Indocyanine green matching phantom for fluorescence-guided surgery imaging system characterization and performance assessment

Real-time identification of life-threatening necrotizing soft-tissue infections using indocyanine green fluorescence imaging

Significance

Necrotizing soft-tissue infections (NSTIs) are life-threatening infections with a cumulative case fatality rate of 21%. The initial presentation of an NSTI is non-specific, frequently leading to misdiagnosis and delays in care. No current strategies yield an accurate, real-time diagnosis of an NSTI.

Aim

A first-in-kind, observational, clinical pilot study tested the hypothesis that measurable fluorescence signal voids occur in NSTI-affected tissues following intravenous administration and imaging of perfusion-based indocyanine green (ICG) fluorescence. This hypothesis is based on the established knowledge that NSTI is associated with local microvascular thrombosis.

Approach

Adult patients presenting to the Emergency Department of a tertiary care medical center at high risk for NSTI were prospectively enrolled and imaged with a commercial fluorescence imager. Single-frame fluorescence snapshot and first-pass perfusion kinetic parameters-ingress slope (IS), time-to-peak (TTP) intensity, and maximum fluorescence intensity (IMAX)-were quantified using a dynamic contrast-enhanced fluorescence imaging technique. Clinical variables (comorbidities, blood laboratory values), fluorescence parameters, and fluorescence signal-to-background ratios (SBRs) were compared to final infection diagnosis.

Results

Fourteen patients were enrolled and imaged (six NSTI, six cellulitis, one diabetes mellitus-associated gangrene, and one osteomyelitis). Clinical variables demonstrated no statistically significant differences between NSTI and non-NSTI patient groups (p -value ≥ 0.22 ). All NSTI cases exhibited prominent fluorescence signal voids in affected tissues, including tissue features not visible to the naked eye. All cellulitis cases exhibited a hyperemic response with increased fluorescence and no distinct signal voids. Median lesion-to-background tissue SBRs based on snapshot, IS, TTP, and IMAX parameter maps ranged from 3.2 to 9.1, 2.2 to 33.8, 1.0 to 7.5, and 1.5 to 12.7, respectively, for the NSTI patient group. All fluorescence parameters except TTP demonstrated statistically significant differences between NSTI and cellulitis patient groups (p -value < 0.05 ).

Conclusions

Real-time, accurate discrimination of NSTIs compared with non-necrotizing infections may be possible with perfusion-based ICG fluorescence imaging.

Semi-automatic standardized analysis method to objectively evaluate near-infrared fluorescent dyes in image-guided surgery

Significance

Near-infrared fluorescence imaging still lacks a standardized, objective method to evaluate fluorescent dye efficacy in oncological surgical applications. This results in difficulties in translation between preclinical to clinical studies with fluorescent dyes and in the reproduction of results between studies, which in turn hampers further clinical translation of novel fluorescent dyes.

Aim

Our aim is to develop and evaluate a semi-automatic standardized method to objectively assess fluorescent signals in resected tissue.

Approach

A standardized imaging procedure was designed and quantitative analysis methods were developed to evaluate non-targeted and tumor-targeted fluorescent dyes. The developed analysis methods included manual selection of region of interest (ROI) on white light images, automated fluorescence signal ROI selection, and automatic quantitative image analysis. The proposed analysis method was then compared with a conventional analysis method, where fluorescence signal ROIs were manually selected on fluorescence images. Dice similarity coefficients and intraclass correlation coefficients were calculated to determine the inter- and intraobserver variabilities of the ROI selections and the determined signal- and tumor-to-background ratios.

Results

The proposed non-targeted fluorescent dyes analysis method showed statistically significantly improved variabilities after application on indocyanine green specimens. For specimens with the targeted dye SGM-101, the variability of the background ROI selection was statistically significantly improved by implementing the proposed method.

