In vivo blood velocity measurements with particle image velocimetry in echocardiography using spontaneous contrast

Abstract

The present study tested the feasibility of applying the particle image velocimetry technique in echocardiography (Echo-PIV), in humans, using echocardiographic images displaying spontaneous contrast. This technique is based on digital image processing of echocardiographic images acquired with ultrasound contrast agents. The measurement of blood flow velocity within the cardiac chambers and blood vessels is essential for the accurate diagnosis, treatment and prognosis of a variety of cardiovascular diseases. Echo-PIV velocimetry technique allows the calculation of relevant information, such as shear rate and vorticity fields. Indeed, the influence of shear rate on the vascular endothelium is related with aneurysms formation and atherosclerosis disease. The pattern and intensity of the vorticity field in the left ventricle seems to indicate different stages of heart failure. In the present work a novel implementation of the technique was tested, whereby spontaneous echocardiographic contrast provided by the blood was used as flow tracers. The knowledge of the image acquisition frame rate and the displacement of the tracers allow the determination of the desired instantaneous blood flow velocity field. Ten patients were selected from clinical routine of diagnostic investigation of the echocardiographic laboratory of Antonio Pedro University Hospital, from the Fluminense Federal University, Niteroi, RJ. The echocardiographic exams were selected among those patients displaying spontaneous contrast classified as medium-moderate, moderate and severe. The presence of spontaneous contrast in the analyzed images allowed the cross-correlation of image pairs and the measurements of instantaneous velocity fields. Shear rate and vorticity fields for the blood flow were then calculated from the measured velocity fields. The analysis of the results proved the feasibility of the utilization of the Echo-PIV in humans, using images with spontaneous contrast. This novel implementation eliminates the risk of side effects associated with the use of intravenous contrast solutions and allows the implementation of Echo-PIV technique with a significant cost reduction.