At the cellular level, ultrasound can cause which change to tissue permeability?

• A. Micro streaming to increase permeability
• B. Decreased permeability
• C. No change
• D. An increase in thickness

Answer: (A)

When ultrasound interacts with tissue at the cellular level, the oscillation of microbubbles creates microstreaming—tiny, directional fluid movement around the bubbles. This generates shear stresses on nearby cell membranes, producing transient openings in the membrane (sonoporation). Those temporary pores raise the membrane’s permeability, allowing molecules that normally don’t cross easily to enter or exit cells. This mechanical effect explains why ultrasound can increase permeability. The idea that permeability would decrease or that there would be no change isn’t consistent with the typical cellular response to these mechanical forces, and an increase in thickness isn’t a characteristic outcome at the membrane level.