Investigation of the effects of ultrasound on vegetal tissues during solvent extraction.

Ultrasonic exposures localized to regions smaller than a wavelength minimize the thermal mechanism, but promote nonthermal mechanisms of ultrasonic bioeffects. Microsonation experiments with vibrating needles or wires exploit this situation for the study of nonthermal mechanisms such as acoustic microstreaming flow. Shear stress in microstreaming flow, which is in excess of critical values for biomembranes, leads to cell lysis. Plane wave exposure of small bodies of gas also yields localized exposure, with further amplification of nonthermal mechanisms by resonance activation of oscillation. Gas body activation in vitro causes gathering of suspended cells by radiation forces, aggregation, cellular effects and lysis by microstreaming. When suitable gas bodies are present, these effects may occur at levels below the threshold for ultrasonic cavitation. In vivo, gas body activation generates intracellular microstreaming in Elodea leaves and disrupts the cells for super-critical shear stress levels. Similar phenomena seem to account for cell death, growth and mitotic index reductions in other plant tissues, and developmental abnormalities and delayed death in fruit flies. Only fragmentary and equivocal evidence presently exists on the medically relevant question of whether such subthreshold cavitation-like activity and bioeffects occur in vertebrates.

A review of the ultrasonic bioeffects of microsonation, gas-body activation, and related cavitation-like phenomena.

Therapeutic ultrasound is currently enjoying increasingly widespread clinical use especially for the treatment of cancer of the prostate, liver, kidney, breast, pancreas and bone, as well as for the treatment of uterine fibroids. The optimum method of treatment delivery varies between anatomical sites, but in all cases monitoring of the treatment is crucial if extensive clinical acceptance is to be achieved. Monitoring not only provides the operating clinician with information relating to the effectiveness of treatment, but can also provide an early alert to the onset of adverse effects in normal tissue. This paper reviews invasive and non-invasive monitoring methods that have been applied to assess the extent of treatment during the delivery of therapeutic ultrasound in the laboratory and clinic (follow-up after treatment is not reviewed in detail). The monitoring of temperature and, importantly, the way in which this measurement can be used to estimate the delivered thermal dose, is dealt with as a separate special case. Already therapeutic ultrasound has reached a stage of development where it is possible to attempt real-time feedback during exposure in order to optimize each and every delivery of ultrasound energy. To date, data from MR imaging have shown better agreement with the size of regions of damage than those from diagnostic ultrasound, but novel ultrasonic techniques may redress this balance. Whilst MR currently offers the best method for non-invasive temperature measurement, the ultrasound techniques under development, which could potentially offer more rapid visualisation of results, are discussed.

https://www.tandfonline.com/doi/pdf/10.1080/02656730701207842

Treatment monitoring and thermometry for therapeutic focused ultrasound.

This work was aimed at the effects of ultrasound (US) on the growth and secondary metabolite biosynthesis of cultured plant cells. Suspension cultures of Panax ginseng cells were exposed to US at power density below 82 mW/cm3 for short periods of time (1-4 min) in a US bath (38.5-kHz fixed frequency and 810 W maximum peak power). Under most exposure conditions, US stimulated the biosynthesis of secondary metabolites, the ginsenoside saponins of ginseng cells, increasing the total saponin content of the cell by up to 75%. The growth and viability of ginseng cells were usually depressed immediately after the exposure to US, but recovered gradually to levels similar to those of a normal culture in a few days, with virtually no net loss of biomass yield at the end of the culture period. At some lower US doses, sonicated cultures could even reach slightly higher biomass yields than that of normal cultures. The effects of US on cell growth and secondary metabolite yield showed a significant correlation with the total US energy emitted (i.e., the product of US power and exposure time). Mechanical stress and microstreaming induced by acoustic cavitation were considered as the most possible causes of the various physiological effects of US on ginseng cells. In particular, the stimulation of secondary metabolite production by US may be a result of US-induced plant cell defense response.

B.D. Cook

Papers

Mapping ultrasonic fields with cholesteric liquid crystals