Img Prod. Flashcards
If a Dual Spin Echo has a short T1 and a long T2, can it have both T1 and T2 in a sequence?
False, there can only be one weighting
What parameters control T1 and T2 weighting on images?
TR controls T1
TE controls T2
Do T1 recovery and T2 dephasing occur at the same time? If not, which one is faster?
T1 recovery and T2 dephasing occur at the same time, but at different rates. T2 dephasing occurs faster than T1 recovery
What is T2 relaxation/decay time?
T2 relaxation/decay time refers to the time it takes for 63% of transverse net magnetization to be lost (or recovered in the longitudinal plane)
What is the Larmor Equation? What does each parameter represent?
w = yB0
w = angular precessional frequency of the proton
y = gyromagnetic ratio
B0 = strength of external magnetic field
What does NMV stand for?
Net Magnetization Vector
What is it called when Rf is transmitted at the same Larmor Frequency as hydrogen?
Resonance
True or False: the three gradient echoes have no function during spin echo sequences, they are only used in gradient echoes
False
If you minimize T1 and T2 effects, what type of weighting are you going to get?
PD
PD = short TE and long TR
TR
repetition time (time from initial excitation pulse to the next one)
TE
echo time (time from initial excitation pulse to the signal readout)
Flip Angle
degree at which the NMV is deflected from the longitudinal axis
TI
inversion time (time between an inversion pulse and a 90 pulse)
Echo Train Length/Turbo Factor
number of echoes acquired after the initial excitation
T1 SE
short TE (10 ms)
short TR (500 ms)
T2 SE
long TE (100 ms)
long TR (5000 ms)
PD SE
short TE (10 ms)
long TR (5000 ms)
T1 GE
large flip angle (70)
short TE (5-10 ms)
short TR (<50 ms)
T2 GE
small flip angle (20)
long TE (15-25 ms)
long TR (>200 ms)
PD GE
small flip angle (20)
short TE (5-10 ms)
long TR (<200 ms)
What is the name of the signal produced by the excitation pulse?
FID = free induction decay, rephased by the gradients
Scan time Calculation
(TRxNEXxphase)/ETL
Looking at a FSE pulse sequence, count how many RF pulses occur during each TR period
Count all pulses on diagram, including the 90 and 180
What determines the depth dimension of a voxel?
Slice thickness
voxel size = (FOV/matrix)* slice thickness
Pixel size = (FOV/matrix)
Pulses that employ multiple RF pulses (such as IR) should be used sparingly because they have the same tissue effects such as heating
False
What do Inversion Recovery pulse sequences start with?
180 pulse
What are the units of the Larmor Equation?
MHz
When the matrix is finer
the resolution is higher but the signal is lower
STIR
short tau inversion recovery
If you increase NEX
n = sqr(n)
What does a FLAIR sequence null?
CSF
