voxelsize

Voxel size is a basic property of 3D image data that describes the physical edge length of a voxel, the smallest unit in a three-dimensional grid. It is typically expressed as a three‑value vector [dx, dy, dz], with units such as millimeters or micrometers. If dx = dy = dz, the voxels are isotropic; otherwise they are anisotropic, which is common when in-plane resolution differs from slice thickness.

Voxel size is determined by acquisition and reconstruction parameters. In medical imaging, it depends on factors such as the field of view, image matrix, and slice thickness, as well as scanner geometry. In microscopy and micro-CT, voxel sizes are often in micrometers or nanometers. The chosen voxel size sets the spatial sampling of the data and influences the detectable detail.

Voxel size matters for quantitative analysis. Volumes and surfaces are computed from voxel counts via the voxel volume (dx × dy × dz). Smaller voxels provide higher apparent resolution but require more memory and processing time and can amplify noise. Analyses may prefer isotropic voxels, but resampling to isotropy is common when algorithms assume equal spacing, though resampling does not restore true resolution.

Metadata and formats: voxel size is stored in image metadata. DICOM represents this as Pixel Spacing and Slice Thickness; NIfTI uses pixdim or spacing; other formats use equivalent fields. Clear reporting of voxel size is essential for reproducibility and for comparing measurements across datasets.

Common considerations include avoiding the assumption of isotropy, accounting for partial volume effects, and distinguishing voxel counts from real-world dimensions when interpreting results.