Improving Nonlinearity Parameter Imaging Using Compounding

Ultrasound is an imaging modality widely used for clinical applications such as disease diagnosing and tissue characterization. The quality of ultrasound images is generally restricted by speckle noise, which degrades the quality of not only conventional ultrasonographic imaging but also novel quantitative ultrasound techniques. In this work, we used both frequency and spatial plane wave compounding to improve the quality of nonlinearity parameter (B/A) imaging. In silico backscattered echo data were acquired by simulating a linear array transducer and a media excited with a 5 MHz pulse at two excitation peak pressures, 80 kPa and 400 kPa. A nonuniform nonlinear simulated media was composed of an 18-mm diameter circular inclusion (with B/A=11) in an otherwise uniform background (with B/A = 6). Using plane wave compounding with 21 plane waves allowed reducing the standard deviation of the resulting B/A images by a factor of 2 when compared to a single plane wave transmission sequence. This can be further improved to a threefold reduction when plane wave compounding is combined with frequency compounding. The results show how spatial plane wave and frequency compounding methods improve contrast and background smoothing when the B/A is estimated. Clinical Relevance- Ultrasonic tissue characterization could be improved by the estimation of the nonlinearity parameter (B/A), a source of contrast in ultrasonic imaging, with a novel pulse-echo approach called the depletion method. However, B/A images suffer from low signal-to-noise ratios. Using a combination of spatial and frequential compounding, the quality of B/A images using a depletion method is significantly improved, with potential to be used in commonly available clinical scanners.