Ultrasound instrumentation and physics—a review with test questions
Ultrasound refers to any sound whose frequency is above the audible range (i.e., >20 kHz). Ultrasound transducers use piezoelectric crystals to convert electric signals into mechanical vibrations and pressure waves, and can detect any returning pressure waves converting them back into electric signals; serving a dual role of both pulse transmission and echo detection. Oscillations per second of the piezoelectric element in the transducer establish the frequency of the ultrasound wave. Frequency is expressed in cycles per second, or hertz (Hz). Diagnostic ultrasound transducers use transducer-emitting frequencies in the 1 MHz to 30 MHz (1 million to 30 million Hz) frequency range. Transducer frequencies used in clinical applications are: