PARP1-targeted fluorescence molecular endoscopy as novel tool for early detection of esophageal dysplasia and adenocarcinoma

BACKGROUND

Esophageal cancer is one of the 10 most common cancers worldwide and its incidence is dramatically increasing. Despite some improvements, the current surveillance protocol with white light endoscopy and random untargeted biopsies collection (Seattle protocol) fails to diagnose dysplastic and cancerous lesions in up to 50% of patients. Therefore, new endoscopic imaging technologies in combination with tumor-specific molecular probes are needed to improve early detection. Herein, we investigated the use of the fluorescent Poly (ADP-ribose) Polymerase 1 (PARP1)-inhibitor PARPi-FL for early detection of dysplastic lesions in patient-derived organoids and transgenic mouse models, which closely mimic the transformation from non-malignant Barrett's Esophagus (BE) to invasive esophageal adenocarcinoma (EAC).

METHODS

We determined PARP1 expression via immunohistochemistry (IHC) in human biospecimens and mouse tissues. We also assessed PARPi-FL uptake in patient- and mouse-derived organoids. Following intravenous injection of 75 nmol PARPi-FL/mouse in L2-IL1B (n = 4) and L2-IL1B/IL8Tg mice (n = 12), we conducted fluorescence molecular endoscopy (FME) and/or imaged whole excised stomachs to assess PARPi-FL accumulation in dysplastic lesions. L2-IL1B/IL8Tg mice (n = 3) and wild-type (WT) mice (n = 2) without PARPi-FL injection served as controls. The imaging results were validated by confocal microscopy and IHC of excised tissues.

RESULTS

IHC on patient and murine tissue revealed similar patterns of increasing PARP1 expression in presence of dysplasia and cancer. In human and murine organoids, PARPi-FL localized to PARP1-expressing epithelial cell nuclei after 10 min of incubation. Injection of PARPi-FL in transgenic mouse models of BE resulted in the successful detection of lesions via FME, with a mean target-to-background ratio > 2 independently from the disease stage. The localization of PARPi-FL in the lesions was confirmed by imaging of the excised stomachs and confocal microscopy. Without PARPi-FL injection, identification of lesions via FME in transgenic mice was not possible.

CONCLUSION

PARPi-FL imaging is a promising approach for clinically needed improved detection of dysplastic and malignant EAC lesions in patients with BE. Since PARPi-FL is currently evaluated in a phase 2 clinical trial for oral cancer detection after topical application, clinical translation for early detection of dysplasia and EAC in BE patients via FME screening appears feasible.

Using reflectometry to minimize the dependence of fluorescence intensity on optical absorption and scattering

The total diffuse reflectance RT and the effective attenuation coefficient µeff of an optically diffuse medium map uniquely onto its absorption and reduced scattering coefficients. Using this premise, we developed a methodology where RT and the slope of the logarithmic spatially resolved reflectance, a quantity related to µeff, are the inputs of a look-up table to correct the dependence of fluorescent signals on the media's optical properties. This methodology does not require an estimation of the medium's optical property, avoiding elaborate simulations and their errors to offer accurate and fast corrections. The experimental demonstration of our method yielded a mean relative error in fluorophore concentrations of less than 4% over a wide range of optical property variations. We discuss how the method developed can be employed to improve image fidelity and fluorochrome quantification in fluorescence molecular imaging clinical applications.

Detection of Tumour-Targeted IRDye800CW Tracer with Commercially Available Laparoscopic Surgical Systems

(1) Introduction: Near-infrared fluorescence (NIRF) combined with tumour-targeted tracers, such as bevacizumab-800CW, could aid surgical decision-making. This study explored the use of IRDye800CW, conjugated to bevacizumab, with four commercially available NIRF laparoscopes optimised for indocyanine green (ICG). (2) Methods: A (lymph node) phantom was made from a calibration device for NIRF and tissue-mimicking material. Serial dilutions of bevacizumab-800CW were made and ICG functioned as a reference. System settings, working distance, and thickness of tissue-mimicking material were varied to assess visibility of the fluorescence signal and tissue penetration. Tests were performed with four laparoscopes: VISERA ELITE II, Olympus; IMAGE1 S™ 4U Rubina, KARL STORZ; ENDOCAM Logic 4K platform, Richard Wolf; da Vinci Xi, Intuitive Surgical. (3) Results: The lowest visible bevacizumab-800CW concentration ranged between 13-850 nM (8-512 times diluted stock solution) for all laparoscopes, but the tracer was not visible through 0.8 cm of tissue in all systems. In contrast, ICG was still visible at a concentration of 0.4 nM (16,384 times diluted) and through 1.6-2.4 cm of tissue. Visibility and tissue penetration generally improved with a reduced working distance and manually adjusted system settings. (4) Conclusion: Depending on the application, bevacizumab-800CW might be sufficiently visible with current laparoscopes, but optimisation would widen applicability of tumour-targeted IRDye800CW tracers.

