Multinuclear MRI at 7T
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Transcript of Multinuclear MRI at 7T
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Multinuclear MRI at 7T
Ravinder ReddyRavinder Reddy
Department of RadiologyDepartment of Radiology
University of PennsylvaniaUniversity of Pennsylvania
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Siemens 7 Tesla Magnet 7T Whole body magnet7T Whole body magnet
By MagnexBy Magnex UnshieldedUnshielded 2.4mx3.4 m longx3.8m2.4mx3.4 m longx3.8m 90cm bore90cm bore Weight 35000 kgWeight 35000 kg 5 ppm peak to peak field 5 ppm peak to peak field
variation over a 45 cm variation over a 45 cm diameterdiameter
Shield ~400 tonsShield ~400 tons
QuickTime™ and aTIFF (Uncompressed) decompressor
are needed to see this picture.
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Why?
Multinuclear MRMultinuclear MR High specificity, low sensitivity and resolutionHigh specificity, low sensitivity and resolution
11H MRH MR Low specificity, high sensitivity and resolutionLow specificity, high sensitivity and resolution
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Outline Non-proton MRINon-proton MRI
Field dependent RF wave patternField dependent RF wave pattern SAR SAR SNR and relaxation effects SNR and relaxation effects
Potential Multinuclear ProjectsPotential Multinuclear Projects 2323Na, Na, 3131P MRP MR 1717O NMR, O NMR, 1313C NMRC NMR
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Behavior of the RF filed in biological tissue
==rr is the electric permittivity, is the electric permittivity,
= magnetic permeability, = magnetic permeability, = conductivity in the media, = conductivity in the media, = resonance frequency= resonance frequency
(() attenuation and () attenuation and () phase constants) phase constants
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γ = jω μ (ε − jσ
ω) = α + jβ ...(m−1)
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=
21 + (
σ
ωε)2 −1
⎡
⎣ ⎢
⎤
⎦ ⎥
1/ 2
€
=
21 + (
σ
ωε)2 +1
⎡
⎣ ⎢
⎤
⎦ ⎥
1/ 2
Electromagnetic wave in a uniform conducting medium is given by
Yang et al., MRM
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RF wave properties in tissues
In biological tissuesIn biological tissues RF wave lengthRF wave length = = Skin depth Skin depth = = AsAsincreasesincreases
Conductivity,Conductivity,increases increases dielectric constant, dielectric constant, , decreases., decreases.
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Frequency dependency of the RF wave length in the brain
tissue:
Yang et al., MRM
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Effect of RF field propagation in brain and a phantom at 7T
Yang et al., MRM
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RF Wavelength and Field Strength
C
Pa
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SAR limits on imaging
SAR ~ BSAR ~ Boo2 2 (Flip angle)2 (RF duty cycle). (Patient Size)
Flip angle=γB1tw
For low gama nuclei, high B1 is required to achieve the same flip angle Puts restrictions onPuts restrictions on
Pulse repetition timePulse repetition time Number of RF pulses in a multi-echo sequenceNumber of RF pulses in a multi-echo sequence Slice efficiency in multi-slice imagingSlice efficiency in multi-slice imaging
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Signal as a function of field strength
Sample magnetization is proportional to BSample magnetization is proportional to Boo
MMoo ~ N ~ Nss h hγγBBoo/kT/kT
Induced emf in a coil is proportional to time rate of change of Induced emf in a coil is proportional to time rate of change of transverse magnetizationtransverse magnetization Larmor Precession Frequency= Larmor Precession Frequency= oo = = γγBBoo
€
Signal ∝ωoMo ∝ Bo2
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Noise ∝ σ Coil +system2 + σ Sample
2 ∝ αB01/ 2 + bB0
2
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SNR as a function of field strength
For low fields, sample contribution to noise is negligibleFor low fields, sample contribution to noise is negligible SNR~ BSNR~ B00
7/47/4
For mid field and high fields, sample noise dominates SNR~ BSNR~ B00
€
SNR ∝Bo
2
αB01/ 2 + bB0
2
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Field dependence of SNR
• At ultra-high magnetic fields (≥7T)• Proton SNR dependence on magnetic field is complicated due to RF inhomogeneities
• SNR (proton) B0 x T2*/T1
• T1 also increases
• For other NMR nuclei (13C, 23Na, 17O or 31P)
• SNR B0 7/4 x T2*/T1
• for quadrupolar nuclei•T2* and T1 are not appreciably changed with the field
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Field dependence
0
10
20
30
40
50
60
1 2 3 4 5 6 7 8 9
Field Strength
