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

Weekend Educational Course: Physics for Physicists

Skill Level: Intermediate to Advanced

Organizers: Thomas Foo, Ph.D. & N. Jon Shah, Ph.D.

Saturday 07 May 2016

This course will describe commonly used imaging pulse sequences and their building blocks, data acquisition and artifact suppression strategies and basic and advanced image reconstruction techniques.

Target Audience
MR physicists and engineers, pulse sequence developers and clinicians who want to deepen their understanding of MRI acquisition and reconstruction methods. Individuals who will likely benefit most from the course are those who have recently completed or will complete a graduate educational program in MR physics, chemistry, applied mathematics or engineering and those practitioners of MR with extensive practical experience but seek to obtain a more systematic physics foundation.

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

  • Develop a systematic understanding of pulse sequence building blocks and components;
  • Gain an in-depth understanding of advanced data acquisition strategies, and their potential and limitations;
  • Describe common approaches to address motion;
  • Understand the state-of-the-art fast imaging techniques;
  • Grasp advanced image reconstruction algorithms; and
  • Identify common artifacts and understand how to reduce them.

Moderator: Seung-Kyun Lee, Ed Wu
      An Introduction to the Basics of MRI  
MRI: The Classical Description
Gareth Barker
The NMR (Nuclear Magnetic Resonance) signal can be described classically by considering the motion of the net magnetisation (the vector sum of magnetic moments of individual nuclei). By considering individual isochromats – i.e. subsets of the spins that are behaving identically– we can visualise how the received signal will decay away due to T1, T2 and T2* relaxation. By additionally considering the effects of magnetic field gradients, we can spatially localise the signal, extending NMR to MRI (Magnetic Resonance Imaging). All these effects can be described by the Bloch equations, which give complete classical description of the behaviour of magnetisation.

MRI: A Systems Overview
Mark E. Ladd1
1Medical Physics in Radiology, German Cancer Research Center, Heidelberg, Germany
· Basic understanding of how an MRI works can be achieved by comprehending its major functional subsystems.

· The subsystem currently experiencing the greatest innovation is RF transmission.

· Software defines the look and feel of the system and is the most important differentiator between systems.

Basic MR Safety (Magnetic Fields, Peripheral Nerve Stimulation, etc.)
Harald Kugel1
1Department of Clinical Radiology, University of Muenster, Muenster, Germany
Magnetic resonance techniques are considered to be not harmful. The three electromagnetic fields used for MR - static magnetic field, switched gradient fields, and radio frequency field - do not result in irreversible changes of human tissue, as long as certain limits are not exceeded. However, the applied fields show effects, which may cause severe hazards for patients, staff, and material, if MR examinations are not performed properly.

Break & Meet the Teachers
      Contrast Manipulation  
Bloch Equations & Typical MRI Contrast
Nikolaus Weiskopf1,2
1Department of Neurophysics, Max Planck Institute for Human Cognitive and Brain Sciences, Leipzig, Germany, 2Wellcome Trust Centre for Neuroimaging, University College London, London, United Kingdom
Sequences and Simulations
Martin John Graves1
1Radiology, Cambridge University Hospitals, Cambridge, United Kingdom
This presentation will provide an overview of the main gradient echo based (gradient spoiled, RF spoiled and balanced steady state free precession) and conventional/fast spin echo based pulse sequences and will illustrate some methods by which their behaviour can be simulated

Pulse Sequence Check: Reality vs. Ideal
Oliver Speck1
1Biomedical Magnetic Resonance, Otto von Guericke University, Magdeburg, Germany
The effect of any pulse sequence on the magnetization in an object can be predicted very accurately using the Bloch equation. A general algebraic inversion of the Bloch equation is not possible and thus, the full set of object and system properties and parameters cannot be derived from measurement data directly. Using a few assumptions and neglecting possible deviations, the contrast of a given pulse sequence can be calculated and the spatial encoding can be inverted to reconstruct an image.