Accounting for blood attenuation in intravascular near-infrared fluorescence-ultrasound imaging using a fluorophore-coated guidewire

Significance

Intravascular near-infrared fluorescence (NIRF) imaging aims to improve the inspection of vascular pathology using fluorescent agents with specificity to vascular disease biomarkers. The method has been developed to operate in tandem with an anatomical modality, such as intravascular ultrasound (IVUS), and complements anatomical readings with pathophysiological contrast, enhancing the information obtained from the hybrid examination.

Aim

However, attenuation of NIRF signals by blood challenges NIRF quantification. We propose a new method for attenuation correction in NIRF intravascular imaging based on a fluorophore-coated guidewire that is used as a reference for the fluorescence measurement and provides a real-time measurement of blood attenuation during the NIRF examination.

Approach

We examine the performance of the method in a porcine coronary artery ex vivo and phantoms using a 3.2F NIRF-IVUS catheter.

Results

We demonstrate marked improvement over uncorrected signals of up to 4.5-fold and errors of < 11 % for target signals acquired at distances up to 1 mm from the catheter system employed.

Conclusions

The method offers a potential means of improving the accuracy of intravascular NIRF imaging under in vivo conditions.

Detection of early esophageal neoplastic Barrett lesions with quantified fluorescence molecular endoscopy using cetuximab-800CW

Esophageal adenocarcinoma (EAC) causes 6 % of cancer-related deaths worldwide. Near-infrared fluorescence molecular endoscopy (NIR-FME) uses a tracer that targets overexpressed proteins. In this study we aim to investigate the feasibility of an epidermal growth factor receptor (EGFR) targeted tracer, cetuximab-800CW, to improve detection of early-stage EAC. Methods: We validated EGFR expression in 73 esophageal tissue sections. Subsequently, we topically administered cetuximab-800CW and performed high-definition white-light endoscopy (HD-WLE), narrow band imaging (NBI) and NIR-FME in fifteen patients with Barrett's esophagus (BE). Intrinsic fluorescence values were quantified using multi-diameter single fiber reflectance (MDSFR) and single-fiber fluorescence (SFF) spectroscopy. Back-table imaging, histopathological examination and EGFR immunohistochemistry on biopsies collected during NIR-FME procedures were performed and compared to in vivo imaging results. Results: Immunohistochemical pre-analysis showed high EGFR expression in 67% of dysplastic tissue sections. NIR-FME visualized all 12 HD-WLE visible lesions and 5 HD-WLE invisible dysplastic lesions, with increased fluorescence signal in visible dysplastic BE lesions compared to non-dysplastic BE as shown by MDSFR/SFF, reflecting a target-to-background ratio (TBR) of 1.5. Invisible dysplastic lesions also showed increased fluorescence with a TBR of 1.67. Immunohistochemistry analysis showed EGFR overexpression in 16 out of 17 (94%) dysplastic BE lesions, which all showed fluorescence signal. Conclusion: This study has shown that NIR-FME using cetuximab-800CW can improve detection of dysplastic lesions missed by HD-WLE and NBI.

Intravascular molecular imaging: translating pathophysiology of atherosclerosis into human disease conditions

Progression of atherosclerotic plaque in coronary arteries is characterized by complex cellular and non-cellular molecular interactions. Within recent years, atherosclerosis has been recognized as inflammation-driven disease condition, where progressive stages are characterized by morphological changes in plaque composition but also relevant molecular processes resulting in increased plaque vulnerability. While existing intravascular imaging modalities are able to resolve key morphological features during plaque progression, they lack capability to characterize the molecular profile of advanced atherosclerotic plaque. Because hybrid imaging modalities may provide incremental information related to plaque biology, they are expected to provide synergistic effects in detecting high risk patients and lesions. The aim of this article is to review existing literature on intravascular molecular imaging approaches, and to provide clinically oriented proposals of their application. In addition, we assembled an overview of future developments in this field geared towards detection of patients at risk for cardiovascular events.

Special Section Guest Editorial: Tissue Phantoms to Advance Biomedical Optical Systems

The editorial introduces the JBO Special Section on Tissue Phantoms to Advance Biomedical Optical Systems.

