Fast Spectral Velocity Estimation Using Adaptive Techniques: In-Vivo Results

Adaptive spectral estimation techniques are known to provide good spectral resolution and contrast even when the observation window(OW) is very sbort. In this paper two adaptive techniques are tested and compared to the averaged perlodogram (Welch) for blood velocity estimation. The Blood Power spectral Capon (BPC) method is based on a standard minimum variance technique adapted to account for both averaging over slowtime and depth.

The Blood Amplitude and Phase Estimation technique (BAPES) is based on finding a set of matched filters (one for each velocity component of interest) and filtering the blood process over slow-time and averaging over depth to find the power spectral density estimate. In this paper, the two adaptive methods are explained, and performance Is assessed in controlled steady How experiments and in-vivo measurements.

The three methods were tested on a circulating How rig with a blood mimicking fluid flowing in the tube. The scanning section is submerged in water to allow ultrasound data acquisition. Data was recorded using a BK8804 linear array transducer and the RASMUS ultrasound scanner. The controlled experiments showed that the OW could be significantly reduced when applying the adaptive methods without compromising spectral resolution or contrast.

The in-vivo data was acquired using a BK8812 transducer. OWs of 128, 64, 32 and 16 slow- time samples were tested. Spectrograms with duration of 2 seconds were generated. Welch's method required 128 samples to give a reasonable spectrogram, whereas the BPC only required 32 samples before the SNR became a limiting factor.

The BAPES managed to display the spectrogram with sufficient quality at 16 slow-time samples.