Development of a blood oxygenation phantom for photoacoustic tomography combined with online pO2 detection and flow spectrometry

Abstract

Photoacoustic tomography (PAT) is intrinsically sensitive to blood oxygen saturation (sO 2 ) in vivo. However, making accurate sO 2 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 sO 2 using chemical oxygenation and deoxygenation of blood in the phantom. Using this dynamic assessment of the photoacoustic sO 2 measurement in phantoms in relation to a ground truth, we explore the influence of multispectral processing and spectral coloring on accurate assessment of sO 2 . 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.

Photoacoustics resolves species-specific differences in hemoglobin concentration and oxygenation

“…For the measurements of the ODC, a flow phantom set up was used, which has also been described in detail elsewhere. 39 For each measurement, 5 mL of pooled blood from the respective species was first oxygenated by the addition of 0.2% v/v hydrogen peroxide [ 30% (w/w) in deionized water, Sigma-Aldrich 7722-84-1]. The oxygenated blood was filled into the circuit, carefully avoiding the introduction of air bubbles.…”

“…Absorption spectra were recorded continuously via AvaSoft software as the fluid passed through a flow cell (Hellma Analytics, 170700-0.5-40) as it has been shown that directly measured absorption spectra provide the most accurate endmembers for spectral unmixing. 39 Species-specific absorption spectra at the point of complete oxygenation and deoxygenation were extracted and used for spectral unmixing of the data recorded for the respective species. Between each measurement run, the tubing containing the blood was cleaned with PBS.…”

“…All materials used in the preparation of phantoms are readily available from commercial suppliers as detailed herein and further in Ref. 39 .…”

Photoacoustic imaging resolves species-specific differences in haemoglobin concentration and oxygenation

“…For the measurements of the oxygen-disassociation curve (ODC), a flow phantom setup was used, which has also been described in detail elsewhere 35 . For each measurement, 5mL of pooled blood from the respective species was first oxygenated by the addition of 0.2 % v/v hydrogen peroxide (H2O2 30% (w/w) in deionized water, Sigma-Aldrich 7722-84-1).…”

“…Absorption spectra were measured using a light source (Avantes Avalight-HAL-S-Mini) and spectrometer (AvaSpec-ULS2048-USB2-VA-50). Absorption spectra were recorded continuously via AvaSoft software as the fluid passed through a flow cell (Hellma Analytics, 170700-0.5-40) as it has been shown that directly measured absorption spectra provide the most accurate endmembers for spectral unmixing 35 . Species-specific absorption spectra at the point of complete oxygenation and deoxygenation were extracted and used for spectral unmixing of the data recorded for the respective species.…”