Ultrasonic Nonlinear Imaging- Tissue Harmonic Imaging

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.

Tissue Harmonic Imaging Methods to improve image quality: –Different acoustic window. –Lower frequency. –Adaptive imaging. –Non-linear imaging (or harmonic imaging).

Sound Velocity and Density Change Finite Amplitude Distortion Phase velocity Nonlinearity Particle velocity

When Peak Pressure Is Very High Shock Wave

Non-linear Parameter B/A B/A defines non-linearity of the medium. The larger the B/A, the higher the non- linear response.

B/A Parameters: Typical Values Typical values: –Water:5.5+/-0.3. –Liver: –Fat: –Muscle: 7.5. B/A imaging may be used for tissue characterization.

Nonlinear Propagation transducer

Reduction of Imaging Artifacts

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.

Non-linear Propagation: Numerical Analysis (1) The frequency domain solution to Burgers’ equation: where  1+B/(2A).

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

Non-linear Propagation: Numerical Analysis (2) KZK equation: diffractionloss quadratic nonlinearity

Characteristics in Tissue

Non-Linear Propagation

One way Two way

Non-Linear Propagation

Nonlinear Propagation with Tissue Inhomogeneities

Sidelobe Reduction in Inhomogeneous Tissue

Requisite Field Amplitude

Increasing Harmonic Generation by Multiple Transmit Focusing

Harmonic Generation and Multiple Transmit Focusing

Pulse Bandwidth and Spectral Leakage

Axial Resolution vs. Harmonic Separation

Harmonic Leakage and Image Quality Degradation

Harmonic Leakage and Pulse Types

Harmonic Leakage and Bandwidth

Harmonic Leakage and Tissue Inhomogeneities

Harmonic Leakage from System Nonlinearity

Harmonic Leakage and Pulse Inversion

Motion Artifacts in Pulse Inversion Imaging

Axial Motion

Lateral Motion

Motion Artifacts

Motion Compensation

It is relatively easy to compensate for axial motion, but how about lateral and elevational motion?

Higher Order Nonlinear Imaging (Higher Order  Higher Harmonic)

Amplitude-Encoded Pulse Sequence For a point target:

Amplitude-Encoded Pulse Sequence

Spectral Convolution

Phase-Encoded Pulse Sequence 2-pulse 3-pulse

More Clinical Examples

Clinical Examples (1)

Clinical Examples (2)

Clinical Examples (3)