Conclusion

Semi-automatic methods for standardized quantitative analysis of fluorescence images were successfully developed and showed promising results to further improve the reproducibility and standardization of clinical studies evaluating fluorescent dyes.

Development of a morphologically realistic mouse phantom for pre-clinical photoacoustic imaging

BACKGROUND

Characterizations based on anatomically realistic phantoms are highly effective to perform accurate technical validation of imaging systems. Specifically for photoacoustic imaging (PAI), although a variety of phantom models with simplified geometries are reported, an unmet need still exists to establish morphologically realistic heterogeneous pre-clinical phantoms. So the development of a mouse-mimicking phantom can reduce the use of animals for the validation and standardization studies of pre-clinical PAI systems and thus eventually translate the PAI technology to clinical research.

PURPOSE

Here we designed, developed, and fabricated a stable phantom that mimics the detailed morphology of a mouse, to be used as a realistic tool for PAI.

METHODS

The mouse phantom, has been designed by using a combination of image modeling and 3D-printing techniques. As a tissue-mimicking material, we have used copolymer-in-oil-based material that was recently proposed by the International Photoacoustic Standardization Consortium (IPASC). In particular, the anatomically realistic phantom has been modeled by using the real atlas of a mouse as a reference. The mouse phantom includes a 3D-printed skeleton and the main abdominal organs such as the liver, spleen, and kidneys obtained by using doped copolymer-in-oil material with 3D-printed molds. In addition, the acoustic and optical properties of the tissue-mimicking material and the long-term stability have been broadly characterized.

RESULTS

Furthermore, our studies showed that the phantom is durable and stable for more than 200 days, under normal storage and repeated use. Fabrication protocol is easy to reproduce. As a result, the proposed morphologically realistic mouse phantom offers durability, material compatibility, and an unprecedented realistic resemblance to the actual rodents' anatomy in PAI.

CONCLUSION

This durable morphologically realistic mouse phantom would minimize the animal experiments in compliance with the 3R principle of Replacement, Reduction, and Refinement. To our knowledge, this is the first time an anatomically realistic heterogeneous mouse phantom has been proposed for PAI in pre-clinical animal imaging and tested its durability over 200 days.

Assessment of open-field fluorescence guided surgery systems: implementing a standardized method for characterization and comparison

Significance

Fluorescence guided surgery (FGS) has demonstrated improvements in decision making and patient outcomes for a wide range of surgical procedures. Not only can FGS systems provide a higher level of structural perfusion accuracy in tissue reconstruction cases but they can also serve for real-time functional characterization. Multiple FGS devices have been Food and Drug administration (FDA) cleared for use in open and laparoscopic surgery. Despite the rapid growth of the field, there has been a lack standardization methods.

Aim

This work overviews commonalities inherent to optical imaging methods that can be exploited to produce such a standardization procedure. Furthermore, a system evaluation pipeline is proposed and executed through the use of photo-stable indocyanine green fluorescence phantoms. Five different FDA-approved open-field FGS systems are used and evaluated with the proposed method.

Approach

The proposed pipeline encompasses the following characterization: (1) imaging spatial resolution and sharpness, (2) sensitivity and linearity, (3) imaging depth into tissue, (4) imaging system DOF, (5) uniformity of illumination, (6) spatial distortion, (7) signal to background ratio, (8) excitation bands, and (9) illumination wavelength and power.

Results

The results highlight how such a standardization approach can be successfully implemented for inter-system comparisons as well as how to better understand essential features within each FGS setup.

Conclusions

Despite clinical use being the end goal, a robust yet simple standardization pipeline before clinical trials, such as the one presented herein, should benefit regulatory agencies, manufacturers, and end-users to better assess basic performance and improvements to be made in next generation FGS systems.

