1. Ultrasound Harmonic Imaging
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Ultrasound Harmonic Imaging
Yangmo Yoo, Ph.D
Assistant Professor
Department of Electronic Engineering
Interdisciplinary Program of Integrated Biotechnology
Medical Solutions Institute (MSI)
Sogang Institutes of Advanced Technology (SIAT)
Sogang University, Seoul, Korea

2. References Contrast and Tissue Harmonic Imaging
Refresher Courses RSNA 2003
Ultrasound contrast in general imaging research
White paper, Philips, 2007
Ultrasound contrast imaging
AAPM 2004

3. Residual Tissue Image
Originally thought to be overlap between transmit and receive spectra
Now known to be distortion produced by tissue
Long been assumed that attenuation would make harmonic energy undetectable
Tissue Harmonic Imaging has been found to
improve contrast resolution
reduce clutter
sharpen lesion borders
reduce penetration somewhat

4. Harmonic Generation
Nonlinear effects in tissue distort the sound wave as it goes through tissue
Tissue is somewhat compressible
Sound traveling through the body is a pressure wave
At the wave peaks tissue is more dense so the wave travels faster
The higher the pressure, the greater the distortion
Any change from a perfect sinusoidal wave creates harmonics

5. Nonlinear Propagation
Propagation speed increases with density (pressure)
The wave moves faster when the pressure is higher (peaks) and slower where it is lower (troughs)
Any change from a perfect sinusoid creates harmonics
The higher the amplitude, the more the effect

6. Tissue Harmonic Imaging

7. Reverberation Artifacts
Sound reflects between lungs, ribs and skin
Reflected sound is mostly fundamental
Low energy reverberations appear deeper in image as haze and clutter artifacts
They are low energy so they never develop harmonics
Receiver filters tuned at harmonic frequency remove reverberations at fo and clean up the image

8. Fundamental Processing

9. Harmonic Processing

10. Tissue Aberrations Shallow fat and skin layers distort sound beam
Distortions are low energy but send sound in random directions
Main beam generates harmonics during passage through surface layers
Distortion energy not strong enough to generate harmonics
Harmonic processing removes distortions and cleans image

11. Conventional Processing

12. Harmonic Processing

13. Clinical Benefits of THI
Reduced nearfield artifacts
Reduced haze and clutter from tough acoustic windows an d tissue aberrations
Improved border delineation and contrast resolution
Difficult to image patients addressed (!!)
Surprising since 90% or more of the scattered energy is filtered out wi th harmonic processing
Narrower beam sharpens up easy exams, but aberration reduction is main benefit

14. Tissue Harmonic Imaging
Clinical Examples
liver
liver
aorta
aorta
Conventional imaging
Tissue Harmonic Imaging

15. Clinical Examples: Left Adrenal Mass
Conventional imaging
Tissue Harmonic Imaging

16. Nonlinear Propagation—Theory
Modeled by the KZK equation
Khokhlov, Zabolotskaya, Kuznetsov (1970)
Impossible to solve, must be simulated
One field example takes hours on a high speed computer
Simulations highly accurate
Axial
Lateral

17. Tissue Harmonic Imaging Summary
Tissue harmonic imaging benefits from the nonlinear propa gation process in tissue
Harmonic beam is generated only where fundamental is str ong
Weak fundamental scattered energy does not generate mu ch harmonics
Clutter from tissue aberrations is low in harmonic content
Harmonic beam is low close to transducer where most aberrations occur

18. Nonlinear Imaging Techniques

19. Harmonic Imaging
Designed to extract nonlinear portion of returned signal
Single pulse techniques filter out fundamental, but this limits the available bandwidth
Now used only when high frame rate is essential
Scanhead / beamformer
frequency response
Transmit
frequency
Receive f o 2f
Amplitude

20. Multipulse Nonlinear Techniques
Nearly all current techniques utilize multiple pulses
Linear scattering / propagation assumes that if the transmitted signal chan ges, the same thing will happen to the received signal
Bubble and tissue nonlinearities violate that assumption
Most current nonlinear imaging modes send two or more pulses that a re different, ie. phase, magnitude, or both:
Pulse Inversion (PI) uses 2 or more inverted pulses
Power Modulation (PM) uses 2 or more pulses of different amplitudes
Contrast Pulse Sequence (CPS) combines PI and PM
The processing is designed to remove the large linear components
Whatever is left is the nonlinear component