Lunch & Meet the Teachers
      Echo Planar Imaging  
Basics of an EPI Acquisition
Eric C. Wong1
1UC San Diego
Echo Planar Imaging (1), or EPI, is a prototype for pulse sequences that sample two dimensions of K-space after a single excitation. 2D scanning after a single excitation means that signal modulations unrelated to applied gradient fields, such as transverse relaxation and resonance offsets, distribute across two dimensions in k-space and image space. EPI is highly demanding of gradient performance and fidelity. Gradient hardware advances have enabled the implementation of EPI, and continue to improve the utility and robustness of EPI. There are complex tradeoffs involved in the design of EPI pulse sequences and selection of EPI parameters with regard to gradient performance, SNR, image artifacts, ramp sampling, and other pulse sequence features.

EPI Applications: What we Can See Using EPI as an Engine
Peter Jezzard1
1University of Oxford
Introduction to the uses of EPI as an acquisition ‘engine’ in advanced structural and functional pulse sequences · Overview of the principles of functional MRI, arterial spin labelling, diffusion imaging and chemical exchange saturation transfer imaging. · Description of the pulse sequence modules required to achieve these image contrasts. · Summary of the different flavours of each method, and the tricks required to minimize confounding artifacts.

EPI Artifacts and Correections
Maxim Zaitsev1
1Dept. of Radiology - Medical Physics, University Medical Centre Freiburg, Freiburg, Germany
Since its conception in 1977 echo planar imaging (EPI) remains famous for being a host of a variety of artefacts. Recent improvements in the gradient technology and the availability of receiver arrays offset some of the problems, which however was quickly counterbalanced by a general trend of increasing the main magnetic field strength and a common demand of increasing spatial resolution. Therefore understanding the physics behind the EPI artefacts continues to be important, as it allows one both to compose optimal protocols minimizing the possible damage at source and devise suitable post-acquisition strategies for correcting remaining imperfections.

Break & Meet the Teachers
      Diffusion Imaging for Physicists  
Diffusion Weighted Imaging & Applications
Rita Gouveia Nunes1
1Universidade de Lisboa, Lisboa, Portugal
Diffusion-weighted imaging (DWI) makes use of molecular water motion to probe tissue microstructure. This lecture will focus on the basic principles of DWI acquisition. After introducing the most commonly used diffusion modules, the main acquisition challenges will be discussed.  Typical acquisition approaches will be presented, including single-shot and multi-shot sequences. Examples of frequent DWI image artefacts will be shown, and some of the approaches available for minimizing or correcting for their effect will be presented. The main applications of DWI to brain and body imaging will also be presented, focusing on stroke and lesion characterization.

Diffusion Tensor Imaging & Applications
Ana-Maria Oros-Peusquens1
1Forschungszentrum Juelich, Germany
The presentation will discuss, among others, the diffusion tensor model and diffusion indices, acquisition and data sampling strategies, validation of DTI and applications: tractography in neurosurgery, brain connectivity in vivo, gray matter structure and connectivity in fixed tissue.

Beyond the Tensor Model
Evren Ozarslan1
1Bogazici University
Diffusion tensor imaging (DTI) is widely employed to characterize diffusion anisotropy in multi-directional diffusion MR acquisitions. However, the DTI model has well-known limitations primarily because it assumes diffusion to be Gaussian. In this talk, DTI’s limitations will be discussed for three cases: (i) the presence of orientational complexity, (ii) nonlinearity of the signal decay curves, and (iii) dependence on the timing parameters of the sequence. Several alternative approaches will be outlined and it will be argued that a cost-benefit analysis has to be performed before abandoning the diffusion tensor model.

q-Space: What is it?
Flavio Dell'Acqua1
1Neuroimaging, King's College London, London, United Kingdom
In this lecture the concepts behind q-space and q-space imaging will be reviewed. Starting from an historical overview on the major advances, the development of the q-space formalism and the concept of the diffusion propagator will be described and used to explain the origin of diffraction peaks and their possible application to infer pore sizes and other microstructural features. Q-space and Propagator based imaging techniques will then be introduced highlighting advantages and limitations of these techniques. Finally, the use of diffusion time as an new contrast to probe microstructure at different length scales will be discussed.

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.