12 medphys mri 5 - uni-heidelberg.de...spin-echo: contrast agent - intravenous injection of 0.1...
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RUPRECHT-KARLS-UNIVERSITY HEIDELBERG
Computer Assisted Clinical MedicineProf. Dr. Lothar Schad
12/9/2008 | Page 1Master‘s Program in Medical Physics
Chair in Computer Assisted Clinical MedicineFaculty of Medicine Mannheim University of HeidelbergTheodor-Kutzer-Ufer 1-3D-68167 Mannheim, GermanyLothar.Schad@MedMa.Uni-Heidelberg.dewww.ma.uni-heidelberg.de/inst/cbtm/ckm/
Physics of Imaging Systems
Basic Principles of Magnetic Resonance Imaging V
Prof. Dr. Lothar Schad
RUPRECHT-KARLS-UNIVERSITY HEIDELBERG
Computer Assisted Clinical MedicineProf. Dr. Lothar Schad
12/9/2008 | Page 2
Imaging Contrast
Imaging Contrast
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RUPRECHT-KARLS-UNIVERSITY HEIDELBERG
Computer Assisted Clinical MedicineProf. Dr. Lothar Schad
12/9/2008 | Page 3
kx
k-space: after 1. TR k-space: after 2. TR k-space: after 256. TRky
Spin-Echo Sequence
RUPRECHT-KARLS-UNIVERSITY HEIDELBERG
Computer Assisted Clinical MedicineProf. Dr. Lothar Schad
12/9/2008 | Page 4
PwTR = 2775 ms
TE = 17 ms
T2wTR = 2775 msTE = 102 ms
T1wTR = 575 msTE = 14 ms
Spin-Echo Images
32143421factorT2
2TE/T
factorT1
1TR/TSE ]1[S
−
−
−
− ⋅−⋅= eeρ
- SE gold standard technique for T1 and T2 morphology
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RUPRECHT-KARLS-UNIVERSITY HEIDELBERG
Computer Assisted Clinical MedicineProf. Dr. Lothar Schad
12/9/2008 | Page 5
TR
TE
90
-
60ms
40
-
10ms
T1-weighted
T2-weighted
proton-weighted
300 - 800 ms 1500 - 3000 ms
no contrastSNR low
Spin-Echo Contrast: TR, TE
RUPRECHT-KARLS-UNIVERSITY HEIDELBERG
Computer Assisted Clinical MedicineProf. Dr. Lothar Schad
12/9/2008 | Page 6Spin-Echo: T1 Dependency
source: Reiser and Semmler. “Magnetresonanztomographie” 2002
T1-factor:[1-exp(-TR/T1)]
GM: T1 = 970 msWM: T1 = 600 ms
contrastBA
BA
SSSSC
+−
=
T1 - factor
WM
T1 - contrast
GM
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RUPRECHT-KARLS-UNIVERSITY HEIDELBERG
Computer Assisted Clinical MedicineProf. Dr. Lothar Schad
12/9/2008 | Page 7Spin-Echo: T2 Dependency
T2-factor:exp(-TE/T2)
GM: T2 = 110 msWM: T2 = 90 msT2 - factor
WM GM
T2 - contrast
source: Reiser and Semmler. “Magnetresonanztomographie” 2002
RUPRECHT-KARLS-UNIVERSITY HEIDELBERG
Computer Assisted Clinical MedicineProf. Dr. Lothar Schad
12/9/2008 | Page 8Spin-Echo: TR, TE
source: Schlegel and Mahr. “3D Conformal Radiation Therapy: A Multimedia Introduction to Methods and Techniques" 2007
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RUPRECHT-KARLS-UNIVERSITY HEIDELBERG
Computer Assisted Clinical MedicineProf. Dr. Lothar Schad
12/9/2008 | Page 9Spin-Echo: TR, TE
SE contrast betweengrey and white matter
RUPRECHT-KARLS-UNIVERSITY HEIDELBERG
Computer Assisted Clinical MedicineProf. Dr. Lothar Schad
12/9/2008 | Page 10Spin-Echo: Multi-Slice
measurement #1
measurement #2
- interleaved SE measurement
- multi-slice SETR = 600 ms, TE = 10 ms→ about 60 slices can be measured
simultaneously !
