Impact of Elevational Aperture Blockage on Ultrasound Attenuation Imaging for Liver Fat Quantification

Acoustic attenuation imaging provides quantitative measurement to support definitive diagnosis for liver steatosis assessment. When estimating tissue acoustic attenuation coefficient, several system factors such as the beam diffraction pattern must be compensated by reference calibration. This study examines the impact of elevational aperture blockage, which distorts beam patterns, on acoustic attenuation imaging. Simulations were performed using the Philips curved array transducer C5-1 and simulated abdominal phantoms with known attenuation coefficients of 0.56 dB/cm/MHz and 0.90 dB/cm/MHz. Elevational aperture blockage levels of 10%, 30%, and 40% were modeled, revealing increasing biases in attenuation coefficient estimation with blockage levels. For the 0.56 dB/cm/MHz phantom, relative biases in overestimation averaged around the focal depth (3.0 to 6.5 cm) were 8.5%, 27%, and 36%, while for the 0.90 dB/cm/MHz phantom, relative biases were 5.3%, 16.7%, and 22.3%, for 10%, 30%, and 40% blockage levels, respectively. Phantom experiments using a C5-1, and a micro-convex transducer mC7-2, and a credit card with an open slot confirmed similar trends. These findings highlight the importance of minimizing elevational blockage, especially in patients with narrow intercostal spaces. Furthermore, using smaller aperture probes and optimized positioning techniques can help mitigate these effects of elevational blockages.