Magnitude, origins, and reduction of abdominal ultrasonic clutter

Clutter is a noise artifact in ultrasound images, arising from multiple sources. Experiments were conducted with urine-filled in vivo bladders to differentiate among various clutter sources. Successive-frame image acquisitions with varying transmit PRFs were used to determine the clutter contributions from echoes of previously sent pulses and random electronic and/or acoustic noise. Images acquired during axial displacement of the abdominal wall were assessed to distinguish clutter due to near-field reverberation from clutter due to off-axis scattering. The results indicate that clutter contributions from random noise and echoes of previously sent pulses are weak, while clutter arising from sound reverberation in abdominal tissues are dominant distal to the abdominal wall. Clutter adjacent to the distal and lateral bladder walls is mainly due to off-axis scattering. Clutter was reduced in fundamental and harmonic bladder images by applying Finite Impulse Response (FIR) and Blind Source Separation (BSS) motion filters to images acquired during axial displacement of the abdominal wall.