High line-density pulse wave imaging for local pulse wave velocity estimation using motion matching: A feasibility study on vessel phantoms

High frame rate (≤200 Hz) is required in pulse wave imaging (PWI) to estimate regional pulse wave velocity (PWV) of arteries, and can be achieved by sparse imaging or plane wave imaging at the expense of spatial resolution or signal-to-noise ratio (SNR). However, both high temporal and spatial resolution are required when mapping local PWV variations along inhomogeneous arteries. In this study, the whole imaging field of view (FOV) was divided into 4 sub-sectors, each with 34 beams including a common beam. Ultrasound radiofrequency (RF) data was then acquired sequentially in each sector. A high line density (128 beams, 38 mm width) and high frame rate (~507 Hz, 35 mm depth) RF frame sequence was reconstructed from the sub-sector frames by aligning the estimated vessel motion along the common beam. The composite RF frames were then post-processed using PWI technique. Local PWV was estimated within a sliding kernel of ~10 mm along the vessel wall. For the homogeneous phantom, local PWV measurements of the proposed method show good agreement with the sparse imaging, and undergo less fluctuation compared with plane wave imaging. In the low SNR condition, the proposed method obtains smaller standard deviation (SD) than sparse imaging. For inhomogeneous phantoms, significant difference of local PWV measurements between the stiffer and softer regions is found by using the proposed method, the sparse imaging or plane wave imaging. The proposed method is capable of obtaining both high line density and high frame rate data and mapping local PWV variations.