In k-space, how can the SNR be affected?

In k-space, the signal-to-noise ratio (SNR) can indeed be affected by changing the echo time duration. When the echo time (TE) is adjusted, it influences the degree of T2 weighting in the images, which directly relates to the amount of signal collected from the tissues being imaged. A longer echo time typically results in increased signal decay from tissues with shorter T2 relaxation times, thus reducing the overall SNR. Conversely, a shorter echo time allows for the acquisition of the signal before significant decay occurs, thus improving SNR. This relationship highlights the pivotal role that echo time plays in optimizing the balance between image contrast and the inherent noise present in the acquired signals.

The other methods listed influence various aspects of image acquisition but do not directly manipulate the fundamental relationship between signal strength and noise. For example, adjusting phase encoding steps affects resolution and image clarity but doesn’t directly alter SNR like echo time does. Similarly, while gradient strength impacts spatial encoding and can influence the overall image quality, it doesn't have the direct effect on the tissue signal decay represented by echo time. The number of sampled echoes could affect the amount of data collected and may provide more information, but it does not inherently improve SNR unless it's coupled with techniques