Impact of Surgical Lights on the Performance of Fluorescence-Guided Surgery Systems: A Pilot Study

Fluorescence-guided surgery can aid in the intraoperative visualization of target tissues, with promising applications in human and veterinary surgical oncology. The aim of this study was to evaluate the performances of two fluoresce camera systems, IC-Flow^TM and Visionsense^TM VS3 Iridum, for the detection of two non-targeted (ICG and IRDye-800) and two targeted fluorophores (Angiostamp^TM and FAP-Cyan) under different room light conditions, including ambient light, new generation LED, and halogen artificial light sources, which are commonly used in operating theaters. Six dilutions of the fluorophores were imaged in phantom kits using the two camera systems. The limit of detection (LOD) and mean signal-to-background ratio (mSBR) were determined. The highest values of mSBR and a lower LOD were obtained in dark conditions for both systems. Under room lights, the capabilities decreased, but the mSBR remained greater than 3 (=clearly detectable signal). LOD and mSBR worsened under surgical lights for both camera systems, with a greater impact from halogen bulbs on Visionsense^TM VS3 Iridium and of the LED lights on IC-Flow due to a contribution of these lights in the near-infrared spectrum. When considering implementing FGS into the clinical routine, surgeons should cautiously evaluate the spectral contribution of the lights in the operating theater.

Mucins as contrast agent targets for fluorescence-guided surgery of pancreatic cancer

Pancreatic cancer is difficult to resect due to its unique challenges, often leading to incomplete tumor resections. Fluorescence-guided surgery (FGS), also known as intraoperative molecular imaging and optical surgical navigation, is an intraoperative tool that can aid surgeons in complete tumor resection through an increased ability to detect the tumor. To target the tumor, FGS contrast agents rely on biomarkers aberrantly expressed in malignant tissue compared to normal tissue. These biomarkers allow clinicians to identify the tumor and its stage before surgical resection and provide a contrast agent target for intraoperative imaging. Mucins, a family of glycoproteins, are upregulated in malignant tissue compared to normal tissue. Therefore, these proteins may serve as biomarkers for surgical resection. Intraoperative imaging of mucin expression in pancreatic cancer can potentially increase the number of complete resections. While some mucins have been studied for FGS, the potential ability to function as a biomarker target extends to the entire mucin family. Therefore, mucins are attractive proteins to investigate more broadly as FGS biomarkers. This review summarizes the biomarker traits of mucins and their potential use in FGS for pancreatic cancer.

Stable tissue-mimicking phantoms for longitudinal multimodality imaging studies that incorporate optical, CT, and MRI contrast

Significance

Tissue phantoms that mimic the optical and radiologic properties of human or animal tissue play an important role in the development, characterization, and evaluation of imaging systems. Phantoms that are easily produced and stable for longitudinal studies are highly desirable.

Aim

A new type of long-lasting phantom was developed with commercially available materials and was assessed for fabrication ease, stability, and optical property control. Magnetic resonance imaging (MRI) and x-ray computed tomography (CT) contrast properties were also evaluated.

Approach

A systematic investigation of relationships between concentrations of skin-like pigments and composite optical properties was conducted to realize optical property phantoms in the red and near-infrared (NIR) wavelength range that also offered contrast for CT and MRI.

Results

Phantom fabrication time was < 1    h and did not involve any heating or cooling processes. Changes in optical properties were < 2 % over a 12-month period. Phantom optical and spectral features were similar to human soft tissue over the red to NIR wavelength ranges. Pigments used in the study also had CT and MRI contrasts for multimodality imaging studies.

Conclusions

The phantoms described here mimic optical properties of soft tissue and are suitable for multimodality imaging studies involving CT or MRI without adding secondary contrast agents.

Solid optical tissue phantom tools based on upconverting nanoparticles for biomedical applications

SIGNIFICANCE

Phantoms play a critical role in the development of biophotonics techniques. There is a lack of novel phantom tools in the emerging field of upconverting nanoparticles (UCNPs) for biophotonics application. This work provides a range of UCNP-based phantom tools and a manufacturing recipe to bridge the gap and accelerate the development of UCNP-based biophotonics applications.

