Introduction 12/9/2008 | Page 2

Home , Felix Bloch, Nicolaas Bloembergen

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Computer Assisted Clinical Medicine Prof. Dr. Lothar Schad Master‘s Program in Medical Physics 12/9/2008 | Page 1

Physics of Imaging Systems Basic Principles of Magnetic Resonance Imaging I

Prof. Dr. Lothar Schad

Chair in Computer Assisted Clinical Medicine Faculty of Medicine Mannheim University of Heidelberg Theodor-Kutzer-Ufer 1-3 D-68167 Mannheim, Germany [email protected] www.ma.uni-heidelberg.de/inst/cbtm/ckm/

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Computer Assisted Clinical Medicine Prof. Dr. Lothar Schad Introduction 12/9/2008 | Page 2

Introduction

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Computer Assisted Clinical Medicine Prof. Dr. Lothar Schad Notation: NMR & MRI 12/9/2008 | Page 3

(Nuclear) (Kernspin)

Magnetic Magnet NS

Resonance Resonanz

(Imaging) Tomographie

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Computer Assisted Clinical Medicine Prof. Dr. Lothar Schad NMR History: Discovery 12/9/2008 | Page 4

Germany - Isidor Rabi Columbia • rebuilt a molecular beam apparatus (Otto Stern) 1938 • detected nuclear resonance in a stream of Lithium Chloride molecules E -1/2

+1/2 B

• Nobel prize for physics in 1944

Harvard Edward Purcell, Torrey and Pound

1946 • applied radar technology in investigating magnetic resonance • achieved the first resonance in a practical sample, a block of paraffin

-1/2 E

+1/2 B ν

B © Yves De Deene. University of Gent, Belgium

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Computer Assisted Clinical Medicine Prof. Dr. Lothar Schad NMR History: Theory 12/9/2008 | Page 5 Felix Bloch Leipzig - Stanford • achieved the same in a sample of water • provided the mathematical characterization of the nuclear magnetic 1946 resonance phenomenon • Nobel Prize for physics (Bloch & Purcell) in 1952

B the Bloch equations

M x B dM M = γ. (M x B) dt

-G

L L x G

L = I.ω

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Computer Assisted Clinical Medicine Prof. Dr. Lothar Schad NMR History: Spin Echo 12/9/2008 | Page 6 Erwin Hahn Illinois • discovered a “second” nuclear resonance signal, the spin echo 1949 • achieved T1 and T2 weighting

excitation refocusing pulse pulse The first observed spin echo by E. Hahn (1950)

TE/2 TE/2

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Computer Assisted Clinical Medicine Prof. Dr. Lothar Schad NMR History: Relaxation Times 12/9/2008 | Page 7

excitation refocusing pulse pulse Harvard Nicolaas Bloembergen

1948

Robert Pound

excitation refocusing pulse pulse

Edward Purcell

• characterized the relaxation times of the nuclear response signal in detail

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Computer Assisted Clinical Medicine Prof. Dr. Lothar Schad NMR History: Imaging I 12/9/2008 | Page 8 Downstate Medical Raymond V. Damadian Center Brooklyn • the first scanner for clinical purposes

1972

United States Patent 3,789,832

The method envisioned scanning with a focused “sweet spot” similar to the scanning raster on a television.

Either the “sweet spot” would move, or the patient would move across the “sweet spot”, thereby collecting one tissue data point at a time.

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Computer Assisted Clinical Medicine Prof. Dr. Lothar Schad NMR History: Imaging II 12/9/2008 | Page 9

Paul Lauterbur

1973 • second scanner: collecting many points at once. • the improved method was based on the principle of back projection. • magnetic field gradients were used to realize the projections.

