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1. When travelling through a material, sound is attenuated exponentially for 2 reasons: energy is absorbed & converted to heat OR scattered & partially reflected.

2. The higher the frequency, the higher the attenuation, the higher the spatial resolution.

3. Attenuation is measured in decibels (dB).

4. In soft tissue, sound loses 1 dB / cm for every 1 MHz. In air: 40 dB / cm at 1 MHz.

5. Since there is little absorption or scatter in water, a full bladder can aid penetration.

6. As a rule of thumb: penetration (cm) = 40 / frequency (MHz)


1. Bushberg, J. T. (2012). The essential physics of medical imaging. Philadelphia: Wolters Kluwer Health/Lippincott Williams & Wilkins. Find it at Amazon
2. Heggie, J. C., Liddell, N. A., & Maher, K. P. (1997). Applied imaging technology. Melbourne: St. Vincents Hospital.

Ⓒ A. Manickam 2018

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