Space Environmental Health: Non-Invasive Holographic Imaging Flow Cytometry for Astronauts Biodosimetry

Ionizing radiation exposure defines one of the main risks in the context of space environmental health for astronauts of the International Space Station (ISS) involved in long duration missions. The Galactic Cosmic Radiation (GCR) constitutes a primary source of radiation made of energetic protons and heavy ions, protons and electrons trapped in the Earth's magnetic field and protons from infrequent solar particle events (SPEs). A secondary source of radiation arises from neutrons and light charged particles, created by interactions of high-charge
$(\boldsymbol{Z})$
and energy
$(\boldsymbol{E})$
nuclei (HZE particles) with spacecraft shielding and with the human body itself. The existence of such a heterogeneous exposure scenario causes astronauts to undergo effective doses accumulations at a rate of ~0.2 to ~0.5 mSv or more each day of a mission. This causes high risks of circulatory diseases, central nervous system effects and cancer progression. In this context, biodosimetry initiatives have been implemented to extrapolate organ dose equivalents or risk assessments via direct quantification of cytogenetic aberrations in the peripheral blood lymphocytes of crew members. These datasets offer the distinct advantage of incorporating individual radiosensitivity alongside the effects of microgravity and other stressors. In this framework, the Tomographic Phase Microscopy in Flow-Cytometry (TPM-FC) is proposed as a non-invasive holographic imaging flow cytometry to evaluate the effect of ionizing radiations on blood cells. The technique conjugates the high-throughput analysis typically achievable in flow-cytometry and the label-free tomographic imaging based on digital holographic recording in microscopy configuration. The reconstruction of the interference fringe pattern allows to decode the 3D spatial distribution of the single cell's refractive indexes (RIs). The method proposed here belongs to the Quantitative Phase Imaging (QPI) techniques that enable to detect morphological alterations into irradiated blood cells, thus opening to further investigations aiming at the development of a portable, label-free, and non-invasive tool for crew health monitoring.