Design and evaluation of a diffusion MRI fibre phantom using 3D printing

Diffusion weighted magnetic resonance imaging (dMRI) has enabled the in vivo imaging of structures with a highly fibrous composition, such as brain white matter due to the ability to detect the hindered and restricted diffusion of water along its defined tracts. In order to increase this non-invasive technique's sensitivity to the intricate fibrous structure and to better calibrate diffusion pulse sequences and validate fibre reconstruction modelling techniques, physical diffusion phantoms have been developed. These phantoms have a known structure and diffusion behaviour. This work aims to simplify the process of creating complex fibre-based diffusion phantoms using 3D printing material to model and mimic brain white matter fiber architecture for dMRI. We make use of a printing material consisting of a mixture of polyvinyl alcohol (PVA) and a rubber-elastomeric polymer (Gel-Lay by Poro-Lay), printed using a fused deposition modelling (FDM) printer. It is 3D printed as a rigid object but, following immersion in room-temperature water, the PVA dissolves away leaving behind the porous rubber-elastomeric polymer component to mimic the structure of brain white matter tracts. To test the validity of the methodology, two preliminary main phantoms were created: a linear 10mm x 10mm x 30mm block phantom and an orthogonal fiber-crossing phantom where two blocks cross at a 90-degree angle. This was followed by creating 3 disk phantoms with fibres crossing at 30, 60 and 90 degrees. Results demonstrate reproducible high diffusion anisotropy (FA=0.56 and 0.60) for the phantoms aligned with the fibre direction for the preliminary linear blocks. With multi-fibre ball & stick modelling in the orthogonal fibre-crossing phantom and the disk phantoms at 30, 60 and 90 degrees, image post-processing yielded crossing fibre populations that reflected the known physical architecture. These preliminary results reveal the potential of 3D-printed phantoms to validate fibre-reconstruction models and optimize acquisition protocols, paving the way for more complex phantoms and the investigation of long-term stability and reproducibility.