On the interaction between ultrasound and contrast agents during Doppler investigations

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. We then show that external factors, such as tissue acceleration, restrict the detection of perfusion at the capillary level with linear Doppler, even if long Doppler ensembles are considered. Hence, perfusion at the capillary level can only be detected with ultrasound through combined microbubbles and Doppler imaging. Finally, plane-wave contrast-enhanced power and color Doppler are performed on a rabbit kidney in vivo as a proof of principle. We establish that long pulse-inversion Doppler sequences and conventional wall-filters can create an image that simultaneously resolves both the vascular morphology of veins and arteries, and perfusion at the capillary level with frame rates above 100 Hz.

Section: Discussionmentioning

confidence: 98%

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

Tremblay-Darveau

Williams

Milot

et al. 2014

“…In later sections, we deduce parameter values that are more suitable to describe the observed F04E bubble behavior. The microbubbles have acoustic properties similar to albumin-shelled contrast agents [43], but they are chemically very stable and pressure resistant, which makes them ideal for bubble model validation. For optimal mixing, one drop of surfactant (Symperonic N, BDH Laboratory, Poole, UK) was added, after which the emulsion was gently stirred with a magnetic stirrer for at least 30 minutes.…”

Section: A Microbubblesmentioning

confidence: 99%

Method for Microbubble Characterization Using Primary Radiation Force

Vos

Guidi

Boni

et al. 2007

Medical ultrasound contrast agents (UCAs) have evolved from straight image enhancers to pathophysiological markers and drug delivery vehicles. However, the exact dynamic behavior of the encapsulated bubbles composing UCAs is still not entirely known. In this article, we propose to characterize full populations of UCAs, by looking at the translational effects of ultrasound radiation force on each bubble in a diluted population. The setup involves a sensitive, fully programmable transmitter/receiver and two unconventional, real-time display modes. Such display modes are used to measure the displacements produced by irradiation at frequencies in the range 2-8 MHz and pressures between 150 kPa and 1. MPa. The behavior of individual bubbles freely moving in a water tank is clearly observed, and it is shown that it depends on the bubble physical dimensions as well as on the viscoelastic properties of the encapsulation. A new method also is distilled that estimates the viscoelastic properties of bubble encapsulation by fitting the experimental bubble velocities to values simulated by a numerical model based on the modifiedHerring equation and the Bjerknes force. The fit results are a shear modulus of 18 MPa and a viscosity of 0.23 Pas for a thermoplastic PVC-AN shell. Phospholipid shell elasticity and friction parameter of the experimental contrast agent are estimated as 0.8 N/m and 1 10 ;7 kg/s, respectively (shear modulus of 32 MPa and viscosity of 0.19 Pas, assuming 4-nm shell thickness).

“…Experimental results have shown that, when such translations are related to full populations of contrast agents suspended in moving fluids, they may yield to considerable distortions in the corresponding Doppler spectra [4], [5]. A Doppler approach was used to indirectly validate a simple theoretical model, in which the microbubble movements are evaluated through the combination of the primary US force with the drag force of the fluid in which they are suspended.…”

Section: Introductionmentioning

confidence: 99%

Optical observations of acoustical radiation force effects on individual air bubbles

Palanchon

Tortoli

Bouakaz

et al. 2005

Abstract-Previous studies dealing with contrast agent microbubbles have demonstrated that ultrasound (US) can significantly influence the movement of microbubbles. In this paper, we investigated the influence of the acoustic radiation force on individual air bubbles using high-speed photography. We emphasize the effects of the US parameters (pulse length, acoustic pressure) on different bubble patterns and their consequences on the translational motion of the bubbles. A stream of uniform air bubbles with diameter ranging from 35 m to 79 m was generated and insonified with a single US pulse emitted at a frequency of 130 kHz. The bubble sizes have been chosen to be above, below, and at resonance. The peak acoustic pressures used in these experiments ranged from 40 kPa to 120 kPa. The axial displacements of the bubbles produced by the action of the US pulse were optically recorded using a high-speed camera at 1 kHz frame rate. The experimental results were compared to a simplified force balance theoretical model, including the action of the primary radiation force and the fluid drag force. Although the model is quite simple and does not take into account phenomena like bubble shape oscillations and added mass, the experimental findings agree with the predictions. The measured axial displacement increases quasilinearly with the burst length and the transmitted acoustic pressure. The axial displacement varies with the size and the density of the air bubbles, reaching a maximum at the resonance size of 48 m. The predicted displacement values differ by 15% from the measured data, except for resonant bubbles for which the displacement was overestimated by about 40%. This study demonstrates that even a single US pulse produces radiation forces that are strong enough to affect the bubble position.