Non‐Invasive 3‐Dimensional Facial Modeling for the Quantification of Facial Edema

Abstract

BACKGROUNDWith the lengthening of spaceflight mission durations, many crewmembers have experienced in‐flight and/or post‐flight visual and anatomical changes including optic‐disc edema, globe flattening, choroidal folds, and hyperopic shifts. These changes define the visual impairment/intracranial pressure (VIIP) syndrome. Although the underlying mechanism behind VIIP is unknown at this time, it is suspected that the microgravity‐induced cephalad fluid shift plays a significant role. Therefore, quantification of the microgravity‐induced fluid shifts may provide important prognostic information. However, there are limited non‐invasive tools currently available to assess volume changes and facial edema. A standardized method for quantifying the fluid shift and establishing reliability across repeated trials also remains to be clarified. Accordingly, using a commercially available Structure Sensor 3‐dimensional (3D) scanner, our lab developed a protocol to acquire and analyze 3D facial images in seated and supine positions and assessed the validity and reliability of the method. We hypothesized that within day coefficient of variation and across day coefficient of variation would be low (<5%).METHODSVolume measurement validity was assessed by acquiring and analyzing 3D scans of an object with a known volume across three trials. Reliability was assessed in 10 subjects. Structure Sensor 3D scanner (Occipital Inc., San Francisco, CA) images were obtained in two positions: upright and supine on three separate days. Images were immediately viewed on an Apple IPad with ItSeezit3D (ItSeez3D Inc., San Francisco, CA) application to ensure complete scans were obtained. Participants were instructed to look at the same spot each time to ensure constancy across scans. Analysis was completed in Rhinoceros (Robert McNeel & Associates, Seattle, WA, version 5, 64‐bit) software with a standardized technique developed by our lab.RESULTSValidity assessments yielded a mean absolute difference of 1.13 in3 . Average intra‐trial and intra‐day variability (CV) was 2.79%. Upon initial analysis, a cephalic fluid shift was evident in participants in a seated position when compared to the supine position. The mean fluid shift across participants was approximately 600 mL.CONCLUSIONOur findings indicate that the Structure Sensor 3D scanner and accompanying analysis software are valid and reliable tools in the assessment of cephalic fluid shift across different positions. This technology may be useful in identifying inter‐individual differences in cephalic fluid shifts in crewmembers. Future studies should examine the potential applications of this technology in response to a microgravity environment.