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Academic Report by the Division of Precision Scientific Instrumentation at APM on September 12, 2023

Title:Model-free approach to the interpretation of restricted and anisotropic self-diffusion in MRI of biological tissues
Speecher: Professor Daniel Topgaard from Lund University                                                   
Time: September 12,2023(Tue) 10:00-12:00 
Location: Conference Room M426, Building M
Magnetic resonance imaging (MRI) is the method of choice for noninvasive studies of micrometer-scale structures in biological tissues via their effects on the time/frequency-dependent (restricted) and anisotropic self-diffusion of water. Traditional MRI relies on pulsed magnetic field gradients to encode the signal with information about translational motion in the direction of the gradient, which convolves fundamentally different aspects—such as bulk diffusivity, restriction, anisotropy, and flow—into a single effective observable lacking specificity to distinguish between biologically plausible microstructural scenarios. To overcome this limitation, we introduce a formal analogy between measuring rotational correlation functions and interaction tensor anisotropies in nuclear magnetic resonance (NMR) spectroscopy and investigating translational motion in MRI, which we utilize to convert data acquisition and analysis strategies from NMR of rotational dynamics in macromolecules to MRI of diffusion in biological tissues, yielding model-independent quantitative metrics reporting on relevant microstructural properties with unprecedented specificity. This lecture includes the basic physical principles of using spectrally modulated gradient waveforms to separate and correlate specific aspects of translational motion, as well as examples of applications to liquid crystals, yeast cells, tumors, and brains.