Ultrasonography

Ultrasonography, or ultrasound imaging, is a medical imaging modality that uses high-frequency sound waves to produce real-time images of internal structures. A transducer emits short pulses and records echoes returned from tissue interfaces; the time delay and intensity of echoes are used to construct two- or three-dimensional images. Because the technique relies on non-ionizing sound, it is broadly considered safe for patients and can be used repeatedly at the bedside.

Clinical ultrasound uses several imaging modes. B-mode or brightness mode renders cross-sectional grayscale images; M-mode records motion along a single line for cardiac or fetal monitoring. Doppler techniques measure blood flow velocity and direction; color Doppler encodes flow as colors, while spectral Doppler provides waveforms. Modern systems may employ contrast-enhanced ultrasound using microbubble agents to improve visualization of perfusion. Common clinical transducers operate in the megahertz range (roughly 2–15 MHz), with higher frequencies for superficial structures and lower frequencies for deeper anatomy. Image quality is affected by factors such as body habitus, bowel gas, and bone.

Applications span obstetrics (fetal imaging), gynecology, abdominal and pelvic imaging, breast and musculoskeletal assessment, urology, and vascular/cardiac imaging (echocardiography) often under real-time guidance for procedures such as needle placement or biopsies.

Limitations include operator dependence, limited penetration through air or bone, and artifacts (shadowing, speckle). Safety guidelines emphasize minimizing exposure while maintaining diagnostic yield.

History notes: ultrasound imaging began in the mid-20th century, with early work by researchers including Ian Donald; it has since become a routine, versatile tool in medicine.