Author: Izabella L. Barreto, Benjamin Taylor Heggie, Stephanie M. Leon 👨🔬
Affiliation: University of Florida College of Medicine, University of Florida 🌍
Purpose: 3D printing has the potential for producing materials useful for the imaging field. This work aims to identify absorption (attenuation coefficient) and material properties (effective atomic number and electron density) similar to anatomical tissues.
Methods: The absorption properties of over twenty filament samples were characterized using Monte-Carlo (PHITs) software. X-ray beam characteristics were determined for one CT scanner using a medium bow-tie filter, all energy spectrums (80-135 kVp), and narrow collimation. Air kerma was measured at isocenter using sheets of aluminum for each tube potential to calculate and simulate each energy spectrum using SpekCalc software. Simulated linear attenuation coefficients and calculated effective atomic number and electron density were recorded for filaments (i.e., PLA, PLA+, ASA, ABS, HIPS, PC, TPU, PETG, PEI, and PMMA), tissues (head, chest, abdominal, & pelvis), and iodine concentrations (1-20 mg/mL) using composition information supplied by manufacturers and ICRU reports 44 and 46. A dual-energy CT scanner and multi-energy CT phantom was used to measure effective atomic number and electron density for filaments showing simulated linear attenuation coefficients within ±5% of simulated tissue data.
Results: Some filaments (e.g., ASA, ABS, PC, PMMA, TPU, & PLA) had attenuation coefficients within ±5% of tissue equivalent materials (e.g., general adipose, gray matter, liver +5mg/mL, calcium 50 mg/mL, & calcium 100 mg/mL). However, smaller effective atomic numbers were observed for all filaments using Mayneord’s formula and higher electron densities, expressed relative to water.
Conclusion: While certain filaments may produce similar attenuation coefficients, this does not guarantee similar effective atomic number and electron density. Collectively, thermoplastics show a lower effective atomic number compared to most tissues and iodine concentrations, recommending that applied additives with heavier atomic masses be investigated. This is especially challenging for substances marked as a trade secret, limiting vital information to simulate or calculate accurate data remotely.