Nature 1973;242:190-191

Richard R. Ernst Zurich • 2D Fourier transform MRI 1974

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Computer Assisted Clinical Medicine Prof. Dr. Lothar Schad NMR History: Scanner 12/9/2008 | Page 10

The first MR scanners ...

interventional MRI unit open MRI unit mobile MRI unit

… and the most recent © Yves De Deene. University of Gent, Belgium

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Computer Assisted Clinical Medicine Prof. Dr. Lothar Schad Facts 2002 12/9/2008 | Page 11

• routine method in diagnostic of diseases since 1985

• worldwide more than 60 million examinations

• worldwide about 22 000 MRI-scanners for clinical routine

• world market volume of imaging systems (X-ray, CT, MRI, PET, US) about 10 Billion EUR

• European market for medical 3D imaging systems: 2001: 386 Million US-Dollar 2008: 733 Million US-Dollar

source: Frost and Sullivan http://www4.medica.de/cipp/md_medica/custom/pub/content,lang,1/ticket,g_a_s_t/oid,479, 12.06.2002

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Computer Assisted Clinical Medicine Prof. Dr. Lothar Schad Imaging Examples: MR & CT 12/9/2008 | Page 12 patient: astrocytoma II

MRI

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Computer Assisted Clinical Medicine Prof. Dr. Lothar Schad Why MRI ? 12/9/2008 | Page 13

CT CT WMS: 1025 Hu GMS: 1035 Hu } Δ = 1% CSF: 1000 Hu

ρ T2 T1 T2 T1 MRI WMS: 90 ms 550 ms GMS: 100 ms 1000 ms } Δ = 100% CSF: >1000 ms 2000 ms

example: patient astrocytoma II

1. best soft tissue contrast 2. no radiation exposure

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Computer Assisted Clinical Medicine Prof. Dr. Lothar Schad Imaging Examples: Contrast 12/9/2008 | Page 14

T1 T2 w w MRI properties:

+ best soft tissue contrast

+ different contrast

+ arbitrary slice orientation

+ morphology and function

+ no radiation

- only protons visible (no bones)

- no electron density

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Computer Assisted Clinical Medicine Prof. Dr. Lothar Schad Fast Imaging Technique (EPI) 12/9/2008 | Page 15

40 slices in about 4 sec

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Computer Assisted Clinical Medicine Prof. Dr. Lothar Schad Nobel Prizes NMR 12/9/2008 | Page 16

1944 Nobel prize in physics Isidor Rabi spin of nuclei (1939)

1952 Nobel prize in physics Felix Bloch and Edward Purcell discovery of NMR (1946)

1991 Nobel prize in chemistry Richard Ernst Fourier transformation, MRS (1966)

2002 Nobel prize in chemistry Kurt Wüthrich 3D structure of proteins, MRS (1982)

2003 Nobel prize in medicine Paul Lauterbur and Peter Mansfield MR imaging, MRI (1973)

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Computer Assisted Clinical Medicine Prof. Dr. Lothar Schad Functional MRI 12/9/2008 | Page 17

brain activation using finger tapping: - primary motor and sensory cortex (M1/S1) - supplementary motor cortex area (SMA) - Cingulum - secondary motor cortex (SII)

activation pattern: 15 s finger-tapping followed by 15 s silent.

Posse et al. Hum Brain Mapp 2001

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Computer Assisted Clinical Medicine Prof. Dr. Lothar Schad Ultra-High-Field MRI: 8.0 Tesla 12/9/2008 | Page 18 morphology diffusion tensor imaging (DTI)

Bammer et al. Eur J Radiol 2003

courtesy of Robitaille. Center for Advanced Biomedical Imaging Department of Radiology, Ohio State University, USA

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Computer Assisted Clinical Medicine Prof. Dr. Lothar Schad Safety and Risk I 12/9/2008 | Page 19

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Computer Assisted Clinical Medicine Prof. Dr. Lothar Schad Safety and Risk II 12/9/2008 | Page 20

TLZ 01.08.2001

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Computer Assisted Clinical Medicine Prof. Dr. Lothar Schad What means MRI ? 12/9/2008 | Page 21

• tomographic imaging technique (gr. tomos (τομοσ) - slice) • MR-scanner provides multi-dimensional data array (image) of spatial distribution of physical quantities - 2D images with arbitrary orientation - 3D volume data - 4D images (spatial/temporal distributions) • MR-signals originate directly from the human body no “Emission”-Tomography; see PET, SPECT no radioactive substance necessary! notice: CT = “Transmission-Tomography”

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Computer Assisted Clinical Medicine Prof. Dr. Lothar Schad Comparison: CT - MRI 12/9/2008 | Page 22 CT = transmission tomography MRI = “direct” tomography

