A Review of Image Sensors Used in Near-Infrared and Shortwave Infrared Fluorescence Imaging

To translate near-infrared (NIR) and shortwave infrared (SWIR) fluorescence imaging into the clinic, the paired imaging device needs to detect trace doses of fluorescent imaging agents. Except for the filtration scheme and excitation light source, the image sensor used will finally determine the detection limitations of NIR and SWIR fluorescence imaging systems. In this review, we investigate the current state-of-the-art image sensors used in NIR and SWIR fluorescence imaging systems and discuss the advantages and limitations of their characteristics, such as readout architecture and noise factors. Finally, the imaging performance of these image sensors is evaluated and compared.

AAPM Task Group Report 311: Guidance for performance evaluation of fluorescence-guided surgery systems

The last decade has seen a large growth in fluorescence-guided surgery (FGS) imaging and interventions. With the increasing number of clinical specialties implementing FGS, the range of systems with radically different physical designs, image processing approaches, and performance requirements is expanding. This variety of systems makes it nearly impossible to specify uniform performance goals, yet at the same time, utilization of different devices in new clinical procedures and trials indicates some need for common knowledge bases and a quality assessment paradigm to ensure that effective translation and use occurs. It is feasible to identify key fundamental image quality characteristics and corresponding objective test methods that should be determined such that there are consistent conventions across a variety of FGS devices. This report outlines test methods, tissue simulating phantoms and suggested guidelines, as well as personnel needs and professional knowledge bases that can be established. This report frames the issues with guidance and feedback from related societies and agencies having vested interest in the outcome, coming from an independent scientific group formed from academics and international federal agencies for the establishment of these professional guidelines.

Imaging peripheral lymphatic dysfunction in chronic conditions

The lymphatics play important roles in chronic diseases/conditions that comprise the bulk of healthcare worldwide. Yet the ability to routinely image and diagnose lymphatic dysfunction, using commonly available clinical imaging modalities, has been lacking and as a result, the development of effective treatment strategies suffers. Nearly two decades ago, investigational near-infrared fluorescence lymphatic imaging and ICG lymphography were developed as routine diagnostic for clinically evaluating, quantifying, and treating lymphatic dysfunction in cancer-related and primary lymphedema, chronic venous disease, and more recently, autoimmune and neurodegenerative disorders. In this review, we provide an overview of what these non-invasive technologies have taught us about lymphatic (dys) function and anatomy in human studies and in corollary animal studies of human disease. We summarize by commenting on new impactful clinical frontiers in lymphatic science that remain to be facilitated by imaging.

Biomimetic tissue phantoms for neurosurgical near-infrared fluorescence imaging

SIGNIFICANCE

Neurosurgical fluorescence imaging is a well-established clinical approach with a growing range of indications for use. However, this technology lacks effective phantom-based tools for development, performance testing, and clinician training.

AIM

Our primary aim was to develop and evaluate 3D-printed phantoms capable of optically and morphologically simulating neurovasculature under fluorescence angiography.

APPROACH

Volumetric digital maps of the circle of Willis with basilar and posterior communicator artery aneurysms, along with surrounding cerebral tissue, were generated. Phantoms were fabricated with a stereolithography printer using custom photopolymer composites, then visualized under white light and near-infrared fluorescence imaging.

RESULTS

Feature sizes of printed components were found to be within 13% of digital models. Phantoms exhibited realistic optical properties and convincingly recapitulated fluorescence angiography scenes.

CONCLUSIONS

Methods identified in this study can facilitate the development of realistic phantoms as powerful new tools for fluorescence imaging.

Applications of Indocyanine Green-Guided Near-Infrared Fluorescence Imaging in Pediatric Minimally Invasive Surgery Urology: A Narrative Review

