BLOOD NOISE-REDUCTION IN INTRAVASCULAR ULTRASOUND IMAGING

Scattering from red blood cells (blood noise) increases significantly as the ultrasound frequency is increased above 10 MHz. This reduces th e contrast between the vessel wall and the lumen in intravascular ultr asound imaging which makes it difficult to localize the vessel wall an d plaque. A blood noise filter based on beam tilting and digital later al low pass filtering is described. Beam tilting introduces a Doppler shift from blood which results in a frequency separation of the vessel wall signal and the blood noise. The performance of the filter is inv estigated by simulations and by in vitro experiments. The filter is fo und to be effective for blood velocities exceeding approximately 50 cm s(-1) at a 20 MHz ultrasound frequency with a beam tilt angle of 10 d egrees and a frame rate of 15 f.p.s. By increasing the system frequenc y to 40 MHz, increase the beam tilt angle to 15 degrees and reduce the frame rate to 10 f.p.s., the fitter is effective for blood velocities below 10 cm s(-1).