MR Lab Rotation, Mannheim. Basics of MRI. Andreas Lemke and Prof. Dr. Lothar Schad

Transcription

1 1 12/22/2010 Page 1 MR Lab Rotation, Mannheim Basics of MRI and Prof. Dr. Lothar Schad Chair in Faculty of Medicine Mannheim University Heidelberg Theodor-Kutzer-Ufer 1-3 D Mannheim, Germany Lothar.Schad@MedMa.Uni-Heidelberg.de 12/22/2010 Page 2 Seite 1

2 2 12/22/2010 Page 3 Literature Reiser, Semmler, Hricak: Magnetic Resonance Tomography Chapter 2, 2008 Vlaardingerbroek and den Boer: Magnetic Resonance Imaging Theory and Practice, 2003 Haacke: Magnetic Resonance Imaging: Physical Principles and Sequence Design 12/22/2010 Page 4 Brief Review Brief Review Seite 2

3 3 12/22/2010 Page 5 Zeeman Effect Curie s law: M 0 = ρ I(I+1) γ 2 h 2 B 0 3kT B 0 m = -1/2 M 0 m = +1/2 B = 0 B = B 0 splitting of energy levels (Zeeman effect) 12/22/2010 Page 6 Quantum Mechanic Classical Mechanic quantum mechanic classical mechanic Schrödinger equation: r dm ( t) dt = γ r r M B notice: M is a macroscopic quantity, all nutation angles are allowed CM μ is a microscopic quantity, only +1/2 and -1/2 are allowed QM Slichter. Principles of Magnetic Resonance 1978 Bloch equation Seite 3

4 4 12/22/2010 Page and Pulses laboratory system rotating system 90 -pulse (π/2-pulse) in the laboratory and rotating coordinate system N -1/2 = N +1/2 to : 3x10 18 spins per 1 mm 3 at 1.5 T 180 -pulse (π-pulse) in the laboratory and rotating coordinate system N -1/2 > N +1/2 = -M 0 to : 6x10 18 spins per 1 mm 3 at 1.5 T source: Lissner and Seiderer. Klinische Kernspintomographie /22/2010 Page 8 Movie: Spin Excitation Plewes DB, Plewes B, Kucharczyk W. The Animated Physics of MRI, University Toronto, Canada Seite 4

5 5 12/22/2010 Page 9 NMR Excitation and Signal Detection B 0 B 0 M magnetic field RF transmit coil with ν = ω 0 M RF receive coil excitation detection RF receive coil 12/22/2010 Page 10 Faraday Induction bicycle dynamo loop with rotating magnet rotating magnetic moments z N S x M y y Seite 5

6 6 12/22/2010 Page 11 Movie: Free Induction Decay FID free induction decay: FID M xy signal intensity time Plewes DB, Plewes B, Kucharczyk W. The Animated Physics of MRI, University Toronto, Canada 12/22/2010 Page 12 Radio Frequency Coils: Coil Arrays II 102 seamlessly integrated coil elements at 32 receiving channels matrix coils: head neck stem leg courtesy: Siemens AG, Erlangen Seite 6

7 7 12/22/2010 Page 13 MRI Components: Physical Parameters radio- gradients G xyz static field B 0 frequency RF shim coils gradient shim transmitter receiver technical component physical parameter static field B 0 M 0 radiofreq. RF signal control panel computer 350 MHz 350 MHz image processor gradients G xyz image 12/22/2010 Page 14 Relaxation Relaxation Seite 7

8 8 12/22/2010 Page 15 Magnetization: M z and M xy longitudinal magnetization: M z transversal magnetization: M xy transversal magnetization: M xy - phase synchronization after a 90 -pulse - the magnetic moments μ of the probe start to precede around B 1 leading to a synchronization of spin packages M xy - after 90 -pulse M xy = M 0 12/22/2010 Page 16 Movie: M z and M xy source: Schlegel and Mahr. 3D Conformal Radiation Therapy: A Multimedia Introduction to Methods and Techniques" 2007 Seite 8

