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Concerning the attenuation of ultrasound: a. In contrast to the attenuation of X-rays, it is not an exponential process b. It is mostly due to loss of energy from the primary beam due to scattering and reflection c. In a particular medium, it depends on the frequency of the ultrasound d. The attenuation coefficient of water is similar to that of non-clotted blood e. A thickness of tissue equal to the half-value layer (HVL) attenuates the ultrasound beam by 3 dB |
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Answer» a. False. The attenuation of ultrasound is also exponential. b. False. Attenuation is mostly caused by energy absorption by frictional and viscous forces in the medium, with some contribution from scattering and partial reflection. c. True. The attenuation coefficient of most tissues increases linearly with the frequency, and for soft tissues is typically in the range of 0.3–0.6 dB cm-1 MHz=-1 . d. False. Water attenuates ultrasound waves to a lesser degree than blood. e. True. In the logarithmic scale, log 0.5 = 0.3 Bel = 3 dB. |
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