What happens to SNR when TE is increased?

Signal-to-noise ratio (SNR) is an important factor in MRI, indicating how much useful information (signal) can be distinguished from background noise. When the echo time (TE) is increased, there are several key effects that occur.

As TE increases, the time between RF pulse and the signal acquisition becomes longer. During this extended period, the tissues begin to relax, leading to a decrease in signal amplitude. The longer the TE, the more the signal decays due to T2 relaxation processes. This decline in signal amplitude directly affects the SNR negatively, as noise in the system remains relatively constant, thus reducing the overall ratio of signal versus noise.

Therefore, with an increase in TE, SNR decreases because the signal intensity continues to diminish without a compensatory increase in noise, resulting in a poorer quality image. This relationship is crucial for optimizing MRI imaging parameters to achieve the best diagnostic information while minimizing artifacts.