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Blood-mimicking Dye Phantoms for Evaluating Photoacoustic Imaging Devices

Catalog of Regulatory Science Tools to Help Assess New Medical Devices 

This regulatory science tool is a lab method that may be helpful while evaluating Photoacoustic Imaging devices.

Technical Description

This tool is a tissue-mimicking phantom developed for bench-top evaluation of oximetry measurement accuracy of photoacoustic imaging (PAI) devices. The phantom is composed of tissue-mimicking polyacrylamide hydrogel and contains an array of embedded fluid channels at various depths that can be filled with novel blood-mimicking dye solutions. Dye solutions are based on binary mixtures of commercially available near-infrared organic dyes with various specific dye recipes optimized to mimic the photoacoustic properties of blood at optical wavelengths of 750 nm and 850 nm and for blood oxygen saturation (sO2) levels from 40% to 100%. 

Intended Purpose 

This tool may be used to support objective, quantitative assessment of PAI device oximetry measurement accuracy. Imaging this phantom with a PAI device enables comparison of measured sO2 values against a known sO2 value emulated by a given injected dye mixture.  Because this phantom does not use actual animal or human blood, these dye-based phantoms may enable simpler, more precise, and more stable PAI oximetry testing, while also lowering biohazard risks to phantom users and reducing reliance on specialized biosafety lab facilities. 

Testing

Dye formulations were characterized and adjusted using spectrophotometry and photoacoustic spectroscopy [2]. Specific dye properties assessed include: extinction coefficient spectra from 600-1100 nm, extinction linearity vs. concentration, temporal stability, photoacoustic amplitude response spectra from 720-880 nm, and accuracy of simulated sO2 values. The optical and acoustic properties of polyacrylamide gel material were also characterized and compared to literature reported values for soft tissue [2]. Results yielded specific dye combinations that accurately simulate sO2 values from a range of 40% to 100% (root mean square error <1%), and that simulated sO2 drifted less than 1% over 15 days and less than 2% over 45 days.

To demonstrate utility of this tool, phantoms were filled with either blood-mimicking dyes or actual bovine blood that was chemically deoxygenated, then imaged using a custom PAI system. PAI-measured sO2 values were derived from acquired photoacoustic image data and compared against known simulated sO2 values for dyes or against gold-standard CO-oximetry measurements of sO2 for deoxygenated blood. Results showed that testing using dyes produced comparable estimates of PAI oximetry accuracy as testing using blood (RMSE 4-18% vs. RMSE 6-17%).

Limitations

  • Characterized binary dye mixtures are only demonstrated for mimicking blood sO2 values for photoacoustic measurements at optical wavelengths of 750 nm and 850 nm.
  • Dye solutions should ideally be prepared fresh and used within one day, but may be stored up to 15 days after preparation to minimize sO2 drift.
  • Dye phantom evaluation was performed with a single PAI system, which used an optical parametric oscillator (OPO) as its optical source. Dye performance has not been evaluated for optical sources with different operating parameters (e.g., pulse duration).

Supporting Documentation

  • [1] Zhou, Y., Wang, Z., Wear, K. A., Pfefer, T. J., Jokerst, J. V., Vogt, W. C., “Blood-mimicking Dye Phantoms for Evaluating Photoacoustic Oximetry Accuracy”, Photoacoustics 47, 100795, 2026, https://doi.org/10.1016/j.pacs.2026.100795
  • [2] Palma-Chavez, J., Wear, K. A., Mantri Y., Jokerst, J. V., Vogt, W. C., Photoacoustic imaging phantoms for assessment of object detectability and boundary buildup artifacts. Photoacoustics, 26, 100348, 2022, https://doi.org/10.1016/j.pacs.2022.100348.

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