Magnetic resonance resonance imaging imaging

Magnetic

Magnetic resonance resonance imaging imaging

J.Lisý

J.Lisý

MR MR

shows changes in behavior (spin, precese) of atomic nuclei with odd atomic number in strong magnetic field after their vibration (resonancy) caused by

radiofrequency (RF) puls

most commonly uses proton of hydrogen H⁺

physically vector (it has certain size and orientation)

in external magnetic field H⁺ behaves like small linear magnet

MRI MRI equipment equipment

permanent magnet permanent magnet

0,2 0,2 - - 3T (0,5 1,0 a 3T (0,5 1,0 a 1,5T 1,5T ) )

Stronger Stronger magnet. magnet. field field faster

faster scan scan better

better spatial spatial resolution resolution x larger artefacts

x larger artefacts

Radiofrekvency Radiofrekvency coils coils

gradient gradient coils coils

Elektromagnetic

Elektromagnetic induction induction

electricelectric currentcurrent willwill bebe inducedinduced in in anyany closedclosed circuitcircuit whenwhen thethe magneticmagnetic fluxflux throughthrough a a surfacesurface boundedbounded by by thethe conductorconductor changeschanges

1831 Michael Faraday

Lauterbur

Lauterbur , , Masfield Masfield

Nobel Nobel prizeprize 20032003

originally rejected originally rejected paper

paper to Natureto Nature

Damadian Damadian

1975 1 image of thorax

1 hour

Spin, precese protonu Spin, precese protonu

Spin H Spin H

small small magnet magnet North North / / South South pole pole vector

vector ( ( size size of of magnetisation magnetisation and and its its direction

direction ) )

Precession Precession rotation rotation H H

aroud aroud two two cone cone shaped shaped shell

shell accord accord . . gyromagnetic

gyromagnetic constant constant

1. 1. Outside Outside of of magnetic magnetic field field

weak magnetic field of the earth nucleus, doesn´t influence H⁺ in human tissue

random orientation of H⁺ in human body

no magnetisation

T2 H⁺ precesion out of phase (H⁺ in different phase)

no magnetisation

2. 2. External External magnet magnet

T1 majority HT1 ⁺ paralel, minority antiparalel

longitudinal magnetisation

T2 H⁺ precesion f out of phase no magnetisation

Larmor equation

f = B x ^ω

f frequency

B strength magnetic field (depends on strength of external magnetic field, i.e. magnet MR equipment) in T(Tesla) ( 0,2T-1,5T-3T) ω (omega) gyromagnetic constant (specific for

given particle) H⁺ 42 MHz

3.RF puls

T1 part of H

absorb energy of RF puls tilt themselves about 180 dg., antiparalelly

reduction of longitudinal magnetisation

T2 phase coherence synchronisation of precesion H

appears maximal transversal magnetisation

4.After RF puls

T1 part of antiparalelly orientated H+ returns back paralelly

longitudinal magnetisation appears again T1 relaxation time

T2 loss of phase coherence (dephasing)

transvesal magnetisation is reduced

T2 relaxation time

T1 T1 relaxation relaxation

spin spin of of protons protons

length T1 RT related to spin (H length T1 RT related to spin (H

) ) – – lattice lattice (lattice of particles around H

(lattice of particles around H

) )

shorter shorter T1 RT T1 RT increased increased SI SI

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T1 T1 relaxation relaxation

LongitudinalLongitudinal relaxationrelaxation interaction

interaction spinspin HH⁺⁺--lattice lattice ((latticelattice ofof particlesparticles aroundaround HH⁺⁺) )

T1 T1 relaxation timerelaxation time shorter

shorter –– increasedincreased SI SI

((fatfat shortshort T1T1--RT RT highhigh SISI Fluid

Fluid longlong T1T1--RT lowRT low SI)SI)

0 1 2 3 4 5

-1.0 -0.5 0.0 0.5 1.0

180^o Pulse

Inversion Recovery

t/T1 M z/M 0

T2 T2 relaxation relaxation

Precesion Precesion of of H H

protons protons

Lenght of T2 RT related to spin (H Lenght of T2 RT related to spin (H

) ) – – spin spin (H (H

) interaction ) interaction

Longer Longer T2 RT T2 RT increased increased signal signal intensity intensity

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T2 relaxace T2 relaxace

ttransverransversal relaxationsal relaxation dephasing

dephasing ofof protonsprotons spinspin--spin spin relaxationrelaxation (H(H⁺⁺ -H-H⁺⁺))

T2 T2 relaxationrelaxation timetime longer

longer –– increasedincreased signalsignal Fluid

Fluid highhigh signalsignal ((whitewhite) )

0 1 2 3 4 5

0.0 0.2 0.4 0.6 0.8 1.0

t/T2^* M x(t)/M x(0)

Contrast media

Gadolinium 7 electrons (weak magnetic field)

toxic (bound in komplexotvorné sloučenině- chelátu) DTPA DietylenTetraPentaAcetát

decrease of both relaxation times (T1 i T2)

dose 0,1 mmol/kg, i.e. 1ml/5kg (till 50 kg, more kg 10 ml)

expensive 950 Kč/10 ml

nefrogenic (renal excretion)

enhancement of SI in case of broken blood brain barrier (BBB) ( lack of BBB physiologically in chorioidal plexus, adenohypophysis)

Gadolinium

Preparation

any

questionnaire

mettalic objects (heart pacemaker, cochlear implant)

pregnancy (1.trimestr of gravidity) breast feeding (Gd isn´t applied)

general anaesthesia (small, uncooperative children + claustrophobia)

Indications Indications

Neuro (brain, spinal cord and canal) Neuro (brain, spinal cord and canal)

Musculosceletal Musculosceletal system system , soft , soft tissue tissue

Bile ducts (MRCP) B ile ducts (MRCP) and liver and liver

Small Small pelvis pelvis ( ( staging staging carcinoma carcinoma rectum rectum , , prostate prostate , , uterinne

uterinne cervix cervix ) )

ENT ENT

Vessels Vessels ( ( without without Gad Gad application application , , renal renal insufficiency

insufficiency ) )

Absolute

Absolute contraindications contraindications

Heart pacemaker (from 2008 MR compatible) Heart pacemaker (from 2008 MR compatible)

Cochlear Cochlear implant implant

from nonferromagnetic material, dont´t disclotated in magnetic field programable by external magnet

strong external magnet would cancel this programation

Relative

Relative contraindications contraindications

metallic objects

made from nonferomagnetic material not disclocated in magnetic field, but metallic artefact

pregnancy

breast feeding (Gd)

claustrofobia

small uncooperative children