AIM

The study aims to provide a well-characterized UCNP-based solid phantom recipe and set of phantom tools to address a wide range of UCNP-based biophotonics applications.

APPROACH

A solid phantom recipe based on silicone matrix was developed to manufacture UCNP-based phantoms. A lab built UCNP imaging system was used to characterize upconverted fluorescence emission of phantoms for linearity, homogeneity, and long-term stability. A photon time-of-flight spectroscopy technique was used to characterize the optical properties of the phantoms.

RESULTS

In total, 24 phantoms classified into 4 types, namely homogeneous, multilayer, inclusion, and base phantoms, were manufactured. The phantoms exhibit linear behavior over the dosage range of UCNPs. The phantoms were found to be stable over a limited observed period of 4 months with a coefficient of variation of < 4 % . The deep tissue imaging case showed that increasing the thickness of tissue reduced the UCNP emission.

CONCLUSIONS

A first-of-its-kind UCNP-based solid phantom recipe was developed, and four types of UCNP phantom tools to explore biophotonics applications were presented. The UCNP phantoms exhibited a linear behavior with dosage and were stable over time. An example case showed the potential use of the phantom for deep tissue imaging applications. With recent advance in the use of UCNPs for biophotonics, we believe our recipe and tools will play a pivotal role in the growth of the UCNPs for biophotonics applications.

3D-Printed Tumor Phantoms for Assessment of In Vivo Fluorescence Imaging Analysis Methods

PURPOSE

Interventional fluorescence imaging is increasingly being utilized to quantify cancer biomarkers in both clinical and preclinical models, yet absolute quantification is complicated by many factors. The use of optical phantoms has been suggested by multiple professional organizations for quantitative performance assessment of fluorescence guidance imaging systems. This concept can be further extended to provide standardized tools to compare and assess image analysis metrics.

PROCEDURES

3D-printed fluorescence phantoms based on solid tumor models were developed with representative bio-mimicking optical properties. Phantoms were produced with discrete tumors embedded with an NIR fluorophore of fixed concentration and either zero or 3% non-specific fluorophore in the surrounding material. These phantoms were first imaged by two fluorescence imaging systems using two methods of image segmentation, and four assessment metrics were calculated to demonstrate variability in the quantitative assessment of system performance. The same analysis techniques were then applied to one tumor model with decreasing tumor fluorophore concentrations.

RESULTS

These anatomical phantom models demonstrate the ability to use 3D printing to manufacture anthropomorphic shapes with a wide range of reduced scattering (μ_s': 0.24-1.06 mm^-1) and absorption (μ_a: 0.005-0.14 mm^-1) properties. The phantom imaging and analysis highlight variability in the measured sensitivity metrics associated with tumor visualization.

CONCLUSIONS

3D printing techniques provide a platform for demonstrating complex biological models that introduce real-world complexities for quantifying fluorescence image data. Controlled iterative development of these phantom designs can be used as a tool to advance the field and provide context for consensus-building beyond performance assessment of fluorescence imaging platforms, and extend support for standardizing how quantitative metrics are extracted from imaging data and reported in literature.

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.

Optical Tissue Phantoms for Quantitative Evaluation of Surgical Imaging Devices

Optical tissue phantoms (OTPs) have been extensively applied to the evaluation of imaging systems and surgical training. Due to their human tissue-mimicking characteristics, OTPs can provide accurate optical feedback on the performance of image-guided surgical instruments, simulating the biological sizes and shapes of human organs, and preserving similar haptic responses of original tissues. This review summarizes the essential components of OTPs (i.e., matrix, scattering and absorbing agents, and fluorophores) and the various manufacturing methods currently used to create suitable tissue-mimicking phantoms. As photobleaching is a major challenge in OTP fabrication and its feedback accuracy, phantom photostability and how the photobleaching phenomenon can affect their optical properties are discussed. Consequently, the need for novel photostable OTPs for the quantitative evaluation of surgical imaging devices is emphasized.