ν X-ray tube h M detector 0 detector electronics

high voltage projection data

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Computer Assisted Clinical Medicine Prof. Dr. Lothar Schad What do we measure with MRI ? 12/9/2008 | Page 23

• MRI works in the radiofrequency domain (e.g. 40 – 300 MHz) - no ionizing radiation • MRI image gives an abundance of information, image pixel grey value (signal intensity) dependent of: - proton density ρ - spin-lattice-relaxation time T1 - spin-spin-relaxation time T2 - molecular motion (e.g. flow, diffusion, perfusion) - susceptibility (e.g. hemoglobin concentration) - chemical shift (e.g. fat)

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Computer Assisted Clinical Medicine Prof. Dr. Lothar Schad Electromagnetic Spectrum 12/9/2008 | Page 24

Frequency Wave Length Photon Energy Radiation Molecular Impact [Hz] [m] [eV]

1026 10-18 1012 1024 10-16 1010 1022 10-14 10 8 x- and γ-ray DNA break 1020 10-12 10 6 1018 10-10 10 4 1016 10 -8 10 2 UV-radiation e--excitation (orbital) 14 -6 0 visible light 10 10 10 oscillation IR-radiation 1012 10 -4 10 -2 rotation 1010 10 -2 10 -4 8 0 -6 10 10 10 UKW 6 2 -8 MRI 10 10 10 KW 10 4 10 4 10 -10 MW 10 2 10 6 10 -12 LW 10 0 10 -14 source: Lissner and Seiderer. “Klinische Kernspintomographie” 1987

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Computer Assisted Clinical Medicine Prof. Dr. Lothar Schad MRI Components 12/9/2008 | Page 25

• strong magnet producing a homogeneous static magnetic field (0,1 - 8,0 Tesla) (for comparison: earth magnetic field 30 µT - 60 µT) • radiofrequency unit creating a periodical magnetic field used for spin excitation and signal detection • gradient coils producing a linear magnetic field gradient for spatial encoding

• receiver coils for signal detection • computer for controlling the MRI scanner • input/ouput panel for data-flow and -evaluation

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Computer Assisted Clinical Medicine Prof. Dr. Lothar Schad Magnetic Field B 12/9/2008 | Page 26 0

static magnetic field B0 field strength 1.5 – 3.0 Tesla homogeneity < 1.0 ppm

nitrogen 77 K helium 4.2 K M0 vacuum

copper wires with niobium-titanium-fibers cryostat super contacting coil cooling liquid NbTi, Nb3Sn He, (N2)

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Computer Assisted Clinical Medicine Prof. Dr. Lothar Schad MRI Components: Schema 12/9/2008 | Page 27 magnet RF-unit (receiver)

input/output-panel

gradient system RF-unit (transmitter) computer

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Computer Assisted Clinical Medicine Prof. Dr. Lothar Schad MRI Components: Network 12/9/2008 | Page 28

console

mass storage RF low signal processing image & computer video storage

central central RF pulse amplifier shim magnet clock pulse generator current current synthe- sequence supply supply sizer

1 magnet with cryotank and cryoshield 6 transmit/receive duplexer 2 shim coils 7 preamplifier 3 gradient coils 8 low/high-pass filter 4 RF-resonator 9 ESB-module 5 patient couch 10 RF leak proof connections

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Computer Assisted Clinical Medicine Prof. Dr. Lothar Schad MRI Components: Physical Parameters 12/9/2008 | Page 29

radio- gradients Gxyz static field B0 frequency RF shim coils technical physical component Æ parameter gradient transmitter shim receiver static field B0 Æ M0 radiofreq. RF Æ signal

350 MHz gradients Gxyz Æ image control 350 MHz

panel image

computer processor

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Computer Assisted Clinical Medicine Prof. Dr. Lothar Schad MRI Systems 12/9/2008 | Page 30

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Computer Assisted Clinical Medicine Prof. Dr. Lothar Schad MRI Hosting 12/9/2008 | Page 31

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Computer Assisted Clinical Medicine Prof. Dr. Lothar Schad MRI Installation 12/9/2008 | Page 32

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