In MRI, spatial resolution is primarily defined by which characteristic?

• A. Repetition time
• B. Fat saturation
• C. Voxel size
• D. Field strength

Answer: (C)

Spatial resolution in MRI refers to the ability to distinguish between two closely spaced objects within the image. It is fundamentally determined by voxel size, which is the three-dimensional equivalent of a pixel. The volume of a voxel is defined by the dimensions of the pixel in the two-dimensional image plane and the slice thickness in the third dimension.

A smaller voxel size allows for finer detail to be captured in the MRI images, which enhances the spatial resolution. This is particularly crucial when imaging structures that are adjacent to one another, as larger voxels might blend these structures together, leading to a loss of detail and clarity in the image.

In contrast, repetition time relates to the timing of the radio frequency pulses and their recovery, affecting image contrast rather than resolution. Fat saturation is a technique used to suppress signals from fat but does not influence the ability to resolve spatial details in an image. Field strength can impact overall image quality and signal-to-noise ratio, but it does not directly dictate spatial resolution in the same way that voxel size does.