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Published byBritney Johnson Modified over 9 years ago
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Ultrasonic Nonlinear Imaging- Tissue Harmonic Imaging
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Tissue Nonlinear Imaging Imaging based on nonlinear propagation in tissue. Motivation: –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.
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Tissue Harmonic Imaging Methods to improve image quality: –Different acoustic window. –Lower frequency. –Adaptive imaging. –Non-linear imaging (or harmonic imaging).
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Sound Velocity and Density Change Finite Amplitude Distortion Phase velocity Nonlinearity Particle velocity
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When Peak Pressure Is Very High Shock Wave
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Non-linear Parameter B/A B/A defines non-linearity of the medium. The larger the B/A, the higher the non- linear response.
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B/A Parameters: Typical Values Typical values: –Water:5.5+/-0.3. –Liver: 7.23. –Fat: 10.9. –Muscle: 7.5. B/A imaging may be used for tissue characterization.
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Nonlinear Propagation transducer
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Reduction of Imaging Artifacts
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Advantages of Tissue Harmonic Imaging Low sidelobes. Better spatial resolution compared to fundamental imaging at the original frequency. Less affected by tissue inhomogeneities – better performance on technically difficult bodies.
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Non-linear Propagation: Numerical Analysis (1) The frequency domain solution to Burgers’ equation: where 1+B/(2A).
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Non-linear Propagation Wave at distance z Linear propagation to z+ z Nonlinear propagation at z+ z angular spectrum method frequency domain solution to Burgers’ equation
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Non-linear Propagation: Numerical Analysis (2) KZK equation: diffractionloss quadratic nonlinearity
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Characteristics in Tissue
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Non-Linear Propagation
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One way Two way
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Non-Linear Propagation
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Nonlinear Propagation with Tissue Inhomogeneities
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Sidelobe Reduction in Inhomogeneous Tissue
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Requisite Field Amplitude
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Increasing Harmonic Generation by Multiple Transmit Focusing
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Harmonic Generation and Multiple Transmit Focusing
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Pulse Bandwidth and Spectral Leakage
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Axial Resolution vs. Harmonic Separation
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Harmonic Leakage and Image Quality Degradation
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Harmonic Leakage and Pulse Types
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Harmonic Leakage and Bandwidth
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Harmonic Leakage and Tissue Inhomogeneities
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Harmonic Leakage from System Nonlinearity
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Harmonic Leakage and Pulse Inversion
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Motion Artifacts in Pulse Inversion Imaging
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Axial Motion
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Lateral Motion
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Motion Artifacts
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Motion Compensation
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It is relatively easy to compensate for axial motion, but how about lateral and elevational motion?
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Higher Order Nonlinear Imaging (Higher Order Higher Harmonic)
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Amplitude-Encoded Pulse Sequence For a point target:
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Amplitude-Encoded Pulse Sequence
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Spectral Convolution
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Phase-Encoded Pulse Sequence 2-pulse 3-pulse
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More Clinical Examples
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Clinical Examples (1)
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Clinical Examples (2)
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Clinical Examples (3)
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