Potential applications of low-energy shock waves in functional urology.

A shock wave, which carries energy and can propagate through a medium, is a type of continuous transmitted sonic wave with a frequency of 16 Hz-20 MHz. It is accompanied by processes involving rapid energy transformations. The energy associated with shock waves has been harnessed and used for various applications in medical science. High-energy extracorporeal shock wave therapy is the most successful application of shock waves, and has been used to disintegrate urolithiasis for 30 years. At lower energy levels, however, shock waves have enhanced expression of vascular endothelial growth factor, endothelial nitric oxide synthase, proliferating cell nuclear antigen, chemoattractant factors and recruitment of progenitor cells; shock waves have also improved tissue regeneration. Low-energy shock wave therapy has been used clinically with musculoskeletal disorders, ischemic cardiovascular disorders and erectile dysfunction, through the mechanisms of neovascularization, anti-inflammation and tissue regeneration. Furthermore, low-energy shock waves have been proposed to temporarily increase tissue permeability and facilitate intravesical drug delivery. The present review article provides information on the basics of shock wave physics, mechanisms of action on the biological system and potential applications in functional urology.

Sonothrombolysis.

Ultrasound (US) applied as an adjunct to thrombolytic therapy improves the recanalization of occluded vessels, and microbubbles can amplify this effect. New data suggests that the combination of US and microbubbles without tissue plasminogen activator may achieve recanalization with a lower risk of hemorrhage. Further possibilities include specific targeting of thrombus with immunobubbles as well as local drug delivery with US-sensitive liposomes. Clinical studies support the use of US for ischemic stroke therapy, and the first trials of enhancing sonothrombolysis with microbubbles have been encouraging. One emerging clinical application is sonothrombolysis of intracranial hemorrhages for clot evacuation. Microcirculation, irrespective of recanalization, may also be improved by US and microbubbles, and this effect may open new opportunities for the application of sonothrombolysis in acute ischemic stroke. Understanding the mechanisms of therapeutic action and relating this knowledge to issues of efficacy and safety are important objectives of ongoing research. This review will discuss the translational capacities of in vitro studies and preclinical research and will assess the first clinical studies of this promising therapeutic strategy.

A scanned, focused, multiple transducer ultrasonic system for localized hyperthermia treatments. 1987.

A commercial diagnostic ultrasound scanner (Octoson) was modified for performing hyperthermia treatments. The temperature elevations were induced in tissues by four large, focused ultrasonic transducers whose common focal zone was scanned along a computer controlled path as determined from B-scan images. The system is described and the results of preliminary tests demonstrating some of its capabilities are given. Extensive tests with canine thighs and kidneys were performed. The blood flow to the kidneys was controllable, and thus tumours having different blood perfusion rates could be simulated. The results showed that the system is capable of inducing a local temperature maximum deep in tissues (up to 10 cm was tested) and that tissues with high perfusion rates could be heated.

Hyperthermia classic commentary: 'A scanned, focused, multiple transducer ultrasonic system for localised hyperthermia treatments', by K. Hynynen, R. Roemer, D. Anhalt, et al., International Journal of Hyperthermia 1987;3:21-35.

This commentary reviews the development of image-guided focused ultrasound treatments since the publication of the above paper. The impact of the research presented in the paper on the development of the current image-guided noninvasive surgery and treatments will also be discussed.

Mechano-physical and biophysical properties of power-driven scalers: driving the future of powered instrument design and evaluation.

This review has highlighted the importance of standardizing future investigations to enable more meaningful interstudy comparisons to be made. This report also makes recommendations for factors that should be considered and incorporated into future investigations, both in vitro and in vivo, in order to achieve more standardization. These recommendations are listed below.

Biological aspects and clinical importance of ultrasound therapy in bone healing.

OBJECTIVES: The purpose of this study was to review past and recent literature findings regarding the effects of ultrasound therapy on bone healing and its clinical efficacy in medical and dental interventions. METHODS: A literature review was conducted on the effects of ultrasound therapy on bone healing. The studies regarding clinical applications in long bones and maxillofacial bones were evaluated separately from each other. RESULTS: The effects of therapeutic ultrasound on bone healing have been studied for half a century. Numerous clinical and experimental studies have addressed this relationship, and many of them have shown positive correlations. Although several theories have been proposed to explain the mechanism of action, the exact mechanism has not been fully understood. CONCLUSIONS: Therapeutic ultrasound therapy in clinical settings is a noninvasive application and has no serious complications or side effects. It may be an acceptable treatment of choice in many types of clinical procedures involving maxillofacial bones.

