Subject: How does radio wave absorbtion work in MRI?

For my hsc course there are limited sources offering the information i need. 
My problem is that my sources contradict eachother. Both are similar in that 
they explain how the radio frequency matches that of the hydrogen protons and 
that protons absorb the incident wave and all begin to precess in phase with 
each other. One source though, explains "Once in phase, the nuclei will stay 
in phase until the external radio pulse is turned off. The nuclei now start to 
lose energy. They go out of phase and release a radio frequency signal at 
their Larmor frequency. The radio receiver detects these." While the other 
source states "Although the nuclei are precessing they will not be doing so in 
phase (in time). As a result there will be no net transverse (across the 
external field) magnetism. A pulse of radio waves at the Larmor frequency will 
force the precessing nuclei to do so in phase, ie they all precess together. 
This means that they will have a net transverse magnetism component which 
rotates. The precessing transverse magnetic field is in effect a changing 
field. It will induce a small AC emf in a receiving coil. This emf will have 
the same frequency as the precessing nuclei ie the Larmor frequency." So one 
sates the radio wave is reemitted after the pulse turns off while the other 
states the radio wave is reemitted while the pulse is on. Which one is correct?
Thankyou very much for taking the time to read my question.

Re: How does radio wave absorbtion work in MRI?