Purpose To introduce and characterize inexpensive and easily produced 3D‐printed axon‐mimetic diffusion MRI phantoms in terms of pore geometry and diffusion kurtosis imaging metrics. Methods Phantoms were 3D‐printed with a composite printing material that, after the dissolution of the polyvinyl alcohol, exhibits microscopic fibrous pores. Confocal microscopy and synchrotron phase‐contrast micro‐CT imaging were performed to visualize and assess the pore sizes. Diffusion MRI scans of four identical phantoms and phantoms with varying print parameters in water were performed at 9.4 T. Diffusion kurtosis imaging was fit to both data sets and used to assess the reproducibility between phantoms and effects of print parameters on diffusion kurtosis imaging metrics. Identical scans were performed 25 and 76 days later, to test their stability. Results Segmentation of pores in three microscopy images yielded a mean, median, and SD of equivalent pore diameters of 7.57 μm, 3.51 μm, and 12.13 μm, respectively. Phantoms had T1/T2 = 2 seconds/180 ms, and those with identical parameters showed a low coefficient of variation (~10%) in mean diffusivity (1.38 × 10−3 mm2/s) and kurtosis (0.52) metrics and radial diffusivity (1.01 × 10−3 mm2/s) and kurtosis (1.13) metrics. Printing temperature and speed had a small effect on diffusion kurtosis imaging metrics (< 16%), whereas infill density had a larger and more variable effect (> 16%). The stability analysis showed small changes over 2.5 months (< 7%). Conclusion Three‐dimension‐printed axon‐mimetic phantoms can mimic the fibrous structure of axon bundles on a microscopic scale, serving as complex, anisotropic diffusion MRI phantoms.

AbstractPurposeTo introduce and characterize inexpensive and easily produced 3D-printed axon-mimetic (3AM) diffusion MRI (dMRI) phantoms in terms of pore geometry and diffusion kurtosis imaging (DKI) metrics.MethodsPhantoms were 3D-printed with a composite printing material that exhibits microscopic fibrous pores. Confocal microscopy and synchrotron phase contrast micro-CT imaging were performed to visualize and assess the pore sizes. dMRI scans of four identical phantoms and phantoms with varying print parameters were performed at 9.4T. DKI was fit to both datasets and used to assess the reproducibility between phantoms and effects of print parameters on DKI metrics. Identical scans were performed 25 and 76 days later to test their stability.ResultsPore segmentation showed 33.6% of pores with diameters of 1.5-8μm with mean, median, and standard deviation of 20μm, 13μm, and 20μm, respectively. Phantoms with identical parameters showed a low coefficient of variation (∼10%) in DKI metrics. Printing temperature and speed had a small effect on DKI metrics (<16%) while infill density had a larger and more variable effect (>16%). The stability analysis showed small changes over 2.5 months (<7%).Conclusion3AM phantoms can mimic the fibrous structure of axon bundles on a microscopic scale, serving as complex, anisotropic dMRI phantoms.

Biome shifts are thought to be relatively rare, but some clades shift among starkly different environments with relative ease. What causes these shifts, and how do they shape phenotypic evolution? Roycroft et al. found that biome shifts in the Pseudomys Division of murid rodents were repeatedly accompanied by body size evolution in accordance with Bergmann's rule, suggesting adaptive evolution in response to changing climate conditions.

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Endosymbionts sometimes help their hosts resist parasites, but does infection of pea aphids (Acyrthosiphon pisum) with different strains of the endosymbiont Spiroplasma confer fitness benefits that offset the costs? Mathé‐Hubert et al. found that across four life‐history traits, Spiroplasma infection induced negative effects on host fitness when compared to controls. Only two of 12 strains of Spiroplasma showed a marginal protective effect against host parasitism by Aphidius ervi, implying Spiroplasma infection is almost entirely detrimental to pea aphid host fitness.