Early identification of life-threatening soft-tissue infection using dynamic fluorescence imaging: first-in-kind clinical study of first-pass kinetics

Necrotizing soft-tissue infections (NSTIs) are aggressive and deadly. Immediate surgical debridement is standard-of-care, but patients often present with non-specific symptoms, thereby delaying treatment. Because NSTIs cause microvascular thrombosis, we hypothesized that perfusion imaging using indocyanine green (ICG) would show diminished fluorescence signal in NSTI-affected tissues, particularly compared to non-necrotizing, superficial infections. Through a first-in-kind clinical study, we performed first-pass ICG fluorescence perfusion imaging of patients with suspected NSTIs. Early results support our hypothesis that ICG signal voids occur in NSTI-affected tissues and that dynamic contrast-enhanced fluorescence parameters reveal tissue kinetics that may be related to disease progression and extent.

Performance of two clinical fluorescence imaging systems with different targeted and non-targeted near-infrared fluorophores: a cadaveric explorative study

Introduction

Near-infrared (NIR) fluorescence-guided surgery is increasingly utilized in humans and pets. As clinical imaging systems are optimized for Indocyanine green (ICG) detection, the usage of targeted dyes necessitates the validation of these systems for each dye. We investigated the impact of skin pigmentation and tissue overlay on the sensitivity of two NIR cameras (IC-Flow^TM, Visionsense^TM VS3 Iridum) for the detection of non-targeted (ICG, IRDye800) and targeted (Angiostamp^TM, FAP-Cyan) NIR fluorophores in an ex vivo big animal model.

Methods

We quantitatively measured the limit of detection (LOD) and signal-to-background ratio (SBR) and implemented a semi-quantitative visual score to account for subjective interpretation of images by the surgeon.

Results

Visionsense^TM VS3 Iridum outperformed IC-Flow^TM in terms of LOD and SBR for the detection of all dyes except FAP-Cyan. Median SBR was negatively affected by skin pigmentation and tissue overlay with both camera systems. Level of agreement between quantitative and semi-quantitative visual score and interobserver agreement were better with Visionsense^TM VS3 Iridum.

Conclusion

The overlay of different tissue types and skin pigmentation may negatively affect the ability of the two tested camera systems to identify nanomolar concentrations of targeted-fluorescent dyes and should be considered when planning surgical applications.

Quantitative tumor depth determination using dual wavelength excitation fluorescence

Quantifying solid tumor margins with fluorescence-guided surgery approaches is a challenge, particularly when using near infrared (NIR) wavelengths due to increased penetration depths. An NIR dual wavelength excitation fluorescence (DWEF) approach was developed that capitalizes on the wavelength-dependent attenuation of light in tissue to determine fluorophore depth. A portable dual wavelength excitation fluorescence imaging system was built and tested in parallel with an NIR tumor-targeting fluorophore in tissue mimicking phantoms, chicken tissue, and in vivo mouse models of breast cancer. The system showed high accuracy in all experiments. The low cost and simplicity of this approach make it ideal for clinical use.

Validation of a surgical training model containing indocyanine green for near‐infrared fluorescence imaging

Objective

To determine the efficacy of a surgical training model for fluorescence‐guided cancer surgery and validate its utility to detect any residual tumors after tumor resection using electrocautery.

Methods

We developed surgical training models containing indocyanine green (ICG) for near‐infrared (NIR) fluorescence imaging using a root vegetable organic material (konjac). After the fluorescence assessment for the models, the surgical simulation for fluorescence‐guided cancer surgery using electrocautery was performed. ICG‐containing tumors were divided into two surgical groups: “Enucleation” (removal of the entire visible tumor) and “Complete resection” (removal of the tumor with an appropriate 5‐mm surgical margin).

