Which imaging technique utilizes radiation to visualize internal structures?

The technique that utilizes radiation to visualize internal structures is X-Rays. This imaging modality works by passing a controlled amount of ionizing radiation through the body, which is then captured on a film or digital detector to create images of the internal anatomy. X-Ray imaging is particularly effective for viewing dense structures, such as bones, and can also be used for imaging soft tissues, although with less contrast.

In contrast, ultrasound employs sound waves to produce images and does not involve any ionizing radiation. Magnetic Resonance Imaging (MRI) uses strong magnetic fields and radio waves to generate detailed images of soft tissues, also avoiding the use of radiation. Computed Tomography (CT) does utilize radiation, similar to X-Rays, but is a more advanced technique that combines multiple X-Ray images taken from different angles to create cross-sectional views of the body. While both X-Rays and CT use radiation, the question specifically refers to the imaging technique known for its foundational role in radiation imaging, which is X-Rays. Therefore, the answer is X-Rays because it most directly aligns with the basic definition of an imaging technique that employs radiation for visualization.