Ultrasound backscatter from blood in the 30 to 70 MHz frequency range

New intravascular ultrasound imaging methods for the visualization of the vascular wall and plaque at frequencies greater than 20 MHz must overcome the obscuring influence of backscatter from blood. This effect can reduce the contrast between the vessel lumen and soft plaque or media adversely affecting the diagnosis. We have extended the approach developed by de Kroon at the Thorax Centre, Rotterdam to study backscatter from blood in the frequency range from 30 to 70 MHz. At a frequency of 35 MHz the transition from low shear stress to high shear stress was accompanied by a reduction of 14.3 dB in the backscatter coefficient. However at 70 MHz this transition resulted in only a 2.9 dB reduction in backscatter coefficient. This is consistent with a breakdown in the Rayleigh scattering assumption. Details of the viscometer design are described and quantitative comparisons of backscatter from blood as a function of shear rate are made to previously measured backscatter properties of media, adventitia, and plaque