If TE is increased in a spin echo pulse sequence, what effect does this have?

Increasing the echo time (TE) in a spin echo pulse sequence primarily enhances the effect of T2 relaxation on the generated signal. The T2 relaxation time is related to how quickly the spinning protons in the tissue lose coherence after being excited by a pulse. As TE is increased, there is more time for T2 decay to occur before the signal is read, which means that tissues with shorter T2 times will lose signal amplitude more quickly. This leads to an increase in T2 weighting because contrast is enhanced between tissues based on their T2 characteristics.

Consequently, tissues with longer T2 times will appear relatively brighter because they retain more signal compared to those with shorter T2 times, which have diminished signal due to the longer TE. This adjustment influences the contrast seen in the final image and highlights differences in tissue types that are sensitive to T2 effects.

For this reason, increasing TE results in greater T2 weighting, making it the correct choice in this scenario.