Results

All 12 ICG‐containing tumors were clearly visible from the normal view but not from the flipped view. The tumor resection time was significantly longer in the “Complete resection” group than in the “Enucleation” group (p < .001). The ICG‐containing tumors showed a high tumor‐to background ratio from the normal (average = 45.8) and flipped (average = 19.2) views, indicating that the models including ICG‐containing tumors were useful for a surgical simulation in fluorescence‐guided surgery. The average mean fluorescence intensity of the wound bed was significantly higher in the “Enucleation” group than in the “Complete resection” group (p < .01). No decrease in fluorescence signal was found in the wound bed even at 2 days postresection.

Conclusion

Our surgical training model containing a fluorescent agent is safe, inexpensive, not harmful for humans, and easy to dispose after use. Our model would be beneficial for surgeons to learn NIR fluorescence imaging and to accelerate fluorescence‐guided cancer surgery into clinical application.

3D-printed tissue-simulating phantoms for near-infrared fluorescence imaging of rheumatoid diseases

SIGNIFICANCE

Fluorescence imaging of rheumatoid diseases with indocyanine green (ICG) is an emerging technique with unique potential for diagnosis and therapy. Device characterization, monitoring of the performance, and further developments of the technique require tissue-equivalent fluorescent phantoms of high stability with appropriate anatomical shapes.

AIM

Our investigations aim at the development of a three-dimensional (3D) printing technique to fabricate hand and finger models with appropriate optical properties in the near-infrared spectral range. These phantoms should have fluorescence properties similar to ICG, and excellent photostability and durability over years.

APPROACH

We modified a 3D printing methacrylate photopolymer by adding the fluorescent dye Lumogen IR 765 to the raw material. Reduced scattering and absorption coefficients were adjusted to values representative of the human hand by incorporating titanium dioxide powder and black ink. The properties of printed phantoms of various compositions were characterized using UV/Vis and fluorescence spectroscopy, and time-resolved measurements. Photostability and bleaching were investigated with a hand imager. For comparison, several phantoms with ICG as fluorescent dye were printed and characterized as well.

RESULTS

The spectral properties of Lumogen IR 765 are very similar to those of ICG. By optimizing the concentrations of Lumogen, titanium dioxide, and ink, anatomically shaped hand and vessel models with properties equivalent to in vivo investigations with a fluorescence hand imager could be printed. Phantoms with Lumogen IR 765 had an excellent photostability over up to 4 years. In contrast, phantoms printed with ICG showed significant bleaching and degradation of fluorescence over time.

CONCLUSIONS

3D printing of phantoms with Lumogen IR 765 is a promising method for fabricating anatomically shaped fluorescent tissue models of excellent stability with spectral properties similar to ICG. The phantoms are well-suited to monitor the performance of hand imagers. Concepts can easily be transferred to other fluorescence imaging applications of ICG.

Conversion of imager-specific response to tissue phantom fluorescence into system of units-traceable units

SIGNIFICANCE

The fluorescence-guided imaging for surgical intervention community recognizes the need for performance standards for these imaging devices. Tissue phantoms are used to track an imager's performance as a fluorescence detector, but imager-specific units are of limited utility.

AIM

Tissue phantoms can be calibrated to be traceable to the international system of units (SI) and in turn be used to calibrate imagers such that fluorescence measurements can be reported in universally accepted units.

APPROACH

The radiometry to convert imager-specific arbitrary digital counts to SI-traceable unit of watts is described in this paper.

RESULTS

An example of an imager calibration is included.

CONCLUSIONS

Calibrated tissue phantoms become a tool for metrological traceability.

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.

