Unit 4 - Gradient Echo Sequences Flashcards
State how gradient echo sequences differ from spin echo sequences
-they use variable excitation pulse flip angle less than 90 degrees
-they use gradients to rephase magnetic moments
Describe how using different flip angles affect NMV
the excitation pulse flip angle is less than 90 degrees so the flip angle can be any angle
Identify the characteristics and the RF pulse flip angle for a gradient echo (GRE)
-FID occurs immediately after RF pulse
Discuss how the spins in the vector are caused to rephase in GRE sequence
a gradient is applied
Define spoilers
gradients that dephase magnetic moments
Define rewinders
gradients that rephase
Describe parameters in GRE T1 weighting
short TE, short TR, large flip angle
Describe parameters in GRE T2* weighting
long TE, long TR, small flip angle
Describe parameters in GRE PD weighting
short TE, long TR, small flip angle
Define steady state
energy in = energy out
Define residual transverse magnetization
leftover transverse magnetization is produced because of previous RF excitation pulses
Discuss coherent gradient echo
will use a reminder gradient to rephase, to then produce a gradient echo
Uses for coherent GRE sequences
typically are used to generate T2* weighted images in a very short scan time
Discuss incoherent gradient echo
aka as a spoiled gradient echo, residual magnetization is dephased or spoiled to minimize effect on image control
Uses for incoherent GRE sequences
used to produce T1 and PD weighted images