Which characteristic does NOT affect voxel size in MRI?

• A. Slice thickness
• B. Matrix size
• C. Field strength
• D. Field of view

Answer: (C)

In MRI, voxel size is determined by factors that influence the dimensions of each three-dimensional pixel. Slice thickness, matrix size, and field of view all play crucial roles in defining voxel size.

Slice thickness directly affects the height dimension of the voxel. A thicker slice increases the volume of the voxel, while a thinner slice reduces it.

Matrix size refers to the number of pixels in the frequency and phase encoding directions. A larger matrix size results in smaller voxels because the same area is now divided into more pixels, thereby decreasing the dimensions of each voxel.

Field of view (FOV) also affects voxel size. A larger FOV will increase the area being imaged but can decrease voxel size if the matrix size remains constant, as more area is divided by the same number of pixels.

Field strength, on the other hand, does not directly influence voxel size. It primarily affects factors like signal-to-noise ratio and image quality, but it does not change the geometrical parameters that define voxel size. Thus, it is the characteristic that does not affect voxel size in MRI.