Acoustic characterization of echogenic liposomes: frequency-dependent attenuation and backscatter

Ultrasound contrast agents (UCAs) are used clinically to aid detection and diagnosis of abnormal blood flow or perfusion. Characterization of UCAs can aid in the optimization of ultrasound parameters for enhanced image contrast. In this study echogenic liposomes (ELIPs) were characterized acoustically by measuring the frequency-dependent attenuation and backscatter coefficients at frequencies between 3 and 30 MHz using a broadband pulse-echo technique. The experimental methods were initially validated by comparing the attenuation and backscatter coefficients measured from 50-μm and 100-μm polystyrene microspheres with theoretical values. The size distribution of the ELIPs was measured and found to be polydisperse, ranging in size from 40 nm to 6 μm in diameter, with the highest number observed at 65 nm. The ELIP attenuation coefficients ranged from 3.7 ± 1.0 to 8.0 ± 3.3 dB/cm between 3 and 25 MHz. The backscatter coefficients were 0.011 ± 0.006 (cm str)(-1) between 6 and 9 MHz and 0.023?±?0.006 (cm str)(-1) between 13 and 30 MHz. The measured scattering-to-attenuation ratio ranged from 8% to 22% between 6 and 25 MHz. Thus ELIPs can provide enhanced contrast over a broad range of frequencies and the scattering properties are suitable for various ultrasound imaging applications including diagnostic and intravascular ultrasound.     

Passive imaging with pulsed ultrasound insonations

Previously, passive cavitation imaging has been described in the context of continuous-wave high-intensity focused ultrasound thermal ablation. However, the technique has potential use as a feedback mechanism for pulsed-wave therapies, such as ultrasound-mediated drug delivery. In this paper, results of experiments and simulations are reported to demonstrate the feasibility of passive cavitation imaging using pulsed ultrasound insonations and how the images depend on pulsed ultrasound parameters. The passive cavitation images were formed from channel data that was beamformed in the frequency domain. Experiments were performed in an invitro flow phantom with an experimental echo contrast agent, echogenic liposomes, as cavitation nuclei. It was found that the pulse duration and envelope have minimal impact on the image resolution achieved. The passive cavitation image amplitude scales linearly with the cavitation emission energy. Cavitation images for both stable and inertial cavitation can be obtained from the same received data set.     

Solitary wave solutions to nonlinear evolution equations in mathematical physics

This paper obtains solitons as well as other solutions to a few nonlinear evolution equations that appear in various areas of mathematical physics. The two analytical integrators that are applied to extract solutions are tan–cot method and functional variable approaches. The soliton solutions can be used in the further study of shallow water waves in (1+1) as well as (2+1) dimensions.