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Abstract
.Photoacoustic tomography (PAT) is intrinsically sensitive to blood oxygen saturation () in vivo. However, making accurate measurements without knowledge of tissue- and instrumentation-related correction factors is extremely challenging. We have developed a low-cost flow phantom to facilitate validation of PAT systems. The phantom is composed of a flow circuit of tubing partially embedded within a tissue-mimicking material, with independent sensors providing online monitoring of the optical absorption spectrum and partial pressure of oxygen in the tube. We first test the flow phantom using two small molecule dyes that are frequently used for photoacoustic imaging: methylene blue and indocyanine green. We then demonstrate the potential of the phantom for evaluating using chemical oxygenation and deoxygenation of blood in the circuit. Using this dynamic assessment of the photoacoustic measurement in phantoms in relation to a ground truth, we explore the influence of multispectral processing and spectral coloring on accurate assessment of . 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.
Highlights
Photoacoustic tomography (PAT) exploits optically generated ultrasound to provide images that combine the high contrast and spectral specificity of optical imaging with the high spatial resolution of ultrasound
The flow system (Fig. 1) enables fluids to be circulated within a vessel-mimicking tube embedded in a tissue-mimicking agar phantom placed in the chamber of a photoacoustic imaging system
The tissue-mimicking phantom used for photoacoustic imaging comprised either static or flowing fluids within a tube embedded within an agar cylinder, 19 mm in diameter
Summary
Photoacoustic tomography (PAT) exploits optically generated ultrasound to provide images that combine the high contrast and spectral specificity of optical imaging with the high spatial resolution of ultrasound. PAT has been widely used to image blood hemoglobin concentration and oxygenation, which have the potential to inform on a range of pathophysiologies, from tumor aggressiveness[1] and treatment response[2,3] to intestinal inflammation associated with Crohn’s disease[4] and colitis.[5] The derivation of such images is usually based on spectral unmixing to resolve the differential absorption contributions of oxy- (HbO2) and deoxyhemoglobin (Hb). Total hemoglobin concentration (THb) is typically taken as the sum of the contributions to the photoacoustic signal Pðr; λÞ from HbO2 and Hb, whereas hemoglobin oxygenation (sO2) is taken as the ratio of HbO2 to THb. the assessment of HbO2 and Hb content from photoacoustic data is not trivial. Hðr; λÞ is the product of the light fluence Φ, Hðr; λÞ 1⁄4 μ ðr; λÞΦ1⁄2r; λ; μ ðr; λÞ; μ ðr; λÞ: EQ-TARGET;temp:intralink-;e001;326;372 a a s (1)
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