Introduction to Magnetic Resonance Imaging

SIEMENS Healthineers Magnetic Resonance Imaging Workshop on Imaging for the Future A S Subramaniyan| HC APC IN SV March 2018 HOOD05162002873707 BME Education_Computed Tomography BME Education_Magnetic Resonance Imaging Effective date: 05/06/2018 Page ‹#› | Restricted © Siemens Healthcare GmbH, 2017 Restricted © Siemens Healthcare GmbH, 2017 How to change paragraph levels Topics to be covered: SIEMENS All levels font Calibri Healthineers - 26 pt. Level 1 is chapter - title: Bold, bulleted. Level 2, 3, 4 and 5 is - chapter description: Regular, no bullet, indent 7.5 mm. 1. MRI Basic Principles Switch between Text- 2. Instrumentation of MRI and bullet levels: 3. Instrumentation of MRI (contd..) ● click 4. Current Trends & Technologies 5. Basic Overview of Applications HOOD05162002873707 Restricted © Siemens Healthcare GmbH, 2017 Effective date: 05/06/2018 Page 2 How to change paragraph levels What is MRI? SIEMENS All levels font Calibri Healthineers - 26 pt. Level 1 is chapter - title: Bold, bulleted. Level 2, 3, 4 and 5 is - chapter description: Hydrogen Regular, no bullet, Lots of Water Molecules A Water Molecule Atom indent 7.5 mm. Proton Switch between Text- H O H and bullet levels: ● click • A method based upon sensitivity to the presence and properties of water in human tissue • The properties and amount of water in tissue can alter with disease and injury which makes MR very sensitive as a diagnostic technique • MR detects subtle changes in the magnetism of the nucleus • MR is used not only to image anatomy and pathology; but to investigate organ function, to probe in vivo chemistry and even to visualize the brain thinking HOOD05162002873707 Restricted © Siemens Healthcare GmbH, 2017 Effective date: 05/06/2018 Page 3 Hardware of MRI system SIEMENS Healthineers Basic components: • Magnet – polarizes the nuclei and produces a net magnetization within the sample • RF Transmit coil – transmits pulses of EM wave, into the sample and detect precessing magnetization • Magnetic field Gradient coils – induce spatial dependence of nuclear precession frequency • Shim coil – used to produce as homogeneous a magnetic field as possible throughout the sample • RF Receiver electronics – amplify, filter, digitize the MR signal for data storage and post-processing • Computers – User interface and Image Reconstruction HOOD05162002873707 Effective date: 05/06/2018 Page 4 Restricted © Siemens Healthcare GmbH, 2017 Main Components of MRI System SIEMENS Healthineers N -O+ PATIENT SIEMENS S Magnet: Generates the static magnetic field Field strength: The strength of the main magnetic field measured in Tesla (T), which is generated by a superconducting magnet. HOOD05162002873707 Effective date: 05/06/2018 Page 5 Restricted © Siemens Healthcare GmbH, 2017 Main Components of MRI System SIEMENS Healthineers Gradient Coil: • generates the additional magnetic fields necessary for spatial encoding • Needed for spatial and temporal resolution HF-Spectrum f ~ B f0 HOOD05162002873707 Effective date: 05/06/2018 Page 6 Restricted © Siemens Healthcare GmbH, 2017 Main Components of MRI System SIEMENS Healthineers Gradient Coil is inserted into magnet PATIENT SIEMENS HOOD05162002873707 Effective date: 05/06/2018 Page 7 Restricted © Siemens Healthcare GmbH, 2017 Main Components of MRI System SIEMENS Healthineers Body Coil (RF Transmit Antenna): Excites and transmits signal to the body PATIENT SIEMENS HOOD05162002873707 Effective date: 05/06/2018 Page 8 Restricted © Siemens Healthcare GmbH, 2017 Main Components of MRI System SIEMENS Healthineers SIEMENS Gradient Coil Body Coil Bore Size T-class MAGNETOM Espree HOOD05162002873707 Effective date: 05/06/2018 Page 9 Restricted © Siemens Healthcare GmbH, 2017 How to change paragraph levels A MR system site SIEMENS All levels font Calibri Healthineers - 26 pt. Level 1 is chapter - title: Bold, bulleted. Level 2, 3, 4 and 5 is - chapter description: (a) (c) Regular, no bullet, indent 7.5 mm. Switch between Text- MAGNETOM and bullet levels: SETMANES click ● (b) Typical MR coils. (a) Body array coil and head coil, (b) peripheral angiography coil and (c) flexible coil. Courtesy of Siemens Medical Solutions. HOOD05162002873707 Effective date: 05/06/2018 Page 10 Restricted © Siemens Healthcare GmbH, 2017 Receive coils SIEMENS Healthineers Local Coil: A device that receives the MR signal. It is connected to the MR scanner and has a dedicated, optimized design for a specific body region that allows for a high image quality. HOOD05162002873707 Effective date: 05/06/2018 Page 11 Restricted © Siemens Healthcare GmbH, 2017 What makes MRI unique? SIEMENS Healthineers • MR does not use X-ray radiation! • MRI delivers an outstanding soft-tissue contrast, e.g. for tumor diagnosis in the brain • MRI can also show function MRI CT (e.g. brain function, cardiac blood flow, tumor viability) T1- T2- PD- SWI-contrast … HOOD05162002873707 Effective date: 05/06/2018 Page 12 Restricted © Siemens Healthcare GmbH, 2017 Hardware characteristics SIEMENS Healthineers Characteristics Specification Static magnetic Field 0.2 – 3 Tesla Proton Frequency 8.2 – 123 MHz Gradient Strength 40 – 80 mT/m RF Transmit coil diameter 10 – 70 cm RF