Unit 4 - Gradient Echo Sequences

Question 1

State how gradient echo sequences differ from spin echo sequences

Answer 1

-they use variable excitation pulse flip angle less than 90 degrees

-they use gradients to rephase magnetic moments

Question 2

Describe how using different flip angles affect NMV

Answer 2

the excitation pulse flip angle is less than 90 degrees so the flip angle can be any angle

Question 3

Identify the characteristics and the RF pulse flip angle for a gradient echo (GRE)

Answer 3

-FID occurs immediately after RF pulse

Question 4

Discuss how the spins in the vector are caused to rephase in GRE sequence

Answer 4

a gradient is applied

Question 5

Define spoilers

Answer 5

gradients that dephase magnetic moments

Question 6

Define rewinders

Answer 6

gradients that rephase

Question 7

Describe parameters in GRE T1 weighting

Answer 7

short TE, short TR, large flip angle

Question 8

Describe parameters in GRE T2* weighting

Answer 8

long TE, long TR, small flip angle

Question 9

Describe parameters in GRE PD weighting

Answer 9

short TE, long TR, small flip angle

Question 10

Define steady state

Answer 10

energy in = energy out

Question 11

Define residual transverse magnetization

Answer 11

leftover transverse magnetization is produced because of previous RF excitation pulses

Question 12

Discuss coherent gradient echo

Answer 12

will use a reminder gradient to rephase, to then produce a gradient echo

Question 13

Uses for coherent GRE sequences

Answer 13

typically are used to generate T2* weighted images in a very short scan time

Question 14

Discuss incoherent gradient echo

Answer 14

aka as a spoiled gradient echo, residual magnetization is dephased or spoiled to minimize effect on image control

Question 15

Uses for incoherent GRE sequences

Answer 15

used to produce T1 and PD weighted images