Therapeutic ultrasound an overview

Therapeutic ultrasound is defined as the use of ultrasound for the treatment of diseased or injured organs or bodily structures and is quite distinct from diagnostic ultrasound. There were many early attempts in the past to use ultrasound in therapy for a variety of applications and while some of these have not been pursued others have led on to clinical applications which are now used routinely. Such progress has been made possible by a number of factors including advances in transducer design, more accurate measurement and calibration of acoustic power and careful experiments to determine the precise nature of chemical processes taking place during and following the exposure of tissue to ultrasound. Major advances have been made in some fields where ultrasound is used such as physiotherapy, surgical instruments, chemotherapy, drug delivery and more recently, high intensity focused ultrasound (HIFU). The last of these has seen enormous activity leading to the formation of the International Society of Therapeutic Ultrasound and a number of very well attended regular specialist meetings. In this review some historical perspectives of therapeutic ultrasound and progress in the field since the early 1990's will be presented.     

Experimental demonstration of noninvasive transskull adaptive focusing based on prior computed tomography scans

Developing minimally invasive brain surgery by high-intensity focused ultrasound beams is of great interest in cancer therapy. However, the skull induces strong aberrations both in phase and amplitude, resulting in a severe degradation of the beam shape. Thus, an efficient brain tumor therapy would require an adaptive focusing, taking into account the effects of the skull. In this paper, we will show that the acoustic properties of the skull can be deduced from high resolution CT scans and used to achieve a noninvasive adaptive focusing. Simulations have been performed with a full 3-D finite differences code, taking into account all the heterogeneities inside the skull. The set of signals to be emitted in order to focus through the skull can thus be computed. The complete adaptive focusing procedure based on prior CT scans has been experimentally validated. This could have promising applications in brain tumor hyperthermia but also in transcranial ultrasonic imaging.     

Large scale sonochemical processing: aspiration and actuality

It has been recognised for many years that power ultrasound has great potential in a wide variety of processes in the chemical and allied industries. Some of these processes have been known for many years and continue to flourish as major commercial applications, e.g. plastic welding and cleaning. Others, like ultrasonic drilling, while showing great potential have not been widely exploited to date. The potential for the industrial use of power ultrasound is enormous, and yet industry seems somewhat reluctant to adopt it. In this article the existing uses of power ultrasound in processing are reviewed and the potentials are explored.     

Sonochemistry and sonoprocessing: the link,the trends and (probably) the future

Traditionally the community of scientists involved with ultrasound has been divided broadly into those who use it as a measurement device with no effect on the medium (high frequency low power ultrasound e.g. non-destructive testing) and those who use it to produce physical or chemical effects in a medium (higher power low frequency ultrasound e.g. sonochemistry). Divisions also exist within the broad spectrum of those involved with the latter. In the early days of sonochemistry this did not prove to be a major problem, the subject was new and the field was expanding within the chemistry community. However at a point some years ago Jean-Louis Luche made the very important observation that sonochemistry applications could be subdivided into reactions which were the result of "true" and "false" effects [Synthetic Organic Chemistry by J.-L. Luche, 1998, p. 376]. Essentially these terms referred to real chemical effects induced by cavitation and those effects that could be mainly ascribed to the mechanical impact of bubble collapse. These mechanical effects have not held the interest of synthetic chemists as much as the so-called true ones but nevertheless they are certainly important in areas such as processing. In this paper I will attempt to show that there are links that can be made across many of the ultrasound "disciplines" and that these links can only serve to strengthen research in the general area of power ultrasound. If research on power ultrasound is strong then research into "pure" sonochemistry will also flourish and "false" sonochemistry will be born again as a significant research area.     

Calorimetric study of the energy efficiency for ultrasound-induced radical formation

Energy conversion in sonochemistry is known to be an important factor for the development of industrial applications, however, the strong influence of the physical properties of the liquid on the ultrasound characteristics usually prevents an accurate determination of the chemical effects. In this study, the energy efficiency of the ultrasound-induced radical formation from methyl methacrylate has been investigated. The energy yield can be quantified by comparison of the ultrasonic power that is transferred to the liquid and the radical formation kinetics. Based on this method the influence of temperature and amplitude of the ultrasound horn on the energy efficiency has been determined. The energy yield for the formation of radicals from ultrasonic waves appears to be in the order of 5 x 10(-6) J/J. The energy conversion is the highest at low temperatures and at low amplitudes.     