Power amplifier 30kW HOOD05162002873707 Effective date: 05/06/2018 Page 13 Restricted © Siemens Healthcare GmbH, 2017 Magnetic field Orientation SIEMENS Healthineers Permanent Magnets Super-Conducting Magnets STEVENS Y Y MAGNETOIM X Z B0 B0 X MAGNETOM Symphony Z HOOD05162002873707 Effective date: 05/06/2018 Page 14 Restricted © Siemens Healthcare GmbH, 2017 MR Safety SIEMENS Healthineers Magnetic Field MAGNETOM Warnzeichen: Warning sign: Signal attention: Symbolo de advertencia: Segnale di avvertimento: NMR - Magnetfeld Hochfrequenzfeld NMR - Magnetic Field High' Frequency Field Champ Magnétique RMN NMR Campo Magnetico Champ Haute Fréquence Campo de alta Frequencia Campo magnetico NMR Campo ad alta frequenza Verbotszeichen: Elektromagnetischeeinflussbare Implantate, z.B. Herzschrittmacher, Defibrillatoren, Hörgeräte, Insulinpumpen, Medikamentendosiergeräte Prohibition Signs: Danger of Electromagnetic Disturbances Implantations, e.g. Cardiac Pacemaker, Defibrillators, Hearing Instruments, Insulin Pumps, Dosage Devices for Medication Panneaux d'avertissement: éléments implantés sensibles aux interférences électromagnétiques, par ex. stimulateurs cardiaques, défibrillateurs, aides auditives, pompes à insuline, doseurs de médicaments Símbolos de prohibición: Implantes sensibles a los campos electromagnéticos, p.ej. Marcapasos, desfibriladores, audífonos, bombas de insulina, dosificadores de medicamentos Segnali di divieto: impianti suscettibili agli effetti elettromagnetici, ad es. pacemaker cardiaci, defibrillatori, apparecchi acustici, pompe per l'insulina, dispositivi per la somministrazione di farmaci Implantate aus Metall und sonstige Metallteile und medizinische Metallgegenstände am Körper z.B. Splitter Instrumente aller Art Implants made of metal and other Metal Parts and Medical Instruments metal objects in the Body such as splinters of All Types Implants en métal et divers objets métalliques intra-corporels, par ex. éclats Eléments métallique et instruments médicaux divers Implantes de metal y otras piezas Elementos metálicos e instrumentos metálicas en el cuerpo p.ej. fragmentos médicos de cualquier tipo Impianti in metallo o altri oggetti metallici Componenti metallici e strumenti medici presenti nel corpo, come ad es. Schegge di qualsiasi tipo Offenes Feuer Rauchverbot Mech.Uhren, elektr. Datenträger wie Taschenrechner, Digitaluhren usw. Open Fire Ban of Smoking Mech. Watches, Electrical data carriers, such as pocket calculators, digital clocks etc. Flammes ouvertes Montres mécaniques Supports de données électr Défense de fumer tels que calculatrice de poche, montres digitales etc. Fuego abierto prohibicó de fumar Rolojes mécanicos, portadores eléctricos de datos, p.ej. Calculadores de bolsillo y relojes digitales Fiamme libere Orologi meccanici, supporti elettronici di dati, Divieto di fumare come calcolatori tascabili, orologi digitali, ecc. Feuerlöscher mit magnetisier- barem Metallgehäuse Datenträger wie Kreditkarten, Scheckkarten und Fire Extinguishers with Ausweise mit Magnetstreifen, Magnetbänder Magnetizable Metal Housing Data carriers, such as credit cards and identity cards with magnetic strips, magnetic tapes Extincteurs avec boîtier metallique magnétisable Supports de données tels que cartes de crédit et de chèque, badges avec bandes magnétiques, bandes magnétiques Apagafuegos con carcasa Portadores de datos, p.ej. tarjetas de crédito, tarjetas metálica magnetizable de cheques y tarjetas de identificación con franja Estintori con alloggiamento magnética; cintas magnéticas metallico magnetizzabile Supporti di dati come carte di credito, Bancomat e tessere di identificazione con bande magnetiche, nastri magnetici HOOD05162002873707 Effective date: 05/06/2018 Page 15 Restricted © Siemens Healthcare GmbH, 2017 MR Safety SIEMENS Healthineers 11 • Magnet Field: Strong attraction of the stray field • Cryogenics: Gases & Liquids U • RF Field Deposition (SAR) • Gradients • Phantoms liquids • Laser HOOD05162002873707 Effective date: 05/06/2018 Page 16 Restricted © Siemens Healthcare GmbH, 2017 Basics: SIEMENS Healthineers Nuclear Polarization - Nuclear Spin • Nuclei with ODD atomic number possess fundamental quantum mechanical property- SPIN • Most important nuclei in human tissue Spin Spin-active: 1H, 13C, 15N,23Na, 17O,31P, 2H - Spin-inactive: 16O, 12C - • Property of Spin – spinning around an internal axis of rotation giving angular momentum (P) N • Proton is a charged particle; this rotation results in a magnetic moment (µ) S • This magnetic moment produces an associated magnetic field – similar to a bar magnet HOOD05162002873707 Effective date: 05/06/2018 Page 17 Restricted © Siemens Healthcare GmbH, 2017 Basics: SIEMENS Healthineers Nuclear Polarization - Magnetic moment & Precession • In terms of nuclear spin quantum number (I), Magnitude of angular momentum P: ℎ 1 𝑃 = 𝐼(𝐼 + 1) 2 2𝜋 N For 1H, 13C, 15N,23Na, 31P  I=1/2. S Therefore, Magnitude of P: ℎ √3 𝑃 = 2𝜋 2 --------------------------------------------------------------- - • Magnetic moment(µ) is given by: 𝒉√𝟑 γ - nuclear gyromagnetic ratio; 𝑷 = 𝜸 B precession 𝝁 = 𝜸 has specific value for different nuclei 𝟒𝝅 -  N When an external magnetic field it tries to twist it parallel to B0 . S B0 is applies, it exerts a torque on Because of the spin (self-rotation) the magnetic moments: the nuclei precess around the magnetic field. HOOD05162002873707 Effective date: 05/06/2018 Page 18 Restricted © Siemens Healthcare GmbH, 2017 Basics: SIEMENS Healthineers Nuclear Polarization – Larmor Equation B precession P  • The frequency of the nuclear N precession is exactly proportional  =  × B S to the magnetic field at the nucleus. 