Volumetric blood flow velocity measurement with multigate pulsed Doppler system using single-channel RF sampling

Presents the performances of a new Doppler system using single channel RF sampling. The conventional quadrature method in Doppler imaging system has to use a minimum of two identical parallel demodulation channels to reconstruct the multigate analytic Doppler signal. However, this system suffers from hardware complexity and the problem of unbalance (gain and phase) between the channels. In order to reduce these problems, the authors realize a multigate pulsed Doppler system using undersampling on a single channel. It requires a sampling frequency at 4f_a and a 12 bits A/D converter. The proposed “Single-Channel RF Sampling” method aims to decrease the required sampling frequency proportionally to 4f_a/(2k+1). To show the influence of the factor k on the measurements, the authors compare the velocity profiles obtained in vitro and in vivo for different intersequence delay times (k=0 to 10). The authors have used a 4 MHz center frequency transducer. For experiments in vitro, on a phantom Doppler system, axial and volumetric velocity profiles in the vessel have been computed according to factor k and have been compared. The influence of the angle between the ultrasonic beam and the flow axis direction, and of the fluid viscosity on the velocity profiles obtained for different values of k factor is presented. For experiments in vivo on the carotid, the authors used a data acquisition system with a sampling frequency of 500 kHz and a dynamic range of 12 bits. The authors compare axial velocity profiles in systolic and diastolic phases obtained for different single channel RF sampling factors