Ultrasound Harmonic Imaging We deliver a SOLUTION for your needs !!! 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

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

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

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

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

Tissue Harmonic Imaging

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

Fundamental Processing

Harmonic Processing

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

Conventional Processing

Harmonic Processing

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

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

Clinical Examples: Left Adrenal Mass Conventional imaging Tissue Harmonic Imaging

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

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

Nonlinear Imaging Techniques

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

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

Pulse Inversion Harmonic Imaging

Power Modulation Imaging

Clinical Examples: Abdominal Aortic Aneurysm Conventional imaging Tissue Harmonic Imaging

Tissue Harmonic Imaging Clinical Examples Conventional imaging Tissue Harmonic Imaging

Contrast Imaging Techniques

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?

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

Contrast Imaging Techniques

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,

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

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

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

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

Clinical Example Hemangioma Courtesy Dr. Wermke, Charite, Berlin

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

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

Power Pulse Inversion

Clinical Example Renal perfusion

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

Flash Contrast Imaging

Tumor Flow Quantification Anti-vascular Therapy

Contrast Replenishment Curves

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

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