A review of attenuation correction techniques for tissue fluorescence

A smartphone-based standalone fluorescence spectroscopy tool for cervical precancer diagnosis in clinical conditions

Real-time prediction about the severity of noncommunicable diseases like cancers is a boon for early diagnosis and timely cure. Optical techniques due to their minimally invasive nature provide better alternatives in this context than the conventional techniques. The present study talks about a standalone, field portable smartphone-based device which can classify different grades of cervical cancer on the basis of the spectral differences captured in their intrinsic fluorescence spectra with the help of AI/ML technique. In this study, a total number of 75 patients and volunteers, from hospitals at different geographical locations of India, have been tested and classified with this device. A classification approach employing a hybrid mutual information long short-term memory model has been applied to categorize various subject groups, resulting in an average accuracy, specificity, and sensitivity of 96.56%, 96.76%, and 94.37%, respectively using 10-fold cross-validation. This exploratory study demonstrates the potential of combining smartphone-based technology with fluorescence spectroscopy and artificial intelligence as a diagnostic screening approach which could enhance the detection and screening of cervical cancer.

Miniature, multi-dichroic instrument for measuring the concentration of multiple fluorophores

Identification of tumour margins during resection of the brain is critical for improving the post-operative outcomes. Due to the highly infiltrative nature of glioblastoma multiforme (GBM) and limited intraoperative visualization of the tumour margin, incomplete surgical resection has been observed to occur in up to 80 % of GBM cases, leading to nearly universal tumour recurrence and overall poor prognosis of 14.6 months median survival. This research presents a miniaturized, SiPMT-based optical system for simultaneous measurement of powerful DRS and weak auto-fluorescence for brain tumour detection. The miniaturisation of the optical elements confined the spatial separation of eight select wavelengths into footprint measuring 1.5 × 2 × 16 mm. The small footprint enables this technology to be integrated with existing surgical guidance instruments in the operating room. It's dynamic ability to subtract any background illumination and measure signal intensities across a broad range from pW to mWs make this design much more suitable for clinical environments as compared to spectrometer-based systems with limited dynamic ranges and high integration times. Measurements using optical tissue phantoms containing mixed fluorophores demonstrate correlation coefficients between the fitted response and actual concentration using PLS regression being 0.95, 0.87 and 0.97 for NADH, FAD and PpIX , respectively. These promising results indicate that our proposed miniaturized instrument could serve as an effective alternative in operating rooms, assisting surgeons in identifying brain tumours to achieving positive surgical outcomes for patients.

5-ALA induced PpIX fluorescence spectroscopy in neurosurgery: a review

The review begins with an overview of the fundamental principles/physics underlying light, fluorescence, and other light-matter interactions in biological tissues. It then focuses on 5-aminolevulinic acid (5-ALA)-induced protoporphyrin IX (PpIX) fluorescence spectroscopy methods used in neurosurgery (e.g., intensity, time-resolved) and in so doing, describe their specific features (e.g., hardware requirements, main processing methods) as well as their strengths and limitations. Finally, we review current clinical applications and future directions of 5-ALA-induced protoporphyrin IX (PpIX) fluorescence spectroscopy in neurosurgery.

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.

In vivo quantitative FRET small animal imaging: Intensity versus lifetime-based FRET

Förster resonance energy transfer (FRET) microscopy is used in numerous biophysical and biomedical applications to monitor inter- and intramolecular interactions and conformational changes in the 2-10 nm range. FRET is currently being extended to in vivo optical imaging, its main application being in quantifying drug-target engagement or drug release in animal models of cancer using organic dye or nanoparticle-labeled probes. Herein, we compared FRET quantification using intensity-based FRET (sensitized emission FRET analysis with the three-cube approach using an IVIS imager) and macroscopic fluorescence lifetime (MFLI) FRET using a custom system using a time-gated-intensified charge-coupled device, for small animal optical in vivo imaging. The analytical expressions and experimental protocols required to quantify the product f D E of the FRET efficiency E and the fraction of donor molecules involved in FRET, f D , are described in detail for both methodologies. Dynamic in vivo FRET quantification of transferrin receptor-transferrin binding was acquired in live intact nude mice upon intravenous injection of a near-infrared-labeled transferrin FRET pair and benchmarked against in vitro FRET using hybridized oligonucleotides. Even though both in vivo imaging techniques provided similar dynamic trends for receptor-ligand engagement, we demonstrate that MFLI-FRET has significant advantages. Whereas the sensitized emission FRET approach using the IVIS imager required nine measurements (six of which are used for calibration) acquired from three mice, MFLI-FRET needed only one measurement collected from a single mouse, although a control mouse might be needed in a more general situation. Based on our study, MFLI therefore represents the method of choice for longitudinal preclinical FRET studies such as that of targeted drug delivery in intact, live mice.

