Edelmen's Sonography Principles and Instrumentation (SPI) Practice Exam 2026 - Free SPI Practice Questions and Study Guide

Measuring ultrasound beam intensity requires capturing the actual acoustic pressure in the beam and converting that into a power value using the known properties of the medium. A calibrated hydrophone does exactly that: it’s a small sensor placed in water that responds to the instantaneous acoustic pressure of the field and outputs an electrical signal whose amplitude is tied to pressure through its calibration. From that pressure data, you can compute intensity with I = p^2/(ρ c), where ρ is the medium’s density and c is the speed of sound. In practice, the hydrophone is used with a measurement system to report spatial-peak or temporal-averaged intensities for beam characterization. The other items aren’t direct, calibrated sensors for intensity: a lateral oscilloscope may display waveforms but doesn’t translate them into calibrated pressure-to-intensity values; a water-filled phantom and a tissue-equivalent phantom are media for testing imaging or acoustic interactions, not standalone, calibrated measurements of the beam’s intensity.