Recent breakthroughs in MRI methodology and biophysical modelling of the MR signal brought quantitative in
vivo MRI markers with sub-millimeter resolution and high specificity to microscopic tissue compartments
within reach (e.g. MRI markers for myelin, axon, or iron concentration). However, ex vivo histology remains
the gold standard against which these MRI markers have to be validated before they can be reliably used for
clinical research or studying neuroscientific questions. Today, several challenges need to be overcome to
achieve quantitative validation of these MRI markers: (i) understanding and modelling the changes occurring
post mortem, e.g. autolysis, temperature changes and fixation, which significantly alter the MRI signal and the
tissue morphology, (ii) accounting for the scale gap between histological methods, which is typically
performed on small 2D sections of tissue (millimeters to few centimeters) with a microscopic resolution (~ 1
micron), and macroscopic MRI, which is performed on the whole three-dimensional brain at a macroscopic
resolution (~ 1 millimeter), (iii) finding the most reliable, reproducible, and quantitative histological techniques
to serve as the gold standard measurement tools for automated quantification of tissue compartments, ideally
over the entire brain. This symposium is comprised of four lectures that introduce a broad range of promising
methods to tackle these challenges.