Frequency and focal depth are _____ related.

Frequency and focal depth are _____ related.

• A. Inversely
• B. Unrelated
• C. Indirectly
• D. Directly

Answer: (D)

The key idea here is how frequency affects focusing of the ultrasound beam. When frequency goes up, the wavelength gets shorter. A shorter wavelength means the beam can be converged more tightly by the transducer’s aperture, which allows the beam to stay narrow farther from the source. As a result, the point where the beam reaches its smallest width—the focal depth—occurs at a greater distance. So frequency and focal depth move in the same direction: higher frequency yields a deeper focus. That said, higher frequency also attenuates more quickly, reducing overall penetration, so there’s a trade-off between resolution and depth.

The key idea here is how frequency affects focusing of the ultrasound beam. When frequency goes up, the wavelength gets shorter. A shorter wavelength means the beam can be converged more tightly by the transducer’s aperture, which allows the beam to stay narrow farther from the source. As a result, the point where the beam reaches its smallest width—the focal depth—occurs at a greater distance. So frequency and focal depth move in the same direction: higher frequency yields a deeper focus. That said, higher frequency also attenuates more quickly, reducing overall penetration, so there’s a trade-off between resolution and depth.