Which of the following is a nonthermal effect of ultrasound?

• A. Increased intracellular calcium levels
• B. Acceleration of metabolic rate
• C. Increased collagen extensibility
• D. Promotion of normal cell function

Answer: (A)

Nonthermal ultrasound effects come from mechanical interactions rather than heat. Cavitation and acoustic streaming can transiently alter cell membrane permeability, allowing calcium ions to enter the cell. That rise in intracellular calcium triggers cellular activities that promote healing, such as fibroblast stimulation and changes in enzyme activity, without warming the tissue.

The other responses are primarily tied to heating: increasing collagen extensibility happens with tissue temperature rise that softens collagen, and metabolic rate typically speeds up when temperature goes up. So the commonly identified nonthermal effect among the options is the rise in intracellular calcium levels.