Voxel size

Voxel size is an important component of image quality. Voxel is the 3-D analog of a pixel. Voxel size is related to both the pixel size and slice thickness.  Pixel size is dependent on both the field of view and the image matrix. The pixel size is equal to the field of view divided by the matrix size. The matrix size is typically 128x, 256x or 512x. Pixel size is typically between 0.5 and 1.5 mm. The smaller the pixel size, the greater the image spatial resolution.

Increased voxel size results in an increased signal-to-noise ratio. The trade-off for increased voxel size is decreased spatial resolution. Voxel size can be influenced by receiver coil characteristics. For examples, surface coils indirectly improve resolution by enabling a smaller voxel size for the same signal-to-noise ratio.

Voxel size can contribute to artifacts in MRI. Many MR artifacts are attributable to errors in the underlying spatial encoding of the radiofrequency signals arising from image voxels. Motion artefacts can occur in the phase-encoding direction because a specific tissue voxel may change location between acquisition cycles, leading to phase encoding errors. This manifests as a streak or ghost in the final image, and can be reduced with image gating and regional presaturation techniques.