Validation of Novel Molecular Imaging Targets Identified by Functional Genomic mRNA Profiling to Detect Dysplasia in Barrett's Esophagus

Barrett’s esophagus (BE) is the precursor of esophageal adenocarcinoma (EAC). Dysplastic BE (DBE) has a higher progression risk to EAC compared to non-dysplastic BE (NDBE). However, the miss rates for the endoscopic detection of DBE remain high. Fluorescence molecular endoscopy (FME) can detect DBE and mucosal EAC by highlighting the tumor-specific expression of proteins. This study aimed to identify target proteins suitable for FME. Publicly available RNA expression profiles of EAC and NDBE were corrected by functional genomic mRNA (FGmRNA) profiling. Following a class comparison between FGmRNA profiles of EAC and NDBE, predicted, significantly upregulated genes in EAC were prioritized by a literature search. Protein expression of prioritized genes was validated by immunohistochemistry (IHC) on DBE and NDBE tissues. Near-infrared fluorescent tracers targeting the proteins were developed and evaluated ex vivo on fresh human specimens. In total, 1976 overexpressed genes were identified in EAC (n = 64) compared to NDBE (n = 66) at RNA level. Prioritization and IHC validation revealed SPARC, SULF1, PKCι, and DDR1 (all p < 0.0001) as the most attractive imaging protein targets for DBE detection. Newly developed tracers SULF1-800CW and SPARC-800CW both showed higher fluorescence intensity in DBE tissue compared to paired non-dysplastic tissue. This study identified SPARC, SULF1, PKCι, and DDR1 as promising targets for FME to differentiate DBE from NDBE tissue, for which SULF1-800CW and SPARC-800CW were successfully ex vivo evaluated. Clinical studies should further validate these findings.

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.

CXCR4 peptide-based fluorescence endoscopy in a mouse model of Barrett's esophagus

Background

Near-infrared (NIR) fluorescence imaging has been emerging as a promising strategy to overcome the high number of early esophageal adenocarcinomas missed by white light endoscopy and random biopsy collection. We performed a preclinical assessment of fluorescence imaging and endoscopy using a novel CXCR4-targeted fluorescent peptide ligand in the L2-IL1B mouse model of Barrett’s esophagus.

Methods

Six L2-IL1B mice with advanced stage of disease (12–16 months old) were injected with the CXCR4-targeted, Sulfo-Cy5-labeled peptide (MK007), and ex vivo wide-field imaging of the whole stomach was performed 4 h after injection. Before ex vivo imaging, fluorescence endoscopy was performed in three L2-IL1B mice (12–14 months old)  by a novel imaging system with two L2-IL1B mice used as negative controls.

Results

Ex vivo imaging and endoscopy in L2-IL1B mice showed that the CXCR4-targeted MK007 accumulated mostly in the dysplastic lesions with a mean target-to-background ratio > 2. The detection of the Sulfo-Cy5 signal in dysplastic lesions and its co-localization with CXCR4 stained cells  by confocal microscopy further confirmed the imaging results.

Conclusions

This preliminary preclinical study shows that CXCR4-targeted fluorescence endoscopy using MK007 can detect dysplastic lesions in a mouse model of Barrett’s esophagus. Further investigations are needed to assess its use in the clinical setting.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13550-021-00875-7.

Targeted Hsp70 fluorescence molecular endoscopy detects dysplasia in Barrett's esophagus

PURPOSE

The incidence of esophageal adenocarcinoma (EAC) has been increasing for decades without significant improvements in treatment. Barrett's esophagus (BE) is best established risk factor for EAC, but current surveillance with random biopsies cannot predict progression to cancer in most BE patients due to the low sensitivity and specificity of high-definition white light endoscopy.

METHODS

Here, we evaluated the membrane-bound highly specific Hsp70-specific contrast agent Tumor-Penetrating Peptide (Hsp70-TPP) in guided fluorescence molecular endoscopy biopsy.

RESULTS

Hsp70 was significantly overexpressed as determined by IHC in dysplasia and EAC compared with non-dysplastic BE in patient samples (n = 12) and in high-grade dysplastic lesions in a transgenic (L2-IL1b) mouse model of BE. In time-lapse microscopy, Hsp70-TPP was rapidly taken up and internalized  by human BE dysplastic patient-derived organoids. Flexible fluorescence endoscopy of the BE mouse model allowed a specific detection of Hsp70-TPP-Cy5.5 that corresponded closely with the degree of dysplasia but not BE. Ex vivo application of Hsp70-TPP-Cy5.5 to freshly resected whole human EAC specimens revealed a high (> 4) tumor-to-background ratio and a specific detection of previously undetected tumor infiltrations.

CONCLUSION

In summary, these findings suggest that Hsp70-targeted imaging using fluorescently labeled TPP peptide may improve tumor surveillance in BE patients.

