Which imaging modality primarily uses ionizing radiation to create cross-sectional images?

• A. MRI
• B. Ultrasound
• C. CT
• D. Scintigraphy

Answer: (C)

Cross-sectional imaging using ionizing radiation is provided most directly by computed tomography. In CT, an X-ray source and detectors rotate around the patient, capturing many projections that are then mathematically reconstructed into thin cross-sectional slices of anatomy. The radiation involved is ionizing, which is a defining feature of CT. Magnetic resonance imaging uses strong magnetic fields and radiofrequency energy and does not involve ionizing radiation, though it also produces cross-sectional slices. Ultrasound relies on sound waves and carries no ionizing radiation. Scintigraphy uses radiopharmaceuticals with a gamma camera to show tracer distribution, offering functional information and often 3D reconstructions, but its primary aim is not detailed cross-sectional anatomy and it involves ionizing radiation as well. Therefore, CT best fits the description.