Which tissue property is a primary determinant of ultrasound absorption?

• A. Protein content of tissues
• B. Water content of tissues
• C. Lipid content of tissues
• D. Vascularity

Answer: (A)

Ultrasound energy is absorbed as it passes through tissue when molecular interactions convert mechanical energy into heat. The amount of protein in a tissue is the strongest predictor of this energy loss because proteins provide many dipole bonds and associated relaxation mechanisms that more effectively dissipate energy at the frequencies used. This makes protein-rich tissues, such as muscle and connective tissue, absorb more ultrasound than lipid-rich or fatty tissues, which have lower absorption. Water content also influences attenuation, but the overall pattern across tissue types aligns most closely with protein content. Vascularity affects heat removal via blood flow rather than the intrinsic ability of tissue to absorb energy, so it’s a secondary factor. Thus, protein content best explains the observed differences in ultrasound absorption between tissues.