2pf =  × B f = /2p × B for the 1H nucleus: Natural Relative Gyro Magnetic Resonant Frequency Nuclide Abundance Spin Sensitivity Ratio Y in [MHz] at f = 42,577 MHz for 1T [%] [radians*Hz/T] 0.19T 0.95T 1.49T 1 H 99.980 1/2 1.000 2.675*108 8.25 40.45 63.60 19 F 100.000 1/2 0.83 2.517*108 7.61 38.06 59.69  = magnetic moment / spin 31 P 100.000 1/2 0.066 1.082*108 3.27 16.36 25.66 HOOD05162002873707 Effective date: 05/06/2018 Page 19 Restricted © Siemens Healthcare GmbH, 2017 Basics: SIEMENS Healthineers Nuclear Polarization - Proton Alignment • Magnetic moment µ has three components - µx , µy , µz . In presence of strong magnetic field B0 magnetic moment: ℎ , 𝜇𝑧 = 𝛾 2𝜋 𝑚𝐼 • mI =nuclear magnetic quantum number. For proton, mI = ±1/2. ℎ 𝜇𝑧 = ± 𝛾 4𝜋 The interaction of static magnetic field B0 with µz results in Zeeman splitting producing two energy levels: one aligning parallel to B0 𝑬 = 𝝁 . 𝑩𝟎 another aligning anti-parallel to B0 𝜸𝒉 𝑬 = + 𝟒𝝅 𝑩𝟎 E+ - - –1/2 == E DE A 𝜸𝒉 E- +1/2 𝑬 = − IT 𝑩𝟎 - - HOOD05162002873707 𝟒𝝅 Effective date: 05/06/2018 Page 20 Restricted © Siemens Healthcare GmbH, 2017 Basics: SIEMENS Healthineers Nuclear Polarization - Net magnetization S Net magnetization M0 of tissue containing Ns m Mo protons is proportional to the population BOT difference between the two energy levels. 1111 m N = m S N 11 𝑁𝑠 𝛾ℎ 𝛾 2ℎ 𝑁𝑝𝑎𝑟𝑎𝑙𝑙𝑒𝑙 − 𝑁𝑎𝑛𝑡𝑖 −𝑝𝑎𝑟𝑎𝑙𝑙𝑒𝑙 2𝑁𝑠 𝑩𝟎 𝑀0 = 𝜇𝑧,𝑛 = = 4𝜋 16𝜋 2𝑘𝑇 - 𝑛=1 - HOOD05162002873707 Effective date: 05/06/2018 Page 21 Restricted © Siemens Healthcare GmbH, 2017 Basics: SIEMENS Healthineers RF Transmit coil - Excitation The resonance frequency (f0 ) in Hz: To detect MR signal, energy must be applied to the nuclear spins to stimulate transitions between two energy levels. 𝒇𝟎 = 𝜸 𝑩𝟎 - 𝟐𝝅 RF pulse at specific resonance frequency (f0 ) which corresponds to energy difference The resonance angular frequency (0 ) in between the two levels. radians/s. 𝝎𝟎 = 𝜸𝑩𝟎 ℎ𝑓0 = ∆𝐸 = 𝛾ℎ 2𝜋 𝐵0 HOOD05162002873707 Effective date: 05/06/2018 Page 22 Restricted © Siemens Healthcare GmbH, 2017 Basics: SIEMENS Healthineers RF Transmit coil - Excitation • From Classical mechanics, action of RF pulse • Net magnetization now becomes: applied along one axis produces a torque perpendicular to that axis 𝑀𝑧 = 𝑀0 cos 𝛼 - - 𝑀𝑥 = 0 Magnetic field component B1 𝑀𝑦 = 𝑀0 sin 𝛼 • is - created perpendicular to B0 to interact with magnetization (a) (b) Z Z • angle to which the magnetization is rotated  Flip angle α: 𝛼 = 𝛾𝐵1𝜏𝐵1 x y x y B , + HOOD05162002873707 Effective date: 05/06/2018 Page 23 Restricted © Siemens Healthcare GmbH, 2017 RF Receive coil SIEMENS Healthineers • In MRI, a single coil is used to transmit. Excitation Reception Many coils are used to receive MR signal. z Coil Coil • Time-varying magnetic field produce by the precession of the magnetization vectors results in voltage induced in the receiver coil RF Signal x y x y Resonance í Energy transfer Rotating MXY component induces a signal in the coil. Induced voltage V: 𝜕∅(𝑡) 𝜕 𝐵1 𝑉 = − 𝜕𝑡 𝑀𝑥𝑦 𝑑𝑟 = − 𝜕𝑡 𝑠𝑎𝑚𝑝𝑙𝑒 𝐼 HOOD05162002873707 Effective date: 05/06/2018 Page 24 Restricted © Siemens Healthcare GmbH, 2017 Chemical Shift SIEMENS Healthineers • Signal Proton in difference chemical environments within a molecule The fat molecule: resonate at slightly different frequencies: their precession H water frequencies are shifted OH-C-C-C- The water molecule: H - • The cause of the shift: fat H exact magnetic field experienced by the proton is lower than B0 owing to shielding effects of the electron cloud surrounding each proton 3.4 ppm frequency [chemical shift) 𝜔𝑝𝑟𝑒𝑐𝑒𝑠𝑠𝑖𝑜𝑛 = 𝝎𝟎 = 𝜸𝑩𝟎 • fluids – cerebrospinal fluid (CSF), synovial fluid, oedema; • water-based tissues – muscle, brain, cartilage, kidney; • fat-based tissues – fat, bone marrow. HOOD05162002873707 Effective date: 05/06/2018 Page 25 Restricted © Siemens Healthcare GmbH, 2017 Magnetic Susceptibility SIEMENS Healthineers Diamagnetic: ferromagnetic.  very weak susceptibility;  Examples include iron oxide particles  produces an internal field opposite to B0 (used as MR contrast agents), ferritin and . haemosiderin.  Most body tissues are diamagnetic; • Ferromagnetic:  air and dense bone have almost zero susceptibility.  strongly magnetized;  experience a large force when placed in an • Paramagnetic: external field.  stronger susceptibility  Metal alloys containing iron, nickel and  produces a field in the same direction of B0 cobalt are often ferromagnetic.  