During his 46-year Illinois ECE faculty career, William D O'Brien, Jr. has conducted pioneering research that enhances the imaging safety of ultrasound for expectant mothers and their babies. He has also compiled a formidable body of work on applying quantitative ultrasound to diagnosing fatty liver disease and improving the ability to determine the risk of pre-term births. On December 1, 2021, he will receive the Acoustical Society of America (ASA) Silver Medal in Biomedical Acoustics for contributions to ultrasound bioeffects, dosimetry, and quantitative tissue characterization. The Silver Medal is the highest research award in medical and biomedical acoustics conferred by ASA.