ultrasounds

Ultrasound refers to sound waves with frequencies above the upper audible limit of human hearing, traditionally above 20 kHz. In medical contexts, clinical ultrasound uses frequencies roughly from 1 to 20 MHz. Ultrasound devices generate short pulses with piezoelectric transducers and listen for echoes from tissue interfaces. By analyzing the time delay and strength of echoes, the system constructs real-time images; Doppler modes detect frequency shifts from moving blood cells to measure flow.

Medical uses include diagnostic imaging, especially obstetric ultrasound, abdominal imaging, echocardiography, and musculoskeletal studies. Advances include three-dimensional and four-dimensional imaging and ultrasound guidance for procedures. Doppler ultrasound assesses vascular supply. Therapeutically, high-intensity focused ultrasound (HIFU) can ablate tissue, and lower-intensity ultrasound has applications in physiotherapy and drug delivery research.

Non-medical uses include non-destructive testing and inspection of metals and composites, thickness measurements, material characterization, and cleaning. In marine contexts, sonar uses similar principles for navigation and object detection.

Safety and regulation: Ultrasound is generally non-ionizing and considered safe when used within recommended exposure levels, but high intensities can heat tissue or cause cavitation. Practitioners follow ALARA guidelines, and equipment is regulated by medical device standards and professional guidelines.

History and limitations: Research in the 20th century led to practical medical ultrasound imaging; notable milestones include obstetric imaging and Doppler techniques. Limitations include operator dependence, attenuation in obese or gas-filled areas, and image artifacts. Continuous development aims to improve resolution, penetration, and portability.