Introduction to MRI: Basic Pulse Sequences, TR, TE, T1 and T2 weighting 

isn't fat saturation just some inversion recovery, where you give a 180° RF impulse with specific timing for fat and apply a 90° RF puls when the fat is at a 90° angle so it wont be affected? thus the 90° RF impulse only affects every other proton that is not parallel to this impulse?

If im not mistaken, it is because we want some amount of dephasing, such that fat and water will give of different signal intensity. If they are all in phase (short te), it will be harder to tell the difference in tissue composition.

@@9cobil299 You are right Well out

An RF pulse is transmitted to the tissue. The tissue absorbs part of the energy of this RF pulse. Then the tissue releases this energy in the form of another RF pulse (that has a different shape). I think this is what is referred to as "echo". It's the echo of the RF pulse transmitted by the MRI machine, that comes from the tissue that is being scanned. The tissue abrorbs the RF pulse and (kind of) releases it back so it can be received by the MRI machine.

the echo is the frequency of the precession of the protons that if you activate the antenna at a specific time (TE) will net you a current in the coils, which can be interpreted via an algorithm

The echo is the rf signal received back into the coil from the body. This signal is what we use to create images

​@@amartinezsilberstein your comment is all i need today 😭