Background: Indocyanine green (ICG) is a fluorescent dye used for several indications in adult surgery, and, more recently, adopted also in the pediatric patients. This study aimed to review the literature published on the use of ICG near-infrared fluorescence (NIRF) in pediatric urology, to address its shortcomings and disadvantages and to detect the future perspectives. Materials and Methods: An electronic literature search of PubMed on all studies reporting use of ICG-NIRF in pediatrics was performed. We included only studies reporting ICG-NIRF application in minimally invasive surgery (MIS) for pediatric urology indications. Results: Forty-two articles reporting MIS procedures performed using ICG-NIRF in children were obtained, but only 15 studies that focused on urological applications of ICG-NIRF in children were included in this review. The included studies described use of ICG-NIRF for kidney malformations such as duplex system, kidney tumors, renal cysts, ureteral pathology, bladder malformations, varicocele, and lymph node sampling in tumors. The pediatric urological applications in which ICG-NIRF provided significant advantages included partial nephrectomy, lymphatics sparing varicocele repair, and oncological procedures. The ICG-NIRF use was clinically safe, without reported adverse systemic reactions in all pediatric series. The main drawback of this technology is the need of specific laparoscopic equipment such as camera system, light sources, and telescopes or the da Vinci Xi Robot, with the software for ICG-NIRF, Firefly^®, already integrated within. Conclusions: ICG-enhanced fluorescence-guided surgery is gaining growing popularity among pediatric surgeons due to the excellent results that have been published until now. ICG-NIRF technology has proven to be safe, easy to use, not time-consuming, cheap, and very effective to improve intraoperative view and surgical ability. Nonetheless, further evidence, including larger series, longer follow-up, and more specific assessments, is necessary to confirm the preliminary results and enlarge the applications.

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

A lack of accepted standards and standardized phantoms suitable for the technical validation of biophotonic instrumentation hinders the reliability and reproducibility of its experimental outputs. In this Perspective, we discuss general criteria for the design of tissue-mimicking biophotonic phantoms, and use these criteria and state-of-the-art developments to critically review the literature on phantom materials and on the fabrication of phantoms. By focusing on representative examples of standardization in diffuse optical imaging and spectroscopy, fluorescence-guided surgery and photoacoustic imaging, we identify unmet needs in the development of phantoms and a set of criteria (leveraging characterization, collaboration, communication and commitment) for the standardization of biophotonic instrumentation.

Standardization and implementation of fluorescence molecular endoscopy in the clinic

SIGNIFICANCE

Near-infrared fluorescence molecular endoscopy (NIR-FME) is an innovative technique allowing for in vivo visualization of molecular processes in hollow organs. Despite its potential for clinical translation, NIR-FME still faces challenges, for example, the lack of consensus in performing quality control and standardization of procedures and systems. This may hamper the clinical approval of the technology by authorities and its acceptance by endoscopists. Until now, several clinical trials using NIR-FME have been performed. However, most of these trials had different study designs, making comparison difficult.

AIM

We describe the need for standardization in NIR-FME, provide a pathway for setting up a standardized clinical study, and describe future perspectives for NIR-FME. Body: Standardization is challenging due to many parameters. Invariable parameters refer to the hardware specifications. Variable parameters refer to movement or tissue optical properties. Phantoms can be of aid when defining the influence of these variables or when standardizing a procedure.

CONCLUSION

There is a need for standardization in NIR-FME and hurdles still need to be overcome before a widespread clinical implementation of NIR-FME can be realized. When these hurdles are overcome, clinical outcomes can be compared and systems can be benchmarked, enabling clinical implementation.

Propagation of structured light through tissue-mimicking phantoms

Optical interrogation of tissues is broadly considered in biomedical applications. Nevertheless, light scattering by tissue limits the resolution and accuracy achieved when investigating sub-surface tissue features. Light carrying optical angular momentum or complex polarization profiles, offers different propagation characteristics through scattering media compared to light with unstructured beam profiles. Here we discuss the behaviour of structured light scattered by tissue-mimicking phantoms. We study the spatial and the polarization profile of the scattered modes as a function of a range of optical parameters of the phantoms, with varying scattering and absorption coefficients and of different lengths. These results show the non-trivial trade-off between the advantages of structured light profiles and mode broadening, stimulating further investigations in this direction.

Performance test methods for near-infrared fluorescence imaging

PURPOSE

Near-infrared fluorescence (NIRF) imaging using exogenous contrast has gained much attention as a technique for enhancing visualization of vasculature using untargeted agents, as well as for the detection and localization of cancer with targeted agents. In order to address the emerging need for standardization of NIRF imaging technologies, it is necessary to identify the best practices suitable for objective, quantitative testing of key image quality characteristics. Toward the development of a battery of test methods that are rigorous yet applicable to a wide variety of devices, we have evaluated techniques for phantom design, measurement, and calculation of specific performance metrics.

METHODS

Using a NIRF imaging system for indocyanine green imaging, providing excitation at 780 nm and detection above 830 nm, we explored methods to evaluate uniformity, field of view, spectral crosstalk, spatial resolution, depth of field, sensitivity, linearity, and penetration depth. These measurements were performed using fluorophore-doped multiwell plate and high turbidity planar phantoms, as well as a 3D-printed multichannel phantom and a USAF 1951 resolution target.

