General Considerations for Ultrasound Applications in Head and Neck

Ultrasonography (US) is performed using physical properties of ultrasound, i.e., acoustic waves with a frequency above 20,000 Hz (20 kHz). Feasibility of an ultrasound unit depends on the applied probes typically in head and neck applications waves with frequency from 2 to 30 MHz are used. The higher the frequency is, the higher the resolution is, but at the same time penetration depth diminishes. Advantages of ultrasonography include availability, no ionizing radiation applied thus no harmful effects observed (even in pregnant females and infants), high image resolution, real-time imaging, and a relatively low cost. Disadvantages of US include high dependency on the operator’s skills and experience, post-acoustic shadowing influencing examinations of dense objects such as intact cortical bone surface or enamel, as well as image artifacts. Within the head and neck US is used in diagnostic imaging of salivary glands, thyroid gland, lymph nodes, muscles (masticatory, neck, facial), tongue, oral floor and oropharynx, palate, periodontal tissues, temporomandibular joint (in a limited range), extracranial nerves, paranasal sinuses, large blood vessels, and larynx. Ultrasound scanning is also applied as guidance for fine needle aspiration biopsy, core biopsy, abscess drainage, TMJ arthrocentesis, TMJ injections, e.g., with steroids or sodium hyaluronate, intramasseteric injections of botuline toxin for bruxism and/or masseter hypertrophy.