Further progress on lateral flow estimation using speckle size variation with scan direction

Abstract

Conventional blood flow velocity measurement using ultrasound is capable of resolving the axial component (i.e., that aligned with the ultrasound propagation direction) of the blood flow velocity vector. However, these Doppler-based methods are incapable of detecting blood flow in the direction normal to the ultrasound beam. In addition, these methods require repeated pulse-echo interrogation at the same spatial location. In this paper, we report additional data on a new method recently introduced. This method estimates the lateral component of blood flow within a single image frame using the observation that the speckle pattern corresponding to the blood reflectors (typically red blood cells) stretches (i.e., is ?smeared?) if the blood is moving in the same direction as the electronically-controlled transducer line selection in a 2D image. The situation is analogous to the observed elongation of a subject photographed with a moving camera. Experiments were performed with a blood flow phantom and high-frequency transducer of a commercially available ultrasound machine. Data was captured through an interface allowing access to the raw beamformed data. Blood flow with velocities ranging from 50 to 110 cm/s were investigated in this paper. Previously, we showed results indicating a linear relationship between the reciprocal of the speckle stretch factor and blood flow velocity when the scan velocity is greater than the blood flow velocity [1]. When the scan velocity is 64.8 cm/s, compared with the theoretical model, fitting results based on experimental data gave us a linear relationship with average flow estimation error of 1.74?1.48 cm/s. When the scan velocity is 37.4 cm/s, the average estimation error is 0.65?0.45 cm/s. The new experiments reported here include blood flow velocities that are close to and greater than the scan velocity. Results show that the linear relationship degrades under these conditions, which we hypothesize is due to speckle decorrelation and flow gradients.