1. slice
2. slice
3. slice
4. slice
5. slice
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RUPRECHT-KARLS-UNIVERSITY HEIDELBERG
Computer Assisted Clinical MedicineProf. Dr. Lothar Schad
12/9/2008 | Page 11Inversion Recovery Sequence
Mz
|Mz|
source: Reiser and Semmler. “Magnetresonanztomographie” 2002
RUPRECHT-KARLS-UNIVERSITY HEIDELBERG
Computer Assisted Clinical MedicineProf. Dr. Lothar Schad
12/9/2008 | Page 12Inversion Recovery Images
321444 3444 21factorT2
TE/T2
factorT1
TR/T1TI/T1IR ]21[S
−
−
−
−− ⋅+−⋅= eeeρ
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RUPRECHT-KARLS-UNIVERSITY HEIDELBERG
Computer Assisted Clinical MedicineProf. Dr. Lothar Schad
12/9/2008 | Page 13Inversion Recovery Contrast
- WM and GM contrast dependency on TI, TR and TE- IR gold standard technique for T1 contrast
source: Reiser and Semmler. “Magnetresonanztomographie” 2002
T1-contrast
T2-contrast
contrast [a.u.]
T2-contrast
RUPRECHT-KARLS-UNIVERSITY HEIDELBERG
Computer Assisted Clinical MedicineProf. Dr. Lothar Schad
12/9/2008 | Page 14
α
- example: α = 20° Mz - reduction by 6%Mxy- value 34% of Mz!!
M
x´,y´
z
Mz
Mxy
Gradient-Echo Sequence
spoiler
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RUPRECHT-KARLS-UNIVERSITY HEIDELBERG
Computer Assisted Clinical MedicineProf. Dr. Lothar Schad
12/9/2008 | Page 15
txGtdxGtx x
t
x ⋅⋅⋅−=⋅⋅−⋅= ∫ γγφ0
ˆ),(τ≤≤ t0
)(
ˆ),(
τγτγ
γγφτ
−⋅⋅⋅+⋅⋅⋅−=
⋅⋅⋅+⋅⋅⋅−= ∫txGxG
tdxGtxGtx
xx
t
xxττ 2≤≤ t
source: Liang and Lauterbur. “Principles of Magnetic Resonance Imaging” 2000
in rot. frame:
Gradient-Echo: Phase
RUPRECHT-KARLS-UNIVERSITY HEIDELBERG
Computer Assisted Clinical MedicineProf. Dr. Lothar Schad
12/9/2008 | Page 16Gradient-Echo: Steady-State
αcos1)1(MM TR/T1
TR/T10SS
z −
−
−−⋅
=e
enumber of RF
example: WMT1 ~ 600 msTR = 25 ms
*TE/T2SSzxy sinMMS −⋅=∝ eα
Mz steady-state:
Mxy steady-state:source: Reiser and Semmler. “Magnetresonanztomographie” 2002
dephasing oftransversal
magnetization
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RUPRECHT-KARLS-UNIVERSITY HEIDELBERG
Computer Assisted Clinical MedicineProf. Dr. Lothar Schad
12/9/2008 | Page 17Gradient-Echo: FLASH
Haase et al. JMR 1986
FLASH signal: 3214434421 actor*T2
*TE/T2
actorT1
1
1FLASH cosE1
sin)E1(Sf
f
e−
−
−
⋅−−
⋅=ααρ with E1 = exp(-TR/T1)
Ernst-angle: ( )TR/T1E arccos −= eα
FLASH: “fast low angle shot”
contrast [a.u.] contrast [a.u.]
T1-contrast
ρ-contrast
RUPRECHT-KARLS-UNIVERSITY HEIDELBERG
Computer Assisted Clinical MedicineProf. Dr. Lothar Schad
12/9/2008 | Page 18
SE GE
α = 90° / 180°TE = 20 ms
TR = 600 ms
Taq: minutes
α = 25°TE = 7 ms
TR = 20 ms
Taq: seconds !!
Gradient-Echo: Measuring Time
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RUPRECHT-KARLS-UNIVERSITY HEIDELBERG
Computer Assisted Clinical MedicineProf. Dr. Lothar Schad
12/9/2008 | Page 19Gradient-Echo: Examples I
spin-echoTR = 680 msTE = 15 msα = 90°
T1-contrast
3D FLASHTR = 60 msTE = 40 msα = 25°
T2*-contrast
2D FLASHTR = 170 ms
TE = 5 msα = 70°
T1-contrast
- no T2 contrast with gradient-echo technique !
