Criteria for the design of tissue-mimicking phantoms for the standardization of biophotonic instrumentation

Abstract

The reliability and reproducibility of experimental results are crucial in the development and regulatory approval of medical technologies, yet represent a challenge for biophotonic instrumentation due to a lack of accepted standards and phantoms suitable for successful technical validations. Here, we discuss the general design considerations for the preparation of tissue-mimicking biophotonic phantoms and then critically review the existing literature on phantom materials and fabrication across the field in light of these criteria and of recent developments at the state-of-the-art. We then focus on three representative examples of biophotonic standardisation related to different modalities, presented in order of their relative maturity: diffuse optical imaging and spectroscopy, fluorescence guided surgery, and photoacoustic imaging. Finally, we provide a perspective on future phantom development and the unmet needs of the biophotonic field, identifying a set of criteria, termed the "4Cs", for biophotonic standardisation which highlight the need for characterisation, collaboration, communication and commitment to maximise the achievements of ongoing standardisation efforts.Optical imaging biomarkers enable disease diagnosis and treatment in real-time at relatively low cost, leading to an increase in the use of optical imaging methods in clinical practice 1 . Despite the increasing number of available optical-imaging biomarkers and their significant potential for improving clinical outcomes, published standards for performance evaluation of optical imaging devices are still lacking 2 . As a result, technological progress in the respective imaging communities is hampered by a lack of transparency and comparability between system performance evaluations reported in the literature. The lack of consensus standards alsoimpacts the clinical translation process because regulatory bodies often recognize such standards and/or use them to guide policy. Without technical guidance on performance testing, the execution of clinical studies and the approval of new biophotonic devices may be slower and inconsistent.Test objects to calibrate optical systems have an important subset known as tissuemimicking phantoms, which are used for performance evaluation of a given technology by mimicking light-tissue interactions of human tissue, as well as other crucial elements of the process 3,4 . The diverse landscape of biophotonic applications means that it is likely impossible to have an all-encompassing phantom that fulfils the needs of every optical sub-speciality. As such, a wide range of biophotonic phantoms have been proposed 5,6 , but there has been no consensus on a widely applicable material type nor fabrication method to produce such phantoms. Nevertheless, finding consensus on broadly applicable materials would be beneficial to enable comparison of devices between vendors and institutions; advance hybrid modalities; allow complementary use of different modalities within one clinical session; and further the development of inte...

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