If the ultrasound soundhead has a 2 cm diameter, the treated area should be approximately how many times larger than the soundhead area to achieve heating within five minutes?

• A. The same size
• B. Half the size
• C. Four times the size
• D. Twice the size

Answer: (D)

Therapeutic ultrasound heats tissue where the beam is applied, and spreading the energy over a larger area helps achieve a stable temperature rise within a short time. A common rule of thumb is to treat about twice the area of the transducer to allow heat to diffuse beyond the beam and reach the target tissue within five minutes.

For a soundhead 2 cm in diameter, the area is πr^2 = π(1 cm)^2 ≈ 3.14 cm^2. Doubling that gives about 6.28 cm^2, which corresponds to treating a region roughly 2.8 cm in diameter. This aligns with the idea that twice the soundhead area is needed to obtain heating within the allotted time.