examples gadolinium (used as an MR contrast agent) • Superparamagnetic:  intermediate between paramagnetic and HOOD05162002873707 Effective date: 05/06/2018 Page 26 Restricted © Siemens Healthcare GmbH, 2017 Design aspect SIEMENS Healthineers Cylindrical geometry: Superconducting magnet, RF Transmit (volume) coil, Shim coil, Gradient coil. Operating frequencies: Magnet & Shim coils: DC Gradients: few 100 kHz RF coils: ten to hundreds of MHz Most common mathematical formalisms to produce the desired magnetic field Biot-Savart Law - Spherical harmonic decomposition3 - HOOD05162002873707 Effective date: 05/06/2018 Page 27 Restricted © Siemens Healthcare GmbH, 2017 Mathematical tools: SIEMENS Healthineers Maxwell’s Equations and Biot-Savart Law • Maxwell's Equations: Designs for coils are formulated by simplifying Maxwell’s equations under quasi-static conditions. V.E = Pv (Gauss Law) V.H = 0 3 (Gauss Law for magnetism) • the magnetic field can be estimated quite accurately by OH Biot-Savart law, which can be derived directly from Vx E = - U- at (Faradya's Law) Maxwell’s equations. VXH=J +8- at (Ampere'sLaw) • Biot-Savart law describes magnetic field (dB) at any point P, of distance r from the wire. Biot - Savart Law dB = Ho , ds XF 4TI HOOD05162002873707 Effective date: 05/06/2018 Page 28 Restricted © Siemens Healthcare GmbH, 2017 Mathematical tools: SIEMENS Healthineers Spherical Harmonics Decomposition • Spherical harmonic is defined by spatial perturbations in terms of increasing orders. m=+2 m=+1 m=0 m =- 1 m =- 2 three 1 st order n=C Zonal harmonics five 2 nd order Rotationally invariant seven 3 rd order and so on • Within order(n), many number of degrees(m) n=1 zero order term(m=0, n=0)  homogeneous three 1 st order (n=1) linear variation in x, y, z (orthogonal directions) OO n=2 m= +1  x; m= 0  z; m= -1 y 'ure 1.29 Visual representation of lower order spherical harmonics. HOOD05162002873707 Effective date: 05/06/2018 Page 29 Restricted © Siemens Healthcare GmbH, 2017 Overview of an MR System SIEMENS Healthineers Host Processor Configuration Imager These functional blocks can be nicely divided for 188.88 18988 Computed Image Computed Image explanatory purposes into Sequence Sequence two groups: & Digitized Digitized &  Processor Configuration Parameters Parameters MR-Signal MR-Signal  Measurement Receiver and Data DataMeasurement System Control Acquisition Digital Digital Pulse Data Pulse Data MR-Signal MR-Signal RF pulses RF pulses Gradient pulses Gradient pulses Data Measurement System HOOD05162002873707 Effective date: 05/06/2018 Page 30 Restricted © Siemens Healthcare GmbH, 2017 This presentation uses the preinstalled Office font Calibri. If you send it to someone internally or externally, please convert it into a pdf to ensure that the SIEMENS content stays as intended. Healthineers Our template contains layout guidelines. Their purpose is to indicate key margins and mandatory areas on slides. Magnet subsystem Copy and paste Copy only full slides when they use the same new design. Otherwise the file size will be very large. Use the function Insert > Insert Content > Unformatted Text to paste a copied text. The text will now use the same existing format. Each presentation needs to be categorized, with the author being responsible for choosing the right category: Unrestricted – Restricted – Confidential – Strictly confidential – The preset default category Edit “Author | Department” for presentations is HOOD05162002873707 “restricted”. Restricted © Siemens Healthcare GmbH, 2017 in the “Header and footer” Effective date: 05/06/2018 for all pages. new category ©” Start > Replace > insert “Restricted ©” and “the Magnets SIEMENS Healthineers • Magnet is the most prominent and most expensive part • Patient comfort of an MRI system • Magnet warm bore and bore diameter • Its design have an influence on different criteria: • Magnet length and total system length • Image quality • Magnetic field strength B0 • Economic aspects • Magnet homogeneity and maximum field of view • Helium boil-off (Zero Helium boil-off for state-of-the- art systems) • Shimming capabilities • Stray field, reduced with active shielding, to reduce • Space requirements • Magnet and system weight, for siting HOOD05162002873707 Effective date: 05/06/2018 Page 32 Restricted © Siemens Healthcare GmbH, 2017 Magnets SIEMENS Healthineers Magnet types: Permanent magnets:  Requires no power, refrigeration  Field strength up to 0.3 T  sensitive to temperature changes  Large weight  Low operating cost  rare earth elements used for production: neodymium-iron-boron  China is major supplier of these materials HOOD05162002873707 Effective date: 05/06/2018 Page 33 Restricted © Siemens Healthcare GmbH, 2017 Magnets SIEMENS Healthineers Magnet types: Superconducting magnets  Cylindrical bore magnet  Field strength up to 1.5 T and 3 T  operate in persistent mode with no need for an external current source  field is intrinsically stable  active shielding to reduce stray field within range  Liquid helium as cryogen to cool the superconducting coil HOOD05162002873707 Effective date: 05/06/2018 Page 34 Restricted © Siemens Healthcare GmbH, 2017 Magnets SIEMENS Healthineers Superconducting magnet - Ramping • Large inductance; virtually no resistance During Power up At Field • Magnet power supply needs to supply low voltage and Power supply high current Heater on =High switch resistance Heater off =Zero switch resistance • Ramp up time ~ 30mins to 1hr. = switch open = switch closed Ramp time = L.I / V www Switch Switch • Superconducting switch: to keep the magnetic field