Quantitative Assessment of the Magnitude, Impact and Spatial Extent of Ultrasonic Clutter

Abstract

Clutter is a noise artifact in ultrasound images that appears as diffuse echoes overlying signals of interest. It is most easily observed in anechoic or hypoechoic regions, such as in cysts, blood vessels, amniotic fluid, and urine-filled bladders. Clutter often obscures targets of interest and complicates anatomical measurements. An analytical expression that characterizes the extent to which clutter degrades lesion contrast was derived and compared to the measured contrast loss due to clutter in a bladder phantom. Simulation and phantom studies were performed to determine ideal and achievable signal-to-clutter ratios. In vivo clutter magnitudes were quantified in simultaneously-acquired fundamental and harmonic bladder images from five volunteers. Clutter magnitudes ranged from −30 dB to 0 dB, relative to the mean signal of the bladder wall. For this range of clutter magnitudes, the analytical expression predicts a contrast loss of 0–45 dB for lesions with clutter-free contrasts of 6–48 dB. A pixel-wise comparison of simultaneously-acquired fundamental and harmonic bladder images from each volunteer revealed an overall signal reduction in harmonic images, with average reductions ranging from 11–18 dB in the bladder interior and 9–11 dB in the tissue surrounding the bladder. Harmonic imaging did not reduce clutter in all volunteers.