Visibility and relaxation time mapping of 3-D printed polymers using ultrashort echo time MRI

The increasing interest in, and affordability of, 3-D printing has made fast prototyping and manufacturing of components and accessories increasingly popular in MRI research. In this work, visibility in magnetic resonance images and T₁ and T₂^∗ relaxation times of 3-D printed thermoplastic materials were investigated with multi-band sweep imaging with Fourier transformation (MB-SWIFT) and single point imaging (SPI). Ten commonly available 3-D printable plastics were investigated at 9.4 T. T₁ relaxation times were estimated with inversion recovery (IR-LL) and saturation recovery Look-Locker (SR-LL) as well as variable flip angle (VFA) MB-SWIFT techniques. T₂^∗ relaxation times were estimated from SPI data. It was observed that acrylonitrile styrene acrylate (ASA), high impact polystyrene (HIPS), acrylonitrile butadiene styrene (ABS) and some poly(lactic acid) (PLA) -based filaments as well as a proprietary thermoplastic formulation generated detectable signal making them "MRI-visible". Glycol-modified polyethylene terephthalate (PET-G) and nylon -based filaments as well as some PLA formulations were observed to be "MRI-invisible" with minimal to non-existent signal. T₁ parameters were estimated to be between 463 and 773 ms (VFA), 520-1004 ms (IR-LL) and 222-296 ms (SR-LL). Average T₂^∗ relaxation times with SPI were between 69 and 273 μs. The results provide a quantitative basis for selecting fused deposition modeling (FDM) materials for ultrashort echo time MRI applications and highlight the importance of both pulse sequence and material composition when designing MRI-compatible structures.