Plain English Summary

Quantitative magnetic resonance imaging (qMRI) techniques are used in assessing neurodegenerative
diseases like stroke, dementia, and multiple sclerosis. Advanced qMRI techniques have the potential
to detect early disease progression by measuring mass transfer of molecules across brain tissues, e.g.,
cerebral blood flow (CBF) and blood-brain barrier (BBB) permeability. The challenge is validating the
mass transfer models which describe such measurements as changes in mass transfer due to disease
can be as small as 1 %. Options for validation include biopsy (harms patient), comparison with other
imaging techniques (none have sufficient accuracy), and comparison with qMRI of reference objects,
i.e., phantoms, with known mass transfer properties. Clearly, due to ethical and practical reasons,
using a phantom is the most feasible validation technique. However, current phantoms bear little
similarity to brain tissues in mass transfer properties such as permeability, diffusivity, and geometry.
Recent evolution in 3D printing holds promise for manufacturing sophisticated and relevant phantoms
specifically designed for validation. 3D printing can reproducibly fabricate structures with complex
features down to the micron scale and customisable material properties.2
However, materials suitable
for printing phantoms which share mass transfer properties of brain tissues require development.