Abstract
Combining diverging ultrasound waves and microbubbles could improve contrast-enhanced echocardiography (CEE), by providing enhanced temporal resolution for cardiac function assessment over a large imaging field of view. However, current image formation techniques using coherent summation of echoes from multiple steered diverging waves (DWs) are susceptible to tissue and microbubble motion artifacts, resulting in poor image quality. In this study, we used correlation-based 2-D motion estimation to perform motion compensation for CEE using DWs. The accuracy of this motion estimation method was evaluated with Field II simulations. The root-mean-square velocity errors were 5.9% ± 0.2% and 19.5% ± 0.4% in the axial and lateral directions, when normalized to the maximum value of 62.8 cm/s which is comparable to the highest speed of blood flow in the left ventricle (LV). The effects of this method on image contrast ratio (CR) and contrast-to-noise ratio (CNR) were tested in vitro using a tissue mimicking rotating disk with a diameter of 10 cm. Compared against the control without motion compensation, a mean increase of 12 dB in CR and 7 dB in CNR were demonstrated when using this motion compensation method. The motion correction algorithm was tested in vivo on a CEE data set acquired with the Ultrasound Array Research Platform II performing coherent DW imaging. Improvement of the B-mode and contrast-mode image quality with cardiac motion and blood flow-induced microbubble motion was achieved. The results of motion estimation were further processed to interpret blood flow in the LV. This allowed for a triplex cardiac imaging technique, consisting of B mode, contrast mode, and 2-D vector flow imaging with a high frame rate of 250 Hz.
Highlights
M ICROBUBBLES are micron-sized spheres with a heavy gas core that is stabilized by a shell made of lipids, polymers, proteins, or surfactants [1]
This paper focuses on the demonstration of the feasibility to make motion compensation to preserve the quality of HFR Contrast-enhanced echocardiography (CEE) when using diverging waves (DWs)
This paper described the implementation of a motion correction method for HFR CEE using coherent DW imaging
Summary
M ICROBUBBLES are micron-sized spheres with a heavy gas core that is stabilized by a shell made of lipids, polymers, proteins, or surfactants [1]. Due to their significant acoustic impedance mismatch relative to the surrounding tissue and blood cells, they are excellent ultrasound scatters and have long been used as ultrasound contrast agents [2]. The use of high-frame-rate (HFR) CEE with a large imaging field of view could lead to better assessment of cardiac function through visualization and quantification of transient events not captured with current CEE techniques
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