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TRANSCRIPT
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Magnetic Field Generation for MRI:
State of the art and future challenges.
Pierre Vdrine,
CEA Saclay, Irfu
1Sminaire Dautreppe 2011 24 novembre 2011
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Medical Imaging
Superconducting Magnet for MRI
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Objectives and challenges for high field MRI
Iseult 11.7 T MRI Magnet
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MEDICAL IMAGING:
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A diagnostic and research tool in
neuroscience
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Neuro-imaging
To study the human brain
Neurology / Neurosurgery- Development, aging, rehabilitation
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- Psychiatry, mental disorders
Health
- Social behavior and culture, art, ..
- Human-Computer Interaction- Learning, education, ...
eurosc ences ...structures & functions of the brain
Interaction, society
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Brain functions and neurodegenerative diseases
Understand how the brain works
Early detection of Alzheimer's disease by MRIusing a dedicated contrast agent
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7 Tesla MRIHistology
Objective: Todevelop the
technique inhumans
Proof of conceptat 7 Tesla on
animal model
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The magnetic resonance imaging tomorrow:
A great tool for neuroscience
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MRI system
High field magnet
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Gradient coilsRF coils
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SUPERCONDUCTING MAGNET
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is the heart of the MRI system
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Superconducting magnet is the heart of the MRI system
supports a very high current density with zero resistance,generates magnetic fields (1.5 to 12 T) with little or no electrical
power.
The quality of the MRI image is linked to:
Ma netic field stren th: Increased Si nal to Noise ratio
1 tesla = 10,000 gauss - Earth's magnetic field = 0.5 gauss in Paris ...
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Field Homogeneityusually defined on a spherical volume of 20mm :B/B0 10
-6 10-8
B/B0 10-9 10-10 for high resolution spectroscopy
10-5 coming from the main coil, 10-7 from superconducting shim coils +resistive correction coils
Field stability : field decay < 10-8/hour (10-9/h high resolution
spectroscopy)
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Magnetic Field Generation
Superconducting Magnet
Main Coils: Long Coil Length or Multicoils
Compensation Coils: z
2
, z
4
, z
6 0Superconducting Shim Coils:
Field Correction
z1, z2, x, y, zx, zy, x2-y2,xy
z
J= current desnity, t= coil thickness
NI/L = ampere turns/unit length L
NI
tJB 00 ==
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Persistent OperationField Homogeneity
Field Stability:
Room Temperature Shim Coils
Field Correctionz0, z1, z2, z3, z4,
x, y, x2-y2,xy
Higher Order ComponentsCourtesy of T. Kyoshi NIMS
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Magnetic Field Shielding
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Shielding coils
Main coil
External Interference Shields
Winding scheme
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zy
x
Gradient coils
Iron shims
Cryo-shims
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Superconducting Materials
1000
10000
(A/mm)
YBCO B|| Tape Plane
YBCO BYBCO B Tape PlaneTape Plane
2212
RRP NbRRP Nb33SnSnNbNb--TiTi
SuperPower tapeSuperPower tape
used in recordused in record
breaking NHMFLbreaking NHMFL
insert coil 2007insert coil 2007
427 filament strand with
Ag alloy outer sheath
tested at NHMFL
Complied fromComplied from
ASC'02 andASC'02 andICMC'03 papersICMC'03 papers
(J. Parrell OI(J. Parrell OI--ST)ST)
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10
100
0 5 10 15 20 25 30 35 40 45
Applied Field (T)
JE
YBCO Insert Tape (B Tape Plane)
MgB2 19Fil 24% Fill (HyperTech)
2212 OI-ST 28% Ceramic Filaments
NbTi LHC Production 38%SC (4.2 K)
Nb3Sn RRP Internal Sn (OI-ST)
Nb3Sn High Sn Bronze Cu:Non-Cu 0.3
BronzeBronzeNbNb33SnSn
MgB2
18+1 MgB18+1 MgB22/Nb/Cu/Monel/Nb/Cu/Monel
Courtesy M. Tomsic, 2007Courtesy M. Tomsic, 2007
Maximal JEfor
entire LHC Nb-Ti
strand production (
) CERN-T. Boutboul
'07, and (- -)
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NbTi Conductor
NbTi
NbTi filaments in a copper matrix
- Standard wire : 54 filaments Cu/Scratio 1.35.
Dimensions 0.4 to 1.6 mm, issulated
or not ou non (Formvar, glass fiber)
- Wire in channel to increase the coppersection
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NMR wire : NbTi/Cu
36 filaments
Copper
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Bronze route Internal Tin
Nb3Sn Conductor
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Bruker-EAS
Nb3Sn Externally stabilized, rectangular NbSn wire.
Cross section: 0.8 to 7.0 mm2
Number of filaments: 4000 to >100000
Recommended magnetic field range: 12.0 to 23.5 T
Oxford OST
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Cryostat design
Coils fit inside cryostats, to keep the coilat low temperature, with moderately lowconsumption.
Thanks to persistent mode and very
accurate cryostat design, LHe refillingis required every 6 to 12 months : 1-2l/day, up to 6-7 l/day for biggersystems.
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Since a certain amount of LHe isusually present, up to 1000 l, thecryogenic safety has to be seriouslyconsidered in case of a quench dueto the He boil-off.
Quench valve opening 200 mbar,bursting disk
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Safety
Magnetic Fields :- Strong magnetic fields- Strong magnetic fields gradients
Effect of stray fields on :-Operation of equipments-Implants or prosthetic devices
Effect of field gradients :
Handling of cryogenic substances :Helium & Nitrogen- during a refill- during a quench (rapid He boil-off )
avoid cold burning, suffocation
Protective clothing, no smoking,Ventilation (emergency exhausts)
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- arge attract ve orces n uce on
ferromagnetic objects (especially for
active shielded magnet)
displacement of objects could causeinjuries
Definition of zones:- Exclusion zone (5 Gauss line): noaccess for individuals with implants- Security zone : no ferromagneticobjects
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State of the art
MRI for animals MRI for humans
Courtesy Agilent
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11.7T /680 mm
11.7T /900 mm
9.4T /900 mm
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OBJECTIVES AND CHALLENGES
for high field MRI:
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A global competition
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Why MRI at high field ?
