Which imaging modality is known to utilize ionizing radiation?

The imaging modality that utilizes ionizing radiation is X-ray. X-rays are a form of electromagnetic radiation that, when directed towards a patient, can penetrate various tissues to produce images of the internal structures of the body. The exposure to ionizing radiation is what differentiates X-ray from other imaging modalities such as ultrasound and MRI.

Ultrasound uses high-frequency sound waves to create images and does not involve any radiation, making it safe for various populations, including pregnant women. MRI operates using strong magnetic fields and radiofrequency waves, also without the use of ionizing radiation, which is a significant advantage when considering patient safety, particularly for repeated imaging. CT scans do use ionizing radiation as well; however, in answering the question specifically about the recognized modality primarily known for the use of ionizing radiation, X-ray stands out due to its widespread use and historical significance in medical imaging. Thus, X-ray is the correct answer.