Presentation 25

4/22/2014
“When to use What sequences”
Govind Chavhan, MD, DNB, DABR
Assistant Professor and Staff Radiologist
The Hospital For Sick Children, Toronto
Outline
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TR, TE and Imaging time
4 groups of sequences and their subtypes
Comparison of contrast, resolution and speed of
acquisition offered by each sequence
Why should we use a sequence in particular situation
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Basic Principles:
Few terms
 TR
 TE
 Transverse
Relaxation
 Magnitude of TM =
Strength of MR signal
Basic Principles:
Imaging time
 No. of TRs
 No. of k-space lines
 128x128 matrix =
128 k-space lines
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Sequences:
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Spin-echo
Gradient echo
Inversion Recovery
Echo Planar
Imaging
Classification
 Sequences
 Spin-echo
Spin-echo sequence:
 Gradient echo
Design
 900 -1800 pulses
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Spin-echo sequence:
 Dual SE
 Fast (Multi) SE
 FRFSE
 Single-shot FSE
Modifications
 ETL
 Turbo
Factor
Spin-echo sequences:
SEQUENCES
Trade names
SIEMENS*
GE *
PHILIPS*
Conventional SE (900 -1800 RF pulses)
SE
SE
SE
Double SE
(900 followed by two 1800 RF pulses)
PD/T2
PD/T2
PD/T2
Multi SE
(900 followed by multiple 1800 RF pulses)
Turbo SE
Fast SE
Turbo SE
Multi SE with flip-back 900 pulse
RESTORE
FRFSE
DRIVE
Single-shot Multi SE
(Multi SE with half k-space filling)
HASTE
Single Shot
FSE
Ultrafast
SE
Spin Echo sequences
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Gradient Echo sequence:
Design
 No 1800 pulse
 No 900 pulses
 T2* relaxation
Gradient Echo sequence:
Types
 GRE Sequences
 Depends on what
is done to
residual TM after
signal is received
 Residual TM
 Residual TM
 Spoiled- T1-w
SPOILED
REFOCUSED
 SS- T2-w
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Gradient Echo sequences:
Trade names
Gradient Echo Sequences
Siemens
GE
Philips
A. Incoherent spoiled TM
FLASH
SPGR
T1-FFE
3D FLASH
VIBE
LAVA
FAME
THRIVE
1. Post excitation refocused (FID sampled)
FISP
GRASS
FFE
2. Pre-excitation refocused
(Spin echo sampled)
PSIF
SSFP
T2-FFE
3. Fully refocused
(both FID & spin echo sampled)
True FISP
FIESTA
Balanced
FFE
3D versions
B. Coherent/Rephased TM
 T1-w GRE
T1 FLASH
Pre-Gd
Late arterial
Portal venous
Delayed venous
8 min
11 min
Dyn VIBE
In-phase
TE 4.6ms
Out-phase
TE 2.3ms
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 T2-w GRE
MPGR
PSIF
TrueFISP
T2 FFE
DESS
Inversion Recovery sequence:
Design
 1800 Inversion
pulse
 T1 differences
increased
 Contrast between
H2O and fat
increased
 Tissue suppression
TI = Time to invert
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Inversion Recovery sequence: Types
 Depending on TI
used
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Short TI (80-150 ms)
e.g. STIR
Medium TI (200-1000 ms)
e.g. MPRAGE
Long TI (1500-2500 ms)
e.g. FLAIR
IR sequences: STIR vs FLAIR
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IR sequences: STIR vs FLAIR
STIR
Vs
FLAIR
Short TI of 80-150 ms
1.
Long TI of 1500-2500 ms
Combined T1 and T2 weighting
2.
Heavily T2 weighted images
Fat, white matter are suppressed
3.
CSF, water is suppressed
Mainly used in body imaging
4.
Used in neuroimaging
Cannot be used in post contrast
5.
Can be used in post contrast
imaging.
Echo Planar Imaging:
 Single TR
 SE-EPI
 GRE-EPI
Design
 All k-space lines filled in a single TR
Limitations: Very sensitive to
susceptibility artifacts, Low resolution
and SNR
 Multishot EPI to improve SNR- a
portion of k-space is filled per TR
 Hybrid EPI combines SE (to reduce
susceptibility) and GRE (speed)
 Diffusion, Perfusion and fMRI
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Comparison of Sequences
 T1-w
3-5 Min
Speed
T1 contrast
T1 TSE
1-3 Min
T1 FLASH
15-20
Sec
T1 VIBE
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T2 TSE
 T2-w
3-5 Min
STIR
Resolution
TruFisp
Speed
4-6 Min
SS TSE
In Sec
BH
EPI T2 b=0
bTFE
15-20
Sec
In Sec
BH
 T2*-w
T2FFE
MPGR
EPI T2*
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 Post Gd T1-w
3-5 Min
Speed
T1 contrast
T1 TSE
1-3 Min
T1 TFE
15-20
Sec
THRIVE
What sequence?
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Solid organ imaging
Bowel imaging
Fluid imaging
Anatomic imaging
Vessel imaging
Marrow imaging
Cartilage imaging
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 Solid organ
imaging: Abd
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Lesion detection
Characterization by pre and
post Gd signal intensity
T1-w: TSE, In-out-phase, pre
dynamic 3D GRE
T2 FSE FS
T2-w: T2 TSE FS, STIR,
Post Gd: dyn- T13D GRE, T1TSE FS
Opt: single-shot if patient uncooperative and irregular breathing,
Balanced- vascular anatomy
T2 SS FSE FS
Trufi
 Solid organ
imaging: Brain
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Lesion detection
Characterization by pre and
post Gd signal intensity
T1-w: TSE, 3D T1 GRE
T2-w: T2 TSE, FLAIR
Post Gd: T13D GRE, T1TSE FS
Congenital malformation/
dysplasia- Medium TI IR
Opt: single-shot if patient uncooperative
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 Moving target
Imaging
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Bowel
Fetal
T1-w: TFE>TSE, pre 3D T1 GRE
T2-w: Single-shot, Balanced
Post Gd: T13D GRE, T1TFE FS
T2 FSE FS
T2 SS FSE FS
Gd+ T1 FS
 Moving target
Imaging
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Gd+ Thrive
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bTFE FS
Heart
T2 SS FSE
Balanced SSFP
– T2/T1
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 Anatomic
Imaging
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SNR
Thin
sections
bTFE
T2
bTFE
 Anatomic
Imaging
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T2
Soft tissue, bone & vessel anatomy
 Thin sections
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T1-w and T2-w 3 planes
TSE>TFE, FSE>SS
Balanced- vascular anatomy
bTFE
T2 FSE
T2 FSE FS
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 Anatomic
Imaging
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T1-w and T2-w 3
planes
TSE>TFE, FSE>SS
Balanced- vascular
anatomy
T1 TFE
T1 TSE
T2 FSE FS
 Marrow Imaging
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T2 FSE FS
T2 FFE
STIR/T2 FS
T1
T1 FSE
T2 FFE
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 Vessel Imaging
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Anatomic
continuity
Patency
MRA/MRV
 CEMRA
 Balanced TFE
 T1 SE thin
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T1 TSE
T1 TSE
2D TOF MRV
 Vessel Imaging
T1 TSE
DWI
2D TOF MRV
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 Cartilage
Imaging
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T2 FFE
OCD
PD
Sequences:
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T2 FSE FS
Summary
Sequences offer different contrast, resolution
and speed of acquisition
They should be used to suit our needs
In general, SE offer better contrast and
resolution and GRE offer speed
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Thank You
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