9 9 12/22/2010 Page 17 Longitudinal Relaxation Time: T1 thermal equilibrium excited state after 90 -pulse: -N -1/2 = N +1/2 and M z = 0, M xy = M 0 after RF switched off: - magnetization turns back to thermal equilibrium -M z = M 0, M xy = 0 T1 relaxation longitudinal relaxation time T1 spin-lattice-relaxation time T1 12/22/2010 Page 18 Physical Model of T1 Relaxation J(ω) B 0 source: Liang and Lauterbur. Principles of Magnetic Resonance Imaging in a real spin system (tissue) every nuclei is surrounded by intra- and intermolecular magnetic moments - thermal motion (rotation, translation, oscillation) leads to an additional fluctuating magnetic field B loc (t) with typical spectral distribution J(ω) - transversal components of J(ω) at ω 0 allow energy transfer hω 0 from the spin system to the lattice T1 relaxation Seite 9

10 10 12/22/2010 Page 19 Phenomological Description of T1 B 0 the longitudinal magnetization M z relaxes exponential to the equilibrium state M z = M 0 with a typical time constant T1 dm z /dt = (γ x B) z + (M 0 M z )/T1 : Bloch equation with T1 with M z = 0 at t = 0: M z (t) = M 0 (1 exp(-t/t1)) solution of Bloch equation 12/22/2010 Page 20 Transversal Relaxation Time: T2 after 90 -pulse: -N -1/2 = N +1/2 and M z = 0, M xy = M 0 after RF switched off: - magnetization M xy starts to rotate in the x,y-plane at Larmor frequency - all longitudinal components J(ω) of the fluctuating magnetic field B loc (t) result in a dephasing of M xy spin-spin interaction - mainly static frequency components J(ω) of the fluctuating magnetic field B loc (t) at ω = 0 are contributing - no energy transfer in the spin system (entropy ) J(ω) B 0 T2 relaxation (also called spin-spin-relaxation) - although technical in homogeneities of B 0 cause dephasing of M xy T2* (effective relaxation) J(ω=0) Seite 10

11 11 12/22/2010 Page 21 Movie: Spin Dephasing Plewes DB, Plewes B, Kucharczyk W. The Animated Physics of MRI, University Toronto, Canada 12/22/2010 Page 22 T1 and T2 Relaxation Times in-vivo tissue liver T2 [ms] at 3 T 42 ± 3 T1 [s] at 3 T 0,81 ± 64 T2 [ms] at 3 T 46 ± 6 T1 [s] at 3 T 0,58 ± 0,03 skeletal muscle 50 ± 4 1,41 ± 0,03 44± 6 1,01 ± 0,02 heart 47 ± 11 1,47 ± 0,06 40 ± 6 1,03 ± 0,34 white matter 69 ± 3 1,08 ± 0,04 72 ± 4 0,88 ± 0,03 grey matter 99 ± 7 1,82 ± 0,11 95 ± 8 1,13 ± 0,05 - T1 increases with increasing B 0 - T2 decreases with increasing B 0 Bottomley et al. Med Phys 1984 Seite 11

12 12 12/22/2010 Page 23 Standard Techniques for T1 and T2 Saturation-Recovery Sequence Inversion-Recovery Sequence Spin-Echo Sequence 12/22/2010 Page 24 Saturation-Recovery Sequence saturation-recovery sequence 90 -pulse moves the longitudinal magnetization M 0 to the x-, y plane FID transversal magnetization M xy decays with T2* longitudinal magnetization starts to recover to thermal equilibrium M z with T1 after TR actual (reduced) magnetization M z is moved to the x-, y plane FID repeat measurement with different TR T1 determination by S ~ ρ [1 - exp(-tr / T1)] with TR >> T2* Seite 12

13 13 12/22/2010 Page 25 Inversion-Recovery Sequence inversion-recovery sequence 180 -pulse invert the longitudinal magnetization M 0 to M 0 at the z-axes longitudinal magnetization starts to recover to thermal equilibrium M z with T1 inversion time TI after TI 90 -pulse moves the actual (reduced) longitudinal magnetization M z to the x-, y plane FID transversal magnetization M xy decays with T2* repeat measurement with different TI T1 determination by S ~ ρ [1 2 exp(-ti / T1)] with TR > 5 T1 12/22/2010 Page 26 T1 Measurement: Inversion Recovery inversion recovery (M z (0) = -M 0 ): M z (t) = M 0 (1 2 exp(-ti/t1)) with M z = 0 at TI = TI 0 : 0.5 = exp(-ti 0 /T1) T1 = -TI 0 / ln(0.5) = TI 0 / 0.7 TI 0 Seite 13