Gain = 3.8 Gain = 2.8 Gain = ?
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7T
CNR = 7.9
1.5T
CNR = 0.6 CNR =2.3
3T
Comparison in Contrast to Noise ratio
11,7T
CNR = ?
High-field MRI = higher sensitivity, new contrasts
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Spatial and time resolution
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A few millimeters tobetter than a tenth of amillimeter
From seconds to milliseconds
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MRI for the future: towards the high fields ...
Medical : 0.1-3 teslas
Research : 3 5 teslas
High Field : 7 teslas and +
Push the limits
Ultra high field : 11.7 teslas
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Aimant 1.5T (GE) SHFJ/CEA
Aimant 3.0T (Siemens)
Aimant 9.4 T GE 600 mm
(USA)
Iseult 11,7 T
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High Field MRI in the world
2011- 3T : 850 systems in operation
- 7T : 50 systems in operation
11.7T, 65cm,Passive shielding
2011
11.7T, 90cm,
Active shielding
2013
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2007
- 3T : 700 systems in operation
- 7T : 30 systems in operation
- 1 system 8T WB, 3 systems 9.4T WB
- 4 projects 11.7T WB
(NeuroSpin, Tokyo, Berkeley, NIH)
- sys em , sys ems .
- 1 funded project 10.5T WB Minneapolis- 2 funded project 11.7T WB : CEA et NIH
- 2 potential projects: Tokyo, Boston
- 1 potential project 14T Seoul
2003
- 3T : 100 systems in operation
- 2 systems7T WB
- 1 system8T WB
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Neurospin Centre - CEA Saclay
17.2 T
Novembre 2006
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3 T
7 T11.7 T
MEG
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When art meets science: the archesof Neurospin
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Claude
Vasconi,Architect
1940-2009
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ISEULT
11.7 T MRI MAGNET
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Objectives and Challenges
OBJECTIVES
Development of molecular imaging at high field
Three complementary aspects:
Construction of an MRI scanner at ultra high field (11.7T) whole body (CEA, Siemens)
Development of new technologies (MRI Univ.de Fribourg, Bruker, Siemens)Study of new contrast agents for high field MRI on target
following pathologies: Alzheimer's, stroke, brain tumors (Guerbet, CEA)
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CHALLENGES
Obtain a spatial or temporal resolution unequaled in humans,
discover new contrasts
Completion of the MRI magnet = first world for the field and the technology used
Important technological innovations for the other elements of the imager 11.7T MRI
Innovative developments for contrast agents: EST, Gd / USPIO, 19F
Perspectives for industrial development & support industrial Guerbet
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Iseult 11.7 T MRI Magnet
Observer
QUANTITY Unit Value
Stored Energy MJ 338Inductance H 308Current A 1483Length m 5.2Diameter m 5Weight t 132
B0 / Aperture 11.75T / 900mm
Field stability 0.05 ppm/h
Homogeneity < 0.5 ppm on 22 cm DSV
Stray field 5 G 13.5 m axial, 10.5 m radial
An innovative design- NbTi conductor 9,2 mm x 4,9 mm
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11.7 T magnet section : in orange the windings, in blue the mechanical
structure at 1.8 K and in violet the cryostat
-170 double pancakes for the main coil- 2 shielding coils- Cryostat for liquid helium at 1.8 K, 1.25 bars- Voltage +/- 2000 V- 3,9 bars maximum pressure in case of
quench- Dedicated refrigerator 70 l/h + 40 W 4.2 K
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Winding layout and design
Blocks designHomogeneity (cancellation of terms up to the 12th order included)
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Cancelation of the straight field
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Double pancake design for Homogeneity
Original Double Pancake design
The objective is to design a magnet theoretically intrinsicallyhomogeneous
= =
+++=
1 1
0)(cos
sin
cos
)(cos),,(n
n
m
m
n
m
n
mn
m
n
nn
n
zPW
mY
mX
PZrBrB
x
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yz
O O
2s
O
2s
Windings
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Windings
Inter-pancakeInsulation [ IPI ]
(fiberglass)
Specific design Main coil made of cryostable double-pancakes
Shielding coils vacuum impregnated with epoxy resin
32CC3D 9 juin 2010
Conductor [ SC ]
Inter-turn
Insulation [ ITI ](impr. Kapton)
Double pancake stacking
170 Double-Pancakes 82 turns
Main coil structure(real size)
D i ti lid t d b t t
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Design options validated by prototypes
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Conductor manufacturing
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Conductor manufacturing
160 km of main coil conductor: 1500 A at 11.7 T and 2.8 K, 9.2 mm x 4.9 mm
60 km of shielding coil conductor: 2100 A at 5T, 1.8 K , 9.1 mm x 4.2 mm
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10 Cu/NbTi strands in a copper channel using SnSb solder
Shielding coil conductor: Cu/NbTi strand in acopper channel
Double pancake manufacturing
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Double pancake manufacturing
Winding of 10 preseries double pancake coils
Start of the serie production of 170 doublespancakes in december 2011
Winding machine at Alstom Belfort
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First double pancake April 2011Double pancake coil on 3D measuring bench
11 7 T 68 cm MRI magnet for NIH
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11.7 T 68 cm MRI magnet for NIH
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See you in 2013 !.......
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See you in 2013 !.......
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