What is the effect of increasing the matrix size on SNR, assuming other parameters are constant?

• A. Increases SNR
• B. Decreases SNR
• C. No effect on SNR
• D. Undefined effect on SNR

Answer: (B)

Increasing the matrix size in magnetic resonance imaging (MRI) typically leads to reduced signal-to-noise ratio (SNR). This occurs because a larger matrix size means that the acquired signals are spread across a greater number of pixels or voxels, resulting in smaller individual signal contributions for each pixel.

When the number of pixels is increased, the effective volume of each pixel decreases, which directly reduces the amount of signal received from each voxel. As a result, with the same total signal acquisition, the individual pixels receive less signal, while the noise level remains relatively constant. Therefore, the overall SNR decreases.

This fundamental relationship highlights an important trade-off in MRI imaging: while increasing matrix size can improve image resolution, it can compromise the clarity and quality of the signal due to the reduction in SNR. Understanding this balance is crucial for technologists when optimizing imaging parameters for specific clinical scenarios.