Studying the Origin of Reverberation Clutter in Echocardiography: In Vitro Experiments and In Vivo Demonstrations

Clutter in echocardiography hinders the visualization of the heart and reduces the diagnostic value of the images. The detailed mechanisms that generate clutter are, however, not well understood. We present five different hypotheses for generation of clutter based on reverberation artifact with a focus on apical four-chamber view echocardiograms. We demonstrate the plausibility of our hypotheses by in vitro experiments and by comparing the results with in vivo recordings from four volunteers. The results show that clutter in echocardiography can be originated both at structures that lie in the ultrasound beam path and at those that are outside the imaging plane. We show that reverberations from echogenic structures outside the imaging plane can make clutter over the image if the ultrasound beam gets deflected out of its intended path by specular reflection at the ribs. Different clutter types in the in vivo examples show that the appearance of clutter varies, depending on the tissue from which it originates. The results of this work can be applied to improve clutter reduction techniques or to design ultrasound transducers that give higher quality cardiac images. The results can also help cardiologists have a better understanding of clutter in echocardiograms and acquire better images based on the type and the source of the clutter

Resolution Measured as Separability Compared to Full Width Half Maximum for Adaptive Beamformers

Spatial resolution is defined as a system's ability to separate targets using some kind of criterion, such as the Rayleigh criterion. However, in practice, lateral resolution is often evaluated by measuring the Full Width Half Maximum (FWHM at -6dB) of the point spread function (PSF). We hypothesize that FWHM overestimates the system resolution for some adaptive beamformers, compared to using the Rayleigh criterion. Simulation results seem to confirm this hypothesis

The dark region artifact in adaptive ultrasound beamforming

An undesired effect, the dark region artifact (DRA), has been under-communicated in our research community. The DRA appear next to acoustically strong targets for some of the many adaptive beamformers introduced in the literature. This study investigates the DRA for a collection of adaptive beamformers and shows that this effect originates because some of the methods fail to estimate which signals arise in the mainlobe and which originates from sidelobes. The DRA results in darker regions in the ultrasound images, indicating the wrong acoustical amplitude. Therefore, the measured contrast can falsely appear higher for adaptive beamformers affected by the DRA

High frame rate color Doppler echocardiography: a quantitative comparison of different approaches

Ultrasound color Doppler imaging (CDI) provides a map of the axial blood flow velocities in a 2-D/3-D region of interest. While CDI is clinically effective for a qualitative analysis of abnormal blood flows, e.g., for valvular disease in cardiology, it is in limited use for quantitative measures, mainly hampered by low frame rate and measurement bias. These limitations can be reduced by different approaches toward high-frame-rate (HFR) imaging at the expense of reduced image quality and penetration depth. The aim of this study was to compare the impact of different HFR sequences on CDI quantitatively. Different cardiac scan sequences, including diverging waves and multiline transmission, were designed, implemented on a research system, and compared in terms of patient safety parameters, image quality, and penetration depth. Furthermore, in vivo images were acquired and compared for healthy volunteers. Results showed that the HFR techniques spread artifacts on larger areas than the standard single-line scans (> +50%). In addition, due to patient safety limitations, they reduce the penetration depth up to -5 cm. On the other hand, the HFR techniques provide comparable velocity estimates (relative difference <6%) and enhance the time resolution of the color Doppler images, achieving frame rates up to 625 Hz in continuous acquisition.status: accepte

The influence of speckle statistics on contrast metrics in ultrasound imaging

Adaptive beamformers aim for improved resolution and contrast in the ultrasound images, and their performance is typically benchmarked using metrics such as contrast ratio (CR) and contrast-to-noise ratio (CNR). Using synthetic aperture Field II simulations, we show that certain beamformers alter speckle statistics and that this opens up for cherry picking of contrast metrics

The influence of speckle statistics on contrast metrics in ultrasound imaging

Adaptive beamformers aim for improved resolution and contrast in the ultrasound images, and their performance is typically benchmarked using metrics such as contrast ratio (CR) and contrast-to-noise ratio (CNR). Using synthetic aperture Field II simulations, we show that certain beamformers alter speckle statistics and that this opens up for cherry picking of contrast metrics

Improved Lesion Detection Using Nonlocal Means Post-Processing

Software beamforming allows more flexible and complex algorithms, often referred to as adaptive beamforming techniques, that are blurring the boundaries between beamforming and image processing. Many adaptive beamforming algorithms claim to improve lesion detectability. Based on recent advances, we hypothesize that image processing techniques that reduce speckle variability yield better lesion detectability than state-of-the-art adaptive beamformers.This hypothesis is investigated on six algorithms: two image processing techniques, and four adaptive beamformers. As a target we use Field II simulations of a hypoechoic cyst with noise added to simulate different SNR conditions. Lesion detectability is estimated using the Generalized Contrast-to-Noise Ratio (GCNR). The results support our hypothesis