Toward Printing the Brain: A Microstructural Ground Truth Phantom for MRI

Abstract

Magnetic resonance imaging (MRI) has become the prime imaging technique for in vivo examination of the brain. In addition to anatomical and functional MRI, diffusion MRI (dMRI) is widely used in both clinics and research to assess tissue structure and fiber directions, particularly in the nervous system. While diffusion tensor imaging is the most widespread approach for assessing orientation measures, other, more sophisticated models have also been proposed. Validation of dMRI is, however, a challenging endeavor that requires specialized test samples. Here it is shown that two‐photon polymerization (2PP) 3D printing allows for manufacturing such test objects, a.k.a. phantoms. After upscaling the 2PP fabrication process, 3D structures at high spatial resolution and sufficient size to image in a human 7T MRI scanner are created. These phantoms reliably mimic human white matter and thus enable the systematic validation and verification of dMRI data and their analyses. The 3D‐printed structures include up to 51 000 microchannels that mimic the diffusion behavior of larger axons, with a cross‐section of 12 × 12 µm2 each, in parallel and crossing arrangements. The acquired dMRI data demonstrates and verifies the utility of these novel brain phantoms.

ACID: A Comprehensive Toolbox for Image Processing and Modeling of Brain, Spinal Cord, and Post-mortem Diffusion MRI Data

“…The Pre-processing module consists of state-of-the-art methods for retrospective correction of the dMRI data. The Diffusion tensor/kurtosis imaging module contains tensor and kurtosis models that can be flexibly applied to any dMRI data, regardless of the tissue or sample, including gray and white matter, as well as diffusion phantoms (Woletz et al, 2024). In contrast, the Biophysical models module can only be applied to samples that fall within their validity ranges (see Section 4.2.2).…”