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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


Objectives and challenges for high field MRI

Iseult 11.7 T MRI Magnet


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MEDICAL IMAGING:


A diagnostic and research tool in

neuroscience


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Neuro-imaging

To study the human brain

Neurology / Neurosurgery- Development, aging, rehabilitation


- 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


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


Gradient coilsRF coils


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SUPERCONDUCTING MAGNET


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 ...


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 ==


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


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)


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


NMR wire : NbTi/Cu

36 filaments

Copper


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Bronze route Internal Tin

Nb3Sn Conductor


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.


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)


- 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


11.7T /680 mm

11.7T /900 mm

9.4T /900 mm


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OBJECTIVES AND CHALLENGES

for high field MRI:


A global competition


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Why MRI at high field ?

Gain = 3.8 Gain = 2.8 Gain = ?


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


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


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


2007



- 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


- 2 systems7T WB

- 1 system8T WB


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Neurospin Centre - CEA Saclay

17.2 T

Novembre 2006


3 T

7 T11.7 T

MEG


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When art meets science: the archesof Neurospin


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)


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


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)


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


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


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


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


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


See you in 2013 !.......


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See you in 2013 !.......


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