Which of the following adjustments helps to improve SNR in an MR image?

Increasing the repetition time (TR) enhances the signal-to-noise ratio (SNR) in an MR image because a longer TR allows for greater relaxation of the spins in the tissue before the next excitation pulse. This extended relaxation time enables more longitudinal magnetization to develop, leading to a stronger signal when the MRI system captures the data.

In this context, enhanced SNR is critical for better image quality, as it reduces the impact of noise relative to the actual signal being measured. A higher SNR results in more detailed images that are easier to interpret.

The other options may affect image parameters but do not specifically target SNR improvement as effectively as increasing TR. Reducing the phase matrix, for instance, may lead to faster imaging times and potentially less overall scan time, but it risks losing resolution and detail. Reducing pixel size can actually lead to a decreased SNR because smaller pixels each capture less signal; they may also introduce more noise. Increasing the field of view (FOV) can potentially increase SNR, but it generally does so by sacrificing spatial resolution since larger FOVs can dilute the signal in larger areas.