RUPRECHT-KARLS-UNIVERSITY HEIDELBERG
Computer Assisted Clinical MedicineProf. Dr. Lothar Schad
12/9/2008 | Page 20
CT SETE = 20 ms
GETE = 20 ms
normal bone
osteoporosis
Gradient-Echo: Examples II
susceptibilityeffect
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RUPRECHT-KARLS-UNIVERSITY HEIDELBERG
Computer Assisted Clinical MedicineProf. Dr. Lothar Schad
12/9/2008 | Page 21Gradient-Echo: FISP
- FISP: “fast imaging with steady precession”- steady-state free precession sequence: SSFP- no spoiler, all phases are compensated- Mxy contributes to Mz→ more signal !- FISP signal for TR<<T1 and TR<<T2*:
Oppelt et al. Electromedica 1986
321444444 3444444 21 factor*T2
*TE/T2
factor*T1/T2
FISP cos)T1/T2*1(*T1/T21sinS
−
−
−
⋅⋅−++
⋅= eα
αρ
- FISP contrast: T1/T2*water: ~ 1, all other tissues: ~ 10
slice selection gradient
gradient-echo
phase encoding gradient
frequency encoding gradient
RUPRECHT-KARLS-UNIVERSITY HEIDELBERG
Computer Assisted Clinical MedicineProf. Dr. Lothar Schad
12/9/2008 | Page 22Gradient-Echo: FISP Problem
concept• transverse magnetization is not spoiled
(as in FLASH)• complete refocusing of all gradients in
one TR
problem• signal equation yields T1/T2 contrast• susceptibility differences can cause
artifacts• high flip angles (SAR)
solution• strong gradients• very short TR (< 5 ms)
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RUPRECHT-KARLS-UNIVERSITY HEIDELBERG
Computer Assisted Clinical MedicineProf. Dr. Lothar Schad
12/9/2008 | Page 23Gradient-Echo: FISP Contrast
- FISP sequence parameters:TR/TE/α = 2.6 ms / 1.4 ms / 55°⎟⎟
⎠
⎞⎜⎜⎝
⎛+−
=1*T1/T21*T1/T2arccosoptα
RUPRECHT-KARLS-UNIVERSITY HEIDELBERG
Computer Assisted Clinical MedicineProf. Dr. Lothar Schad
12/9/2008 | Page 24Gradient-Echo: Fat-Water Separation
- chemical shift between protons of water H2O and fatty tissue CH2 is about 3.5 ppm or 220 Hz at 1.5 T
- 1/220 Hz = 4.55 ms →TE = 4.55, 9.1 … ms fat / water: “in-phase”TE = 6.8, 11.4 … ms fat / water: “opposed-phase”
B0
90°
α
RF
S
fat water
W WFF
“in-phase” TE = 9.1 ms
“op.-phase” TE = 6.8 ms
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RUPRECHT-KARLS-UNIVERSITY HEIDELBERG
Computer Assisted Clinical MedicineProf. Dr. Lothar Schad
12/9/2008 | Page 25Spin-Echo: Fat-Suppression
- no fat-water separation possible since refocusing 180° pulse- preparation by frequency selective 90°-pulse to select only fat resonance (CHESS) and to destroy fat signal by spoiling
B0
90°180°
90°180°
RFS
fat water W
W
F
F
no fat-suppression with fat-suppression
x
RUPRECHT-KARLS-UNIVERSITY HEIDELBERG
Computer Assisted Clinical MedicineProf. Dr. Lothar Schad
12/9/2008 | Page 26Spin-Echo: Contrast Agent
- intravenous injection of 0.1 mmol/kg paramagnetic contrast agent Gd-DTPA- shortens locally T1 (ca. 1000 ms → 100 ms)- signal increase at SE imaging by a factor of 2 - 4 !- detects disruption of blood brain barrier → tumor grading !- also ferromagnetic nano-particles (SPIO ~ 100 nm, USPIO < 50 nm) available → liver
+
++
+
++
++
+
e-N S
Gd-DTPA complex
Gd
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RUPRECHT-KARLS-UNIVERSITY HEIDELBERG
Computer Assisted Clinical MedicineProf. Dr. Lothar Schad
12/9/2008 | Page 27
(by the different changes in relaxation times after their injection)
