Transparent Gellan Gum as an Efficient Coupling Media For Photoacoustic Imaging Applications

Photoacoustic imaging (PAI) is a powerful screening tool for cancer detection, capable of mapping vasculature, measuring blood oxygenation, and providing material specificity. For clinical applications such as in vivo skin imaging, PAI laser systems must be highly efficient in light delivery. Several types of material have been proposed for coupling light and sound from a laser to the tissue interface. One approach combines an US probe with an inline adapter using a photoacoustic prism/reflector filled with water, agarose gel or optically transparent rubber for coupling. However, this approach falls short due to suboptimal material properties (optical/acoustic), which may significantly degrade image quality (e.g., artifacts, lower signal-to-noise ratios, etc.). We propose the use of low acyl gellan gum as a novel photoacoustic coupling medium due to its low acoustic attenuation, high optical transparency, and gelling capabilities. To quantify gellan gum's benefits, we determined the acoustic attenuation, impedance, density, speed of sound, optical transmittance, and optical absorbance of gellan gum at 1.5 – 2.5% (w/w) and compared to agarose at 1.5% (w/w), Humimic Medical Gelatin #0, and diH20. From our data, we saw a decrease in photoacoustic signal loss of 0.35 ± 0.06 dB and 0.20 ± 0.06 dB per centimeter of gellan gum compared to agarose and Humimic #0, respectively. Furthermore, gellan gum had smaller acoustic attenuation coefficients at 0.64 ± 0.16 dB.cm
⁻¹
.MHz
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and 0.94 ± 0.16 dB.cm
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.MHz
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less than agarose and Humimic #0. These results suggest that low acyl gellan gum should be implemented as a coupling medium for improved handheld PAI probes used for imaging skin and other clinical uses.