Diffusion: from basic Physics to Exploration of Microscopic Structure

Date and Location: September 17-19, Cardiff, Wales/UK
Cardiff University Brain Research Imaging Centre (CUBRIC), School of Psychology, Cardiff University

Course Organisers: Valerij Kiselev
Department of Diagnostic Radiology Medical Physics, University Hospital of Freiburg, Freiburg/DE
Local Organiser: Derek K. Jones
CUBRIC, School of Psychology, Cardiff University, Cardiff, Wales/UK
Faculty: Daniel C. Alexander, Roland Bammer, Marco Catani, Derek K. Jones, Valerij G. Kiselev, Geoff Parker, Klaus Scheffler

Course description:
The basic idea of MR diffusion measurements is easy to explain, but its practical implementations require real knowhow. How to select optimal b-factors and directions of gradients? What is the effect of eddy currents? Having measured the ADC, what is it actually? Why does it depend on the diffusion time, the pulse sequence involved and the b-factor? This advanced course is designed to provide a stable basis for those who wish to develop methods of diffusion measurement or apply them to biomedical content. A significant part of time will be spent on exercises, which will be performed by participants individually under guidance of the lecturers.

Learning objectives:
Theory: Diffusion in heterogeneous media
• Physics of diffusion in heterogeneous media
• More Physics: Propagators, cumulants, and boundaries
• Restricted diffusion: 'biexponential' diffusion vs cumulant expansion
• ADC, q-space, diffusion diffraction, and the microscopic structure
• Anisotropic diffusion: Diffusion tensors and beyond
• Bloch – Torrey equation versus cumulant expansion

Methods for measurement of diffusion
• Diffusion-weighted imaging sequences
• Single shot and multi-shot sequences
• Single shot diffusion-weighted EPI sequence
• Practical sequence design and parameter optimisation
• Potential artifacts
• Alternative diffusion-weighted imaging methods: Spirals, RARE/UFLARE, Linescan and others
• Diffusion sensitivity of SSFP sequences
• Diffusion sensitivity of Hyperechoes
• Influence of diffusion on sequences not intended for diffusion imaging
• Signal-to-noise considerations and optimising the b-values
• Choice of diffusion encoding directions for DTI

Postprocessing
• Basics of diffusion tensor calculation
• Simple method of b-factor and b-matrix calculation.
• Correction of susceptibility related distortions of EPI images
• Correction of eddy currents distortions
• Artifacts of multi-shot / segmented DWI and possible methods of compensation
• Basics principle of fibre tracking
• Main approaches to fibre tracking
• Possibilities and limitations of fibre tracking
• Fibre tracks and probability of neuronal connection
• Some software packages for DTI calculation and fibre tracking

Applications
• Diffusion-weighted imaging in biomedical studies
• Fibre tracking