B.Hargreaves - RAD 229Section A2
Magnetization Preparation Sequences• Acquisition method may not give desired contrast
• “Prep” block adds contrast (and/or encoding) • MP-RAGE = Magnetization prepared rapid acquisition with
gradient echo (Mugler, ~1990) • Inversion-recovery (IR) prep • Fat saturation • T2-prep • Diffusion-weighted imaging
1
Mag Prep
Imaging Sequence
Mag Prep...
B.Hargreaves - RAD 229Section A2
Contrast Review
• Spin Echo
• PD, T1, T2
• Echo-train effects
• Gradient Echo
• bSSFP, Gradient Spoiled (T2/T1)
• RF spoiled (T1)
• PD (how?) is inefficient, T2 is not possible
2
B.Hargreaves - RAD 229Section A2
Fast Recovery (FR) or Driven Equilibrium
RF
Gz
Gy
Gx
Signal
...
...
...
...
...
180º180º90º -90º
180º
Fast-Recovery
3
B.Hargreaves - RAD 229Section A2
Fat-Saturated FSE
RF
Gz
Gy
Gx
Signal
...
...
...
...
...
180º180º90º
Fat-Sat
4
B.Hargreaves - RAD 229Section A2
Fat Suppression for Contrast
5
PD FSE Fat-Sat PD FSE
Radial cyst was otherwise iso-intense with fatCoronal Wrist Coronal Wrist
B.Hargreaves - RAD 229Section A2
Fat Saturation
• Chemically-selective excitation
• Dephaser gradient
• Normal imaging sequence
6
Frequency
. . . Sequence
Fat Water
RF BandwidthTime
Excite Fat Only
Dephase Fat Signal
FatSuppression
WaterSuppression
Unsuppressed Fat Signal
B.Hargreaves - RAD 229Section A2
Effect of Fat Saturation
Fat-Saturated (PD) Not Fat-Saturated (T1w)
7
B.Hargreaves - RAD 229Section A2
Inversion-Recovery
180º 180º
RF
Sig
nal
1
-1
0
• Fat suppression based on T1
• Short TI Inversion Recovery (STIR)
TI
8
90º
B.Hargreaves - RAD 229Section A2
Fat Suppression near B0 Inhomogeneity
Fat Sat STIR9
B.Hargreaves - RAD 229Section A2
Fluid Attenuated Inversion-Recovery
180º 180º
RF
Sig
nal
1
-1
0
• Fluid suppression based on T1
• FLAIR
TI
10
B.Hargreaves - RAD 229Section A2
Long Inversion Time (TI) - FLAIR
Long TI suppresses fluid signal11
B.Hargreaves - RAD 229Section A2
Mag-Prep: Inflow-enhanced MRA
Preparation: • Background Suppression • Fat Suppression
12
Courtesy Pauline Worters
B.Hargreaves - RAD 229Section A2
T2-Prep (Enhance T2 contrast)
RF
Gz
180º90º -90º
180º
Regular Imaging
Sequence
T2-prep + Fat-Sat Renal Artery13
B.Hargreaves - RAD 229Section A2
T2-Prep: Flow-Independent Angiography
No Prep T2-prep + IR prep14
• Inversion: Suppress synovial fluid • T2-prep: Arterial-venous contrast
Courtesy Neal Bangerter
B.Hargreaves - RAD 229Section A2
Spatial Saturation• Reduced FOV imaging
• Saturate “bands” outside FOV to prevent aliasing
15
Product full FOV SSFSE SSFSE w/ Spatial Sat.
SSFSE SSFSE w/ Sp. Sat
B.Hargreaves - RAD 229Section A2
Myocardial Tagging• Spatially selective saturation pattern (lines, grid)
• Often ‘cine’ acquisition
16
TrueFISP (bSSFP) FLASH (RF Spoiled)Courtesy J. Zwanenburg (MRM 2003)
McVeigh ER, MRI 1996
Zerhouni E, 1988
B.Hargreaves - RAD 229Section A2
Diffusion-Weighted Imaging (DWI)
RF
Gz
180º
No Diffusion
17
B.Hargreaves - RAD 229Section A2
Diffusion-Weighted Imaging (DWI)
RF
Gz
180º
Diffusing Spins
18
B.Hargreaves - RAD 229Section A2
Diffusion-Weighted Imaging (DWI)
Low b-value High b-value ADC T2 FSE
19
B.Hargreaves - RAD 229Section A2
Phase ContrastRF
Gz
x
Frequency
Position
Phase is not zero! (any position)
20
� = �(x
ZG
x
dt+ x
0Z
G
x
tdt)
“Zero Moment” “First Moment”
B.Hargreaves - RAD 229Section A2
Flow Encoded Imaging
Krishna NayakMarcus Alley21
B.Hargreaves - RAD 229Section A2
Magnetization Transfer (MT)• Saturate very-short-T2 water bound to macromolecules
• MT effect causes saturation of free water (signal loss)
• More RF generally causes more MT saturation (adverse)
• CEST: Saturation at specific frequency
22 Henkelman RM et al. NMR in Biomedicine 2001; 14(2):57-64.
Courtesy of Feliks Kogan
B.Hargreaves - RAD 229Section A2
Other Preparations
• Double IR: Non-selective, then selective
• “Black Blood”
• Multiple IR: Null multiple species simultaneously
• Arterial spin labeling (Invert blood, subtract reference)
• Diffusion preparation (tip-up)
• Motion-sensitized driven equilibrium (MSDE)
• Null vessel signal
23
B.Hargreaves - RAD 229Section A2
Summary of Magnetization Prep
• Suppression: Spatial, Fat, Blood, Fluid
• Contrast: Inversion, T2-prep, Diffusion
• Encoding: Flow/motion, Diffusion, Tagging
24
