In-Vivo Real-Time Contrast-Free Ultrasonic Blood Flow Velocity Profile Measurement

Recently, Ultrasonic Perpendicular Velocimetry (UPV) based algorithms, as opposed to commonly used Doppler technique (Figure 1), were applied to Radio Frequency (RF)-data acquired in an in-vitro setup [1,3]. Thus, the estimation of velocity components perpendicularly to the ultrasound beam and the simultaneous and accurate assessment of wall position and axial velocity profiles were made feasible. By integrating the measured velocity profile an accurate flow estimation was made possible. Furthermore, the ratio between the changes in flow Q(t) and the changes in cross-sectional area of the vessel A(t) was found to offer an accurate estimation of the local Pulse Wave Velocity (PWV). By combining the PWV with the diameter waveform, accurate local pressure estimation was obtained indicating that a non-invasive pressure assessment by means of ultrasound is feasible [3]. However, the abovementioned method is time consuming due to the data size and the post-processing procedure required. Additionally, the Fast Fourier Transform (FFT) on Butterworth Band Pass Filters (BPF) for vessel’s wall removal requires contrast agents dispersion in the fluid for the application of UPV. A real-time approach, of the previously described techniques, was applied [2] in-vitro using a Blood Mimicking Fluid (BMF), as contrast agent, resembling the rheological (shear thinning) and acoustical (backscattering) properties of blood and ex-vivo using BMF or contrast-free real blood implementing Wavelet Transform (WT) filtering. The use of a Graphics Processing Unit (GPU) [4], succeeded in considerable acceleration and WT [5] filtering on the rough RF-data, in improvement of the discrimination between reflections from the vessel wall and scattering from small particles. In this research the method is extended to include in-vivo measurements.