Abstract

While many imaging modalities operate in the visible and near infrared (VIS-NIR, 400-1000 nm) range, there is increasing interest in developing short-wave infrared (SWIR, 1000-1700 nm) optical technologies. For example, because melanin absorption decreases significantly from VIS-NIR to SWIR, SWIR imaging (unlike VIS-NIR) offers an equitable pigment-insensitive modality for skin imaging. To facilitate device development, it is useful to test devices with optical phantoms that have tissue-matching wavelength-dependent scattering and absorption (µs’, µa). However methods to generate phantoms that match SWIR skin optical properties are not well established. To address this need, we extend our previous VIS-NIR work with 3D-printed resin-based skin-mimicking phantoms to the SWIR.

We generated phantoms using a resin-based 3D-printer, where flexible and optically clear resin (Monocure Flex 100) is mixed with melanin-like chromophores (India ink, synthetic melanin, or nigrosin), and scattering agents (titanium dioxide TiO2). Phantom µa and µs’ were measured from 400-1700 nm by the Inverse Adding Double method using a VIS-NIR (Ocean Optics HDX-XR, 0.2-1.1µm) and SWIR (Ocean Optics NIRQuest, 0.9-1.7µm) spectrometers. Phantom (µa, µs’ ) values were compared to published (µa, µs’) of human skin spanning 400-1700 nm. Adjusting resin TiO2 concentration achieved phantom µs’ that matched published skin µs’ from 400-1700 nm. Adjusting resin India Ink concentration achieved µa that matched published human skin µa from 400-1000 nm, but failed to recapitulate the broad skin absorption peak around 1400 nm. To overcome this limitation, we added increasing volumes of water to the resin mixture. We found that in the range of water volumes where print quality remained high, peak µa near 1400 (1436 nm) could be boosted over 300%. Our results suggest that by careful selection of chromophores and scattering agents, a resin-based 3D-printed phantom can be tuned to have optical properties that match human skin ranging from VIS-NIR to SWIR wavelengths.