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There has been recent interest in therapeutic applications of ultrasound, primarily because of the medical and cost benefits that could be realized by the non-invasive nature of the procedure. High intensity therapeutic ultrasound (HITU) has been applied in cancer treatment, drug delivery, lithotripsy and thromobolysis amongst other applications. Each application contains its own challenges. Treatment of liver metastases for example, requires careful planning to avoid over-heating overlaying tissue on the ribs. Treatment within the cranium requires safe passage through the bone and characterization of the ultrasound field within the skull to ensure that hot spots are not setup up by acoustical interference.
Currently, the activity with the regulatory bodies to produce necessary standards are increasing with the emergence of HITU . It is important that manufacturers and researchers in the HITU field remain up-to-date with these standards. To this end Onda Corporation sits on the IEC committee to help steer the test requirements for HITU development. These standards describe the regulatory criteria for making power measurements and for characterizing the ultrasound field. In HITU, it is particularly important that the ultrasound field is accurately characterized so that the interaction of side lobes with over-laying or adjacent tissue can be assessed.
Onda offers the measurement instruments to meet regulatory requirements. Important parameters in HITU include the rarefactional pressure and temporal average intensity and these can be measured with the AIMS system, where acoustic sources and hydrophones can be uniquely translated or rotated about 5 axis. This is very important in focused fields, where the directivity of the hydrophone is a particularly important factor in the accuracy of acoustic measurements.
For simple, easy-to-use, accurate total power measurements, the RFB-2000™ can be used. This is the only radiation force balance on the market that controls both the measurement system and the acoustic source to enable automated measurements. This makes the device suitable for power measurements within a production environment and for applications that require extended averaging.
For R&D applications, the OptiSon Schlieren system is an invaluable tool that offers real-time visualization of the beam for qualitative analysis. The OptiSon enables one to accelerate the R&D of a therapeutic device by identifying unexpected artifacts in real-time.
For high power applications, Onda offers the HNA hydrophone which is susceptible to cavitation damage and can be used to measure high intensity focused fields at therapeutic power levels. This method is inherently more accurate than current techniques of extrapolating from low power measurements, since the effect of non-linear propagation is difficult to account for.
Onda has also developed a specific phantom gel for HIFU applications, which is used to visualize thermal and mechanical properties from high intensity sonication.