2. negative contrast agents- short T2 relaxation time - dark on MRI (decreased signal intensity)- small aggregates often termed superparamagnetic iron oxide(SPIO) and ultrasmall superparamagnetic iron oxides (USPIO) - crystalline iron oxide core and a shell of polymer (e.g. dextrane)
1. positive contrast agents- a reduction in the T1 relaxation time (increased signal intensity)- bright on MR images- small molecular weight compounds containing gadolinium, iron ormanganese
- unpaired electrons in their outer shells
Contrast Agent: Classification
RUPRECHT-KARLS-UNIVERSITY HEIDELBERG
Computer Assisted Clinical MedicineProf. Dr. Lothar Schad
12/9/2008 | Page 28
• good solubility in water • high thermodynamic and possibly kinetic stability to ensure against the in vivo release of toxic Gd3+ ions and free ligand molecules
• short T1 relaxation time
gadolinium:
• large magnetic moment • long electron spin relaxation time (~10-9 s at the magnetic field strengths of interest for MRI applications)
• optimum efficiency for nuclear spin relaxation of the interacting nuclei
Parker and Williams. J Chem Soc 1996 Aime et al. Chem Soc Rev 1998
Contrast Agent: Gd Requirements
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RUPRECHT-KARLS-UNIVERSITY HEIDELBERG
Computer Assisted Clinical MedicineProf. Dr. Lothar Schad
12/9/2008 | Page 29
- all considered safe enough for clinical use
- octadentate ligands: one water molecule in the inner coordination sphere - rapid exchange with the bulk solvent to affect the relaxation of all solvent protons
Paul-Roth and Raymond. Inorg Chem 1995
Contrast Agent: Gd Ligands and Complexes
RUPRECHT-KARLS-UNIVERSITY HEIDELBERG
Computer Assisted Clinical MedicineProf. Dr. Lothar Schad
12/9/2008 | Page 30
Gadopentetate(Magnevist)
courtesy: Weinmann, Schering AG
Contrast Agent: Gd Spherical Models
Gadoterate(Dotarem)
Gadodiamide(Omniscan)
Gadoteridol(ProHance)
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RUPRECHT-KARLS-UNIVERSITY HEIDELBERG
Computer Assisted Clinical MedicineProf. Dr. Lothar Schad
12/9/2008 | Page 31
• octadentate coordination of gadolinium
• one free coordination side is occupied by a water molecule
• relationships between the chemical structure and the factors determining the ability to enhance the water protons relaxation rates
• for a positive CA → short T1 time → high longitudinal relaxation rate
Contrast Agent: Gd-DTPA Complex
RUPRECHT-KARLS-UNIVERSITY HEIDELBERG
Computer Assisted Clinical MedicineProf. Dr. Lothar Schad
12/9/2008 | Page 32
dipolar interaction between the paramagnetic ion and the proton nuclei of coordinated water molecules
Bloemenbergen and Morgan. J Chem Phys 1961 Solomon. Phys Rev 1955
1. the number of metal bound water molecules q2. molecular reorientation time τR3. electron-spin relaxation time τS4. and chemical exchange time τM
described in detail by the Solomon-Bloembergen-Morgan theory
Gd-DTPA Relaxation Mechanism
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Computer Assisted Clinical MedicineProf. Dr. Lothar Schad
12/9/2008 | Page 33Spin-Echo: Gd-DTPA Example
SE T1w SE T2w SE T1w
- typical measuring protocol in brain diagnostics
intravenous injection of 0.1 mmol/kg Gd-DTPA
patient: glioblastoma
RUPRECHT-KARLS-UNIVERSITY HEIDELBERG
Computer Assisted Clinical MedicineProf. Dr. Lothar Schad
12/9/2008 | Page 34
Fast Imaging
Fast Imaging
