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Physics, Techniques and Procedures

Attenuation coefficient

a quantification of the energy intensity loss of either electromagnetic or mechanical waves due to attenuation. In diagnostic radiology, the most important attenuation coefficients for electromagnetic radiation are the linear attenuation coefficient and the mass attenuation coefficient, quantifying the loss of intensity per centimetre travelled distance and mass unit, respectively. The attenuation coefficient of ultrasound is measured in units of dB/cm, which is the log relative energy intensity loss per travelled centimetre. In biological soft tissues, the ultrasound attenuation coefficient is roughly proportional to the ultrasound frequency (for the frequency range used in medical imaging). This means that the attenuation coefficient divided by the frequency (unit dB/cm/MHz) is nearly constant in a given tissue. Typical soft tissue values are 0.51.0 dB/cm/MHz.

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