Spatial peak intensity is measured in which units?

Spatial peak intensity is measured in which units?

• A. Watts per square centimeter
• B. Watts per square meter
• C. Joules per square centimeter
• D. Newtons per square meter

Answer: (A)

Spatial peak intensity is the maximum power carried by a beam per unit area. By definition, intensity equals power divided by area, so its units are watts per unit area. In ultrasound practice, this is typically expressed as watts per square centimeter because beam dimensions are on the centimeter scale. Using joules per square centimeter would describe energy per area (fluence) rather than instantaneous power, which isn’t the same concept. Newtons per square meter is a pressure unit (Pascal), not power per area. While watts per square meter is a valid SI unit for intensity, the standard convention in this field uses watts per square centimeter.

Spatial peak intensity is the maximum power carried by a beam per unit area. By definition, intensity equals power divided by area, so its units are watts per unit area. In ultrasound practice, this is typically expressed as watts per square centimeter because beam dimensions are on the centimeter scale. Using joules per square centimeter would describe energy per area (fluence) rather than instantaneous power, which isn’t the same concept. Newtons per square meter is a pressure unit (Pascal), not power per area. While watts per square meter is a valid SI unit for intensity, the standard convention in this field uses watts per square centimeter.