Ultrasound thrombolysis

Ultrasound energy for thrombolysis dates back to 1976. Trubestein et al. demonstrated first in vitro that a rigid wire delivery low frequency ultrasound energy could disrupt clot. These investigators also showed that this system had potential for peripheral arterial clot dissolution in vivo in animal studies [G. Trubestein, C. Engel, F. Etzel, Clinical Science 51 (1976) 697s-698s]. Subsequently, four basic approaches to ultrasonic thrombolysis have been pursued - two without pharmacological agents: (1) catheter-delivered external transducer ultrasound, (2) transcutaneous-delivered HIFU external ultrasound without drug delivery and ultrasound in conjunction with thrombolytic drugs and/or microbubbles or other agents, (3) Catheter-delivered transducer-tipped ultrasound with local drug delivery, and (4) transcutaneous-delivered low frequency ultrasound with concomitant systemic (intravenous) drug delivery for site specific ultrasound augmentation. This article reviews recent data on therapeutic ultrasound for thrombolysis in vitro, in vivo, in animal studies, as well as in human clinical trials.     

Ultrasound supported catalysis

An overview on the application of ultrasound in several chemical reactions is given. Ultrasound is used in the preparation of catalysts for various reactions, i.e. dehydration reactions. The beneficial effect of ultrasound results in clean reactions and short reaction times. Criteria for scale-up are also discussed.     

Ultrasound in medical diagnosis

The physical basis for applications of ultrasound in medical diagnosis is introduced. The main features of the chief types of equipment used, including the A- B- and M-mode scanners are presented, together with examples of their application in various fields such as abdominal investigations and cardiology. The use of the Doppler effect in studying the cardiovascular system is also outlined. The safety, and the present and likely future place of ultrasonic investigation in medical practice are outlined, and the role of the physicist in developing its possibilities is discussed.     

Ultrasound attenuation in ferrofluids

The absorption of acoustic energy by internal degrees of freedom of short chains is proposed as a new viable mechanism of ultrasound attenuation in ferrofluids. It is demonstrated that even though the volume fraction of the chains may be quite small, such an effect may reach the order of magnitude of viscous damping. In addition, by investigating the statistical properties of dimers in ferrofluids, it is shown that an applied magnetic field modifies the sound attenuation in a highly anisotropic manner. The proposed mechanism provides new insight into the fundamental issue of colloidal response, and, in particular, may lead to its utilization in novel experimental concepts.     

Ultrasound in spin glasses

The change of the sound velocity v(,T) and the damping of sound waves (,T) in spin glasses are calculated in the frame-work of an Ising model with a random distribution of exchange interactions. The calculation is based on linearized equations of motion for the spins and on an improved mean field approximation which includes the Onsager reaction field. Near to the freezing temperatureT _f and at high temperatures v(,T) and (,T) turn out to be approximately proportional to the real and the imaginary parts of the dynamical susceptibility. For the special case of infinite range interactions atT=T _f one has v(, T_f) ( )^1/2 and (, T_f) (/)^1/2 where is the relaxation time of independent spins. However, already slightly aboveT _f the frequency dependence of both quantities becomes rather small for RKKY spin glasses. At high temperatures both, v(,T) and (,T) vary asT ^–1.SFB 125 Aachen-Jülich-Köln     

Ultrasound assisted microwave digestion

Simultaneous microwave and ultrasound irradiation is shown as a new technique for digestion of solid and liquid samples suitable for chemical and food analysis. Its application in analytical chemistry has been shown by decreases in digestion time: determination of copper in edible oils and total Kjeldahl nitrogen.     

Ultrasound in organic electrosynthesis

Mechanical effects induced by ultrasonication can be very helpful for the activation of electrochemical reactions. The continuous cleaning of the electrodes by ultrasound irradiation of the electrochemical cell or the enhancement of mass transfer at the electrodes are examples of such activation. Finally, ultrasonication can play an important part for the orientation of reactions whose selectivities are very sensitive to stirring. Two very different examples have been chosen to illustrate these phenomena: the indirect electrooxidation of di-ketone-L-sorbose into the corresponding ketogulonic acid and the direct electroreduction of acetophenone into pinacol.     

Ultrasound in spin glasses II

General expressions are derived for the change of the sound velocity Δv(ω,T) and the damping of sound waves γ(ω,T) in spin glasses for all temperatures and without assuming a specific spin dynamics. The calculation is based on the modulation of the exchange interactions by the sound waves. Explicit results are obtained for diffusive or relaxing spin excitations.     

Ultrasound detection through turbid media

Optical coherence-domain reflectometry and laser-based ultrasound detection have been combined with the use of adaptive optics to detect ultrasound through turbid media. The dynamic hologram in a photorefractive quantum-well device performs as a coherence gate that eliminates multiply scattered background. Quadrature homodyne detection conditions are selected by the choice of center wavelength of the pulse spectrum, requiring no active stabilization or feedback. A depth resolution of 30 microm was achieved, with a pulse duration of nominally 120 fs for ultrasound detection through turbid media up to optical thicknesses of 11 mean free scattering lengths.     