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RUPRECHT-KARLS-UNIVERSITY HEIDELBERG
Computer Assisted Clinical MedicineProf. Dr. Lothar Schad
12/9/2008 | Page 35Fast Spin-Echo Imaging
Gs
Gp
Gr
RF90°
TEeff
1 total k-space line is acquired with every echo
signal-acquisition
180° 180° 180°
echo spacing
echo 1
echo 2
echo 3
signalfluid
muscle
time
- “turbo-SE-technique” (TSE) withacceleration-factor 3
- acquired k-space data afterfirst TR
compensation of Gp after signal acquisition
Hennig et al. MRM 1986
RUPRECHT-KARLS-UNIVERSITY HEIDELBERG
Computer Assisted Clinical MedicineProf. Dr. Lothar Schad
12/9/2008 | Page 36PSF: K-Space Inhomogeneity
k-space
15 echoesΔTE = 10 msT2 = 50 ms
position [pixel]
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RUPRECHT-KARLS-UNIVERSITY HEIDELBERG
Computer Assisted Clinical MedicineProf. Dr. Lothar Schad
12/9/2008 | Page 37Fast Spin-Echo Imaging: Examples
TSEturbo-factor: 3
TR / TE = 4 s / 11 msmatrix: 320 x 256
3:36 min
- tissue with long T2 (water) → sharp (see arrow)- tissue with short T2 (fat) → blurred
TSEturbo-factor: 33
TR / TE = 4 s / 11 msmatrix: 320 x 256
16 s TSE heartturbo-factor: 23ECG-triggered
breath hold
RUPRECHT-KARLS-UNIVERSITY HEIDELBERG
Computer Assisted Clinical MedicineProf. Dr. Lothar Schad
12/9/2008 | Page 38Fast Spin-Echo Imaging: FLAIR
- “turbo-inversion-recovery”-sequence (TIR) for fluid suppression followed by TSE readout
- “fluid-attenuated-inversion-recovery” (FLAIR)
- patient with brain tumourTSE: 4000/115 ms, TF = 15FLAIR: 9000/115 ms, TF = 21,
TI = 2500 ms
TSE FLAIR
TI
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RUPRECHT-KARLS-UNIVERSITY HEIDELBERG
Computer Assisted Clinical MedicineProf. Dr. Lothar Schad
12/9/2008 | Page 39Fast Spin-Echo Imaging: HASTE
- HASTE:“half-Fourier acquisitionsingle-shot turbo spin-echo”
- HASTE lung imaging:TE = 29 ms, ΔTE = 3.6 ms,N = 50 echoes, GRAPPA = 2,taq = 200 ms ! - lung parenchyma
is visible !
sequence
differenceimage
acquiredhologram
calculation ofmissing pointsby mirroring
at origin
reconstructedMR-image
k-space frequency encodingph
ase
enco
ding
Fourier transformation
RUPRECHT-KARLS-UNIVERSITY HEIDELBERG
Computer Assisted Clinical MedicineProf. Dr. Lothar Schad
12/9/2008 | Page 40
Mansfield and Pykett. JMR 1978
Fast Gradient-Echo Imaging: EPI
- “echo-planar imaging” EPI- multi-gradient imaging technique- single-shot technique with strong requirementsto the gradient power
- strong T2* dependency → susceptibility artifacts !- fastest imaging technique
Sir Mansfield2003 Nobel prize in medicine
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RUPRECHT-KARLS-UNIVERSITY HEIDELBERG
Computer Assisted Clinical MedicineProf. Dr. Lothar Schad
12/9/2008 | Page 41Fast Gradient-Echo Imaging: EPI Technique
RUPRECHT-KARLS-UNIVERSITY HEIDELBERG
Computer Assisted Clinical MedicineProf. Dr. Lothar Schad
12/9/2008 | Page 42EPI Problem: N/2 Ghosts
gradient echo EPI
echo shift ofodd againsteven echoes
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RUPRECHT-KARLS-UNIVERSITY HEIDELBERG
Computer Assisted Clinical MedicineProf. Dr. Lothar Schad
12/9/2008 | Page 43EPI Problem: Field Inhomogeneities
gradient echo EPI
RUPRECHT-KARLS-UNIVERSITY HEIDELBERG
Computer Assisted Clinical MedicineProf. Dr. Lothar Schad
12/9/2008 | Page 44
40 slices in 4 s !
