Tissue Harmonic Imaging
Tissue Harmonic Imaging 1
• Performance of ultrasound has been sub-
optimal on technically difficult bodies.
• Most recent new developments have bigger
impact on technically satisfactory bodies.
• Poor image quality leads to uncertainty in
diagnosis and costly repeat examinations.
Tissue Harmonic Imaging 2
• Methods to improve image quality:
– Different acoustic window.
– Lower frequency.
– Adaptive imaging.
– Non-linear imaging (or harmonic imaging).
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Origin of Tissue Non-linearity
• Finite amplitude distortion: peaks of the
waveform travels faster than the troughs.
Tissue Harmonic Imaging 4
• Tissue harmonics are virtually zero at the
probe face.The intensity continues to
increase until attenuation dominates.
• The higher the intensity is, the more tissue
harmonics are generated.
• Such a mechanism automatically increase
the difference between signal and acoustic
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Advantages of Tissue Harmonic
• Low sidelobes.
• Better spatial resolution compared to
fundamental imaging at the original
• Less affected by tissue inhomogeneities –
better performance on technically difficult
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Non-linear Parameter B/A
P 1 2P
0 2 0 2
s; 0 2 s ;
0 B 0
P P0 A
• B/A defines non-linearity of the medium.
The larger the B/A, the higher the non-
Tissue Harmonic Imaging 7
B/A Parameters: Measurements
• Finite amplitude method:
– B/A is related to the second harmonic
generation. Thus, it can be found by relating the
signal amplitude at the fundamental frequency
to the second harmonic component.
• Thermodynamic method:
– The B/A value is determined by measuring the
change of sound speed with pressure and
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B/A Parameters: Typical Values
• Typical values:
– Liver: 7.23.
– Fat: 10.9.
– Muscle: 7.5.
• Results from both methods have excellent
• B/A imaging may be used for tissue
Tissue Harmonic Imaging 9
• The frequency domain solution to Burgers’
un ( z z; i ) un ( z z; i ) j
n 1 N
( kuk ( z z; i)un k ( z z; i ) nuk ( z z; i )u*k n ( z z; i))
k 1 k n
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Wave at distance z
Nonlinear Burgers’ equation
propagation at z+z
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Reduction of Imaging Artifacts
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Reduction of Imaging Artifacts
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• Similarities to contrast imaging:
– Minimal harmonics on transmit.
– Maximal fundamental suppression on receive.
– Configurable beamformer.
– Wide transducer and system bandwidths.
– Alternate phasing and pulse inversion may both
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• Differences from contrast imaging:
– High harmonic generation during propagation,
i.e. high fundamental amplitude through a large
depth of field.
– The fundamental amplitude must not exceed
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• In contrast imaging, in which the tissue
harmonic signals are un-desirable, the
amplitude of the propagating wave needs to
• Large apertures (smaller f-numbers) may be
• It was reported that tissue harmonic signal
can be reduced by 3dB by doubling the
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• Harmonic cancellation system: non-linear
propagation is reduced by using a new
signal at the harmonic frequency.
• Phase and magnitude of the signal may be
pre-calculated, but on-line adjustment is
• Due to attenuation, optimal effects may
only be achieved locally.
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