Ultrasound and polar homogeneous reactions

The effect of ultrasound on the rates of homogeneous heterolytic reactions not switched to a free radical pathway can be explained by the perturbation of the molecular organization of or the solvation in the reacting system. A quantitative analysis of the sonochemical acceleration on the basis of the microreactor concept was carried out. It was found that (1) the Diels-Alder reaction cannot be accelerated by ultrasound except when SET or free radical processes are promoted, (2) the rectified diffusion during cavitation cannot be responsible for the acceleration of reactions, and (3) the sonochemical acceleration of polar homogeneous reactions takes place in the bulk reaction medium. This implies the presence of a 'sound-field' sonochemistry besides the 'hot-spot' sonochemistry. The occurrence of a sonochemical deceleration effect can be predicted.     

Ultrasound fields in attenuating media

For medical ultrasonic imaging and for nondestructive testing, the attenuation of pressure waves and the resulting shift in wave velocity are important features in commonly used transmission media such as biological tissue. An algorithm for the numerical evaluation of pressure field distributions generated by ultrasonic transducers is presented. The attenuation and dispersion of the sound transmission medium are taken into consideration. The sound fields are computed numerically for continuous wave as well as pulse excitation. The transducer has plane or gently curved geometry and is embedded in a plane rigid baffle. The numerically determined pressure fields are presented as 3D plots, as gray-scale images for a fixed time stamp (like a snapshot), or as isobars regarding the maximum values over time for each local point in the area under investigation. The algorithm described here can be utilized as a tool for design of ultrasound transducers, especially array antennas.     

Ultrasound in contemporary physiotherapy practice

The use of therapeutic ultrasound as an element of physiotherapy practice is well established, but the nature of that practice has changed significantly over the last 20 years. This paper aims to review the rationale and range of applications for which this modality is employed in current practice. Whereas in the past, its primary use was as a thermal modality, it is argued that currently, it is the ‘non-thermal’ aspects of the intervention that are most commonly employed. The predominant use of therapeutic ultrasound is in relation to tissue repair and soft tissue lesion management, where the evidence would support its application in the inflammatory, proliferative and remodelling phases. The clinical outcomes appear to be dose dependent, and whilst this paper does not detail dose related clinical decision making, the broad issues are considered. The future possibilities for the use of the modality are reviewed, and although outside the immediate remit of this paper, the use of therapeutic ultrasound in fracture management is briefly considered.     

Ultrasound propagation in dielectric glasses

The susceptibility of a two-level system coupled to a phonon heat bath is calculated by setting up its equation of motion and expanding the memory function (or self energy) and the inhomogeneity to second order in the coupling potential. Averaging over disorder yields attenuation and variation with temperature of sound velocity, which are compared to previous results obtained in the framework of the Bloch equations. The relaxation time approximation is avoided; there are new terms in both relaxation and resonant contributions.     

Ultrasound speckle and equivalent scatterers

B-mode ultrasound images are characterised by the speckle artefact, which introduces fine-false structures whose apparent resolution is beyond the imaging system capabilities. Speckle presence is due to interference effects between overlapping echoes and its occurrence is related to a great number of randomly distributed structure scatterers within a resolution cell. Basing our analysis on linear system theory, we show that a dense random set of scatterers can be substituted by an equivalent one with a much smaller number of periodic scatterers. This new structure with regularly distributed scatterers is able to give rise to the same B-mode image and the same speckle pattern, for a given ultrasound pulse. This new approach helps the understanding of the deterministic nature of speckle and may reduce drastically the computing time in numerical simulations. Additionally, it can contribute to periodicity analysis used in tissue characterisation.     

Ultrasound enhances liposome-mediated gene transfection

Previous studies have shown that some series of liposomes, usually containing cationic lipids, are useful tools for gene introduction into cells. To investigate the effect of ultrasound (US) on liposome-mediated transfection, three types of liposomes (designated L1, L2 and L3, in the order of increasing transfection efficiency) containing O,O′-ditetradecanoyl-N-(-trimethylammonioacetyl) diethanolamine chloride, dioleoylphosphatidylethanolamine, and/or cholesterol at varying ratios, were used in this study. HeLa cells were treated with liposome–DNA complexes containing luciferase genes for 2 h before sonication. Optimal US condition for the enhancement was determined to be 0.5 W/cm², 1 MHz continuous wave for 1 min and was above threshold for inertial cavitation based on EPR detection of free radicals. Luciferase expressions 24 h after the treatments were significantly increased by sonication to 2.4 fold with L1, and 1.7 fold with L2. However, with L3, which showed the highest level of expression among the liposomes, significant but minimal enhancement was observed when sonication was done 15 min after the DNA-L3 treatment, suggesting that efficiency of the liposome also determines the proper timing for sonication. The 2 h pre-sonication incubation with liposome–DNA complexes for L1 and L2 (30 min for L3) required to attain enhancement, suggests that US works to enhance transfection only after cells had enough DNA uptake.