ISMRM 24th Annual Meeting & Exhibition 07-13 May 2016 Singapore

Weekend Educational Course: MR Systems Engineering

Skill Level: Intermediate

Organizers: Thomas Foo, Ph.D. & Simone Winkler, Ph.D.

Saturday 07 May 2016

This one-day Educational Course is targeted at scientists and clinicians interested in understanding the engineering of magnetic resonance systems on a subsystems level. In a series of lectures from experts in MR Systems Engineering, attendees will first be provided with an overview of an MR system, and then learn about the design of magnet, gradients and shim systems, as well as the operation of the radiofrequency (RF) electronic subsystems that interface with RF coils. Issues relating to the site preparation and installation of new MR systems will also be discussed. In addition attendees will be taught about the key elements of MR safety as it relates to peripheral nerve stimulation (low frequency electromagnetic field interactions with the body) as well as energy deposition in the body from high frequency electromagnetic field interactions. The compatibility of medical devices and implants with an MRI scanner will be discussed. This course is aimed at scientists and clinicians with a technical background and interest in MR systems hardware. It is expected to provide attendees with an understanding of fundamental aspects of MR system operation.

Target Audience
Scientists and clinicians who are starting to work in the field of MRI and would like to have an overview of the engineering of an MR system. More experienced researchers in particular areas of MR Engineering will also benefit from hearing about recent advances in the engineering of MR systems.

Educational Objectives
Upon completion of this course, participants should be able to:

  • Assess the basic subsystems hardware components of an MRI scanner, including how they interact and function;
  • Evaluate issues related to installing a new MR scanner, including space, venting, power and cooling considerations;
  • Recognize practical limitations in the design and construction of magnets, gradients and shim systems;
  • Identify the basic mechanisms by which medical devices interact with the magnet and gradients within an MRI scanner;
  • Describe the interactions of electromagnetic fields (both low frequency gradient switching and high frequency RF) with the human body; and
  • Explain the RF electronic subsystems that interface with RF coils, including interactions between separate transmit and receive coils.

Moderator: Ergin Atalar, Simone Winkler
MR Systems Overview - Permission Withheld
Saban Kurucay
A general overview of the Magnetic Resonance Imaging (MRI) system design is presented with focus on main subsystems, their desired properties and impacts on imaging system performance.
      Magnets & Shims  
Magnet Design, Manufacturing & Installation
Johannes Van Oort1
1Alltech Medical Systems America
A brief introduction will be given to the various magnet types and geometries for MR Imaging. Design of superconducting magnets will be treated in more detail, including a short introduction to the phenomenon of superconductivity in NbTi wires, magnet design considerations, magnet ramp, stability and quench protection. Manufacturing of superconducting magnets will be discussed, followed by common installation guidelines and industry practices.
Shimming: Superconducting & Passive Shims; Higher Order Shims & Application to Imaging
Trong-Kha Truong1 and Allen W Song1
1Brain Imaging and Analysis Center, Duke University, Durham, NC, United States
Having a homogeneous magnetic field is an essential requirement to ensure high image quality in MRI. Significant field inhomogeneity can result in severe signal losses or geometric distortions. To achieve the desired uniformity, effective and efficient shimming strategies are needed. Specifically, passive and active shimming strategies have been developed to correct for both the intrinsic and extrinsic magnetic field inhomogeneities. Advantages and disadvantages of these various solutions are reviewed. In addition, specific applications in imaging experiments for some advanced shimming strategies are discussed, when the conventional shimming solutions are inadequate.

Break & Meet the Teachers
Coil Design Considerations, Manufacturing & Limitations - Permission Withheld
Eva Eberlein
Improvements in resolution and speed in recent MRI scanner generations were only possible with the development of high-performant gradient systems. Present gradient technology allows gradient amplitudes of up to 80mT/m and slew rates of up to 200T/m/s simultaneously for conventional whole-body systems. Even higher amplitudes and slew rates are possible using dedicated coils and special gradient systems. In this talk we will describe gradient coil design methods including boundary conditions like available space, stray field, forces and vibration. We show limitations to the usage of the possible technical performance due to physiological conditions and other constraints. Several approaches are discussed how to overcome the different limitations.

