Basics of ultrasound
Ultrasound or ultrasonography (US) has become an increasingly common applied modality in oral and maxillofacial radiology.1 It is not used just in diagnosis but also in therapy. Therapeutically, diagnostic US can be used to guide microsurgery for calculi or strictures; therapeutic US can be used to break up larger calculi by lithotripsy.
Overview of US Technology and Terminology
US is a medical imaging technique that uses high frequency sound waves and their echoes. The range of diagnostic US lies between 1–20 MHz. A US scanner transducer converts electrical energy into sonic energy. The piezoelectric crystal, the most important component of the transducer, undergoes rapid changes in thickness in response to an electric current. Such changes induce the sound waves (ultrasound), which then enter the patient.
Each tissue has a different acoustic impedance, determining what proportion of the ultrasound energy is absorbed and how much is reflected back. It is this reflected energy which, upon reaching the transducer, carries the clinically important information. Upon reaching the transducer, it causes a change in the crystal’s thickness. This information, after amplification and processing, is displayed. Modern equipment processes the reflected echoes with such rapidity that a perception of motion or real-time imaging can be appreciated. The acoustic impedance of a tissue changes with disease.
Clinical Applications of Ultrasound