Point-of-care devices based on fluorescence imaging and spectroscopy for tumor margin detection during breast cancer surgery: Towards breast conservation treatment

OBJECTIVE

Fluorescence-based methods are highly specific and sensitive and have potential in breast cancer detection. Simultaneous fluorescence imaging and spectroscopy during intraoperative procedures of breast cancer have great advantages in detection of tumor margin as well as in classification of tumor to healthy tissues. Intra-operative real-time confirmation of breast cancer tumor margin is the aim of surgeons, and therefore, there is an urgent need for such techniques and devices which fulfill the surgeon's priorities.

METHODS

In this article, we propose the development of fluorescence-based smartphone imaging and spectroscopic point-of-care multi-modal devices for detection of invasive ductal carcinoma in tumor margin during removal of tumor. These multimodal devices are portable, cost-effective, noninvasive, and user-friendly. Molecular level sensitivity of fluorescence process shows different behavior in normal, cancerous and marginal tissues. We observed significant spectral changes, such as, red-shift, full-width half maximum (FWHM), and increased intensity as we go towards tumor center from normal tissue. High contrast in fluorescence images and spectra are also recorded for cancer tissues compared to healthy tissues. Preliminary results for the initial trial of the devices are reported in this article.

RESULTS

A total 44 spectra from 11 patients of invasive ductal carcinoma (11 spectra for invasive ductal carcinoma and rest are normal and negative margins) are used. Principle component analysis is used for the classification of invasive ductal carcinoma with an accuracy of 93%, specificity of 75% and sensitivity of 92.8%. We obtained an average 6.17 ± 1.66 nm red shift for IDC with respect to normal tissue. The red shift and maximum fluorescence intensity indicates p < 0.01. These results described here are supported by histopathological examination of the same sample.

CONCLUSION

In the present manuscript, simultaneous fluorescence-based imaging and spectroscopy is accomplished for the classification of IDC tissues and breast cancer margin detection.

Challenges in, and recommendations for, hyperspectral imaging in ex vivo malignant glioma biopsy measurements

The visualization of protoporphyrin IX (PPIX) fluorescence with the help of surgical microscopes during 5-aminolevulinic acid-mediated fluorescence-guided resection (FGR) of gliomas is still limited at the tumor margins. Hyperspectral imaging (HI) detects PPIX more sensitively but is not yet ready for intraoperative use. We illustrate the current status with three experiments and summarize our own experience using HI: (1) assessment of HI analysis algorithm using pig brain tissue, (2) a partially retrospective evaluation of our experience from HI projects, and (3) device comparison of surgical microscopy and HI. In (1), we address the problem that current algorithms for evaluating HI data are based on calibration with liquid phantoms, which have limitations. Their pH is low compared to glioma tissue; they provide only one PPIX photo state and only PPIX as fluorophore. Testing the HI algorithm with brain homogenates, we found proper correction for optical properties but not pH. Considerably more PPIX was measured at pH 9 than at pH 5. In (2), we indicate pitfalls and guide HI application. In (3), we found HI superior to the microscope for biopsy diagnosis (AUC = 0.845 ± 0.024 (cut-off 0.75 µg PPIX/ml) vs. 0.710 ± 0.035). HI thus offers potential for improved FGR.

Fluorescence and diffuse reflectance provide similar accuracy in recovering fluorophore concentration at short source-detector separations

Quantitative fluorescence spectroscopy requires corresponding reflectance measurements to correct for tissue absorption and scattering. However, it is unclear whether fluorescence adds value beyond the diffuse reflectance measurements necessary for correction. The goal of this study was to compare the accuracy of fluorescence and diffuse reflectance spectroscopy in recovering the concentration of a high-extinction fluorophore, methylene blue (MB), using a compact fiber-optic probe. Fluorescence and diffuse reflectance measurements of tissue simulating phantoms were made using a fiber-optic probe with source-detector separations of 288-1300 μm. Average error in recovered fluorophore concentration was 20.4% for fluorescence and 15.0% for reflectance, though this difference was not significant (p=0.77). Both methods returned concentrations that were similar to known MB concentrations (p≥0.79 in both cases). Fluorescence quantification of the concentration of a high extinction fluorophore did not significantly improve accuracy relative to diffuse reflectance. Investigators should consider whether fluorescence measurements are necessary for a given application.