Gradient Drivers: Amplifier Considerations, Power, Tuning & Cooling
Juan A Sabate1
1GE Global Research, Niskayuna, NY, United States
Gradient driver high capability is needed in the magnetic resonance imaging (MRI) for better image quality, better resolution and faster imaging. Imaging speed and SNR require increased PSD reproduction fidelity and higher power capability. Higher power has been possible with the change of implementation from linear amplifiers to much lower internal losses switched amplifiers. Switched amplifiers consist on a power stage combining multiple switching semiconductors, commanded with high performance digital control. The digital controller requires precise feedback control, gradient coil model and compensation of nonlinearities. The design has to consider efficiency for operation cost and practical thermal management. 

Eddy current calibration, compensation and pre-emphasis; and gradient non linearity: Impact on application
Thomas L. Chenevert1
1Radiology - MRI, University of Michigan, Ann Arbor, MI, United States
Imperfections in applied gradient fields are manifest as deviation from ideal temporal waveforms and spatial nonlinearity.  Eddy currents induced in conductive surfaces are mitigated to a great extent by pre-emphasis of gradient demand to compensate for known inductive loss thereby yielding near-ideal temporal waveforms.  However, residual eddy currents do impact demanding applications and may still require post-acquisition software correction.  Spatial non uniformity of applied gradient fields induce geometric distortions which are effectively removed via automatic 2D or 3D (un)warping, although there is residual bias in diffusion weighting.  This lecture will focus on practical impact of these effects.

Lunch & Meet the Teachers
      RF Transmit & Receive Chain  
RF Transmit: Power Delivery, Decoupling, & Duty Cycle
J. Vaughan
RF Receivers: Signal Detection Chain, Digitization, System Noise Figures - from MRI Signal to Bits
Greig Scott
This presentation provides an overview of the receive chain in an MRI scanner.  Topics to be discussed are preamplifiers, device protection, analog to digital conversion, and high speed data links.  Effort will in particular be placed on looking under the hood of basic ADCs to better understand how their performance limits MRI dynamic range.  Finally we will look at the technology future of wireless MRI and local digital MRI receivers.
      Controlling the MR Scanner  
Controlling the MR Subsystems: Pulse Sequence Control, Waveform Generation & Real-Time Control
J. Andrew Derbyshire1
1FMRIF, NIMH / National Institutes of Health, Bethesda, MD, United States
Multi-Modality Imaging in an MRI Scanner: Simultaneous Imaging & Therapy - Making the Systems Compatible
Jan Lagendijk
The use of MRI for treatment guidance is growing. The MRI linac is being developed for guidance of external beam radiotherapy. Linacs and MRI are not easily compatible, solutions will be described. The requirements and challenges of robotics for MRI guided brachytherapy will also be described.

Break & Meet the Teachers
      Systems Safety  
Basic MR Safety, SAR & Power Deposition/Monitoring (Includes Effect of RF Coils & Ultra High Fields)
Roger Luechinger1
1Institute for Biomedical Engineering, University and ETH Zurich
MR safety is an important topic for all users performing MR procedures on humans. In this presentation we want to limit us on the MR system safety without implants. The potential risk of MRI and the international standard which taking them into account will be presented. Further the topic of testing own RF coils will be discussed. In a last part the additional problems from multi transmit RF coils and their monitoring will be covered.

Peripheral Nerve Stimulation, Implants & Devices: Safe Use & Considerations for MRI
Ergin Atalar1
1UMRAM and Dept. of Electrical and Electronics Engineering, Bilkent University, Ankara, Turkey
Two of the main safety problems of MRI is discussed. First one is the safety concerns due to the gradient induced peripheral nerve stimulation. Current commercial MRI scanners have gradients which are capable of inducing electric field in the body in a level that may cause sensation but fortunately this level is far from the possibility of causing harm. The second one is related to the safety of the patients who wear implantable medical devices. The radiofrequency pulses of MRI may induce currents on its leads. It is feared that this current may reach to a level that it can cause burns.

Adjournment & Meet the Teachers

The International Society for Magnetic Resonance in Medicine is accredited by the Accreditation Council for
Continuing Medical Education to provide continuing medical education for physicians.