21. Pulse Inversion Harmonic Imaging

22. Power Modulation Imaging

23. Clinical Examples: Abdominal Aortic Aneurysm
Conventional imaging
Tissue Harmonic Imaging

24. Tissue Harmonic Imaging
Clinical Examples
Conventional imaging
Tissue Harmonic Imaging

25. Contrast Imaging Techniques

26. Alphabet Soup of Contrast
Harmonic Imaging (HI)
Octave Imaging (OI)
Harmonic Power Doppler (HPD)
Pulse Inversion Doppler (PID)
Native Harmonic Imaging (NHI)
Power Pulse Inversion (PPI)
Power Harmonic Imaging (PHI)
Phase Inversion Imaging (PI)
Loss of Correlation Imaging (LOC)
Ensemble Harmonic Imaging (EHI)
Harmonic Power Angio (HPA)
Power Modulation Imaging (PMI)
Stimulated Acoustic Emission (SAE)
Coherent Contrast Imaging (CCI)
Pulse Inversion Harmonics (PIH)
Coded Harmonics (CH)
Ultraharmonic Imaging (UI)
Agent Detection Imaging (ADI)
Subharmonic Imaging (SI)
Coded Harmonic Angio (CHA)
Contrast Pulse Sequence (CPS)
Contrast Specific Imaging (CSI)
How could this possibly be confusing?

27. Contrast Imaging
Two primary characteristics of bubbles used to differentiate them from tissue:
Destroyed by ultrasound at normal MI—tissue is not
Produce harmonics at low MI— tissue produces very little
Led to two primary imaging modes:
High MI destruction techniques
Low MI real-time techniques
High MI
Low MI
Courtesy N. deJong, Erasmus University

28. Contrast Imaging Techniques

29. High MI Imaging Bubbles are destroyed by ultrasound
Contrast is imaged by detecting change between pulses
No need to change pulses, the ultrasound changes the bubbles but not the tissue
Best results obtained at highest MI
Interval delay scanning required
Inject contrast
Wait (time depending on agent, application)
Sweep through volume of interest or watch veil as agent is destroyed
Freeze and examine cineloop of data
Animation adapted from Dr K Ferrara,UC Davis.
Becher H and Burns PN, Handbook of contrast
Echocardiography, Springer 2000,

30. High MI Pulse Inversion Imaging
baseline
contrast
Multiple liver masses: Late phase scanning with Levovist
Courtesy of Dr. Stephanie Wilson and Dr. Peter Burns

31. Harmonic Power Doppler - ADI
Metastasis (from colorectal) – Levovist, high MI
Courtesy Dr. E. Leen, Royal Infirmary, Glasgow, UK

32. Harmonic Power Doppler - ADI
Metastasis (from colorectal) – Levovist, high MI
Courtesy Dr. E. Leen, Royal Infirmary, Glasgow, UK

33. Low MI for Real-time Contrast Imaging
High MI techniques have high sensitivity but are short live d and difficult to use
Tissue harmonic component competes with bubble signals
Low MI does not destroy bubbles, prolonging useful time
Low MI reduces THI (tissue is removed)
Does not require interval delay or sweeping
Low MI challenging to implement due to low excitation use d
Has taken several years to fully understand and to optimize for diff erent agents

34. Clinical Example Hemangioma
Courtesy Dr. Wermke, Charite, Berlin

35. Low MI Techniques, cont.
Most low MI techniques also work for high MI, but must be optimized differently
eg. Pulse Inversion extracts harmonic well at low MI, but also dete cts pulse-to-pulse differences at high MI
Internal system settings are different for low vs high MI
Turning up the power on a low MI setting will not work as well at h igh MI as one that is optimized for high MI by the manufacturer
Turning down the power on a high MI setting probably won’t work at all at low MI

36. Multipulse Color Overlay Methods
Low MI Grayscale shows little tissue for localization
Additional pulses reduce motion artifacts
Color overlay methods provide tissue background and contrast overlay
Allows independent optimization for contrast and tissue
Allows visualizing tissue and contrast separately
Most imaging modes can be made into overlay modes
eg. Power Pulse Inversion is extension of Pulse Inversion

37. Power Pulse Inversion

38. Clinical Example Renal perfusion

39. Contrast Quantification
Contrast destruction provides method for perfusion quantification
Destroy contrast with high MI frame
Replenishment rate gives indication of microvascular flow rate

40. Flash Contrast Imaging

41. Tumor Flow Quantification Anti-vascular Therapy

42. Contrast Replenishment Curves

43. Harmonic Imaging—Bubbles vs Tissue
In Tissue Harmonic Imaging (THI) the 2nd harmonic component is the result of nonlinear propagation in tissue, then linear scattering from tissue
In contrast agent applications the 2nd harmonic component is the result of nonlinear scattering from the microbubbles after linear propagation through tissue

44. Contrast Imaging Summary
Imaging techniques based on 2 bubble properties: transient nature, nonlinearity
Imaging techniques divided into two groups:
High MI: very sensitive, but transient
Low MI: less sensitive, but real-time
Multipulse schemes eliminate linear signals, detect nonlinear signals
Perfusion is quantified with the destruction-replenishment technique
Image processing techniques like MVI further increase sensitivity
The challenge is to maximize the nonlinear signals while using very small driving amplitudes