14 14 12/22/2010 Page 27 Spin-Echo Schema a) RF impulse schema b) timing of longitudinal magnetization M z rephasing part of signal dephasing part of signal c) induced measured signal: spin-echo SE source: Schlegel and Bille. Medizinische Physik Bd /22/2010 Page 28 Movie: Spin-Echo II Plewes DB, Plewes B, Kucharczyk W. The Animated Physics of MRI, University Toronto, Canada Seite 14

15 15 T2 Measurement: Spin-Echo 12/22/2010 Page 29 spin-echo (M xy (0) = M 0 ): M xy (t) = M 0 exp(-t/t2) 12/22/2010 Page 30 Imaging Imaging Seite 15

16 16 12/22/2010 Page 31 Magnetic Resonance Imaging: Principle interaction of spins with static magnetic field B 0 M 0 interaction of protons with resonant magnetic radiofrequency field B 1 FID signal linear magnetic field gradient across the object G spatial encoding ω = γ. B 0 ΔE = hω ω(x) = γ. B(x) B 0 B(x) = B 0 + G x x x 12/22/2010 Page 32 Gradient Coil: Principle I coil for static B 0 field typical value for G: 1-25 (40) mt/m y-gradient example: x = 30 cm, B 0 = 1 T, G = 10 mt/m B = T T z-gradient x-gradient Seite 16

17 17 12/22/2010 Page 33 Gradient Field: Slice Selection magnetic field gradient, i.e. G z G z radiofrequency: ω(z) = γ (B 0 + G z z) gradient G z 12/22/2010 Page 34 Slice Selective Excitation frequency spectra of RF pulse ω ω (z 2 ) ω (z 1 ) ω ω = γ (B 0 +G z z) ω( z) γ (B + G z z) = 0 I(ω) ω 0 z 1 z 2 z d Δω 2πΔf = = z z γ G γ G d 1. slice thickness d = z 2 -z 1 can be varied by RF bandwidth (frequency width) or gradient strength G z. 2. slice position can be changed by shifting the frequency spectra with constant RF bandwidth Seite 17

18 18 12/22/2010 Page 35 Gradient Compensation excited slice dephasing of transversal magnetization after unipolar gradient pulse z-gradient with compensation and RF sinc-pulse for creating a homogeneous transversal magnetization source: Dössel. Bildgebende Verfahren in der Medizin /22/2010 Page 36 Frequency Encoding: Gradient Schema RF G z signal acquisition t - superposition of a gradient field B x = G x x during the acquisition phase results in: ω(x) = γ (B 0 + G x x) t where the Lamor frequency is linked with the spatial information x G x - spatial information is encoded in the precision frequency of the transversal magnetization t Seite 18

19 19 12/22/2010 Page 37 Frequency Encoding: Spatial Resolution - FID-signal S(t) is digitalized by using an analog to digital converter ADC and a discrete timing interval Δt in a total acquisition window t aq - for the Fourier-analysis of the FID-signal there are in total N = t aq /Δt measured data points: S(Δt), S(2Δt), S(3Δt),, S(NΔt) - spatial resolution in x-direction Δx is given by the sampling theorem: Δx = X / N = 2π / γ G x N Δt with X: the maximum object diameter (FOV), N: number of sampling points, G x : gradient strength, Δt: sampling interval (1/Δt = bandwidth BW in Hz/pixel) 12/22/2010 Page 38 Phase Encoding: Gradient Schema - phase encoding gradient includes a spatial dependency of the spin phase according to: G z G y slice selection gradient phase encoding gradient y T y φ p = γ G y y t y - phase encoding is performed before signal acquisition - gradient field is switched on for a constant time T y -gradient strength is increased stepwise by ΔG y after every sequence passage Seite 19

20 20 12/22/2010 Page 39 k-raum K-Space: Definition the k-space construction is a relation between spatial encoding (phase and frequency encoding) and the Fourier transformation frequency encoded signal: S ( t) = k S ( k ) = = ρ ( x ) e γ G t 2 π ρ ( x ) e i γ G x t i 2 π k x d d x x 12/22/2010 Page 40 Surfing through k-space read read phase phase 180 -pulse RF constant gradient results in a straight trajectory change in polarity inverts the trajectory refocusing pulse (180 ) inverts phase (mirroring at origin) Seite 20

