High-Frequency Nonlinear Doppler Contrast-Enhanced Ultrasound Imaging of Blood Flow.

Current methods for in vivo microvascular imaging (<1 mm) are limited by the tradeoffs between the depth of penetration, resolution, and acquisition time. Ultrasound Doppler approaches combined at elevated frequencies (<7.5 MHz) are able to visualize smaller vasculature and, however, are still limited in the segmentation of lower velocity blood flow from moving tissue.

SUSHI: Sparsity-Based Ultrasound Super-Resolution Hemodynamic Imaging.

Identifying and visualizing vasculature within organs and tumors has major implications in managing cardiovascular diseases and cancer. Contrast-enhanced ultrasound scans detect slow-flowing blood, facilitating noninvasive perfusion measurements. However, their limited spatial resolution prevents the depiction of microvascular structures.

3-D Perfusion Imaging Using Principal Curvature Detection Rendering.

Three-dimensional contrast-enhanced ultrasound (CEUS) imaging presents a clear advantage over its 2-D counterpart in detecting and characterizing suspicious lesions as it properly surveys the inherent heterogeneity of tumors. However, 3-D CEUS is also slow compared to 2-D CEUS and tends to undersample the microbubble wash-in. This makes it difficult to resolve the feeding vessels, an important oncogenic marker, from the background perfusion cloud.

The Role of Microbubble Echo Phase Lag in Multipulse Contrast-Enhanced Ultrasound Imaging.

In this paper, we assess the importance of microbubble shell composition for contrast-enhanced imaging sequences commonly used on clinical scanners. While the gas core dynamics are primarily responsible for the nonlinear harmonic response of microbubbles at diagnostic pressures, it is now understood that the shell rheology plays a dominant role in the nonlinear response of microbubbles subjected to low acoustic pressures. Of particular interest here, acoustic pressures of tens of kilopascal can cause a reversible phase transition of the phospholipid coatings from a stiff elastic organized state to a less stiff disorganized buckled state.

Impact of Encapsulation on in vitro and in vivo Performance of Volatile Nanoscale Phase-Shift Perfluorocarbon Droplets.

Phase-shift droplets can be converted by sound from low-echogenicity, liquid-core agents into highly echogenic microbubbles. Many proposed applications in imaging and therapy take advantage of the high spatiotemporal control over this dynamic transition. Although some studies have reported increased circulation time of the droplets compared with microbubbles, few have directly explored the impact of encapsulation on droplet performance.

Improved Contrast-Enhanced Power Doppler Using a Coherence-Based Estimator.

While plane-wave imaging can improve the performance of power Doppler by enabling much longer ensembles than systems using focused beams, the long-ensemble averaging of the zero-lag autocorrelation R(0) estimates does not directly decrease the mean noise level, but only decreases its variance. Spatial variation of the noise due to the time-gain compensation and the received beamforming aperture ultimately limits sensitivity. In this paper, we demonstrate that the performance of power Doppler imaging can be improved by leveraging the higher lags of the autocorrelation [e.

Concepts and Tradeoffs in Velocity Estimation With Plane-Wave Contrast-Enhanced Doppler.

While long Doppler ensembles are, in principle, beneficial for velocity estimates, short acoustic pulses must be used in microbubble contrast-enhanced (CE) Doppler to mitigate microbubble destruction. This introduces inherent tradeoffs in velocity estimates with autocorrelators, which are studied here. A model of the autocorrelation function adapted to the microbubble Doppler signal accounting for transit time, the echo frequency uncertainty, and contrast-agent destruction is derived and validated in vitro.

Fast Vascular Ultrasound Imaging With Enhanced Spatial Resolution and Background Rejection.

Ultrasound super-localization microscopy techniques presented in the last few years enable non-invasive imaging of vascular structures at the capillary level by tracking the flow of ultrasound contrast agents (gas microbubbles). However, these techniques are currently limited by low temporal resolution and long acquisition times. Super-resolution optical fluctuation imaging (SOFI) is a fluorescence microscopy technique enabling sub-diffraction limit imaging with high temporal resolution by calculating high order statistics of the fluctuating optical signal.

Visualizing the Tumor Microvasculature With a Nonlinear Plane-Wave Doppler Imaging Scheme Based on Amplitude Modulation.

Imaging with ultrasonic plane waves enables the combination of Doppler and microbubble contrast-enhanced imaging without compromising the Doppler ensemble length, as is the case for conventional line-by-line imaging, thus maintaining flow sensitivity. This permits the separation of conduit flow in large vessels from the perfusion background and the presentation of velocity estimates in real-time. However, the ability to differentiate perfusion from the tissue signal is limited by the contrast-to-tissue (CTR) ratio achieved with the contrast-enhanced pulsing sequence, independently of the acquisition length.

Dynamic contrast enhanced ultrasound for therapy monitoring.

Quantitative imaging is a crucial component of the assessment of therapies that target the vasculature of angiogenic or inflamed tissue. Dynamic contrast-enhanced ultrasound (DCE-US) using microbubble contrast offers the advantages of being sensitive to perfusion, non-invasive, cost effective and well suited to repeated use at the bedside. Uniquely, it employs an agent that is truly intravascular.

Denoising of Contrast-Enhanced Ultrasound Cine Sequences Based on a Multiplicative Model.

Background: Speckle noise is an inherent characteristic of dynamic contrast-enhanced ultrasound (DCEUS) movies and ultrasound images in general. Speckle noise considerably reduces the quality of these images and limits their clinical use. Currently, temporal compounding and maximum intensity persistence (MIP) are among the most widely accepted processing methods enabling the visualization of vasculature using DCEUS.

Combined perfusion and doppler imaging using plane-wave nonlinear detection and microbubble contrast agents.

Plane-wave imaging offers image acquisition rates at the pulse repetition frequency, effectively increasing the imaging frame rates by up to two orders of magnitude over conventional line-by-line imaging. This form of acquisition can be used to achieve very long ensemble lengths in nonlinear modes such as pulse inversion Doppler, which enables new imaging trade-offs that were previously unattainable. We first demonstrate in this paper that the coherence of microbubble signals under repeated exposure to acoustic pulses of low mechanical index can be as high as 204 ± 5 pulses, which is long enough to allow an accurate power Doppler measurement.

Measuring absolute blood pressure using microbubbles.

Gas microbubbles are highly compressible, which makes them very efficient sound scatterers. As another consequence of their high compressibility, the radii of the microbubbles are affected by the pressure of the fluid around them, which changes their resonance frequency. Although the pressures present within the human body cause only minor variations in the radii of uncoated microbubbles (∼0.