Fast Gradient-Echo Imaging: EPI Examples
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RUPRECHT-KARLS-UNIVERSITY HEIDELBERG
Computer Assisted Clinical MedicineProf. Dr. Lothar Schad
12/9/2008 | Page 45
classical EPI
Fast Gradient-Echo Imaging: EPI Methods
spin-echo EPISE-EPI
diffusion-weighted EPIDW-EPI
RUPRECHT-KARLS-UNIVERSITY HEIDELBERG
Computer Assisted Clinical MedicineProf. Dr. Lothar Schad
12/9/2008 | Page 46Fast Gradient-Echo Imaging: 3D FLASH
- whole brain imaging: 3D FLASH: 20/6/30°, 256 slices- 3D isotropic resolution: 1 x 1 x 1 mm3, taq ~ 20 minHaase et al. MRM 1986
measured
reconstructed
z
HF
G
G
G
x
y
AQ
Echo
TETR
Nslice
Nphase
N freq
Spin-dephasierung
3D-FLASH-Sequenz3D FLASH sequence
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RUPRECHT-KARLS-UNIVERSITY HEIDELBERG
Computer Assisted Clinical MedicineProf. Dr. Lothar Schad
12/9/2008 | Page 473D FLASH: Example
- high resolution heel imaging:- 3D FLASH: 25/11/30°, 100 slices, taq ~ 10 min - 3D isotropic resolution: 0.4 x 0.4 x 0.4 mm3 !!!
16201630164016501660167016801690170017101720173017401750176017701780179018001810
directionhorizontal vertical 45° 135°
run
leng
th n
onun
iform
ity- clinical application: osteoporosis
RUPRECHT-KARLS-UNIVERSITY HEIDELBERG
Computer Assisted Clinical MedicineProf. Dr. Lothar Schad
12/9/2008 | Page 48Fast Gradient-Echo Imaging: MP-RAGE
- MP-RAGE: 3D “magnetization prepared rapid gradient echo” technique
- volunteer whole brain imaging:MP-RAGE: 10/4/10°, TI = 200 ms, 128 slices
- 3D isotropic resolution: 0.9 x 0.9 x 1.2 mm3
taq ~ 8 min !Mugler and Brookeman. MRM 1990
TI
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RUPRECHT-KARLS-UNIVERSITY HEIDELBERG
Computer Assisted Clinical MedicineProf. Dr. Lothar Schad
12/9/2008 | Page 49Fast Gradient-Echo Imaging: PSIF
- PSIF: 3D reversed timing of FISP “noissecerp etats ydaets htiw gnigami
tsaf” technique - volunteer whole brain imaging:PSIF: 17/7/50°, 128 slices
- 3D “isotropic” resolution: 0.9 x 0.9 x 1.2 mm3
taq ~ 10 min !Bruder et al. MRM 1988
phase development excitation refocusing
RUPRECHT-KARLS-UNIVERSITY HEIDELBERG
Computer Assisted Clinical MedicineProf. Dr. Lothar Schad
12/9/2008 | Page 50Clinical Application: MP-RAGE, PSIF
Friedlinger et al. Comp Med Ima Graph 1995
- brain volumetry (GM, WM, CSF) in Alzheimer disease
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RUPRECHT-KARLS-UNIVERSITY HEIDELBERG
Computer Assisted Clinical MedicineProf. Dr. Lothar Schad
12/9/2008 | Page 51Clinical Application: 3D Visualization
- functional MRI overlaid to MP-RAGE - planning of neurosurgery
RUPRECHT-KARLS-UNIVERSITY HEIDELBERG
Computer Assisted Clinical MedicineProf. Dr. Lothar Schad
12/9/2008 | Page 52Fast Imaging: Hybrid Technique GRASE
- GRASE: “gradient and spin-echo” technique- TGSE: “turbo-gradient-spin-echo” technique- TSE technique mixed with GE’s- k-space variability: SE’s in center of k-space
GE’s at border of k-space
- volunteer high resolution imaging:GRASE: 2030/112/90° ms
- resolution: 0.4 x 0.4 x 2 mm3 !
