Let’s see how we can create a T1-weighted image with this signal equation. To do so, we would want any contribution from T2 to go towards 1. Why 1 (one)? Because if we were to drive the T2 contribution to ZERO, we would have no signal at all. So remembering a bit more math, we need to somehow make the second term go towards one:

So, how do we do that with an exponential? A number to the 0 (zero) power is equal to 1. By decreasing TE (or echo time), we can drive this part within the parentheses towards 1. We do NOT want a large TE, because that would instead drive the term towards 0 (zero).

If you are reading this at your PACS station, pull up a T1-weighted and a T2-weighted sequence. In general, The T1-weighted sequence should have a much much shorter TE (typically a few milliseconds) than a T2 weighted sequence (typically high double digit milliseconds). Since it is difficult (not impossible!) to have ZERO TE sequences, we tend to have these single digit TE T1-weighted sequences.