Which one of the following principles of physics is primarily used in sonography, a medical diagnostic process?

Sonography, also known as ultrasonography, is a medical diagnostic process that utilizes high-frequency sound waves to create images of internal body structures. While standard ultrasound imaging relies on the 'pulse-echo' principle—where piezoelectric crystals emit sound pulses that reflect off tissue interfaces —the Doppler effect is a primary principle used to assess dynamic functions such as blood flow and cardiac activity [1]. The Doppler effect involves a change in the observed frequency of sound waves when there is relative motion between the source (transducer) and the receiver (moving blood cells). This frequency shift allows clinicians to calculate the velocity and direction of blood flow, making it indispensable for diagnosing vascular patency and organ perfusion [1]. Other principles like resonance are primarily associated with MRI rather than ultrasound [1].

Sources

1. [1] https://www.ncbi.nlm.nih.gov/books/NBK580539/