Contrast biases the autocorrelation phase shift estimation in Doppler tissue imaging

Area of Science:

• Cardiovascular Imaging
• Biomedical Ultrasound Engineering

Background:

• Doppler tissue imaging (DTI) is crucial for assessing regional myocardial function.
• Image quality and border delineation challenges in DTI often necessitate ultrasound contrast agents (UCAs).
• Understanding UCA effects on DTI is vital for accurate myocardial motion interpretation.

Purpose of the Study:

• To investigate how UCA signal contribution and nonlinear wave propagation affect DTI velocity estimation.
• To evaluate the impact of UCA destruction on DTI measurements.

Main Methods:

• Model experiments using a clinical 2-D grayscale scanner.
• Computational simulations of DTI velocity estimators with synthetic pulses and bubble echoes.
• Analysis of experimentally-sampled RF data of transmitted and backscattered contrast echoes.

Main Results:

• UCA destruction causes bidirectional velocity bias in individual estimates.
• Spatial averaging of DTI measurements with UCA results in a negative velocity bias.
• UCA destruction significantly impacts integrated mean velocity over time (displacement).

Conclusions:

• Performing DTI with UCAs at low acoustic power (Mechanical Index <= 0.3) minimizes bubble rupture effects.
• Employing a 'Flash imaging'-like destruction burst before each Doppler pulse package can clear the area of microbubbles.
• These strategies enhance visualization and ensure accurate DTI measurements when using UCAs.