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The literature is replete with preclinical and some clinical studies showing the utility of fluorescence guided surgery with fluorescence images reported in “arbitrary units” or (AUs) that can vary with radiometric set-up, tissue optical properties, and agent characteristics. Despite several attempts, it is highly unlikely that AUs can be reliably and routinely calibrated to international standard units (SI units) that is reflective of the amount of probe distributed within tissues. Perhaps more concerning is that there is no industry standard or radiometric performance criteria for preclinical or clinical fluorescence imaging devices, even though IEC 60601, an international series of technical standards, requires numerical indications of performance of medical devices to be in SI units or SI-units for traceability. Using stable phantoms developed by us and our colleagues at NIST1, we have devised approaches to use radiometric principles to qualify device performance and calibrate image output in terms of SI units. In this presentation, we review the performance of marketed clinical devices as reported in SI units and compare SI-derived metrics of commercially available fluorescence imaging devices. Clearly, the efficacy of a fluorescence molecular imaging agent is critically dependent upon the performance of an imaging device and the future success of fluorescence guided surgery depends critically upon community and industry adoption of performance standards for devices.
1Zhu, B., Rasmussen, J.C., Litorja, M., and E.M. Sevick-Muraca, “Determining the performance of fluorescence imaging devices using traceable working standards with SI units of radiance,” IEEE Trans. Med. Imaging, 35(3): 802-11, 2016, PMID: 26552078
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