Facile Synthesis of a Croconaine-Based Nanoformulation for Optoacoustic Imaging and Photothermal Therapy

Near-infrared (NIR) light absorbing theranostic agents can integrate optoacoustic imaging and photothermal therapy for effective personalized precision medicine. However, most of these agents face the challenges of unstable optical properties, material-associated toxicity, and nonbiodegradability, all of which limit their biomedical application. Several croconaine-based organic agents able to overcome some of these limitations have been recently reported, but these suffer from complicated multistep synthesis protocols. Herein, the use of CR760, a croconaine dye with excellent optical properties, is reported for nanoparticle formulation and subsequent optoacoustic imaging and photothermal therapy. Importantly, CR760 can be conveniently prepared in a single step from commercially available materials. Furthermore, CR760 can be covalently attached, via a polyethylene glycol linker, to the α_v β₃ integrin ligand c(RGDyC), resulting in self-assembled nanoparticles (NPs) with cancer-targeting capability. Such CR760RGD-NPs exhibit strong NIR absorption, high photostability, high optoacoustic generation efficiency, and active tumor-targeting, making them ideal candidates for optoacoustic imaging. Due to favorable electron transfer, CR760RGD-NPs display a 45.37% photothermal conversion efficiency thereby rendering them additionally useful for photothermal therapy. Targeted tumor elimination, biosafety, and biocompatibility are demonstrated in a 4T1 murine breast tumor model. This work points to the use of CR760RGD-NPs as a promising nanoagent for NIR-based cancer phototheranostics.

Imaging atherosclerotic plaques by targeting Galectin-3 and activated macrophages using (89Zr)-DFO- Galectin3-F(ab')2 mAb

Rationale: The high expression of Galectin-3 (Gal3) in macrophages of atherosclerotic plaques suggests its participation in atherosclerosis pathogenesis, and raises the possibility to use it as a target to image disease severity in vivo. Here, we explored the feasibility of tracking atherosclerosis by targeting Gal3 expression in plaques of apolipoprotein E knockout (ApoE-KO) mice via PET imaging. Methods: Targeting of Gal3 in M0-, M1- and M2 (M2a/M2c)-polarized macrophages was assessed in vitro using a Gal3-F(ab')₂ mAb labeled with AlexaFluor®488 and ⁸⁹Zr- desferrioxamine-thioureyl-phenyl-isothiocyanate (DFO). To visualize plaques in vivo, ApoE-KO mice were injected i.v. with ⁸⁹Zr-DFO-Gal3-F(ab')₂ mAb and imaged via PET/CT 48 h post injection. Whole length aortas harvested from euthanized mice were processed for Sudan-IV staining, autoradiography, and immunostaining for Gal3, CD68 and α-SMA expression. To confirm accumulation of the tracer in plaques, ApoE-KO mice were injected i.v. with Cy5.5-Gal3-F(ab')₂ mAb, euthanized 48 h post injection, followed by cryosections of the body and acquisition of fluorescent images. To explore the clinical potential of this imaging modality, immunostaining for Gal3, CD68 and α-SMA expression were carried out in human plaques. Single cell RNA sequencing (scRNA-Seq) analyses were performed to measure LGALS3 (i.e. a synonym for Gal3) gene expression in each macrophage of several subtypes present in murine or human plaques. Results: Preferential binding to M2 macrophages was observed with both AlexaFluor®488-Gal3-F(ab')₂ and ⁸⁹Zr-DFO-Gal3-F(ab')₂ mAbs. Focal and specific ⁸⁹Zr-DFO-Gal3-F(ab')₂ mAb uptake was detected in plaques of ApoE-KO mice by PET/CT. Autoradiography and immunohistochemical analyses of aortas confirmed the expression of Gal3 within plaques mainly in macrophages. Moreover, a specific fluorescent signal was visualized within the lesions of vascular structures burdened by plaques in mice. Gal3 expression in human plaques showed similar Gal3 expression patterns when compared to their murine counterparts. Conclusions: Our data reveal that ⁸⁹Zr-DFO-Gal3-F(ab')₂ mAb PET/CT is a potentially novel tool to image atherosclerotic plaques at different stages of development, allowing knowledge-based tailored individual intervention in clinically significant disease.

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.

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

SIGNIFICANCE

Expanded use of fluorescence-guided surgery with devices approved for use with indocyanine green (ICG) has led to a range of commercial systems available. There is a compelling need to be able to independently characterize system performance and allow for cross-system comparisons.

AIM

The goal of this work is to expand on previous proposed fluorescence imaging standard designs to develop a long-term stable phantom that spectrally matches ICG characteristics and utilizes 3D printing technology for incorporating tissue-equivalent materials.

APPROACH

A batch of test targets was created to assess ICG concentration sensitivity in the 0.3- to 1000-nM range, tissue-equivalent depth sensitivity down to 6 mm, and spatial resolution with a USAF test chart. Comparisons were completed with a range of systems that have significantly different imaging capabilities and applications, including the Li-Cor® Odyssey, Li-Cor® Pearl, PerkinElmer® Solaris, and Stryker® Spy Elite.

