Side lobes in ultrasound beam patterns are best described as energy:

• A. Inside the main beam
• B. In the main lobe
• C. Outside the main beam
• D. Along the beam axis

Answer: (C)

Side lobes are energy that radiates away from the central axis, outside the main beam. When an ultrasound transducer emits, most energy goes into the main lobe along the beam direction, where intensity is highest. However, due to the finite aperture and wave interference, secondary peaks occur at off-axis angles—these are the side lobes. They are lower in amplitude than the main lobe but represent energy outside the central beam, which is why the correct description is energy outside the main beam. The other phrases refer to the main lobe or the beam axis, not to these off-axis, secondary regions.