Heterogeneity in Utilization of Optical Imaging Guided Surgery for Identifying or Preserving the Parathyroid Glands—A Meta-Narrative Review

Background: Postoperative hypoparathyroidism is the most common complication after total thyroidectomy. Over the past years, optical imaging techniques, such as parathyroid autofluorescence, indocyanine green (ICG) angiography, and laser speckle contrast imaging (LSCI) have been employed to save parathyroid glands during thyroid surgery. This study provides an overview of the utilized methods of the optical imaging techniques during total thyroidectomy for parathyroid gland identification and preservation. Methods: PUBMED, EMBASE and Web of Science were searched for studies written in the English language utilizing parathyroid autofluorescence, ICG-angiography, or LSCI during total thyroidectomy to support parathyroid gland identification or preservation. Case reports, reviews, meta-analyses, animal studies, and post-mortem studies were excluded after the title and abstract screening. The data of the studies were analyzed qualitatively, with a focus on the methodologies employed. Results: In total, 59 articles were included with a total of 6190 patients. Overall, 38 studies reported using parathyroid autofluorescence, 24 using ICG-angiography, and 2 using LSCI. The heterogeneity between the utilized methodology in the studies was large, and in particular, regarding study protocols, imaging techniques, and the standardization of the imaging protocol. Conclusion: The diverse application of optical imaging techniques and a lack of standardization and quantification leads to heterogeneous conclusions regarding their clinical value. Worldwide consensus on imaging protocols is needed to establish the clinical utility of these techniques for parathyroid gland identification and preservation.

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.

The Impact of Temporal Variation in Indocyanine Green Administration on Tumor Identification During Fluorescence Guided Breast Surgery

BACKGROUND

On average, 21% of women in the USA treated with Breast Conserving Surgery (BCS) undergo a second operation because of close positive margins. Tumor identification with fluorescence imaging could improve positive margin rates through demarcating location, size, and invasiveness of tumors. We investigated the technique's diagnostic accuracy in detecting tumors during BCS using intravenous indocyanine green (ICG) and a custom-built fluorescence camera system.

METHODS

In this single-center prospective clinical study, 40 recruited BCS patients were sub-categorized into two cohorts. In the first 'enhanced permeability and retention' (EPR) cohort, 0.25 mg/kg ICG was injected ~ 25 min prior to tumor excision, and in the second 'angiography' cohort, ~ 5 min prior to tumor excision. Subsequently, an in-house imaging system was used to image the tumor in situ prior to resection, ex vivo following resection, the resection bed, and during grossing in the histopathology laboratory to compare the technique's diagnostic accuracy between the cohorts.

RESULTS

The two cohorts were matched in patient and tumor characteristics. The majority of patients had invasive ductal carcinoma with concomitant ductal carcinoma in situ. Tumor-to-background ratio (TBR) in the angiography cohort was superior to the EPR cohort (TBR = 3.18 ± 1.74 vs 2.10 ± 0.92 respectively, p = 0.023). Tumor detection reached sensitivity and specificity scores of 0.82 and 0.93 for the angiography cohort and 0.66 and 0.90 for the EPR cohort, respectively (p = 0.1051 and p = 0.9099).

DISCUSSION

ICG administration timing during the angiography phase compared with the EPR phase improved TBR and diagnostic accuracy. Future work will focus on image pattern analysis and adaptation of the camera system to targeting fluorophores specific to breast cancer.

Evaluation of standardized performance test methods for biomedical Raman spectroscopy

SIGNIFICANCE

Raman spectroscopy has emerged as a promising technique for a variety of biomedical applications. The unique ability to provide molecular specific information offers insight to the underlying biochemical changes that result in disease states such as cancer. However, one of the hurdles to successful clinical translation is a lack of international standards for calibration and performance assessment of modern Raman systems used to interrogate biological tissue.

AIM

To facilitate progress in the clinical translation of Raman-based devices and assist the scientific community in reaching a consensus regarding best practices for performance testing.

APPROACH

We reviewed the current literature and available standards documents to identify methods commonly used for bench testing of Raman devices (e.g., relative intensity correction, wavenumber calibration, noise, resolution, and sensitivity). Additionally, a novel 3D-printed turbid phantom was used to assess depth sensitivity. These approaches were implemented on three fiberoptic-probe-based Raman systems with different technical specifications.