RESULTS AND CONCLUSIONS

Based on a wide range of approaches described in medical and fluorescence imaging literature, we have developed and demonstrated a cohesive battery of test methods for evaluation of fluorescence image quality in wide-field imagers. We also propose a number of key metrics that can facilitate direct, quantitative comparison of device performance. These methods have the potential to facilitate more uniform evaluation and inter-comparison of clinical and preclinical imaging systems than is typically achieved, with the long-term goal of establishing international standards for fluorescence image quality assessment.

Optical and Optoacoustic Imaging

The present chapter summarizes progress with optical methods that go beyond human vision. The focus is on two particular technologies: fluorescence molecular imaging and optoacoustic (photoacoustic) imaging. The rationale for the selection of these two methods is that in contrast to optical microscopy techniques, both fluorescence and optoacoustic imaging can achieve large fields of view, i.e., spanning several centimeters in two or three dimensions. Such fields of views relate better to human vision and can visualize large parts of tissue, a necessary premise for clinical detection. Conversely, optical microscopy methods only scan millimeter-sized dimensions or smaller. With such operational capacity, optical microscopy methods need to be guided by another visualization technique in order to scan a very specific area in tissue and typically only provide superficial measurements, i.e., information from depths that are of the order of 0.05-1 mm. This practice has generally limited their clinical applicability to some niche applications, such as optical coherence tomography of the retina. On the other hand, fluorescence molecular imaging and optoacoustic imaging emerge as more global optical imaging methods with wide applications in surgery, endoscopy, and non-invasive clinical imaging, as summarized in the following. The current progress in this field is based on a volume of recent review and other literature that highlights key advances achieved in technology and biomedical applications. Context and figures from references from the authors of this chapter have been used here, as it reflects our general view of the current status of the field.

Prototype Small-Animal PET-CT Imaging System for Image-guided Radiation Therapy

Molecular imaging is becoming essential for precision targeted radiation therapy, yet progress is hindered from a lack of integrated imaging and treatment systems. We report the development of a prototype positron emission tomography (PET) scanner integrated into a commercial cone beam computed tomography (CBCT) based small animal irradiation system for molecular-image-guided, targeted external beam radiation therapy. The PET component consists of two rotating Hamamatsu time-of-flight PET modules positioned with a bore diameter of 101.6 mm and a radial field-of-view of 53.1 mm. The measured energy resolution after linearity correction at 511 KeV was 12.9% and the timing resolution was 283.6 ps. The measured spatial resolutions at the field-of-view center and 5 mm off the radial center were 2.6 mm × 2.6 mm × 1.6 mm and 2.6 mm × 2.6 mm × 2.7 mm respectively. 18F-Fluorodeoxyglucose-based PET imaging of a NEMA NU 4-2008 phantom resolved cylindrical volumes with diameters as small as 3 mm. To validate the system in-vivo, we performed 64Cu-DOTA-M5A PET and computed tomography (CT) imaging of carcinoembryonic antigen (CEA)-positive colorectal cancer in athymic nude mice and compared the results with a commercially available Siemens Inveon PET/CT system. The prototype PET system performed comparably to the Siemens system for identifying the location, size, and shape of tumors. Regions of heterogeneous 64Cu-DOTA-M5A uptake were observed. Using 64Cu-DOTA-M5A PET and CT images, a Monte Carlo-based radiation treatment plan was created to escalate the dose to the 64Cu-DOTA-M5A-based, highly active, biological target volume while largely sparing the normal tissue. Results demonstrate the feasibility of molecular-image-guided treatment plans using the prototype theranostic system.

Multi-Parametric Standardization of Fluorescence Imaging Systems Based on a Composite Phantom

OBJECTIVE

Fluorescence molecular imaging (FMI) has emerged as a promising tool for surgical guidance in oncology, with one of the few remaining challenges being the ability to offer quality control and data referencing. This paper investigates the use of a novel composite phantom to correct and benchmark FMI systems.

METHODS

This paper extends on previous work by describing a phantom design that can provide a more complete assessment of FMI systems through quantification of dynamic range and determination of spatial illumination patterns for both reflectance and fluorescence imaging. Various performance metrics are combined into a robust and descriptive "system benchmarking score," enabling not only the comprehensive comparison of different systems, but also for the first time, correction of the acquired data.