Oshio and Feinberg. MRM 1991
spin-echo
gradient-echoes
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RUPRECHT-KARLS-UNIVERSITY HEIDELBERG
Computer Assisted Clinical MedicineProf. Dr. Lothar Schad
12/9/2008 | Page 53
conventional1 echo / TR
hybridmultiple echoes / TR
single-shotall echoes / TR
SEGE / FLASH
FLAIRMP-RAGE
FISPPSIF
TSETGSE / GRASE
HASTEEPI
Summary: K-Space Scan Options
RUPRECHT-KARLS-UNIVERSITY HEIDELBERG
Computer Assisted Clinical MedicineProf. Dr. Lothar Schad
12/9/2008 | Page 54Summary: K-Space / Speed
spin-echoes
gradient-echoes
spee
d
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RUPRECHT-KARLS-UNIVERSITY HEIDELBERG
Computer Assisted Clinical MedicineProf. Dr. Lothar Schad
12/9/2008 | Page 55Sequence Family
RUPRECHT-KARLS-UNIVERSITY HEIDELBERG
Computer Assisted Clinical MedicineProf. Dr. Lothar Schad
12/9/2008 | Page 56
FourierFourier--CodingCodingKK--SpaceSpace
CSECSE
IRIR
TIR, TIRM, TIR, TIRM, TFLAIRTFLAIRHASTEHASTE
TSE, FSETSE, FSERARERARE
GREGRE
FLASHFLASHSPGRSPGR
T1T1--FFEFFEspoiled FASTspoiled FAST
FISPFISPGRASSGRASS
FASTFASTT2T2--FFEFFE
trueFISPtrueFISPCISSCISS
DESSDESS
PSIFPSIFCECE--FASTFAST
turboFLASHturboFLASHsnapshotFLASHsnapshotFLASH
FSPGRFSPGRMPRAGEMPRAGE
EPIEPITGSETGSE
GSEGSEGRASEGRASE
© W. Nitz, Siemens AG
TIR
TGSE
FLASHTSE
PSIF
MPREPI
SESE GEGE
trueFISP
Sequence Family with Examples
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RUPRECHT-KARLS-UNIVERSITY HEIDELBERG
Computer Assisted Clinical MedicineProf. Dr. Lothar Schad
12/9/2008 | Page 57Babylonian Confusion of Tongues I
name also turbo-FLASH, TURBO-FFE, Snapshot-FLASH
GRE, fast FLASH with preparation pulse for contrast enhancement
Fast spoiled GRASSFSPGR
TSE, RARESE with multiple 180°-pulses, one raw data line per echoFast spin echoFSE
-SE with 180°-pulse at the beginning, long inversion time for fluid attenuation
Fluid attenuated inversion recovery
FLAIR
T1-FFE, Spoiled GRASSGRE with small angle excitationFast low angle shotFLASH
name also GRASS, FASTGRE using steady state magnetizationFast imaging with steady precession
FISP
FISPGRE with small angle excitationFast field echoFFE
name also FISP, FASTGRE using steady state magnetizationFast acquired steady state technique
FAST
multiple GRE after one excitation; mostly all raw data in one pulse train
Echo planar imagingEPI
double-GRE-sequence where GRE- and SE-parts are measured separately and added afterwards
Double echo steady stateDESS
two GRE-sequences with SE-part where single signals are added constructive
Constructive interference in steady state
CISS
name also PSIF, CE-FASTGRE with SE-part using steady state magnetizationContrast enhanced GRASSCE-GRASS
name also PSIF, CE-GRASS
GRE with SE-part using steady state magnetizationContrast enhanced FASTCE-FAST
SynonymsExplanationNameAcronym
RUPRECHT-KARLS-UNIVERSITY HEIDELBERG
Computer Assisted Clinical MedicineProf. Dr. Lothar Schad
12/9/2008 | Page 58Babylonian Confusion of Tongues II
SE-sequence with 180°-pulse at the beginning, imaging of absolute signal
Short TI inversion recoverySTIR
Pulse train with three 90°-pulsesStimulated echo acquisition mode
STEAM
name also FLASH, FFEGRE with small angle excitationSpoiled gradient refocused acquisition in the steady state
Spoiled GRASS
name also turbo-FLASH, FSPGR, TFE
GRE, fast FLASH with preparation pulse for contrast enhancement
Snapshot FLASHsnapshotFLASH
90°-180°-pulse trainSpin echoSE
name also TSE, FSESE with multiple 180°-pulses, one raw data line per echoRapid acquisition with relaxation enhancement
RARE
name also CE-FAST, CE-GRASS
GRE with SE-part using steady state magnetization“mirrored" FISPPSIF
FLASH, Spoiled GRASSGRE with small angle excitationT1 fast field echoT1-FFE
3D-variant of Turbo-FLASHMagnetization prepared rapid gradient echo
MP-RAGE
SE with 180°-pulse at the beginningInversion recoveryIR
