Medical ultrasonography (sonography) is an ultrasound-based diagnostic imaging technique used to visualize muscles and internal organs, their size, structure and any pathological lesions, making them useful for scanning the organs. Obstetric sonography is commonly used during pregnancy.

In physics the term "ultrasound" applies to all acoustic energy with a frequency above human hearing (20,000 Hertz), its common usage as a term of medical imaging applies to just a band of frequencies hundreds of times higher. Ultrasonography (sonography) is widely utilized in medicine. It is possible to perform diagnosis or therapeutic procedures with the guidance of ultrasonography (for instance biopsies or drainage of fluid collections). Ultrasound typically uses a hand-held probe (often called a scan head or transducer) that is placed directly on and moved over the patient: a water-based gel ensures good coupling between the patient and scan head.

Medical ultrasonography is used in, for example:

• Cardiology
• Endocrinology
• Gastroenterology
• Gynoecology
• Obstetrics
• Ophthalmology
• A-scan Ultrasonography
• B-scan Ultrasonography
• Urology
• Intravascular Ultrasound
• Contrast enhanced ultrasound

*Definition provided by Wikipedia