Acoustic characterization of contrast agents for medical ultrasound imaging

Abstract

Nycomed’s ultrasound contrast agent NC100100 has been investigated by in vitro acoustic measurements. Acoustic attenuation spectra were used to determine resonance frequencies of the particles. The spectra were correlated with size distributions, and it was found that the shell-encapsulated gas bubbles can be described as viscoelastic particles with bulk modulus 700 kPa. When exposed to hydrostatic overpressures mimicking those found in vivo during the systolic heart cycle, the resonance frequency increased, as expected by the particles’ increased stiffness. This effect was reversible: After the pressure was released, the particles went back to giving the original attenuation spectrum. This shows that the particles are not destroyed or otherwise changed by the pressure. Acoustic backscatter measured as a function of distance through a contrast agent was used to estimate the backscatter efficiency of the particles, that is, the ratio between scattered and absorbed ultrasound. Results from these measurements agree with theoretical estimates based on the attenuation spectra. Measurements on NC100100 were compared with earlier results from measurements on Albunex® and measurements on an experimental polymer-encapsulated contrast agent, showing how different shell materials cause differences in particle stability and stiffness.

Complexity reduction of ultrasound sub-ultra-harmonic modeling by an input modified volterra approach

“…The sampling frequency is f s =60 MHz [7]. The parameters of the microbubble are given in the table I [21]. Fig.…”

“…The oscillation of microbubbles is simulated using a free simulation program Bubblesim developed by Hoff [21]. The incident burst to the microbubble is a sinusoidal wave of frequency f 0 = 4 MHz, at 1.6 MPa pressure, and consists of 32 cycles.…”

Modeling of thermal effects in antivascular ultrasound therapy

“…For shelled microbubbles the damping constant (d t ) has three major components: Mechanical resistance due to shell viscosity, d sh , mechanical resistance from viscous forces, d L , and re-radiation of acoustic energy, d rad (Hoff et al, 2000;Hoff, 2001;Holt and Roy, 2001), (4) and (7) for spherical microbubbles yields a direct relationship between microbubble characteristics and b Bub ,…”

“…According to the Rayleigh-Plesset equation, the resonance frequency of small free bubbles (bubbles without encapsulating shell) is dominated by surface tension and viscosity terms. The resonance frequency of the shelled bubbles, on the other hand, is related to shear modulus, G sh , and thickness d sh of the shell and is described by (Church, 1995;Hoff et al, 2000;Hoff, 2001;Razansky et al, 2006),…”

Inverter-based 1 V analog front-end amplifiers in 90 nm CMOS for medical ultrasound imaging

“…Ultrasound imaging has been in use since the 1970s for medical diagnosis for a wide variety of medical investigation purposes [1]. It has also become common practice to use ultrasound imaging during surgery, including intravascular ultrasound (IVUS) imaging.…”