RESULTS

While traditional approaches demonstrated fundamental differences due to detectors, spectrometers, and data processing routines, results from the turbid phantom illustrated the impact of illumination-collection geometry on measurement quality.

CONCLUSIONS

Specifications alone are necessary but not sufficient to predict in vivo performance, highlighting the need for phantom-based test methods in the standardized evaluation of Raman devices.

3D printing fluorescent material with tunable optical properties

The 3D printing of fluorescent materials could help develop, validate, and translate imaging technologies, including systems for fluorescence-guided surgery. Despite advances in 3D printing techniques for optical targets, no comprehensive method has been demonstrated for the simultaneous incorporation of fluorophores and fine-tuning of absorption and scattering properties. Here, we introduce a photopolymer-based 3D printing method for manufacturing fluorescent material with tunable optical properties. The results demonstrate the ability to 3D print various individual fluorophores at reasonably high fluorescence yields, including IR-125, quantum dots, methylene blue, and rhodamine 590. Furthermore, tuning of the absorption and reduced scattering coefficients is demonstrated within the relevant mamalian soft tissue coefficient ranges of 0.005-0.05 mm-1 and 0.2-1.5 mm-1, respectively. Fabrication of fluorophore-doped biomimicking and complex geometric structures validated the ability to print feature sizes less than 200 μm. The presented methods and optical characterization techniques provide the foundation for the manufacturing of solid 3D printed fluorescent structures, with direct relevance to biomedical optics and the broad adoption of fast manufacturing methods in fluorescence imaging.

Smartphone-based imaging systems for medical applications: a critical review

SIGNIFICANCE

Smartphones come with an enormous array of functionality and are being more widely utilized with specialized attachments in a range of healthcare applications. A review of key developments and uses, with an assessment of strengths/limitations in various clinical workflows, was completed.

AIM

Our review studies how smartphone-based imaging (SBI) systems are designed and tested for specialized applications in medicine and healthcare. An evaluation of current research studies is used to provide guidelines for improving the impact of these research advances.

APPROACH

First, the established and emerging smartphone capabilities that can be leveraged for biomedical imaging are detailed. Then, methods and materials for fabrication of optical, mechanical, and electrical interface components are summarized. Recent systems were categorized into four groups based on their intended application and clinical workflow: ex vivo diagnostic, in vivo diagnostic, monitoring, and treatment guidance. Lastly, strengths and limitations of current SBI systems within these various applications are discussed.

RESULTS

The native smartphone capabilities for biomedical imaging applications include cameras, touchscreens, networking, computation, 3D sensing, audio, and motion, in addition to commercial wearable peripheral devices. Through user-centered design of custom hardware and software interfaces, these capabilities have the potential to enable portable, easy-to-use, point-of-care biomedical imaging systems. However, due to barriers in programming of custom software and on-board image analysis pipelines, many research prototypes fail to achieve a prospective clinical evaluation as intended. Effective clinical use cases appear to be those in which handheld, noninvasive image guidance is needed and accommodated by the clinical workflow. Handheld systems for in vivo, multispectral, and quantitative fluorescence imaging are a promising development for diagnostic and treatment guidance applications.

CONCLUSIONS

A holistic assessment of SBI systems must include interpretation of their value for intended clinical settings and how their implementations enable better workflow. A set of six guidelines are proposed to evaluate appropriateness of smartphone utilization in terms of clinical context, completeness, compactness, connectivity, cost, and claims. Ongoing work should prioritize realistic clinical assessments with quantitative and qualitative comparison to non-smartphone systems to clearly demonstrate the value of smartphone-based systems. Improved hardware design to accommodate the rapidly changing smartphone ecosystem, creation of open-source image acquisition and analysis pipelines, and adoption of robust calibration techniques to address phone-to-phone variability are three high priority areas to move SBI research forward.