In which imaging technique is ionizing radiation NOT used?

Ultrasound is the imaging technique that does not utilize ionizing radiation. Instead, it employs high-frequency sound waves to create images of structures within the body. The sound waves are emitted by a transducer, and when they encounter different tissues, they bounce back, creating echoes that are then converted into images. This technique is safe and non-invasive, making it ideal for a variety of applications, including prenatal imaging and examining soft tissues and organs.

In contrast, other techniques listed, such as X-rays, CT scans, and nuclear medicine, involve the use of ionizing radiation. These methods rely on varying levels of radiation to visualize internal structures or to assess the function of organs. Therefore, ultrasonic imaging stands out as the only method among the choices that avoids the associated risks linked to ionizing radiation.