RESULTS

We show that systems developed for targeted fluorescence imaging can achieve benchmarking scores of up to 70%, while clinically available systems optimized for indocyanine green are limited to 50%, mostly due to greater leakage of ambient and excitation illumination and lower resolution. The image uniformity can also be approximated and employed for image flat-fielding, an important milestone toward data referencing. In addition, we demonstrate composite phantom use in assessing the performance of a surgical microscope and of a raster-scan imaging system.

CONCLUSION

Our results suggest that the new phantom has the potential to support high-fidelity FMI through benchmarking and image correction.

SIGNIFICANCE

Standardization of the FMI is a necessary process for establishing good imaging practices in clinical environments and for enabling high-fidelity imaging across patients and multi-center imaging studies.

Multiplexed imaging for diagnosis and therapy

Complex molecular and metabolic phenotypes depict cancers as a constellation of different diseases with common themes. Precision imaging of such phenotypes requires flexible and tunable modalities capable of identifying phenotypic fingerprints by using a restricted number of parameters while ensuring sensitivity to dynamic biological regulation. Common phenotypes can be detected by in vivo imaging technologies, and effectively define the emerging standards for disease classification and patient stratification in radiology. However, for the imaging data to accurately represent a complex fingerprint, the individual imaging parameters need to be measured and analysed in relation to their wider spatial and molecular context. In this respect, targeted palettes of molecular imaging probes facilitate the detection of heterogeneity in oncogene-driven alterations and their response to treatment, and lead to the expansion of rational-design elements for the combination of imaging experiments. In this Review, we evaluate criteria for conducting multiplexed imaging, and discuss its opportunities for improving patient diagnosis and the monitoring of therapy.

Benchmarking of fluorescence cameras through the use of a composite phantom

Fluorescence molecular imaging (FMI) has shown potential to detect and delineate cancer during surgery or diagnostic endoscopy. Recent progress on imaging systems has allowed sensitive detection of fluorescent agents even in video rate mode. However, lack of standardization in fluorescence imaging challenges the clinical application of FMI, since the use of different systems may lead to different results from a given study, even when using the same fluorescent agent. In this work, we investigate the use of a composite fluorescence phantom, employed as an FMI standard, to offer a comprehensive method for validation and standardization of the performance of different imaging systems. To exclude user interaction, all phantom features are automatically extracted from the acquired epi-illumination color and fluorescence images, using appropriately constructed templates. These features are then employed to characterize the performance and compare different cameras to each other. The proposed method could serve as a framework toward the calibration and benchmarking of FMI systems, to facilitate their clinical translation.

Comprehensive phantom for interventional fluorescence molecular imaging

Fluorescence imaging has been considered for over a half-century as a modality that could assist surgical guidance and visualization. The administration of fluorescent molecules with sensitivity to disease biomarkers and their imaging using a fluorescence camera can outline pathophysiological parameters of tissue invisible to the human eye during operation. The advent of fluorescent agents that target specific cellular responses and molecular pathways of disease has facilitated the intraoperative identification of cancer with improved sensitivity and specificity over nonspecific fluorescent dyes that only outline the vascular system and enhanced permeability effects. With these new abilities come unique requirements for developing phantoms to calibrate imaging systems and algorithms. We briefly review herein progress with fluorescence phantoms employed to validate fluorescence imaging systems and results. We identify current limitations and discuss the level of phantom complexity that may be required for developing a universal strategy for fluorescence imaging calibration. Finally, we present a phantom design that could be used as a tool for interlaboratory system performance evaluation.

Skeletal muscle perfusion and stem cell delivery in muscle disorders using intra-femoral artery canulation in mice

Muscular dystrophies are among major inherited muscle disorders characterized by progressive muscle damage and fibrosis with no definitive cure. Recently, gene or cell based therapies have been developed to restore the missing gene expression or replace the damaged tissues. In order to test the efficiency of these therapies in mice models of muscular dystrophies, the arterial route of delivery is very advantageous as it provides uniform muscle exposure to the therapeutic agents or cells. Although there are few reports of arterial delivery of the therapeutic agents or cells in mice, there is no in-depth description and evaluation of its efficacy in perfusion of downstream muscles. This study is aimed to develop a practical method for intra-femoral artery perfusion in mice and to evaluate perfusion efficiency using near-infrared-fluorescence (NIRF) imaging as well as histology following stem cell delivery. Our results provide a practical guide to perform this delicate method in mice. By using a sensitive fluorescent dye, different muscle groups of the hindlimb have been evaluated for proper perfusion. As the final step, we have validated the efficiency of arterial cell delivery into muscles using human iPS-derived myogenic cells in an immunodeficient mouse model for Duchenne muscular dystrophy (NSG-mdx(4cv)).

