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12_MRI_LOCALIZATION - Coggle Diagram
12_MRI_LOCALIZATION
SLICE SELECTION
Gss - Gz
during the entire duration of RF pulse excitation
linear space resonance relationship
single dimension selection
plane
sagittal
transverse
coronal
dimension
alti -> slice sottili
bassi -> slice larghe
RF pulse
caso ideale
spatial selection function
rectuangular
FT
sinc
homogeneus flip angle
flat angle
hard pulses
poco selettivi
caso reale
trunucated sinc envelope
Gibbs ringing
slice cross- talk artifacts
slice edges blurred
Refocusing gradient needed
duration
half of the area under Gss
tp/2
immediately after RF pulse
if 180, no need
FREQUENCY ENCODING
Gfe - Gx
during entire RO phase
different LF frequencies
apply the right gradient while sampling
assegno diverse frequenze ai segnali locali
il gradiente ruota attorno al volume, ho linee lungo cui integrare e poi sommo
based on the different Larmor frequencies displayed by the parallel planes
varia linearmente
artifacts : CS
PHASE ENCODING
Gpe - Gy
on and off between end excitation and start RO
PE1 PE2 vectorially combined
le differenze di fase vengono accumulate durante tpe
è la fase che varia linearmente attraverso i piani paralleli
K-space
sample= to Fourier space
dimension
spatial frequency in cycles per cm
gradient = time derivative of vector k
trajectory and sampling
preparation inverse gradient Tacq/2
SE inversion pulse
no preparation phase
artifacts: movement
Tecniche di imaging
3D imaging
2D PE
1D FE
Point localization
3D SS
1D imaging
1D FE
1D PE
1D SS