Mesoscopic reflectance angular domain spectroscopic imaging.
The advancement of angular domain imaging in mesoscopic reflectance multispectral imaging is reported. The key component is an angular filter array that performs the angular filtration of the back-scattered photons and generates image contrast due to the variances in tissue optical properties. The proposed modality enables multispectral imaging of subsurface features for samples too thick for transillumination angular domain spectroscopic imaging (ADSI) approaches. The validation was carried out with tissue-mimicking phantoms with multiple absorptive features embedded below the surface. Multispectral images in the range of 666 to 888 nm clearly revealed the location of the features with the background scattering levels up to 20 cm⁻¹. The shape of the features was recoverable at depths of up to three to four times the transport mean free path. The spatial resolution was <1 mm and the field-of-view was larger than 2.5 cm x 30. cm. Furthermore, the attenuation spectra of measured absorptive features were successfully extracted. Target detectability and imaging quality with different background scattering levels, target depths, and illumination focal depths were discussed, as well as the capability of ADSI in reflectance optical mesoscopic imaging and its potential applications.