MRI-derived diffusion parameters in the human optic nerve and its surrounding sheath during head-down tilt

Darius A. Gerlach, Karina Marshall-Goebel, Khader M. Hasan, Larry A. Kramer, Noam Alperin, Joern Rittweger

Research output: Contribution to journalArticle

3 Citations (Scopus)

Abstract

More than half of astronauts present with significant neuro-ophthalmic findings during 6-month missions onboard the International Space Station. Although the underlying cause of this Microgravity Ocular Syndrome is currently unknown, alterations in cerebrospinal fluid dynamics within the optic nerve sheath may play a role. In the presented study, diffusion tensor imaging was used to assess changes in diffusivity of the optic nerve and its surrounding sheath during head-down tilt, a ground-based model of microgravity. Nine healthy male subjects (mean age ± SD: 25 ± 2.4 years; mean body mass index ± SD: 24.1 ± 2.4 kg/m2) underwent 5 head-down tilt conditions: −6°,−12°, −18°,−12° and 1% CO2, and −12° and lower body negative pressure. Mean diffusivity, fractional anisotropy, axial diffusivity, radial diffusivity were quantified in the left and right optic nerves and surrounding sheaths at supine baseline and after 4.5 h head-down tilt for each condition. In the optic nerve sheath, mean diffusivity was increased with all head-down tilt conditions by (Best Linear Unbiased Predictors) 0.147 (SE: 0.04) × 10−3 mm2 /s (P < 0.001), axial diffusivity by 0.188 (SE: 0.064) × 10−3 mm2 /s (P < 0.001), and radial diffusivity by 0.126 (SE: 0.04) × 10−3 mm2 /s (P = 0.0019). Within the optic nerve itself, fractional anisotropy was increased by 0.133 (SE: 0.047) (P = 0.0051) and axial diffusivity increased by 0.135 (SE: 0.08) × 10−3 mm2/s (P = 0.014) during head-down tilt, whilst mean diffusivity and radial diffusivity were unaffected (P > 0.3). These findings could be due to increased perioptic cerebral spinal fluid hydrodynamics during head-down tilt, as well as increased cerebral spinal fluid volume and movement within the optic nerve sheath.

Original languageEnglish (US)
Article number18
Journalnpj Microgravity
Volume3
Issue number1
DOIs
StatePublished - Dec 1 2017

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head down tilt
Head-Down Tilt
Diffusion Magnetic Resonance Imaging
nerves
Optic Nerve
optics
tilt
sheaths
diffusivity
Magnetic resonance imaging
Optics
nerve tissue
microgravity
Weightlessness
Microgravity
Hydrodynamics
lower body negative pressure
eyes
Diffusion tensor imaging
Lower Body Negative Pressure

ASJC Scopus subject areas

  • Physics and Astronomy (miscellaneous)
  • Space and Planetary Science
  • Medicine (miscellaneous)
  • Agricultural and Biological Sciences (miscellaneous)
  • Biochemistry, Genetics and Molecular Biology (miscellaneous)
  • Materials Science (miscellaneous)

Cite this

MRI-derived diffusion parameters in the human optic nerve and its surrounding sheath during head-down tilt. / Gerlach, Darius A.; Marshall-Goebel, Karina; Hasan, Khader M.; Kramer, Larry A.; Alperin, Noam; Rittweger, Joern.

In: npj Microgravity, Vol. 3, No. 1, 18, 01.12.2017.

Research output: Contribution to journalArticle

Gerlach, Darius A. ; Marshall-Goebel, Karina ; Hasan, Khader M. ; Kramer, Larry A. ; Alperin, Noam ; Rittweger, Joern. / MRI-derived diffusion parameters in the human optic nerve and its surrounding sheath during head-down tilt. In: npj Microgravity. 2017 ; Vol. 3, No. 1.
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abstract = "More than half of astronauts present with significant neuro-ophthalmic findings during 6-month missions onboard the International Space Station. Although the underlying cause of this Microgravity Ocular Syndrome is currently unknown, alterations in cerebrospinal fluid dynamics within the optic nerve sheath may play a role. In the presented study, diffusion tensor imaging was used to assess changes in diffusivity of the optic nerve and its surrounding sheath during head-down tilt, a ground-based model of microgravity. Nine healthy male subjects (mean age ± SD: 25 ± 2.4 years; mean body mass index ± SD: 24.1 ± 2.4 kg/m2) underwent 5 head-down tilt conditions: −6°,−12°, −18°,−12° and 1{\%} CO2, and −12° and lower body negative pressure. Mean diffusivity, fractional anisotropy, axial diffusivity, radial diffusivity were quantified in the left and right optic nerves and surrounding sheaths at supine baseline and after 4.5 h head-down tilt for each condition. In the optic nerve sheath, mean diffusivity was increased with all head-down tilt conditions by (Best Linear Unbiased Predictors) 0.147 (SE: 0.04) × 10−3 mm2 /s (P < 0.001), axial diffusivity by 0.188 (SE: 0.064) × 10−3 mm2 /s (P < 0.001), and radial diffusivity by 0.126 (SE: 0.04) × 10−3 mm2 /s (P = 0.0019). Within the optic nerve itself, fractional anisotropy was increased by 0.133 (SE: 0.047) (P = 0.0051) and axial diffusivity increased by 0.135 (SE: 0.08) × 10−3 mm2/s (P = 0.014) during head-down tilt, whilst mean diffusivity and radial diffusivity were unaffected (P > 0.3). These findings could be due to increased perioptic cerebral spinal fluid hydrodynamics during head-down tilt, as well as increased cerebral spinal fluid volume and movement within the optic nerve sheath.",
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