Turbo-SE with Half-Fourier-Acquisition, all raw data in one pulse train
Half Fourier single shot turbo spin echo
HASTE
name also FISP, FASTGRE using steady state magnetizationGradient refocused acquisition in the steady state
GRASS
name also TGSETurbo-SE-sequence where SE is surrounded by GREGradient and spin echoGRASE
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RUPRECHT-KARLS-UNIVERSITY HEIDELBERG
Computer Assisted Clinical MedicineProf. Dr. Lothar Schad
12/9/2008 | Page 59Babylonian Confusion of Tongues III
name also Snapshot-FLASH, FSPGR; TFE
GRE, fast FLASH with preparation pulse for contrast enhancement
Turbo fast low angle shotTFL
name also turbo-FLASH, Snapshot-FLASH, FSPGR
GRE, with multiple 180°-pulses, one raw data line per echoTurbo fast field echoTFE
FSE, RARESE with multiple 180°-pulses, one raw data line per echoTurbo spin echoTSE
GE using steady state magnetization, all gradients are symmetric
True fast imaging with steady precession
trueFISP
Turbo-SE with 180°-pulse at the beginning, imaging of absolute signal
Turbo inversion recovery magnitude
TIRM
Turbo-SE with 180°-pulse at the beginningTurbo inversion recoveryTIR
name also GRASETurbo-SE-sequence where SE is surrounded by GRETurbo gradient spin echoTGSE
- the most important MRI-sequences !!SE / TSE
FLASH / FISP / EPI
RUPRECHT-KARLS-UNIVERSITY HEIDELBERG
Computer Assisted Clinical MedicineProf. Dr. Lothar Schad
12/9/2008 | Page 60
• best soft tissue contrast of allimaging modalities
• multi-planar slice orientation• no ionizing radiation• high flexibility of the method due to complex signal dependencyof physical parameters
It´s fun !!
MRI: Advantage - Disadvantage
• costs• availability• contraindication
- advantage - disadvantage
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RUPRECHT-KARLS-UNIVERSITY HEIDELBERG
Computer Assisted Clinical MedicineProf. Dr. Lothar Schad
12/9/2008 | Page 61
- essential prerequisites for MRI are:
1. nuclear spin (magnetic moment)
2. strong, homogeneous magnetic field (0.1 - 7 Tesla)
3. nuclear magnetic resonance(interaction of magnetization with a high frequency pulse)
4. relaxation (T1, T2)
Summary I
RUPRECHT-KARLS-UNIVERSITY HEIDELBERG
Computer Assisted Clinical MedicineProf. Dr. Lothar Schad
12/9/2008 | Page 62
ω = γ.B0• Larmor-frequency:
• magnetic field gradients for spatial encoding
- slice selection gradient- phase encoding gradient- frequency encoding gradient (readout gradient)
Summary II
ω(x) = γ.B (x) = γ.B0 + γ.Gx.x
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RUPRECHT-KARLS-UNIVERSITY HEIDELBERG
Computer Assisted Clinical MedicineProf. Dr. Lothar Schad
12/9/2008 | Page 63
• pulse sequences are a chronology of RF-pulses and gradients
• the most important basic types of sequences arespin-echo and gradient-echo sequences
• spin-echo sequences are using a 90°-pulse for excitation followedby a 180°-refocussing pulse
• gradient-echo sequences are much faster since they use flip-anglesof less than 90° for excitation without using any 180°-refocussing pulse
• EPI sequences are normally single-shot techniques, i.e. the completeimage is acquired after one RF excitation
Summary III
RUPRECHT-KARLS-UNIVERSITY HEIDELBERG
Computer Assisted Clinical MedicineProf. Dr. Lothar Schad
12/9/2008 | Page 64
• k-space formalism is a very helpful decription in MRI
kx = γ Gx t ky = γ Gy Tp
• the measured signals in MRI are the Fourier transformof the unknown image
( ) ( ) ( ) dydxeyxkkS ykxkiyx
yx +∞
∞−
∞
∞−∫ ∫= πρ 2,,
F.T.
Summary IV
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RUPRECHT-KARLS-UNIVERSITY HEIDELBERG
Computer Assisted Clinical MedicineProf. Dr. Lothar Schad
12/9/2008 | Page 65
source: Liang and Lauterbur. “Principles of Magnetic Resonance Imaging” 2000
Summary V
RUPRECHT-KARLS-UNIVERSITY HEIDELBERG
Computer Assisted Clinical MedicineProf. Dr. Lothar Schad
12/9/2008 | Page 66Finale