180° RF pulse
A 180° RF pulse can rephase spins and reverse static field inhomogeneities.
After a 90° RF pulse, spins dephase and transverse magnetization decreases. If we apply a 180° RF pulse, spins rephase and transverse magnetization reappears.
How can a 180° RF pulse rephase spins? Consider the following race:
- Once the race starts (the relaxation begins), the turtle and the rabbit are at the same place (the starting line): they are in phase.
- As the rabbit runs faster, there is a distance between him and the turtle: they dephase.
- Then both have to turn around and go back (180° RF pulse)
- Assuming they are both going at the same speed as before, they arrive at the same time at the starting (finish) line : they rephase.
The 180° RF pulse restores phase coherence:
- After the 90° RF pulse spins dephase (during a time defined as TE/2)
- After the 180° RF pulse, spins are back in phase at time TE after the 90° RF pulse
- Then they dephase again.
At time TE (Echo Time), the signal is not as high as the initial transverse magnetization intensity. As the 180° RF pulse reverses dephasing due to static field inhomogeneities but not spin-spin relaxation, the signal loss is due to pure T2 effect.
The signal enveloppe joining maximums of echos after 180° RF pulses is corresponding to the pure T2 decay curve.
Increasing interventional radiology capacity while reducing patient radiation
Pourquoi avoir une gestion en temps en réel de la dose d'irradiation des patients ?
BRACCO IMAGING FRANCE
The first fully digital C-arm
Solution integrée, injection et exposition
Clinical uses for CT Liver Analysis application