What factor does not improve SNR during MRI scans?

• A. Decreasing slice thickness
• B. Increasing voxel size
• C. Reducing noise
• D. Increasing repetition time (TR)

Answer: (B)

In MRI, signal-to-noise ratio (SNR) is a critical factor that affects image quality. Understanding the various factors that influence SNR helps in optimizing imaging techniques.

The choice indicating that increasing voxel size does not improve SNR is accurate because it highlights an important relationship in MRI. Voxel size is a product of both the slice thickness and the in-plane resolution (pixel size). When you increase the voxel size, you may capture more signal from the tissue being imaged, but this can also lead to a loss in spatial resolution. Therefore, while larger voxels can sometimes improve SNR, they often compromise the clarity of the image.

On the other hand, decreasing slice thickness, reducing noise, and increasing repetition time (TR) are all factors that can enhance SNR. Decreasing slice thickness helps to concentrate the signal from a thinner volume, while reducing noise related to external factors enhances the ability to distinguish true signals. Increasing TR allows for more relaxation of the spins, which can accumulate more signal over time.

In summary, while increasing voxel size can boost signal reception at the expense of spatial resolution, it does not inherently improve SNR to the same extent as the other factors mentioned.