Large voxels produce a higher SNR than small voxels due to which of the following reasons?

• A. Higher spatial resolution
• B. More H nuclei
• C. Longer echo times
• D. Thinner slice thickness

Answer: (B)

Larger voxels produce a higher signal-to-noise ratio (SNR) primarily because they contain a greater number of hydrogen nuclei (H nuclei). In MRI, the SNR is heavily influenced by the amount of signal that can be received, and this signal is generated from the protons in the tissues being imaged. When larger voxels are used, more protons can contribute their signals during image acquisition, which leads to an overall increase in the SNR.

This increase occurs because the SNR is proportional to the square root of the number of protons within the voxel; therefore, with more protons present in a larger voxel, not only is the amount of signal increased, but the overall statistical representation of that signal is enhanced, thereby improving the SNR.

The other options do not explain the relationship between voxel size and SNR. Higher spatial resolution would typically be associated with smaller voxels, which would actually decrease SNR because fewer protons are available to generate the signal. Longer echo times can impact image contrast and the quality of the signal but do not directly correlate to an increase in SNR due to voxel size. Thinner slice thickness is related to spatial resolution but similarly decreases SNR, as it reduces the volume of tissue