RESULTS

Imaging of the ICG-matching phantoms with all four commercially available systems showed the ability to benchmark system performance and allow for cross-system comparisons. The fluorescence tests were able to assess differences in the detectable concentrations of ICG with sensitivity differences >10× for preclinical and clinical systems. Furthermore, the tests successfully assessed system differences in the depth-signal decay rate, as well as resolution performance and image artifacts. The manufacturing variations, photostability, and mechanical design of the tests showed promise in providing long-term stable standards for fluorescence imaging.

CONCLUSIONS

The presented ICG-matching phantom provides a major step toward standardizing performance characterization and cross-system comparisons for devices approved for use with ICG. The developed hybrid manufacturing platform can incorporate long-term stable fluorescing agents with 3D printed tissue-equivalent material. Further, long-term testing of the phantom and refinements to the manufacturing process are necessary for future implementation as a widely adopted fluorescence imaging standard.

Biodegradable fluorescent nanoparticles for endoscopic detection of colorectal carcinogenesis

Early and comprehensive endoscopic detection of colonic dysplasia - the most clinically significant precursor lesion to colorectal adenocarcinoma - provides an opportunity for timely, minimally-invasive intervention to prevent malignant transformation. Here, the development and evaluation of biodegradable near-infrared fluorescent silica nanoparticles (FSN) is described that have the potential to improve adenoma detection during fluorescence-assisted white-light colonoscopic surveillance in rodent and human-scale models of colorectal carcinogenesis. FSNs are biodegradable (t_1/2 of 2.7 weeks), well-tolerated, and enable detection and delineation of adenomas as small as 0.5 mm² with high tumor-to-background ratios. Furthermore, in the human-scale, APC ^1311/+ porcine model, the clinical feasibility and benefit of using FSN-guided detection of colorectal adenomas using video-rate fluorescence-assisted white-light endoscopy is demonstrated. Since nanoparticles of similar size (e.g., 100-150-nm) or composition (i.e., silica, silica/gold hybrid) have already been successfully translated to the clinic, and, clinical fluorescent/white light endoscopy systems are becoming more readily available, there is a viable path towards clinical translation of the proposed strategy for early colorectal cancer detection and prevention in high-risk patients.

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.

A dual Ucp1 reporter mouse model for imaging and quantitation of brown and brite fat recruitment

OBJECTIVES

Brown adipose tissue (BAT) dissipates nutritional energy as heat through uncoupling protein 1 (UCP1). The discovery of functional BAT in healthy adult humans has promoted the search for pharmacological interventions to recruit and activate brown fat as a treatment of obesity and diabetes type II. These efforts require in vivo models to compare the efficacy of novel compounds in a relevant physiological context.

METHODS

We generated a knock-in mouse line expressing firefly luciferase and near-infrared red florescent protein (iRFP713) driven by the regulatory elements of the endogenous Ucp1 gene.

RESULTS

Our detailed characterization revealed that firefly luciferase activity faithfully reports endogenous Ucp1 gene expression in response to physiological and pharmacological stimuli. The iRFP713 fluorescence signal was detected in the interscapular BAT region of cold-exposed reporter mice in an allele-dosage dependent manner. Using this reporter mouse model, we detected a higher browning capacity in female peri-ovarian white adipose tissue compared to male epididymal WAT, which we further corroborated by molecular and morphological features. In situ imaging detected a strong luciferase activity signal in a previously unappreciated adipose tissue depot adjunct to the femoral muscle, now adopted as femoral brown adipose tissue. In addition, screening cultured adipocytes by bioluminescence imaging identified the selective Salt-Inducible Kinase inhibitor, HG-9-91-01, to increase Ucp1 gene expression and mitochondrial respiration in brown and brite adipocytes.

CONCLUSIONS

In our mouse model, firefly luciferase activity serves as a bona fide reporter for dynamic regulation of Ucp1. In addition, by means of iRFP713 we are able to monitor Ucp1 expression in a non-invasive fashion.

Therapeutic Fluorescent Hybrid Nanoparticles for Traceable Delivery of Glucocorticoids to Inflammatory Sites

Treatment of inflammatory disorders with glucocorticoids (GCs) is often accompanied by severe adverse effects. Application of GCs via nanoparticles (NPs), especially those using simple formulations, could possibly improve their delivery to sites of inflammation and therefore their efficacy, minimising the required dose and thus reducing side effects. Here, we present the evaluation of NPs composed of GC betamethasone phosphate (BMP) and the fluorescent dye DY-647 (BMP-IOH-NPs) for improved treatment of inflammation with simultaneous in vivo monitoring of NP delivery.

