Measurements of temperature and macroscopic and microscopic studies show a relatively normal status of the presenting tissue at the site of focused ultrasonic beam during noninvasive exposure of the heart through the thoracic wall in dogs: the temperature in the subcutaneous fat of the thoracic wall partially submerged in water is no higher than 38~ and 40.5~ in the periosteum. Warming of the periosteum during treatment by noninvasive methods may be the limiting factor at sites where the bones are located close to the surface, for example, the ribs. Skin burns may be prevented by focused ultrasonic exposure through aqueous medium.Key Words: focused ultrasound; noninvasive exposure; microthermocouple Focused ultrasound (FUS) is used in medicine and biology for noninvasive local exposure of organ and tissue structures [ 1,7]. However, we failed to find any reports about biological effects of high-frequency US oscillations on the heart during noninvasive local exposure.The safety of US exposure for the adjacent tissues is an important condition for practical exposure of deep structures of tissues and organs to FUS. One important factor is an increase in the temperature of tissues at the site of a convergent US beam due to absorption of US energy. The contribution of absorption to complete extinguishing of US energy varies from 30 to 70% [3]. Other causes of changes ,in the temperature of tissues exposed to US (periodical changes resulting from oscillations of the medium, heating by gas bubbles in the tissue, thermal changes caused by cavitation, etc.) are negligible in comparison with heating resulting from US absorption.I. P. Pavlov State Medical University, St. Petersburg MATERIALS AND METHODSContact-free methods for measuring the temperature of biological tissues: acoustothermography, acoustothermometry, and radiothermometry have been recently developed [4]. However, there are no commercial devices permitting noninvasive measurements of local changes in the temperature of deep-lying tissues and organs.In order to assess tissue injuries along the US beam and the heating of the chest bones during US exposure of the heart we measured temperature at several sites located at different distances from the surface of US device to the focus of exposure. The temperature was measured with a special device consisting of microthermocouples, direct current amplifier, and a recorder (V7-35 digital voltmeter).The temperature was measured both in vitro and in vivo in order to compare the transformations of temperature in biological tissue under the effect of US under different conditions.Manganin-constantan thermocouples with the diameter of thermojunction no more than 0.2 mm
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