Power ultrasound and its applications: A state-of-the-art review

Ultrasonic processing has attracted increasing attention by people because ultrasonic technology may represent a flexible ‘green’ alternative for energy efficient processes. The major challenges for the power ultrasound application in real situations are the design and development of specific power ultrasonic systems for large-scale operations. Thus, new families of power ultrasonic transducers have been developed in recent years to meet actual needs, and this contributes to the implementation of power ultrasound of application in many fields such as chemical industry, food industry and manufacturing. This paper presents the current state of ultrasonic transducers of magnetostrictiv type and piezoelectric type as well as applications of power ultrasound in various industrial fields including chemical reactions, drying/dehydration, welding, extraction, heat transfer enhancement, de-ice, enhanced oil recovery, droplet atomization, cleaning and fine particle removal. The review paper helps to understand the current development of power ultrasonic technology and its applications in various situations, and induce extended applications of power ultrasound to more and more fields.     

The uses of ultrasound in food technology

The same physical and mechanical effects which have been utilised in sonochemistry, i.e. strong shear forces, particle fragmentation, increased mass and heat transfer, nucleation of seedling, have been applied to food processing. Examples are quoted from various applications where power ultrasound has been used to influence the development of living cells, improve sterilisation and effect enzyme activity. Typically ultrasound can be used as a processing aid in extraction, crystallisation, freezing, emulsification, filtration and drying.     

Nanosonosensitization by Using Copper–Cysteamine Nanoparticles Augmented Sonodynamic Cancer Treatment

Sonodynamic therapy (SDT), as a newly emerging and promising modality for cancer treatment, has been extensively investigated but with limited therapeutic outcome because of the absence of highly efficient sonosensitizer. Copper–cysteamine (Cu–Cy), as a new sensitizer, has been reported for oxidative therapy which can be activated with light, X‐ray, or microwave. Herein, for the first time, Cu–Cy nanoparticles are reported as new sonosensitizers for SDT on breast cancer treatment. Upon exposure of Cu–Cy nanoparticles to ultrasound, a large quantity of reactive oxygen species (ROS) are generated for cancer cell destruction with a high SDT efficiency to induce cell apoptosis and necrosis as observed in vitro. In vivo animal studies show a significant inhibition of tumor growth for the xenografts of 4T1 cancer cells with the combination of 0.75 mg kg⁻¹ Cu–Cy and ultrasound. Overall, the preliminary results show that Cu–Cy nanoparticles can significantly augment the levels of ROS induced by ultrasound, demonstrating Cu–Cy is a new kind of efficient sonosensitzers for SDT applications. Such therapeutic platform by integrating a noninvasive, highly safe, deep‐penetration ultrasound modality. and quickly developed versatile nanosensitizers for tumor eradication will facilitate SDT future clinical translation.     

Basic study on apoptosis induction into cancer cells U-937 and EL-4 by ultrasound exposure

Recently, the low invasive cancer treatments with small aftereffects have been considered. We are studying on the suppression methods of cancer cell proliferation with ultrasound. Cancer cells of mouse T lymphoma (EL-4) have been used in our study. The human histitocytic lymphoma cells (U-937) was used in this time. The cancer cells were cultured in a culture medium of RPMI1640. The standing wave acoustic field was formed in a water tank of our ultrasound exposure system by a vibrating plate driven with a Langevine type transducer. The U-937 and EL-4 were exposed to ultrasound in the acoustic field with spatial average acoustic intensity of 350 mW/cm(2) at 150 kHz. The viable rate of EL-4 decreased with the lapse of culture time after ultrasound exposure. U-937 did not show the remarkable decrease tendency. The proliferation of U-937 which exposed to ultrasound with 700 mW/cm(2) was suppressed. It can be thought that apoptosis was induced in the cancer cells in this condition. We observed the morphological change on the U-937 exposed to ultrasound with this condition. The morphological changes by apoptosis like the shrink of cells, formation of apoptotic bodies etc. can be observed with an optical microscope and a phase contrast microscope.     

Effects of therapeutic ultrasound on the nucleus and genomic DNA

In recent years, data have been accumulating on the ability of ultrasound to affect at a distance inside the cell. Previous conceptions about therapeutic ultrasound were mainly based on compromising membrane permeability and triggering some biochemical reactions. However, it was shown that ultrasound can access deep to the nuclear territory resulting in enhanced macromolecular localization as well as alterations in gene and protein expression. Recently, we have reported on the occurrence of DNA double-strand breaks in different human cell lines exposed to ultrasound in vitro with some insight into the subsequent DNA damage response and repair pathways. The impact of these observed effects again sways between extremes. It could be advantageous if employed in gene therapy, wound and bone fracture-accelerated healing to promote cellular proliferation, or in cancer eradication if the DNA lesions would culminate in cell death. However, it could be a worrying sign if they were penultimate to further cellular adaptations to stresses and thus shaking the safety of ultrasound application in diagnosis and therapy. In this review, an overview of the rationale of therapeutic ultrasound and the salient knowledge on ultrasound-induced effects on the nucleus and genomic DNA will be presented. The implications of the findings will be discussed hopefully to provide guidance to future ultrasound research.