SNR
Low Gamma
Protons
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NucleusNucleus II Resonance Resonance Freq (@7T) Freq (@7T) in MHzin MHz
Natural Abundance Natural Abundance (%)(%)
Abs Sensitivity at constant Abs Sensitivity at constant field (Product of rel field (Product of rel sensitivity and Natural sensitivity and Natural abundance)abundance)
T1T1 T2T2
11HH 1/21/2 298298 99.9899.98 11 0.3-3s 1-600 1-600 msms
2323NaNa 3/23/2 78.978.9 100100 9.3x109.3x10-2-2 20-50ms
0.5-20 ms
3131PP 1/21/2 120.6120.6 100100 6.6x106.6x10-2-2 2-5s 50-1000
1313CC 1/21/2 74.874.8 1.11.1 1.76x101.76x10-4-4 3-15 s 100-100-1000 1000 msms
1717OO 5/25/2 40.3640.36 0.0370.037 1.08x101.08x10-5-5 4-6 ms4-6 ms 1-2 1-2 msms
1414NN 11 21.421.4 99.699.6 1.0x101.0x10-3-3
1515NN 1/21/2 30.030.0 0.370.37 3.85x103.85x10-6-6
1919FF 1/21/2 280280 100100 .83.83
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Potential Multinuclear projects
2323NaNa Alzheimer’s DiseaseAlzheimer’s Disease Diffuse Axonal InjuryDiffuse Axonal Injury Arthritis, Disc DegenerationArthritis, Disc Degeneration
3131PP Head and Neck TumorsHead and Neck Tumors HIV infection HIV infection
1717OO Stroke, AD, CancerStroke, AD, Cancer
1313CC Lactate Mapping in CancerLactate Mapping in Cancer
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Sodium MR
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Sodium and AD Rationale:
1. Loss of neurons increase in the volume of extra-cellular space increase in MRI-detectable sodium (due to the longer T2).
2. Positively charged sodium ions are attracted by the negatively charged side-chains on proteoglycan (PG) macromolecules resulting in an increase in sodium content.
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Sodium and AD
When compared to the control brains [Na] increased in the AD brains, in the circular ROI located in the hippocampus. This 6% increase [Na] may be due to:
1. An increase in extra-cellular volume of sodium.2. AD-related pathology resulting in an increase in [Na]. MRM (submitted)
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Detecting OA in human tissue
mM
NormalNormal
OA specimenOA specimen
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Sodium MR of Cartilage Degeneration
Normal Symptomatic subject
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IVD and Sodium MR
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Tand Sodium image comparison between healthy 26yo male (left)and non healthy 24 yo male (right). Scale bar in milliseconds
T1rho scale bar in ms
Sodium scale bar in mM
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31P MR
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0.0
0.2
0.4
0.6
0.8 PME
Pi
PDE
PCr
γ-ATP-ATP
-ATP
0 -5 -10 -15 -20
0.0
0.1
0.2
0.3
Frequency (ppm)
Pre treatment
Post treatment
PME reduction is an indication of response to therapy
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10 0 -10
10 0 -10 -20
Non-responder
Responder
31P MR Spectroscopy of head and neck tumors
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Proton decoupled 31P MRS of HN Cancer at 3T
3D CSI, TR=1000 ms, elliptical k-space sampling, voxel 2.3x2.3x2.3 cm3, 9 mins
Kim et al, ISMRM2008 #3247 , E-poster computer #27 (May 8, 2:00 pm)
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HIV-1 infection and Phospholipid Ratio
HIV-1 infection alters membrane PDE and PME HIV-1 infection alters membrane PDE and PME during the process of virus entry and/or replication.during the process of virus entry and/or replication.
Changes in PDE/PME ratio Changes in PDE/PME ratio diagnostic for the presence of HIV-1 in primary diagnostic for the presence of HIV-1 in primary
immune cellsimmune cells
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17O MRI in Swine brain
Coronal
Sagittal
Transverse
18.0
18.5
19.0
19.5
20.0
20.5
21.0
21.5
22.0
0 100 200 300 400 500 600
Time (sec)
Computed [H217O]
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Cross polarization 13C Chemical Shift Imaging (CSI)During [1-13C] glucose infusion
RIF-1; 16.7 mM constant serum conc.; 1x2x5 mm3 voxels; 50 min acq. Time
Glucose Lactate
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Multinuclear MR at 7T
Multinuclear MR at 7TMultinuclear MR at 7T RF wave propagation and associated inhomogeneities RF wave propagation and associated inhomogeneities
are negligibleare negligible SNR increases as BSNR increases as Bo o
7/47/4 T1, and T2* do not change significantlyT1, and T2* do not change significantly High B1 requirements for a typical flip angleHigh B1 requirements for a typical flip angle Efficient MR of 23 23Na, Na, 3131P, P, 1313C, and C, and 1717O at high fieldsO at high fields