Methods: BMP-IOH-NP uptake by MH-S macrophages was analysed by fluorescence and electron microscopy. Lipopolysaccharide (LPS)-stimulated cells were treated for 48 h with BMP-IOH-NPs (1×10^-5-1×10^-9 M), BMP or dexamethasone (Dexa). Drug efficacy was assessed by measurement of interleukin 6. Mice with Zymosan-A-induced paw inflammation were intraperitoneally treated with BMP-IOH-NPs (10 mg/kg) and mice with ovalbumin (OVA)-induced allergic airway inflammation (AAI) were treated intranasally with BMP-IOH-NPs, BMP or Dexa (each 2.5 mg/kg). Efficacy was assessed in vivo by paw volume measurements with µCT and ex vivo by measurement of paw weight for Zymosan-A-treated mice, or in the AAI model by in vivo x-ray-based lung function assessment and by cell counts in the bronchoalveolar lavage (BAL) fluid and histology. Delivery of BMP-IOH-NPs to the lungs of AAI mice was monitored by in vivo optical imaging and by fluorescence microscopy.

Results: Uptake of BMP-IOH-NPs by MH-S cells was observed during the first 10 min of incubation, with the NP load increasing over time. The anti-inflammatory effect of BMP-IOH-NPs in vitro was dose dependent and higher than that of Dexa or free BMP, confirming efficient release of the drug. In vivo, Zymosan-A-induced paw inflammation was significantly reduced in mice treated with BMP-IOH-NPs. AAI mice that received BMP-IOH-NPs or Dexa but not BMP revealed significantly decreased eosinophil numbers in BALs and reduced immune cell infiltration in lungs. Correspondingly, lung function parameters, which were strongly affected in non-treated AAI mice, were unaffected in AAI mice treated with BMP-IOH-NPs and resembled those of healthy animals. Accumulation of BMP-IOH-NPs within the lungs of AAI mice was detectable by optical imaging for at least 4 h in vivo, where they were preferentially taken up by peribronchial and alveolar M2 macrophages.

Conclusion: Our results show that BMP-IOH-NPs can effectively be applied in therapy of inflammatory diseases with at least equal efficacy as the gold standard Dexa, while their delivery can be simultaneously tracked in vivo by fluorescence imaging. BMP-IOH-NPs thus have the potential to reach clinical applications.

Optoacoustic sensing of hematocrit to improve the accuracy of hybrid fluorescence-ultrasound intravascular imaging

Hybrid intravascular fluorescence-ultrasound imaging is emerging for reading anatomical and biological information in vivo. By operating through blood, intravascular near-infrared fluorescence (NIRF) detection is affected by hemoglobin attenuation. Improved quantification has been demonstrated with methods that correct for the attenuation of the optical signal as it propagates through blood. These methods assume an attenuation coefficient for blood and measure the distance between detector and the vessel wall by observing the intravascular ultrasound images. Assumptions behind the attenuation employed in correction models may reduce the accuracy of these methods. Herein, we explore a novel approach to dynamically estimate optical absorption by using optoacoustic (photoacoustic) measurements. Adaptive correction is based on a trimodal intravascular catheter that integrates fluorescence, ultrasound and optoacoustic measurements. Using the novel catheter, we show how optoacoustic measurements can determine variations of blood absorption, leading to accurate quantification of the detected NIRF signals at different hematocrit values.

Automated detection of breast cancer in resected specimens with fluorescence lifetime imaging

Re-excision rates for breast cancer lumpectomy procedures are currently nearly 25% due to surgeons relying on inaccurate or incomplete methods of evaluating specimen margins. The objective of this study was to determine if cancer could be automatically detected in breast specimens from mastectomy and lumpectomy procedures by a classification algorithm that incorporated parameters derived from fluorescence lifetime imaging (FLIm). This study generated a database of co-registered histologic sections and FLIm data from breast cancer specimens (N  =  20) and a support vector machine (SVM) classification algorithm able to automatically detect cancerous, fibrous, and adipose breast tissue. Classification accuracies were greater than 97% for automated detection of cancerous, fibrous, and adipose tissue from breast cancer specimens. The classification worked equally well for specimens scanned by hand or with a mechanical stage, demonstrating that the system could be used during surgery or on excised specimens. The ability of this technique to simply discriminate between cancerous and normal breast tissue, in particular to distinguish fibrous breast tissue from tumor, which is notoriously challenging for optical techniques, leads to the conclusion that FLIm has great potential to assess breast cancer margins. Identification of positive margins before waiting for complete histologic analysis could significantly reduce breast cancer re-excision rates.

Rapid fluorescence lifetime estimation with modified phasor approach and Laguerre deconvolution: a comparative study

Fluorescence lifetime imaging has been shown to serve as a valuable tool for interrogating and diagnosis of biological tissue at a mesoscopic level. The ability to analyze fluorescence decay curves to extract lifetime values in real-time is crucial for clinical translation and applications such as tumor margin delineation or intracoronary imaging of atherosclerotic plaques. In this work, we compare the performance of two popular non-parametric (fit-free) methods for determining lifetime values from fluorescence decays in real-time-the Phasor approach and Laguerre deconvolution. We demonstrate results from simulated and experimental data to compare the accuracy and speed of both methods and their dependence on noise and model parameters.

