Ultrasound Imaging

Ultrasound imaging uses high-frequency sound waves to produce pictures of structures inside the body. The sound is above the range of human hearing. A probe called a transducer sends sound into the body and detects returning echoes, allowing a scanner to construct an image without ionizing radiation .¹

Echoes arise where sound meets boundaries between tissues. The scanner uses the time taken for an echo to return, together with the speed of sound, to calculate the boundary’s distance from the probe. Gel applied between the probe and skin helps prevent air pockets from blocking sound transmission .¹

Ultrasound can show anatomy and, with specialized methods, aspects of function. Doppler ultrasound uses information from moving blood to assess its flow. Imaging is limited by how sound travels through different materials, so bone and air can make some structures difficult to examine .¹

Imaging differs from therapeutic ultrasound, which uses sound to change tissue rather than produce pictures. Although diagnostic ultrasound avoids the ionizing radiation used in X-rays, sound can still have biological effects under some conditions .¹