  Photoacoustic tomography (PAT) is intrinsically sensitive to blood oxygen
saturation (sO2) in vivo. However, making accurate sO2 measurements without
knowledge of tissue- and instrumentation-related correction factors is
extremely challenging. We have developed a low-cost flow phantom system to
facilitate validation of photoacoustic tomography systems. The phantom is
composed of a flow circuit, which is partially embedded within a tissue
mimicking phantom, with independent sensors providing online monitoring of the
optical absorption spectrum and partial pressure of oxygen in the tube. We
first establish the flow phantom using two small molecule dyes that are
frequently used for photoacoustic imaging: methylene blue (MB) and indocyanine
green (ICG). We then demonstrate the potential of the phantom for evaluating
sO2 using chemical oxygenation and deoxygenation of blood in the phantom. Using
this dynamic assessment of the photoacoustic sO2 measurement in phantoms in
relation to a ground truth, we explore the influence of multispectral
processing and spectral coloring on accurate assessment of sO2. Future studies
could exploit this low-cost dynamic flow phantom to validate fluence correction
algorithms and explore additional blood parameters such as pH, and also
absorptive and other properties of different fluids.