continuous Magnet Magnet HOOD05162002873707 Effective date: 05/06/2018 Page 35 Restricted © Siemens Healthcare GmbH, 2017 Magnets SIEMENS Healthineers Field Homogeneity  most magnets consists six discrete coil design (Helmholtz pair of coil)  Specification for homogeneity:  Plotted peak-to-peak in ppm  VRMS  Field D Shimming:  Passive shimming with small pieces of iron  Active shimming with additional coil 50cm IV  Shim coil integrated into gradient coil  Copper wire or etched from copper sheet  Called as resistive shim  driven by high-stability power supplies HOOD05162002873707 Effective date: 05/06/2018 Page 36 Restricted © Siemens Healthcare GmbH, 2017 Magnets SIEMENS Healthineers An Overview of Shimming Methods Shim Measuring Shim Calculation Shim Correction Shim Array Device Spherical Harmonics Iron Shim plates 5 4 6 3 7 Iron plates 2 8 positioned in 16 shim trays placed 1 around the 9 circumference of 16 the magnet field. Cover 10 15 11 14 1 mm Packer 12 13 Rubber pad Shim plate 4 Passive Shimming 65 x 20 x 0,05 mm Insulation Shim plate 3 65 x 40 x 0,05 - Shim plate 2 % 65 x 80 x 0,10 mm Shim plate 1 + 65 x 80 x 0,30 mm HOOD05162002873707 Effective date: 05/06/2018 Page 37 Restricted © Siemens Healthcare GmbH, 2017 Magnets SIEMENS Healthineers Shim device 2 Fig. 300: Packing shims (75 x 55 x 1 mm, polypropylene molding 3 4 - Fig. 299: Shim plates Pos. 1 Plate 1 (64.8 x 80 x 0.3 mm) Pos. 2 Plate 2 (64.8 x 80 x 0.1 mm) patient end Pos. 3 Plate 3 (64.8 x 40 x 0.05 mm) Pos. 4 Plate 4 (64.8 x 20 x 0.05 mm) Fig. 301: Insulation shim (80 x 64.8 x 0.19 mm, polyester packer) Rotts to secure the Array shim device Array shim device located in the crate Plates in Tray 1 Thickness Plate 1 Plate 2 Plate 3 Plate 4 Position change (total) |load (total) load (total) load (total) load (total) A 0.000 (0.000) B 0.000 (0.000) 3 C 0:178 (0.178) 3 (3) 2 D 0.000 (2 263) 0 (8) 0 (1) E 0:000 (0.000) F 0:120 (1.360) 0 (4) 1 (2) 4 G 0.000 (0 642) 0 (2) 0 (3) 0 (1) H 0.070 (1.004) 0 (3) 3(7) J 0:012 (0.715) 0 (2) 0 (1) 1 (1) K 0.036 (1.103) 0 (3) 0 (2) 1 (2) 1 (2) HOOD05162002873707 L 0.012 (0 508) 0 (1) 0 (2) 0 (1) 1 (1) Effective date: 05/06/2018 Page 38 nm Restricted © Siemens Healthcare GmbH, 2017 Magnets SIEMENS Healthineers An Overview of Shimming Methods Shim Measuring Shim Calculation Shim Correction 24 cm Ball Phantom 3D Shim Linear Terms: (Phantom Shim) Old: MAP Gradient Coil Measured with a 3D Shim Sequence 2nd Order Terms: Active Shimming RF alpha - pulse 32 partitions 32 Phaseencoding steps in sliceselect direction resulting in ... 38 32 projections, each ...32 MR-Signals belongs to another partition Fourierline1 Partition1 Fourierline1 Partition2 4 Sliceselect Gradient Fourierline1 Partition16 Line 1. Column Partition 4 FFT FFT Fourierline1 Partition31 Fourierline1 Partition32 Line 1. Column FFT FFT 2. Column FFT Phaseencoding Gradient Partition16 .......... 2. Column FFT 32 Phaseencoding steps E-Shim Option in phase encoding direction 32(No of steps in PE-direction) 32 times 32 projections times 32 (No of steps in SL-direction) = 1024signals 3D - Imaging. Example with 32 partitions. HOOD05162002873707 Effective date: 05/06/2018 Page 39 Restricted © Siemens Healthcare GmbH, 2017 Magnets SIEMENS Healthineers Superconducting coil  type II superconductor: niobium-titanium alloy, inside a copper matrix STRANGPRESSLEITER FS 85  Wire-in channel superconductor  Niobium-titanium alloy becomes superconducting below 9.8 K  Cryostat filled with liquid helium at 4.2 K  outer vacuum shield minimizes conduction of heat from the magnet's surroundings.  Active shielding to reduce stray magnetic field HOOD05162002873707 Effective date: 05/06/2018 Page 40 Restricted © Siemens Healthcare GmbH, 2017 Magnets SIEMENS Healthineers Magnet Construction – 10K Magnets Cold Head Fiberglass Unisock Supports Some mechanical features:  6 main coil windings  2 active-shield coils  2 cryo shields Primary winding  Magnet suspended via fiberglass supports 50cm AS winding Imaging Coil former  Vacuum chamber Volume Vacuum vessel bore tube Magnet and shields are wrapped with alu or alu-coated foil 90 cm OVC - outer vacuum vessel  220 cm 80K cryo shield 20K cryo shield  Refrigerator maintains cryo shields at their respective temps Helium vessel (Cryostat) HOOD05162002873707 160 cm Effective date: 05/06/2018 Page 41 Restricted © Siemens Healthcare GmbH, 2017 Magnets SIEMENS Healthineers Magnet System – Cross Section Depressurize valve Venting System Pressure Gauge Quench valve (15 psi) psi 1 Quench venting to atmosphere .5 0 -0.5 1/3 psi bleed-off valves Cold Head Service Coil Magnet shell (OVC) turret 80K Cryoshield 20K Cryoshield Cryostat HELIUM fill line liquid HOOD05162002873707 Effective date: 05/06/2018 Page 42 Restricted © Siemens Healthcare GmbH, 2017 Liquid helium filling SIEMENS Healthineers Fill Line He 4.6 gas Dewar liquid Magnet helium HOOD05162002873707 Effective date: 05/06/2018 Page 43 Restricted © Siemens Healthcare GmbH, 2017 Magnet system SIEMENS Healthineers System RF-Room Magnet System Diagram Compressor RCA Alarm Box W201 X12 W200 X3 Shim Power Supply Magnet OR24, OR70 X1 CCA X10 X8 MSUP CAN X2 X2 X1 X1 W206 Mag ID --- 60 X4 D15-3 W205 W204 Remote Alarm CAN CAN -- X1 X3 X4 MSUP +15V, Magnet PS Power Switch Power X5 X6 supply -I Mag ID LPD X1 PWR X102 F24 F2 X6 RS 232 F5 F4 Mains Host Port 6 HOOD05162002873707 Effective date: 05/06/2018 Page 44 Restricted © Siemens Healthcare GmbH, 2017 Magnet Monitoring SIEMENS Healthineers Refrigerator Alarm Box Emergency Magnet Stop Magnet Monitoring Helium Compressor Cold Head Cabinet Temp Magnet ERDU Stop Helium 88 Helium Level Level Shield Shield Temp Temp System Control CPU ! Processor Customer Alarm He1 He2 CHT Link Bore PHAP MP BV CSS Temp DP RP ZF Magnet parameters 74.3 74.3 20.4 57 66.1 0.26 15.51 23.24 0 20.9 977 0 O HOOD05162002873707 74.3 74.3 20.4 57.7 66.8 0.19 15.5 23.24 0 21.3 965 0.02 0 Effective date: 05/06/2018 Page 45 Restricted © Siemens Healthcare GmbH, 2017 Magnet Refrigerator SIEMENS Healthineers Helium Compressor & Coldhead Fig. 27: F70 Static pressure reading SUPPLY PRESSURE Block Diagram TWEE 400 2000 --- 3000 50 10 bar = 1 MP3 CSTTUTITITT bar MILJOCO MADE IN USA W = = Helium gas pressures CE Cold head Static pressure Dynamic pressure F-70 4 K 13.5 - 14.0 bar (13.6 nominal) 21 - 22 bar + Sumitomo CRYOGENICS A. NOTICE 196 - 203 psi (G) 304 - 319 psi (G) 25831.9 RUN 2 .. MODE OFF ON HOOD05162002873707 Effective date: 05/06/2018 Page 46 Restricted © Siemens Healthcare GmbH, 2017 Magnets SIEMENS Healthineers Quenching • A quench occurs when the magnet ceases to be superconducting due to local heating The quench starts as a small piece of wire is • All the energy stored in the magnet is released as heat. The made slightly resistive. Heat is generated 12R current falls rapidly to zero. • Persistent Mode Quench (PMQ) The heat spreads making more conductor resistive. Resistance and temperature at the start of • ERDU Quench the quench increase. OO When a magnet quenches, high voltages are produced within the coils. These voltages are produced by two effects: • Resistive voltages and Inductive voltages All of the coil becomes A quench runs the magnet down in 10 seconds resistive, heat is deposited into the bath of liquid helium HOOD05162002873707 Effective date: 05/06/2018 Page 47 Restricted © Siemens Healthcare GmbH, 2017 Magnets SIEMENS Healthineers Magnet Venting System - 10K Magnets muummmmmmmm Lhe fill vent line 2 3 Quench Burst 4 1 Valve Disk O-ring 5 psi 6 Mmmmmmmmmm Lhe fill line Quench Vent Line WARNING CANDGENIC VESSEL VENTE HDCL tube 0.5psi UNGSBEFANE FERNPLEGEN EVENMISTE SOMOSTEGERATE LHe fill LHe fill tube Vent line Vacuum chamber Neck tube 80K shield Depressurization 20K shield (bypass) valve cryostat wwww Wwity light blue color signifies pressurized helium HOOD05162002873707 Effective date: 05/06/2018 Page 48 Restricted © Siemens Healthcare GmbH, 2017 Magnets SIEMENS Healthineers Quench protection Super Conductive Switch Quench Protecting System EIS Quench Switch External Interference Shield primary coils Quench Heaters The magnet must be capable of surviving this active shield coils event without permanent damage HOOD05162002873707 Effective date: 05/06/2018 Page 49 Restricted © Siemens Healthcare GmbH, 2017 Active Shielding SIEMENS Healthineers 9m No Shielding: 0.5 mT stray 2.5 m field 1.5 T Magnet 4 m 11m Here a comparison of the stray field limits of a magnet with and without active shielding. Active Schielding: 0.5 mT stray field HOOD05162002873707 Effective date: 05/06/2018 Page 50 Restricted © Siemens Healthcare GmbH, 2017 External Interference Shielding SIEMENS Healthineers In a hospital site there could be sources of “magnetic disturbances” which affect the quality of the images. NEX HOOD05162002873707 Effective date: 05/06/2018 Page 51 Restricted © Siemens Healthcare GmbH, 2017 MR Safety SIEMENS Healthineers Magnetic Field Symbols used in MRI system Terminology for Accessories units. Magnet compatibility signs 3 different levels: MR MR MR MR MR MR MR SAFE MRI Safe Conditional safe Unsafe MR CONDITIONAL Other warning signs MR UNSAFE U Strong Rf-Field Caution Read Risk of Laser Potential Magnet Manual Injury Radiation Injury to Person HOOD05162002873707 Effective date: 05/06/2018 Page 52 Restricted © Siemens Healthcare GmbH, 2017 MR Safety SIEMENS Healthineers Cryogens Cryogens are VERY cold liquefied gasses: Liquid Helium (LHe) is approx. 4 K = – 269°C Cold Burns can result if you do not take care Asphyxiation can result if cryogenic liquids are allowed to evaporate within confined areas: 1 Liter LHe translates to 700 Liter He-Gas 26/7/03 O CRYOGENICS Asphyxiant HOOD05162002873707 Effective date: 05/06/2018 Page 53 Restricted © Siemens Healthcare GmbH, 2017 This presentation uses the preinstalled Office font Calibri. If you send it to someone internally or externally, please convert it into a pdf to ensure that the SIEMENS content stays as intended. Healthineers Our template contains layout guidelines. Their purpose is to indicate key margins and mandatory areas on slides. Gradient system Copy and paste Copy only full slides when they use the same new design. Otherwise the file size will be very large. Use the function Insert > Insert Content > Unformatted Text to paste a copied text. The text will now use the same existing format. Each presentation needs to be categorized, with the author being responsible for choosing the right category: Unrestricted – Restricted – Confidential – Strictly confidential – The preset default category Edit “Author | Department” for presentations is HOOD05162002873707 “restricted”. Restricted © Siemens Healthcare GmbH, 2017 in the “Header and footer” Effective date: 05/06/2018 for all pages. new category ©” Start > Replace > insert “Restricted ©” and “the Gradient Function SIEMENS Healthineers main magnet windinge negative ponitive gradient coil subtracte from B. addo to B. 0.9995 T LOT (9,995 G) (10,000 G) (10,005 G) Figure 27.2 Gradiente and changing field strength. Figure 27.1 A gradient coil, lower than bare centre frequency centre frequency nocentre Figure 27.4 Gradient, axeo. higher than centre frequency HOOD05162002873707 Effective date: 05/06/2018 Page 55 Restricted © Siemens Healthcare GmbH, 2017 How is a gradient field created? SIEMENS Healthineers B  The gradient fields are generated by B0 three pairs of gradient coils, one pair Z for each physical axis X, Y and Z.  These coils are wound to produce linear field changes in each of the three spatial directions.  A Gradient Amplifier provides the Gradient Coil current to the coils. Y B0 X HOOD05162002873707 Effective date: 05/06/2018 Page 56 Restricted © Siemens Healthcare GmbH, 2017 Slice Selection SIEMENS Healthineers RF at 41.20 Mhz resonates the spins at alica position A Z gradient Y gradient AUXgradient axial ofceo coronal aliceo sagittal aliceo selected selected selected TTTTTTT Figure 28.2 Uning X, Y and Z gradiente to select oficeo. RF a$ 43.50 MHz reconates the opine at ofice position B 190¢ alice select gradient TTTTTTT Figure 28.3 Timing of alice selection in a spin-acho pulse sequence. --- HOOD05162002873707 Effective date: 05/06/2018 Page 57 Restricted © Siemens Healthcare GmbH, 2017 Frequency encoding SIEMENS Healthineers magnas bore 90 180% 90 frequency-encoding gradiont range of frequencido lower centre higher frequencies frequency-encoding gradient. frequency frequencies rephasing . dephasing FID apin acho Timing of frequency encoding in a spin echo pulse keyboard rangs of rotes sequence. lower notes middle C higher notes HOOD05162002873707 Effective date: 05/06/2018 Page 58 Restricted © Siemens Healthcare GmbH, 2017 Phase encoding SIEMENS Healthineers Steep and Shallow phase encoding 9,700 G 10,000 G 10,300 G 41.20 MHz 42.57 MHz 43.80 MHz steep gradient Bo big phase shift shallow gradient alower preceoning faster preceoning nuclei lose phase nuclei gain phase omall phase shift HOOD05162002873707 Effective date: 05/06/2018 Page 59 Restricted © Siemens Healthcare GmbH, 2017 Gradient System – Its task SIEMENS Healthineers Readout Encoding Phase Encoding j +90° +45° 0° 45° – 90° – B B0 B B B0 B0 f f0 Df Df Df Df 2 - - f0 f0 + f0 f0 + 2 Spatial Encoding in the readout and phase encoding directions. HOOD05162002873707 Effective date: 05/06/2018 Page 60 Restricted © Siemens Healthcare GmbH, 2017 Use of Gradient to select Slice orientations SIEMENS Healthineers Transverse Coronal N Sagittal The use of physical gradient axes to select the principal slice orientations. By combining physical gradients, oblique and double oblique views are also possible. HOOD05162002873707 Effective date: 05/06/2018 Page 61 Restricted © Siemens Healthcare GmbH, 2017 Gradient system SIEMENS Healthineers DANFYSIK LEM Current Current Sensors Sensors Current Sensor Assembly GSSU GSSU Power Supply Output Choke (behind Power Stages) Power Stages Power Stage Power Supply (D30, D31) HOOD05162002873707 Effective date: 05/06/2018 Page 62 Restricted © Siemens Healthcare GmbH, 2017 Gradient coil SIEMENS Healthineers Shielding coils Water cooling Passive shim pockets Water cooling - Epoxy Primary coils High-order shim HOOD05162002873707 Effective date: 05/06/2018 Page 63 Restricted © Siemens Healthcare GmbH, 2017 Gradient system SIEMENS Healthineers Gradient System X DAC Regulator Modulator Y Fan Test- signals Gradient Fan Control CAN & Small Power Signal Z Service Stages Unit Measurement Grad Fan Current Filter Sensors Panel Coil Power GSSU Stage PS Supply HOOD05162002873707 Effective date: 05/06/2018 Page 64 Restricted © Siemens Healthcare GmbH, 2017 MR Safety SIEMENS Healthineers Gradients NOISE – increases inversely to slice thickness and FoV Peripheral nerve stimulation – dB/dt • Monitored by soft- and hardware HOOD05162002873707 Effective date: 05/06/2018 Page 65 Restricted © Siemens Healthcare GmbH, 2017 This presentation uses the preinstalled Office font Calibri. If you send it to someone internally or externally, please convert it into a pdf to ensure that the SIEMENS content stays as intended. Healthineers Our template contains layout guidelines. Their purpose is to indicate key margins and mandatory areas on slides. Copy and paste Copy only full slides when they use the same new design. Otherwise the file size will be very large. RF system Use the function Insert > Insert Content > Unformatted Text to paste a copied text. The text will now use the same existing format. Each presentation needs to be categorized, with the author being responsible for choosing the right category: Unrestricted – Restricted – Confidential – Strictly confidential – The preset default category Edit “Author | Department” for presentations is