A programmable real-time system for development and test of new ultrasound investigation methods

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The signal backscattered by blood cells crossing a sample volume produces a Doppler power spectrum determined by the scatterers¿ velocity distribution. Because of intrinsic spectral broadening, the peak Doppler frequency observed does not correspond to the peak velocity in the flow. Several methods have been proposed for estimating the maximum velocity component--an important clinical parameter--but these methods are approximate, based on heuristic thresholds that can be inaccurate and strongly affected by noise. Reported here is a method of modeling the Doppler power spectrum of a flow, and from that model, determining what Doppler frequency on the descending slope of the power spectrum corresponds to the peak velocity in the insonated flow. It is shown that, for a fully insonated flow with a parabolic velocity distribution, the peak velocity corresponds to the Doppler frequency at the half-power point on that slope. The method is demonstrated to be robust with regard to the effects of noise and valid for a wide range of acquisition parameters. Experimental maximum velocity measurements on steady flows with rates between 100 and 300 mL/min (peak velocity range 6.6 cm/s to 19.9 cm/s) show a mean bias error that is smaller than 1%.

Section: B Experimental Setupmentioning

confidence: 99%

Finding the peak velocity in a flow from its doppler spectrum

Vilkomerson

Ricci

Tortoli

2013

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“…A sensitive US system capable of recording the signals backscattered from single microbubbles, and equipped with coherent, programmable transmit-receive (Tx-Rx) sections to facilitate Doppler operation [46], [47], has been developed [48], and will be referred to here as bubble behavior testing (BBT) system.…”

Section: B Bubble Behavior Testing Us Systemmentioning

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).

“…The br14 Uca bubbles (bracco, Geneva, switzerland), whose mean diameter is 3 μm, were injected with a syringe. a single-element piezoelectric transducer, with a central frequency of 3 MHz, 70% fractional bandwidth, and a focal distance of about 70 mm, was connected to an ultrasonic bubble behavior testing (bbT) controller (Microelectronics system design laboratory) [33]. The bbT controller made it possible to transmit arbitrary waveforms, to record the signals backscattered from Uca, and to set the PrF, the region of interest (roI), and the storage data size.…”

Section: B a Single Bubble And A Population Of Bubbles Moving In Thementioning

confidence: 99%

Ultrasound contrast imaging: influence of scatterer motion in multi-pulse techniques

Lin¹,

Cachard²,

Mori³

et al. 2013

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In ultrasound contrast imaging, many techniques based on multiple transmissions have been proposed to increase the contrast-to-tissue ratio (CTR). They are generally based on the response of static scatterers inside the imaged region. However, scatterer motion, for example in blood vessels, has an inevitable influence on multi-pulse techniques, which can either enhance or degrade the technique involved. This paper investigates the response of static nonlinear media insonated by multi-pulses with various phase shifts, and the influence of scatterer motion on multi-pulse techniques. Simulations and experimental results from a single bubble and clouds of bubbles show that the phase shift of the echoes backscattered from bubbles is dependent on the transmissions' phase shift, and that the bubble motion influences the efficiency of multi-pulse techniques: fundamental and second-harmonic amplitudes of the processed signal change periodically, exhibiting maximum or minimum values, according to scatterer motion. Furthermore, experimental results based on the second-harmonic inversion (SHI) technique reveal that bubble motion can be taken into account to regulate the pulse repetition frequency (PRF). With the optimal PRF, the CTR of SHI images can be improved by about 12 dB compared with second-harmonic images.