A review of performance of near-infrared fluorescence imaging devices used in clinical studies

Near-infrared fluorescence (NIRF) molecular imaging holds great promise as a new "point-of-care" medical imaging modality that can potentially provide the sensitivity of nuclear medicine techniques, but without the radioactivity that can otherwise place limitations of usage. Recently, NIRF imaging devices of a variety of designs have emerged in the market and in investigational clinical studies using indocyanine green (ICG) as a non-targeting NIRF contrast agent to demark the blood and lymphatic vasculatures both non-invasively and intraoperatively. Approved in the USA since 1956 for intravenous administration, ICG has been more recently used off label in intradermal or subcutaneous administrations for fluorescence imaging of the lymphatic vasculature and lymph nodes. Herein, we summarize the devices of a variety of designs, summarize their performance in lymphatic imaging in a tabular format and comment on necessary efforts to develop standards for device performance to compare and use these emerging devices in future, NIRF molecular imaging studies.

A matter of collection and detection for intraoperative and noninvasive near-infrared fluorescence molecular imaging: to see or not to see?

PURPOSE

Although fluorescence molecular imaging is rapidly evolving as a new combinational drug/device technology platform for molecularly guided surgery and noninvasive imaging, there remains no performance standards for efficient translation of "first-in-humans" fluorescent imaging agents using these devices.

METHODS

The authors employed a stable, solid phantom designed to exaggerate the confounding effects of tissue light scattering and to mimic low concentrations (nM-pM) of near-infrared fluorescent dyes expected clinically for molecular imaging in order to evaluate and compare the commonly used charge coupled device (CCD) camera systems employed in preclinical studies and in human investigational studies.

RESULTS

The results show that intensified CCD systems offer greater contrast with larger signal-to-noise ratios in comparison to their unintensified CCD systems operated at clinically reasonable, subsecond acquisition times.

CONCLUSIONS

Camera imaging performance could impact the success of future "first-in-humans" near-infrared fluorescence imaging agent studies.

A peptide probe for targeted brown adipose tissue imaging

The presence of brown adipose tissue responsible for thermogenic energy dissipation has been revealed in adult humans and has high clinical importance. Owing to limitations of current methods for brown adipose tissue detection, analysing the abundance and localization of brown adipose tissue in the body has remained challenging. Here we screen a combinatorial peptide library in mice and characterize a peptide (with the sequence CPATAERPC) that selectively binds to the vascular endothelium of brown adipose tissue, but not of intraperitoneal white adipose tissue. We show that in addition to brown adipose tissue, this peptide probe also recognizes the vasculature of brown adipose tissue-like depots of subcutaneous white adipose tissue. Our results indicate that the CPATAERPC peptide localizes to brown adipose tissue even in the absence of sympathetic nervous system stimulation. Finally, we demonstrate that this probe can be used to identify brown adipose tissue depots in mice by whole-body near-infrared fluorescence imaging.

Small animal fluorescence and bioluminescence tomography: a review of approaches, algorithms and technology update

Emerging fluorescence and bioluminescence tomography approaches have several common, yet several distinct features from established emission tomographies of PET and SPECT. Although both nuclear and optical imaging modalities involve counting of photons, nuclear imaging techniques collect the emitted high energy (100-511 keV) photons after radioactive decay of radionuclides while optical techniques count low-energy (1.5-4.1 eV) photons that are scattered and absorbed by tissues requiring models of light transport for quantitative image reconstruction. Fluorescence imaging has been recently translated into clinic demonstrating high sensitivity, modest tissue penetration depth, and fast, millisecond image acquisition times. As a consequence, the promise of quantitative optical tomography as a complement of small animal PET and SPECT remains high. In this review, we summarize the different instrumentation, methodological approaches and schema for inverse image reconstructions for optical tomography, including luminescence and fluorescence modalities, and comment on limitations and key technological advances needed for further discovery research and translation.

Toward nodal staging of axillary lymph node basins through intradermal administration of fluorescent imaging agents

As part of a proof-of-concept study for future delivery of targeted near-infrared fluorescent (NIRF) tracers, we sought to assess the delivery of micrograms of indocyanine green to all the axillary lymph nodes following intraparenchymal breast injections and intradermal arm injections in 20 subjects with advanced breast carcinoma and undergoing complete axillary lymph node dissection. Lymphatic vessels and nodes were assessed in vivo. Ex vivo images demonstrated that 87% of excised lymph nodes, including 81% of tumor-positive lymph nodes, were fluorescent. Future clinical studies using microdose amounts of tumor-targeting NIRF contrast agents may demonstrate improved surgical intervention with reduced morbidity.

