Ultrasound frequency refers to the number of complete wave cycles per second, expressed in megahertz (MHz). Diagnostic ultrasound operates in the range of approximately 1–20 MHz. Higher frequency transducers produce shorter wavelengths, yielding better spatial resolution but greater attenuation and therefore reduced penetration depth. Lower frequency transducers penetrate deeper but with lower resolution. A 7–15 MHz linear probe is used for superficial structures; a 2–5 MHz curvilinear probe is used for abdominal imaging.