High intensity focused ultrasound: physical principles and devices.

High intensity focused ultrasound (HIFU) is gaining rapid clinical acceptance as a treatment modality enabling non-invasive tissue heating and ablation for numerous applications. HIFU treatments are usually carried out in a single session, often as a day case procedure, with the patient either fully conscious, lightly sedated or under light general anaesthesia. A major advantage of HIFU over other thermal ablation techniques is that there is no necessity for the transcutaneous insertion of probes into the target tissue. The high powered focused beams employed are generated from sources placed either outside the body (for treatment of tumours of the liver, kidney, breast, uterus, pancreas and bone) or in the rectum (for treatment of the prostate), and are designed to enable rapid heating of a target tissue volume, while leaving tissue in the ultrasound propagation path relatively unaffected. Given the wide-ranging applicability of HIFU, numerous extra-corporeal, transrectal and interstitial devices have been designed to optimise application-specific treatment delivery. Their principle of operation is described here, alongside an overview of the physical mechanisms governing HIFU propagation and HIFU-induced heating. Present methods of characterising HIFU fields and of quantifying HIFU exposure and its associated effects are also addressed.

Clinical applications of focused ultrasound-the brain.

This paper provides a historic and contemporary overview of the use of focused ultrasound for treating brain disorders.

Biological effects of ultrasound: development of safety guidelines. Part II: general review.

In the 1920s, the availability of piezoelectric materials and electronic devices made it possible to produce ultrasound (US) in water at high amplitudes, so that it could be detected after propagation through large distances. Laboratory experiments with this new mechanical form of radiation showed that it was capable of producing an astonishing variety of physical, chemical and biologic effects. In this review, the early findings on bioeffects are discussed, especially those from experiments done in the first few decades, as well as the concepts employed in explaining them. Some recent findings are discussed also, noting how the old and the new are related. In the first few decades, bioeffects research was motivated partly by curiosity, and partly by the wish to increase the effectiveness and ensure the safety of therapeutic US. Beginning in the 1970s, the motivation has come also from the need for safety guidelines relevant to diagnostic US. Instrumentation was developed for measuring acoustic pressure in the fields of pulsed and focused US employed, and standards were established for specifying the fields of commercial equipment. Critical levels of US quantities were determined from laboratory experiments, together with biophysical analysis, for bioeffects produced by thermal and nonthermal mechanisms. These are the basis for safety advice and guidelines recommended or being considered by national, international, professional and governmental organizations.

Biological effects of ultrasound: development of safety guidelines. Part I: personal histories.

After the end of World War II, advances in ultrasound (US) technology brought improved possibilities for medical applications. The first major efforts in this direction were in the use of US to treat diseases. Medical studies were accompanied by experiments with laboratory animals and other model systems to investigate basic biological questions and to obtain better understanding of mechanisms. Also, improvements were made in methods for measuring and controlling acoustical quantities such as power, intensity and pressure. When diagnostic US became widely used, the scope of biological and physical studies was expanded to include conditions for addressing relevant safety matters. In this historical review, a major part of the story is told by 21 investigators who took part in it. Each was invited to prepare a brief personal account of his/her area(s) of research, emphasizing the "early days," but including later work, showing how late and early work are related, if possible, and including anecdotal material about mentors, colleagues, etc.

Ultrasound focal beam surgery.

High intensity beams of ultrasound may be focused at depth within the body, thereby producing selective damage within the focal volume, with no harm to overlying or surrounding tissues. The technique is thus noninvasive, insofar as the source of ultrasound energy is situated outside the body. The mechanism for cell killing is predominantly thermal, although acoustic cavitation may also occur. Ultrasound focal surgery was first conceived in the 1940s as a possible tool for creating selective damage in the brain for neurosurgical research; its potential for more widespread clinical use was not exploited at that time, probably because of the lack of facilities for providing precise visualisation and localisation of the damage. The availability of modern imaging techniques has encouraged a revival of clinical interest, and applications in ophthalmology, urology and oncology are currently being developed.