaging ftx3.4 MHz, frx3.4
MHz
Signal
Noise
9
Cardiac examples 3.5 MHz probe
Fundamental
Octave
10
Cardiac examples 5 MHz probe
Octave
Fundamental
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Cardiac examples 5 MHz probe
Fundamental
Octave
12
Brain - neonatal 5 MHz probe
Fundamental
Octave
13
Brain - 18 week fetus 5 MHz probe
Fundamental
Octave
14
Brain - 18 week fetus 5 MHz probe
Fundamental
Octave
15
Summary

• Harmonic distortion by wavepropagation is
  significant in medical ultrasound
• Acoustical noise is suppressed by filtering out
  the 2. Harm. Component
• Carefull pulse design to obtain short pulse with
  low 2. Harm. Content
• Improved elevation focusing is observed