21 21 12/22/2010 Page 41 Movie: 2D K-Space X and Y Plewes DB, Plewes B, Kucharczyk W. The Animated Physics of MRI, University Toronto, Canada 12/22/2010 Page 42 Movie: 2D K-Space X and Y Plewes DB, Plewes B, Kucharczyk W. The Animated Physics of MRI, University Toronto, Canada Seite 21

22 22 12/22/2010 Page 43 K-Space: Summary y density image Fourier transformation k y x k-space k x hologram 12/22/2010 Page 44 K-Space: Sampling Requirements I sampling theorem: Δk Δk x y 1 W x 1 W source: Liang and Lauterbur. Principles of Magnetic Resonance Imaging 2000 y Δk Δk x y = γ G x Δt = γ ΔG T y pe G x : frequency encoding gradient Δt : frequency encoding interval ΔG y : phase encoding increment T pe : phase encoding interval Seite 22

23 23 12/22/2010 Page 45 K-Space: Sampling Requirements II Δt 2 π γ G W x x = γ G 2 π N x x Δx ΔG y 2 π γ T W pe y = γ T pe 2 π N y Δy Nyquist - interval 12/22/2010 Page 46 Example - during a MR measurement the signal S(t) is discretely sampled (frequency encoding interval Δt) in a total acquisition time t aq (typical 5-30 ms) number of measuring points N = t aq / Δt S(Δt), S(2Δt),... S(NΔt) spatial resolution Δx is limited by: Δx = W N x x = γ G x 2π N x Δt example: N x = 256 Δt = 30 µs G x = 1,566 mt/m Δx = mm W x = N Δx = 50 cm Seite 23

24 24 12/22/2010 Page 47 Spin-Echo Contrast: TR, TE TE ms 40 - no contrast SNR low T1-weighted T2-weighted proton-weighted 10 ms ms ms TR 12/22/2010 Page 48 Spin-Echo Sequence k-space: after 1. TR k-space: after 2. TR k-space: after 256. TR k y k x Seite 24

25 25 12/22/2010 Page 49 Spin-Echo Images S TR/T1 TE/T2 = ρ [ e e123 SE ] T1 factor T2 factor Pw TR = 2775 ms TE = 17 ms T2w TR = 2775 ms TE = 102 ms T1w TR = 575 ms TE = 14 ms - SE gold standard technique for T1 and T2 morphology 12/22/2010 Page 50 Spin-Echo: Multi-Slice - interleaved SE measurement measurement #1 1. slice measurement #2 2. slice 3. slice 4. slice 5. slice - multi-slice SE TR = 600 ms, TE = 10 ms about 60 slices can be measured simultaneously! Seite 25

26 26 12/22/2010 Page 51 Inversion Recovery Sequence source: Reiser and Semmler. Magnetresonanztomographie /22/2010 Page 52 Inversion Recovery Images S TI/T1 TR/T1 TE/T2 = ρ [1 2e + e e IR ] T1 factor T2 factor Seite 26

27 27 12/22/2010 Page 53 Gradient-Echo Sequence spoiler z M M z α M xy x,y -example: α = 20 M z - reduction by 6% M xy - value 34% of M z!! 12/22/2010 Page 54 Gradient-Echo: Measuring Time SE GE α = 90 / 180 TE = 20 ms TR = 600 ms T aq : minutes α = 25 TE = 7 ms TR = 20 ms T aq : seconds!! Seite 27

28 28 12/22/2010 Page 55 Fast Gradient-Echo Imaging: EPI - echo-planar imaging EPI - multi-gradient imaging technique - single-shot technique with strong requirements to the gradient power - strong T2* dependency susceptibility artifacts! - fastest imaging technique Sir Mansfield 2003 Nobel prize in medicine Mansfield and Pykett. JMR /22/2010 Page 56 Fast Gradient-Echo Imaging: EPI Technique Seite 28

29 29 12/22/2010 Page 57 EPI Problem: Static Inhomogeneities gradient echo EPI 1. distortions in phase direction 2. echo shift of odd against even echoes 12/22/2010 Page 58 Fast Gradient-Echo Imaging: EPI Methods classical EPI spin-echo EPI SE-EPI Seite 29

