Performance Test Methods for Evaluation of Fluorescence Imaging Systems
Catalog of Regulatory Science Tools to Help Assess New Medical Devices
Technical Description
This tool is a set of phantom-based test methods for objective, quantitative evaluation of fluorescence imaging system performance. Tests for key image quality characteristics are presented based on simple fluorescence-dye-doped targets and turbid phantoms based on epoxy with scattering dopants. Additionally, the penetration depth phantom was fabricated using photopolymer resins in a 3D printer. The test characteristics include spatial resolution, uniformity, sensitivity, linearity, field of view, depth of field, spectral crosstalk, and penetration depth. Basic optical properties were validated with spectrophotometry. The test methods have been implemented as a demonstration of how this tool can be used to characterize the performance of a custom benchtop near-infrared fluorescence imaging system. Further information is provided in the journal article: Performance test methods for near-infrared fluorescence imaging.
Intended Purpose
This tool was developed to facilitate fabrication of phantom-based performance test methods for near-infrared fluorescence imaging with indocyanine green or optically similar dyes. By changing the dye dopant, it may be possible to adapt this tool for evaluation of exogenous fluorescence imaging systems operating at other visible or near-infrared wavelengths, or those used to detect endogenous tissue fluorescence.
Specific product areas or product codes: MRK, OAY, IZI, QCR, QJF, GCJ, NAY
There are several ways this tool can facilitate product development and regulatory evaluation. It can enable researchers developing/optimizing new imaging systems to evaluate the impact of changes in system design in a well-controlled manner.
It can be used to evaluate and/or compare the performance of imaging systems, using well established objective metrics such as contrast transfer functions, depth of field, etc. The models could also be used for constancy testing over time during clinical use (or clinical study) of an imaging system, or as basic training tools for clinicians.
As regulatory pathways for exogenous fluorescence imagers transition from a combination-product approach to separate evaluations for agents and devices, such test methods can provide evidence of device capability or equivalence with a predicate device for measuring the same fluorescent dye. Alternately, such models could be used to assess the ability of a single imaging system using fluorophores with different spectral characteristics.
The intended tool user population is primarily biophotonics researchers, device developers, medical technologists, although the models may be useful for clinicians as well.
Training in fabrication of polymer phantoms and is recommended to generate high quality tools based on the instructions provided. Specific product areas or product codes. Scope may also be broader (implanted devices, internal use products, reusable device, sterility, biocompatibility, etc.).
Testing
Validation of the optical properties and morphology of phantoms based on the digital files described here is presented in the previously mentioned journal article. This involved performing measurements of fluorescence yield with a high-quality benchtop spectrofluorometer and measuring absorption and scattering coefficients with a spectrophotometer.
Demonstration of the use of this tool in evaluating fluorescence image quality is also provided in the aforementioned journal article as a validation of its basic functionality in objective quantitation of device performance. This demonstration involved imaging phantoms with a custom benchtop fluorescence imaging system and processing acquired data to generate key quality metrics.
Limitations
The fluorescence characteristics of these phantoms are somewhat limited in their stability and may require fabrication of new models every two months. This may reduce the potential of these phantoms for long-term constancy testing.
A method for characterizing device distortion – which is particularly relevant for endoscopic imaging systems – has not yet been developed.
Supporting Documentation
The publication below includes supporting information regarding how to fabricate effective phantoms, and how to acquire and process images to generate key image quality metrics.
Kanniyappan, U., Wang, B., Yang, C., Ghassemi, P., Litorja, M., Suresh, N., Wang, Q., Chen, Y. and Pfefer, T.J. (2020), Performance test methods for near-infrared fluorescence imaging. Med. Phys., 47: 3389-3401. https://doi.org/10.1002/mp.14189
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Tool Reference
In addition to citing relevant publications please reference the use of this tool using DOI: 10.5281/zenodo.8229398
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