In CT, what is voxel size and why does it matter for spatial resolution?

• A. Voxel size is the three-dimensional sampling unit; smaller voxels improve spatial resolution and reduce partial volume effects but may require higher dose or more advanced reconstruction.
• B. Voxel size is the two-dimensional picture element.
• C. Voxel size does not affect spatial resolution.
• D. Voxel size only affects color.

Answer: (A)

Voxel size is the three‑dimensional sampling unit used to discretize the scanned volume. Spatial resolution depends on how finely we sample the anatomy, so smaller voxels provide finer sampling of structures, allowing us to distinguish smaller details and reducing partial volume effects—where a voxel contains more than one tissue type and the signal becomes a blended average, blurring edges.

But making voxels smaller means each voxel contains less tissue signal, which raises image noise if the radiation dose is not increased. To keep image quality acceptable, you either increase the dose to boost the photon count or apply more advanced reconstruction techniques to suppress noise while preserving detail.

Voxel size is set by the field of view, matrix size, and slice thickness, so choosing smaller voxels improves resolution but comes with higher dose or computational demands along with the need for appropriate reconstruction methods.

It’s not a two‑dimensional pixel, and it does matter for spatial resolution; CT voxels describe 3D sampling, not color.