30 30 12/22/2010 Page 59 Exercise: Measurement of the ADC 1. Calculate the apparent diffusion coefficient (ADC) from the DWI images in White Matter (WM), Grey Matter (GM), and Cerebrospinal Fluid (CF) Experiment #1: 2 images were measured (DWI_b0.IMA, DWI_b1000.IMA, data at: Medical Physics: Lab Rotation MR-Radiology ) with b = 0 and 1000 s/mm 2. Plot signal intensity (= pixel mean value of ROI) semi-logarithm as a function of b-value and calculate ADC - group 1: CF ( ) - group 2: WM ( ) - group 3: GM ( ) S = S 0 exp( bd ) 12/22/2010 Page 60 Exercise: Measurement of the FA 2. Calculate the fractional anisotropy (FA) from the DTI images in White Matter (WM), Grey Matter (GM), and Cerebrospinal Fluid (CF) Experiment #2: 6 images were measured (DTI_b1000_1.IMA DTI_b1000_6.IMA, data at: Medical Physics: Lab Rotation MR-Radiology ) with b = 1000 s/mm 2 and 6 different directions. Evaluate signal intensity (= pixel mean value of ROI) for the different directions and calculate FA - group 2: CF ( ) - group 3: WM ( ) λ 3 λ 1 λ 2 - group 1: GM ( ) FA = 3 2 ( λ 1 λ )² + ( λ 2 λ )² + ( λ 3 λ )² λ 1 + λ 2 + λ 3 D D D xx xy xz D D D xy yy yz D D D xz yz zz Seite 30

31 31 12/22/2010 Page 61 Diffusion Diffusion 12/22/2010 Page 62 Free Diffusion mean diffusion length x ² = 6 Dt (D = diffusion coefficient, t = time) Seite 31

32 32 12/22/2010 Page 63 Principle of DWI I without diffusion weighting: with diffusion weighting: 12/22/2010 Page 64 Principle of DWI II after 90 pulse position of the spin in the rotating reference frame constant phase in the rotating reference frame Seite 32

33 33 12/22/2010 Page 65 Principle of DWI III without diffusion: 1. gradient relative phase shift in the rotating frame 12/22/2010 Page 66 Principle of DWI IV without diffusion: 2. gradient rephasing of the phase gradient echo Seite 33

34 34 12/22/2010 Page 67 Principle of DWI V with diffusion: 1. gradient relative phase shift in the rotating frame 12/22/2010 Page 68 Principle of DWI VI with diffusion: diffusion during the gradients spins on a different position Seite 34

35 35 12/22/2010 Page 69 Principle of DWI VII with diffusion: 2. gradient spins not completely rephased signal reduction 12/22/2010 Page 70 Dependence of the Signal Decay strength of the diffusion weighting: signal decay: b 2 2 = γ G δ 2 ( Δ δ / 3) S = S 0 exp( bd ) b-value can be calculated from the sequence two DWIs are necessary to calculate D Seite 35

36 36 12/22/2010 Page 71 Diffusion Measurement: Calculation of D b-values = s/mm 2 ln(signal) [a.u.] S = S 0 e -bd b-value [s/mm 2 ] white matter D ~ mm 2 /s water D ~ mm 2 /s Measurement of D in biological tissue is called ADC 12/22/2010 Page 72 Anisotropic Diffusion 0,5 μm Bealiue, NMR Biomed., μm Axon free diffusion along the fiber restricted orthogonal to the fiber Seite 36

37 37 12/22/2010 Page 73 Diffusion Tensor Imaging (DTI) water molecule λ 1 λ 3 λ 3 diffusion ellipsoid λ 2 λ 2 λ 1 λ 1 diffusion tensor D D D D 0 0 x 0 D 0 y 0 0 D z D D D xx xy xz D D D xy yy yz D D D xz yz zz 12/22/2010 Page 74 DTI: Quantification derived quantities apparent diffusion coefficient ADC = ( λ + λ + ) 1 2 λ 3 3 fractional anisotropy (FA) FA = 3 2 ( λ 1 λ )² + ( λ 2 λ )² + ( λ 3 λ )² λ + λ + λ < FA < 1 Seite 37

38 38 12/22/2010 Page 75 Fractional Anisotropy white matter: FA = grey matter: FA = FA-map FA-colormap 12/22/2010 Page 76 3D Fibertracking - fibertracking method: using main eigenvector of diffusion tensor the main direction of fibers can be tracked pixel by pixel in vivo DTI post mortem atlas Stieltjes et al. Neuroimage 2001 Seite 38