Tumor margin detection using quantitative NIRF molecular imaging targeting EpCAM validated by far red gene reporter iRFP

PURPOSE

Wide-field surgical excision reduces the chance of residual disease, but can also lead to disfigurement and devastating morbidities when resection is close to critical structures. We hypothesize that near-infrared fluorescence (NIRF) imaging can enable accurate detection of tumor margins for image-guided resection.

EXPERIMENTAL DESIGN

An orthotopic model of human prostate cancer (PCa) was used to assess primary tumor margins using a NIRF-labeled antibody against epithelial cell adhesion molecule (EpCAM). PCa cells stably expressing far red fluorescent gene reporter, iRFP, enabled colocalization with NIRF signals for direct assessment of tumor margins.

RESULTS

Using receiver operating characteristic analysis, far red fluorescence was validated against standard pathology of primary and metastatic lesions with >96 % accuracy. Primary tumor margins were more accurately detected by quantitative NIRF imaging using the EpCAM-targeting antibody as compared to a NIRF-labeled isotype control antibody.

CONCLUSIONS

NIRF molecular imaging may enable real-time and accurate assessment of tumor margins.

A compact frequency-domain photon migration system for integration into commercial hybrid small animal imaging scanners for fluorescence tomography

The work presented herein describes the system design and performance evaluation of a miniaturized near-infrared fluorescence (NIRF) frequency-domain photon migration (FDPM) system with non-contact excitation and homodyne detection capability for small animal fluorescence tomography. The FDPM system was developed specifically for incorporation into a Siemens micro positron emission tomography/computed tomography (microPET/CT) commercial scanner for hybrid small animal imaging, but could be adapted to other systems. Operating at 100 MHz, the system noise was minimized and the associated amplitude and phase errors were characterized to be ±0.7% and ±0.3°, respectively. To demonstrate the tomographic ability, a commercial mouse-shaped phantom with 50 µM IRDye800CW and ⁶⁸Ga containing inclusion was used to associate PET and NIRF tomography. Three-dimensional mesh generation and anatomical referencing was accomplished through CT. A third-order simplified spherical harmonics approximation (SP₃) algorithm, for efficient prediction of light propagation in small animals, was tailored to incorporate the FDPM approach. Finally, the PET-NIRF target co-localization accuracy was analyzed in vivo with a dual-labeled imaging agent targeting orthotopic growth of human prostate cancer. The obtained results validate the integration of time-dependent fluorescence tomography system within a commercial microPET/CT scanner for multimodality small animal imaging.

Seeing it through: translational validation of new medical imaging modalities

Medical imaging is an invaluable tool for diagnosis, surgical guidance, and assessment of treatment efficacy. The Network for Translational Research (NTR) for Optical Imaging consists of four research groups working to "bridge the gap" between lab discovery and clinical use of fluorescence- and photoacoustic-based imaging devices used with imaging biomarkers. While the groups are using different modalities, all the groups face similar challenges when attempting to validate these systems for FDA approval and, ultimately, clinical use. Validation steps taken, as well as future needs, are described here. The group hopes to provide translational validation guidance for itself, as well as other researchers.

The role of lymphatics in cancer as assessed by near-infrared fluorescence imaging

The lymphatic system is the secondary circulatory system responsible for fluid homeostasis and protein transport in the body. In addition, because the lymphatic system provides a primary pathway for cancer metastasis, lymph node involvement is routinely used as a determinant in cancer staging. Despite their importance, the lymphatics remain poorly understood, in part because of the historic lack of imaging modalities with sufficient spatial and/or temporal resolution to visualize the fine lymphatic structure and subtle contractile function. In recent years, near-infrared fluorescence (NIRF) imaging has emerged as a new imaging modality to non-invasively visualize the lymphatics and assess contractile lymphatic function in humans following administration of microdose amounts of a NIRF contrast agent. In this contribution, we first review NIRF imaging and its clinical application in sentinel lymph node mapping, intraoperative guidance, and assessing the architecture and contractile function of the lymphatics in health and in cancer-related lymphedema. We then present recent NIRF lymphatic imaging for non-invasive assessment of lymphatics both in preclinical melanoma models and in human subjects with melanoma.