Deep illumination angular domain spectroscopic imaging: tissue-mimicking phantom study

The angular filter array (AFA) is a silicon micro-machined optical collimator, which only accepts photons propagating within a narrow solid angle. It can be used to select photons exiting an imaging sample along a specific direction. This paper describes a novel Angular Domain Spectroscopic Imaging (ADSI) technique that utilizes deep illumination from the front surface of the sample and a camera with an AFA to image features embedded inside a turbid medium. This approach permitted spectroscopic imaging of turbid samples too thick to be imaged in a trans-illumination setup. The tissue-mimicking test phantom contained three groups of Indocyanine Green doped inclusions at depths from 1 to 3 mm embedded within an IntralipidTM/agarose gel. The sample was scanned across the AFA and the intensity of the back scattered light along the direction normal to the surface was acquired as a function of location and wavelength. The resultant spectral images were captured and analyzed. The experiments demonstrated that ADSI could detect subsurface features that differed in wavelength-dependent absorption and/or scattering properties from the surrounding medium with the deep illumination configuration. Deep illumination ADSI may be useful as a non-invasive tissue imaging tool.