MRI Physics II

Outline of the module
This module covers more advanced topics in MRI physics. It is based on the module MRI Physics I. First, the module introduces more advanced mathematical tools to understand MRI echo generation by means of phase graphs. Next, the most important imaging sequences are theoretically and practically discussed: steady state sequences, fast spin echo sequences, and inversion recovery transients, respectively. Afterwards the ultra-fast imaging technique EPI is covered, which is important for the understanding of the imaging sequences for functional MRI, diffusion MRI, and perfusion MRI, respectively. The basic physical concepts of diffusion or perfusion weighting the MRI signal are explained. Finally, more advanced topics such as phase contrast and X-nuclei imaging are discussed.

The module covers the following topics:
• Designing MRI sequences by means of phase graph
• Calculating dynamic steady state signals
• Designing fast imaging sequences for structural and functional imaging
• Obtaining quantitative information from MRI
• Applications of diffusion, perfusion, or susceptibility weighting
• What information provides X-nuclei MRI?


Learning objectives
At the end of this module, students will have knowledge of:
• 
Computation of signal amplitudes in MRI sequences in theory and practice (i.e. in MATLAB)
• Steady state sequences: FLASH, FISP, PSIF, trueFISP and variants
• Typical artefacts in steady state sequences
• Understanding the ultra-fast imaging sequence EPI
• Typical artifacts in EPI sequences
• Implementation and testing of all sequences by means of the MRI simulator JEMRIS
• Application of the EPI sequence in functional MRI
• Basics theory of diffusion MRI and the application of spin echo EPI for in vivo diffusion quantification
• Advanced topics: quantitative MRI, phase contrast, spectroscopic imaging, and X-nuclei MRI


Content
Whereas the first module, MRI Physics I, gives a principle understanding of the involved physical processes, this module aims at explaining more advanced concepts. The methods and MRI sequences to be taught in the first module are important for the principle understanding, but they do not reflect the real-life applications as they are currently in use in clinical or research applications of MRI. The first part of this module, MRI Physics II, aims in explaining state-of-the-art MRI imaging techniques as they are currently in use for rapid acquisition of high-quality MRI data. This requires the introduction of new mathematical and physical concepts in order to successfully model the complexity of MRI experiments. After introduction of the phase graph concept, various steady state imaging sequences as well as multiple spin echo experiments can be handled on a sound theoretical basis. In order to fully appreciate these methods, it is important to review the excitation process and to present more advanced concepts for the design of tailored RF pulses. Then, the physical principles of the ultra-fast imaging technique EPI are covered and the involved manifold problems are discussed. Then, in the second half of the module, important fields of current research and applications are introduced. It is shown how the quantitative nature of the MRI signal can be used to obtain quantitative information from MRI scans. The huge field of magnetic resonance spectroscopy and spectroscopic imaging is presented on an introductory level. Further, the physical mechanism for encoding diffusion and perfusion information to the MRI signal are shown and current methods for the rapid acquisition of those are discussed. In the context of Ultra High-Field MRI new contrast mechanisms and MRI applications reaching the focus of scientific interest. Here, especially phase contrast methods as well imaging other nuclei than hydrogen need to be mentioned. The module will end with examples of current methods and research in these areas.

Overview of tasks and lectures
There will be 10 lectures of 2 hours distributed over 5 days.
• MRI Echoes: the Extended Phase Graph
• Steady-state Imaging Sequences
• Advanced T1 and T2 Weighted Sequences
• Physics of Advanced RF Pulses
• Ultra-fast Imaging: the EPI Technique
• Quantitative Imaging
• Spectroscopic Imaging
• Diffusion Weighted Imaging
• Susceptibility Weighted Imaging
• X-Nuclei: Beyond the Proton

Position within the programme
This is a unique module in this Master programme dealing with the chain of physiological and physical events giving rise to the fMRI signal. The knowledge of these processes is highly relevant for a correct interpretation of fMRI data. This module is complementary to the general modules dealing with MRI physics and data analysis basics and to the modules dealing with advanced analysis methods and applications. 


Teaching format

Structure
The module is a one week-long residential module consisting of 10 lectures of 2 hours. Each day, the students will in addition solve mathematical and physical problems as well as implement computer algorithms relevant to the lecture guided by tutors. Furthermore, the residential part is combined with a preparatory reading phase and post-module marked assignments.

Grading
Passing the module requires an 85% attendance to the lectures and practical sessions, and a satisfactory completion of the practical sessions and the module assignments. The module assignments will be summarised by the students in a written form which will be evaluated by the module coordinator(s).


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