  There is a need for a cost-effective, quantitative imaging tool that can be
deployed endoscopically to better detect early stage gastrointestinal cancers.
Spatial frequency domain imaging (SFDI) is a low-cost imaging technique that
produces near-real time, quantitative maps of absorption and reduced scattering
coefficients, but most implementations are bulky and suitable only for use
outside the body. We present an ultra-miniature SFDI system comprised of an
optical fiber array (diameter $0.125$ mm) and a micro camera ($1\times1$ mm
package) displacing conventionally bulky components, in particular the
projector. The prototype has outer diameter $3$ mm, but the individual
components dimensions could permit future packaging to $<1.5$ mm diameter. We
develop a phase-tracking algorithm to rapidly extract images with fringe
projections at $3$ equispaced phase shifts in order to perform SFDI
demodulation. To validate performance, we first demonstrate comparable recovery
of quantitative optical properties between our ultra-miniature system and a
conventional bench-top SFDI system with agreement of $15$\% and $6$\% for
absorption and reduced scattering respectively. Next, we demonstrate imaging of
absorption and reduced scattering of tissue-mimicking phantoms providing
enhanced contrast between simulated tissue types (healthy and tumour), done
simultaneously at wavelengths of $515$ nm and $660$ nm. This device shows
promise as a cost-effective, quantitative imaging tool to detect variations in
optical absorption and scattering as indicators of cancer.