HOOD05162002873707 “restricted”. Restricted © Siemens Healthcare GmbH, 2017 in the “Header and footer” Effective date: 05/06/2018 for all pages. new category ©” Start > Replace > insert “Restricted ©” and “the RF pulse Transmission SIEMENS Healthineers The amplified RF excitation pulse, a voltage/current signal, must be converted to an electro-magnetic field. It is the magnetic field component, called the B1 field, which interacts with the protons. Digital RF Power Signal Signal Amp Generation Conversion Body TX coil B1 field HOOD05162002873707 Effective date: 05/06/2018 Page 67 Restricted © Siemens Healthcare GmbH, 2017 How to change paragraph levels Array Coils SIEMENS All levels font Calibri Healthineers - 26 pt. Level 1 is chapter - title: Bold, bulleted. Level 2, 3, 4 and 5 is - chapter description: Regular, no bullet, And it saves time and is indent 7.5 mm. patient friendly, too. Switch between Text- and bullet levels: click ● The Result: A large FOV coil without sacrificing S/N. HOOD05162002873707 Effective date: 05/06/2018 Page 68 Restricted © Siemens Healthcare GmbH, 2017 Receive signal processing SIEMENS Healthineers Spine Matrix Matrix Receive Coil Coils Channel Selector OO 8 O 8 YYYYY Neck Matrix ............. OO 8 OO Switch 8 O 8 ..... Matrix 8 Head Matrix OO 6 Receiver 8 Body Matrix 6 Back O 64 x 32 8 CP Flex End 6 6 4 4 64 receive lines for Up to 32 HOOD05162002873707 Peripheral Angio Matrix 76 coil elements receive channels Effective date: 05/06/2018 Page 69 Restricted © Siemens Healthcare GmbH, 2017 RF System Block Diagram SIEMENS Healthineers RFSU RFPA RFAS Bodycoil Modulator PA SSB1 DICO BCCS BC TX1 TTX1 90º Loop1 BC_TX2 PF PR PD CLK TAS from 90º RFIS MC Synthesizer TALES EH AME CLK CV PCI_TX Local Coils PCI RX PCI RX PCI RX PCT RX MRIR RCCS BC_RX2 BC RX1 Receiver Eat extorn LC_TX Test intern Receiver RFAS MRSIG 1-8 Switch SGA Array Receiver MRSIG 9-16 64 Patient MRSIG 17-24 Tune/ Table M Receiver MRSIG 25-32 Detune ta Body Coil RFIS 64 HOOD05162002873707 Effective date: 05/06/2018 Page 70 Restricted © Siemens Healthcare GmbH, 2017 How to change paragraph levels Coil Detuning SIEMENS All levels font Calibri Healthineers - 26 pt. Level 1 is chapter Receive only coils must be de-coupled during RF transmission - - title: Bold, bulleted. Level 2, 3, 4 and 5 is -electronically de-coupled - chapter description: Regular, no bullet, Active switching of PIN diode are used mostly - indent 7.5 mm. R2255 12 0321) 257626 Switch between Text- Cable trap and bullet levels: LNA lewww ● click Signal Matching detection loop To system m Detune switch F Ct L RF choke Cmt Cm2 Vac RF choke HOOD05162002873707 Effective date: 05/06/2018 Page 71 Restricted © Siemens Healthcare GmbH, 2017 RF room shielding SIEMENS Healthineers Exhaust and intake for air conditioning Quench tube exit RF-Filter plate - - - - Viewing RF-shielding window Opening for RF room door pressure equalisation Opening direction to the outside HOOD05162002873707 Effective date: 05/06/2018 Page 72 Restricted © Siemens Healthcare GmbH, 2017 MR Safety SIEMENS Healthineers RF Field Deposition – SAR limits Excessive RF transmit energy can result in overheating tissue (>40°C) causing RF burns Normal mode: (max. 0,5 °C rise in body temperature during exam time) • 2 W/kg [whole body] • 3.3 W/kg [head) • 10 W/kg [local TX coil, non volume coils] 1st level controlled mode: (max. rise in body temp of 1 °C during exam time) • 4 W/kg [whole body] • 3.3 W/kg [head] • 20 W/kg [local TX coil, non volume coils] HOOD05162002873707 Effective date: 05/06/2018 Page 73 Restricted © Siemens Healthcare GmbH, 2017 Hardware Summary SIEMENS Healthineers Components Tasks Magnet and • Provides net magnetization Magnetic Field • The field has to be homogeneous for optimum image fidelity • Generates linear fields resolution Gradient system • Spoils undesired magnetization • Provides special contrast rephasing, diffusion) • Generates RF pulses for excitation (90°, α) and rephasing (180°, α) RF system • Picks up, amplifies, converts from high frequency to low frequency, ADC-converts and demodulates the MR signal HOOD05162002873707 Effective date: 05/06/2018 Page 74 Restricted © Siemens Healthcare GmbH, 2017 Stable Power and Environmental considerations SIEMENS Healthineers • Line voltage • Room temperature • Relative humidity HOOD05162002873707 Effective date: 05/06/2018 Page 75 Restricted © Siemens Healthcare GmbH, 2017 Mathematical concepts SIEMENS Healthineers • vectors • sine and cosine waves • exponentials • complex numbers • simple Fourier analysis HOOD05162002873707 Effective date: 05/06/2018 Page 76 Restricted © Siemens Healthcare GmbH, 2017 RF Transmit SIEMENS Healthineers • RF coil is tuned and impedance matched to 50  at Larmor frequency for high efficiency • Power to the RF transmit coil is supplied by an RF power amplifier RFPA: • Up to 2kW ~ 60kW output power must be available with performance varying over time owing to any component heating • Must be capable of high duty cycles HOOD05162002873707 Effective date: 05/06/2018 Page 77 Restricted © Siemens Healthcare GmbH, 2017 SIEMENS Healthineers Thank you for your Attention HOOD05162002873707 Effective date: 05/06/2018 Restricted © Siemens Healthcare GmbH, 2017