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Concerning safety limits and indices used in ultrasound: a. The time-averaged ultrasound intensity should nowhere exceed 100 mW cm-2 b. The total sound energy (intensity dwell time) should nowhere exceed 100 J cm-2 c. The thermal index (TI) is the ratio of the power emitted to the power required to increase the whole body temperature by 1°C d. The mechanical index (MI) is the peak rarefaction pressure divided by the square root of the ultrasound frequency e. Both TI and MI must always be displayed on the ultrasound control panel |
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Answer» a. True. This is approximately 1000 times greater than the typical intensity in the focal region. b. False. It should not exceed 50 J cm-2 . c. False. TI applies to the temperature rise in the insonated tissue, not the whole body. d. True. e. False. They need to be displayed if the equipment is capable of exceeding a TI or MI of 1.0 in the selected scanning mode (B-mode, spectral Doppler, etc.). In such cases, the indices must be displayed regardless of their value (i.e. even if they are below 1.0). |
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