39 39 12/22/2010 Page 77 Safety Aspects Safety Aspects Page 78 MRI System with Superconducting Magnet Siemens Magnetom Symphony B 0 = 1.5 Tesla Quantum-gradient: 30 mt/m slew rate: 125 T/m/s removable patient couch short magnet: 1.6 m relatively open bore 8 receiving channels Seite 39

40 40 Page 79 Warnings warnings: strong magnetic field radiofrequency interdictions: cardiac pacemaker open fire metallic implants watch, camera magnetic fire extinguisher metal: scissor, key magnetic disc Page 80 Static Magnetic Field: B 0 I control area: 0.5 mt - line source: Reiser and Semmler. Magnetresonanztomographie 2002 Seite 40

41 41 Page 81 B 0 - Danger B 0 missile effect strong forces to ferromagnetic materials forces and torques to implants stent gunshot wound, rest of projectile failure of electromagnetic devices cardiac pacemaker computer controlling system physiologic effects vertigo when entering the magnet (> 3 Tesla) Page 82 B 0 Example II courtesy: Gross. Siemens Erlangen Seite 41

42 42 Page 83 B 0 : MR Compatible Fire Extinguisher Page 84 B 0 : Emergency Switch-Off Magnet when? only in case of emergency if people have to be saved and if saving is not possible due to magnetic field forces how? inducing magnet quench press magnet stop switch all persons should be saved and leave the magnet room quickly acute danger of suffocation protect magnet room Seite 42

43 43 Page 85 B 0 : Danger from Cold Gases and Fluids magnet as pressure tank quench evaporation of fluid helium high pressure quench pipeline to outdoor cold gases can come into the examination room burning at cold surfaces displacement of oxygen danger of suffocation Page 86 B 0 : Magnet Stop and Emergency Stop magnet stop interrupts super-conduction, magnet coil gets normal conducting current in magnet coil comes to rest coil wires get hot and helium evaporates (quench) magnetic field is switched off emergency stop all electric systems of the MR system are switched off magnetic field is still on cooling system is off magnet stop is still possible since battery-operated Seite 43

44 44 Page 87 B 1 : Gradient Field G(t) G(t) temporal variation of magnetic field (db/dt) induction of eddy currents in the object / body eddy currents run through nerves peripheral nerve stimulation stimulation of myocardium? interaction with implants extreme noise ear protection Page 88 RF: Radiofrequency radiofrequency field is directly absorbed critical value: specific absorption rate (SAR) can be resonant induced in conductive structures creates offset currents in tissue massive heating flashover destroys not connected coils Wagle and Smith. AJR 2000 Seite 44

45 45 Page 89 RF: SAR Critical Values body part normal 1. level 2. level whole body part body head local (head, body) local (extremities) temperature increase body stem scales with the ratio of exposed patient mass / total patient mass patient weight and age are relevant for safety! Page 90 RF: Flashover Seite 45

46 46 Page 91 B 0 and RF: Implants contra indication cardiac pacemaker neuro stimulators (deep brain stimulators) ferromagnetic implants gun projectiles paramagnetic stents up to 2 weeks after implantation information Shellock FG. Reference Manual for Magnetic Resonance Safety, Implants, and Devices: 2006 Edition. Page 92 MR Safety Labeling MR safe an item which poses no known hazards in all MR environments MR conditional an item which has been demonstrated to pose no known hazards in a specified MR environment with specified conditions of use. Field conditions that define the specified MR environment include field strength, spatial gradient, db/dt (time rate of change of the magnetic field), radio frequency (RF) fields, and specific absorption rate (SAR). additional conditions, including specific configurations of the item, may be required MR unsafe an item which is known to pose hazards in all MR environments ASTM International. Standard practice for marking medical devices and other items for safety in the magnetic resonance environment. F Seite 46

47 47 Page 93 Light Vizier patient localizing and referencing ask patient for closing eyes before laser switch on Page 94 Danger of Crushing couch movement watch position of arms and fingers save connections, ECG-wires, and alarm ball push couch stop patient couch can be moved manually Seite 47

48 48 Page 95 MR Safety Aspects: Summary static magnetic field missile effect influencing equipments physiological effects gradients peripheral nerve stimulation noise radiofrequency heating coils connected? cold gases / fluids suffocation burning emergency procedures magnet stop emergency stop couch stop patient information patient information sheet alarm ball control area watch and take care about unknown people (i.e. service and cleaning people, anesthesia doctors and staff,...) unknown equipment and systems before bringing into the magnet room Seite 48