Quantifying the benefit of elevated acoustic output in harmonic imaging
Tissue harmonic imaging (THI) has been widely used in abdominal imaging due to its significant reduction in acoustic noise compared to fundamental imaging. However, THI can be both signal-to-noise ratio (SNR) and penetration-depth limited during clinical imaging, resulting in decreased diagnostic utility. A logical approach is to increase the source pressure, but the in situ pressures used in diagnostic imaging have been subject to a de facto upper limit based upon the Food and Drug Administration (FDA) guideline for the Mechanical Index (MI < 1.9) since 1992. A recent AIUM report concluded that exceeding MI of 1.9 up to an estimated in situ value of 4.0, could be warranted without concern for increased risk of cavitation in non-fetal tissues without gas bodies. This work quantifies the benefit of elevated acoustic output in hepatic harmonic imaging. Increasing MI values were shown to be associated with increases in harmonic signal content, penetration depth, and vessel Contrast-to-noise ratio in THI images. Obese patients who suffer from poor ultrasound image quality are more likely to benefit from elevated acoustic output to enable better THI performance.
