Optical phantoms for the characterization and validation of imaging and spectroscopy: a review.

SIGNIFICANCE: Tissue-mimicking optical phantoms are an essential tool in the development, characterization, and calibration of instruments used in optical imaging, spectroscopy, diagnosis, and treatment of disease. AIM: Major developments in optical phantoms have been enabled by recent advances in material development and characterization, as well as sophisticated manufacturing techniques. In this review, we will focus primarily on the developments in the field over the past 20 years since the seminal review paper on this topic by Pogue et al. in 2006. Throughout, we have attempted to provide the reader with practical guidelines to consider when producing phantoms. APPROACH: Here, we review and assess phantom geometries and available materials for phantom matrices, as well as absorbing and scattering agents. We then review and discuss the use of tissue phantoms in a variety of optical imaging and spectroscopic modalities and address the use and challenges of models of light propagation to extract optical properties from the measured physical parameters. Finally, we highlight the use and utility of tissue optical phantoms applied to the specific challenge of accounting for melanin when using optical systems to extract optical properties and by extension, physiological information, through skin. RESULTS: In this paper, we provide a comprehensive review of material selection and fabrication considerations for the design of tissue optical phantoms. We then describe how tissue optical phantoms are designed and used for specific optical modalities, emphasizing both recent developments and current limitations, and making the argument for more standardization and detailed reporting of tissue phantom production. CONCLUSIONS: Throughout this review, we provide the reader with practical "how to" information for the production of tissue phantoms that are targeted for the optical modality and characterization goal. As innovative optical imaging and spectroscopy technologies are continually developed, rigorous testing and validation with well-designed optical phantoms are necessary.