In vivo label-free structural and biochemical imaging of coronary arteries using an integrated ultrasound and multispectral fluorescence lifetime catheter system

Existing clinical intravascular imaging modalities are not capable of accurate detection of critical plaque pathophysiology in the coronary arteries. This study reports the first intravascular catheter combining intravascular ultrasound (IVUS) with multispectral fluorescence lifetime imaging (FLIm) that enables label-free simultaneous assessment of morphological and biochemical features of coronary vessels in vivo. A 3.7 Fr catheter with a fiber-optic channel was constructed based on a 40 MHz clinical IVUS catheter. The ability to safely acquire co-registered FLIm-IVUS data in vivo using Dextran40 solution flushing was demonstrated in swine coronary arteries. FLIm parameters from the arterial wall were consistent with the emission of fluorophores present in healthy arterial wall (collagen, elastin). Additionally, structural and biochemical features from atherosclerotic lesions were acquired in ex vivo human coronary samples and corroborated with histological findings. Current results show that FLIm parameters linked to the amount of structural proteins (e.g. collagen, elastin) and lipids (e.g. foam cells, extracellular lipids) in the first 200 μm of the intima provide important biochemical information that can supplement IVUS data for a comprehensive assessment of plaques pathophysiology. The unique FLIm-IVUS system evaluated here has the potential to provide a comprehensive insight into atherosclerotic lesion formation, diagnostics and response to 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.

Real-Time Visualization of Tissue Surface Biochemical Features Derived From Fluorescence Lifetime Measurements

Fiber based fluorescence lifetime imaging has shown great potential for intraoperative diagnosis and guidance of surgical procedures. Here we describe a novel method addressing a significant challenge for the practical implementation of this technique, i.e., the real-time display of the quantified biochemical or functional tissue properties superimposed on the interrogated area. Specifically, an aiming beam (450 nm) generated by a continuous-wave laser beam was merged with the pulsed fluorescence excitation light in a single delivery/collection fiber and then imaged and segmented using a color-based algorithm. We demonstrate that this approach enables continuous delineation of the interrogated location and dynamic augmentation of the acquired frames with the corresponding fluorescence decay parameters. The method was evaluated on a fluorescence phantom and fresh tissue samples. Current results demonstrate that 34 frames per second can be achieved for augmenting videos of 640 × 512 pixels resolution. Also we show that the spatial resolution of the fluorescence lifetime map depends on the tissue optical properties, the scanning speed, and the frame rate. The dice similarity coefficient between the fluorescence phantom and the reconstructed maps was estimated to be as high as 93%. The reported method could become a valuable tool for augmenting the surgeon's field of view with diagnostic information derived from the analysis of fluorescence lifetime data in real-time using handheld, automated, or endoscopic scanning systems. Current method provides also a means for maintaining the tissue light exposure within safety limits. This study provides a framework for using an aiming beam with other point spectroscopy applications.

Fluorescence Lifetime Imaging Combined with Conventional Intravascular Ultrasound for Enhanced Assessment of Atherosclerotic Plaques: an Ex Vivo Study in Human Coronary Arteries

This study evaluates the ability of label-free fluorescence lifetime imaging (FLIm) to complement intravascular ultrasound (IVUS) for concurrent visualization of human coronary vessel composition, structure, and pathology. Co-registered FLIm and IVUS data from 16 coronary segments were correlated to eight distinct pathological features including thin-cap fibroatheroma (TCFA). The sensitivity, specificity, and positive predictive value for combined FLIm-IVUS (89, 99, 89 %) were better than FLIm (70, 98, 88 %) and IVUS (45, 94, 62 %) alone in distinguishing between pathologies. FLIm can assess compositional changes in luminal surface through variations in fluorescence lifetime values (<3.5 ns for lipid-rich areas; >4 ns for collagen-rich areas) enabling detection of macrophages in fibrous caps (sensitivity, 86 %) and distinguishing between relatively stable thick-cap fibroatheromas and rupture-prone TCFA (sensitivity, 80 %) amongst other features. Current results demonstrate the potential of FLIm-IVUS as a new intravascular method for improved evaluation of plaques that may subsequently aid in guiding coronary intervention.

