Which imaging modality uses a series of X-ray images in layers to construct a three-dimensional picture of the brain?

• A. CAT Scan
• B. MRI
• C. PET
• D. SPECT

Answer: (A)

This describes computed tomography, which builds a 3D image of the brain from multiple X-ray cross-sections. In CT, the X-ray source and detectors rotate around the head, taking many thin slices. A computer stacks these slices and reconstructs them into a three-dimensional volume, allowing clinicians to view the brain in axial, coronal, or sagittal planes. The emphasis on taking X-ray images in layers and compiling them into a 3D picture is the hallmark of CT. Other modalities use different principles: MRI relies on magnetic fields and radio waves for detailed soft-tissue contrast; PET and SPECT image metabolic or chemical activity using radioactive tracers, not plain X-ray layers. CT is fast and widely used for acute brain injury, strokes, and hemorrhage assessment, though it involves ionizing radiation and has less soft-tissue contrast than MRI.