Spatial frequency domain imaging using a snap-shot filter mosaic camera with multi-wavelength sensitive pixels

Spatial frequency domain imaging (SFDI) utilizes a digital light processing (DLP) projector for illuminating turbid media with sinusoidal patterns. The tissue absorption (μ a ) and reduced scattering coefficient (μ , s ) are calculated by analyzing the modulation transfer function for at least two spatial frequencies. We evaluated different illumination strategies with a red, green and blue light emitting diodes (LED) in the DLP, while imaging with a filter mosaic camera, XiSpec, with 16 different multi-wavelength sensitive pixels in the 470-630 nm wavelength range. Data were compared to SFDI by a multispectral camera setup (MSI) consisting of four cameras with bandpass filters centered at 475, 560, 580 and 650 nm. A pointwise system for comprehensive microcirculation analysis was used (EPOS) for comparison. A 5-min arterial occlusion and release protocol on the forearm of a Caucasian male with fair skin was analyzed by fitting the absorption spectra of the chromophores HbO 2 , Hb and melanin to the estimatedμ a . The tissue fractions of red blood cells ( f RBC), melanin (/mel) and the Hb oxygenation ( S 0 2 ) were calculated at baseline, end of occlusion, early after release and late after release. EPOS results showed a decrease in S 0 2 during the occlusion and hyperemia during release ( S 0 2 = 40%, 5%, 80% and 51%). The f RBC showed an increase during occlusion and release phases. The best MSI resemblance to the EPOS was for green LED illumination ( S 0 2 = 53%, 9%, 82%, 65%). Several illumination and analysis strategies using the XiSpec gave un-physiological results (e.g. negative S 0 2 ). XiSpec with green LED illumination gave the expected change in /RBC , while the dynamics in S 0 2 were less than those for EPOS. These results may be explained by the calculation of modulation using an illumination and detector setup with a broad spectral transmission bandwidth, with considerable variation in μ a of included chromophores. Approaches for either reducing the effective bandwidth of the XiSpec filters or by including their characteristic in a light transport model for SFDI modulation, are proposed.