Technique for real-time tissue characterization based on scanning multispectral fluorescence lifetime spectroscopy (ms-TRFS)

We report a novel technique for continuous acquisition, processing and display of fluorescence lifetimes enabling real-time tissue diagnosis through a single hand held or biopsy fiber-optic probe. A scanning multispectral time-resolved fluorescence spectroscopy (ms-TRFS) with self-adjustable photon detection range was developed to account for the dynamic changes of fluorescence intensity typically encountered in clinical application. A fast algorithm was implemented in the ms-TRFS software platform, providing up to 15 Hz continuous display of fluorescence lifetime values. Potential applications of this technique, including biopsy guidance, and surgical margins delineation were demonstrated in proof-of-concept experiments. Current results showed accurate display of fluorescence lifetimes values and discrimination of distinct fluorescence markers and tissue types in real-time (< 100 ms per data point).

Fluorescence lifetime imaging and intravascular ultrasound: co-registration study using ex vivo human coronaries

Fluorescence lifetime imaging (FLIM) has demonstrated potential for robust assessment of atherosclerotic plaques biochemical composition and for complementing conventional intravascular ultrasound (IVUS), which provides information on plaque morphology. The success of such a bi-modal imaging modality depends on accurate segmentation of the IVUS images and proper angular registration between these two modalities. This paper reports a novel IVUS segmentation methodology addressing this issue. The image preprocessing consisted of denoising, using the Wiener filter, followed by image smoothing, implemented through the application of the alternating sequential filter on the edge separability metric images. Extraction of the lumen/intima and media/adventitia boundaries was achieved by tracing the gray-scale peaks over the A-lines of the IVUS preprocessed images. Cubic spline interpolation, in both cross-sectional and longitudinal directions, ensured boundary smoothness and continuity. The detection of the guide-wire artifact in both modalities is used for angular registration. Intraluminal studies were conducted in 13 ex vivo segments of human coronaries. The IVUS segmentation accuracy was assessed against independent manual tracings, providing 91.82% sensitivity and 97.55% specificity. The proposed methodology makes the bi-modal FLIM and IVUS approach feasible for comprehensive intravascular diagnosis by providing co-registered biochemical and morphological information of atherosclerotic plaques.

Rotational multispectral fluorescence lifetime imaging and intravascular ultrasound: bimodal system for intravascular applications

We report the development and validation of a hybrid intravascular diagnostic system combining multispectral fluorescence lifetime imaging (FLIm) and intravascular ultrasound (IVUS) for cardiovascular imaging applications. A prototype FLIm system based on fluorescence pulse sampling technique providing information on artery biochemical composition was integrated with a commercial IVUS system providing information on artery morphology. A customized 3-Fr bimodal catheter combining a rotational side-view fiberoptic and a 40-MHz IVUS transducer was constructed for sequential helical scanning (rotation and pullback) of tubular structures. Validation of this bimodal approach was conducted in pig heart coronary arteries. Spatial resolution, fluorescence detection efficiency, pulse broadening effect, and lifetime measurement variability of the FLIm system were systematically evaluated. Current results show that this system is capable of temporarily resolving the fluorescence emission simultaneously in multiple spectral channels in a single pullback sequence. Accurate measurements of fluorescence decay characteristics from arterial segments can be obtained rapidly (e.g., 20 mm in 5 s), and accurate co-registration of fluorescence and ultrasound features can be achieved. The current finding demonstrates the compatibility of FLIm instrumentation with in vivo clinical investigations and its potential to complement conventional IVUS during catheterization procedures.

Evaluation of a radiative transfer equation and diffusion approximation hybrid forward solver for fluorescence molecular imaging

The solution of the forward problem in fluorescence molecular imaging strongly influences the successful convergence of the fluorophore reconstruction. The most common approach to meeting this problem has been to apply the diffusion approximation. However, this model is a first-order angular approximation of the radiative transfer equation, and thus is subject to some well-known limitations. This manuscript proposes a methodology that confronts these limitations by applying the radiative transfer equation in spatial regions in which the diffusion approximation gives decreased accuracy. The explicit integro differential equations that formulate this model were solved by applying the Galerkin finite element approximation. The required spatial discretization of the investigated domain was implemented through the Delaunay triangulation, while the azimuthal discretization scheme was used for the angular space. This model has been evaluated on two simulation geometries and the results were compared with results from an independent Monte Carlo method and the radiative transfer equation by calculating the absolute values of the relative errors between these models. The results show that the proposed forward solver can approximate the radiative transfer equation and the Monte Carlo method with better than 95% accuracy, while the accuracy of the diffusion approximation is approximately 10% lower.

A binocular machine vision system for three-dimensional surface measurement of small objects

Rendering three-dimensional information of a scene from optical measurements is very important for a wide variety of applications. However, computer vision advancements have not yet achieved the accurate three-dimensional reconstruction of objects smaller than 1 cm diameter. This paper describes the development of a novel volumetric method for small objects, using a binocular machine vision system. The achieved precision is high, providing a standard deviation of 0.04 mm. The robustness, of the system, issues from the lab prototype imaging system with the crucial z-axis movement without the need of further calibration and the fully automated volumetric algorithms.