Analysis of muscle tissue in vivo using fiber-optic autofluorescence and diffuse reflectance spectroscopy

SIGNIFICANCE

Current methods for analyzing pathological muscle tissue are time consuming and rarely quantitative, and they involve invasive biopsies. Faster and less invasive diagnosis of muscle disease may be achievable using marker-free in vivo optical sensing methods.

AIM

It was speculated that changes in the biochemical composition and structure of muscle associated with pathology could be measured quantitatively using visible wavelength optical spectroscopy techniques enabling automated classification.

APPROACH

A fiber-optic autofluorescence (AF) and diffuse reflectance (DR) spectroscopy device was manufactured. The device and data processing techniques based on principal component analysis were validated using in situ measurements on healthy skeletal and cardiac muscle. These methods were then applied to two mouse models of genetic muscle disease: a type 1 neurofibromatosis (NF1) limb-mesenchyme knockout (Nf1Prx1  -  /  -  ) and a muscular dystrophy mouse (mdx).

RESULTS

Healthy skeletal and cardiac muscle specimens were separable using AF and DR with receiver operator curve areas (ROC-AUC) of >0.79. AF and DR analyses showed optically separable changes in Nf1Prx1  -  /  -   quadriceps muscle (ROC-AUC >0.97) with no differences detected in the heart (ROC-AUC <0.67), which does not undergo gene deletion in this model. Changes in AF spectra in mdx muscle were seen between the 3 week and 10 week time points (ROC-AUC = 0.96) and were not seen in the wild-type controls (ROC-AUC = 0.58).

CONCLUSION

These findings support the utility of in vivo fiber-optic AF and DR spectroscopy for the assessment of muscle tissue. This report highlights that there is considerable scope to develop this marker-free optical technology for preclinical muscle research and for diagnostic assessment of clinical myopathies and dystrophies.

Modeling fluorescence reemission in the one-dimensional radiative transfer problem using the P3 approximation

A model of radiative transport in fluorescent, scattering media that accounts for fluorescence reabsorption and reemission effects is discussed. The model is studied in a simplified one-dimensional geometry using the P3 approximation. An example calculation of a model system, sintered polytetrafluoroethylene doped with rhodamine 6G, is used to illustrate the features of the model.

Empirical method for rapid quantification of intrinsic fluorescence signals of key metabolic probes from optical spectra measured on tissue-mimicking turbid medium

SIGNIFICANCE

Optical fluorescence spectroscopy technique has been explored extensively to quantify both glucose uptake and mitochondrial metabolism with proper fluorescent probes in small tumor models in vivo. However, it remains a great challenge to rapidly quantify the intrinsic metabolic fluorophores from the optically measured fluorescence spectra that contain significant distortions due to tissue absorption and scattering.

AIM

To enable rapid spectral data processing and quantify the in vivo metabolic parameters in real-time, we present an empirical ratio-metric method for rapid fluorescence spectra attenuation correction with high accuracy.

APPROACH

A first-order approximation of intrinsic fluorescence spectra can be obtained by dividing the fluorescence spectra by diffuse reflectance spectra with some variable powers. We further developed this approximation for rapid extraction of intrinsic key metabolic probes (2-NBDG for glucose uptake and TMRE for mitochondrial function) by dividing the distorted fluorescence spectra by diffuse reflectance intensities recorded at excitation and emission peak with a pair of system-dependent powers. Tissue-mimicking phantom studies were conducted to evaluate the method.

RESULTS

The tissue-mimicking phantom studies demonstrated that our empirical method could quantify the key intrinsic metabolic probes in near real-time with an average percent error of ∼5  %  .

CONCLUSIONS

An empirical method was demonstrated for rapid quantification of key metabolic probes from fluorescence spectra measured on a tissue-mimicking turbid medium. The proposed method will potentially facilitate real-time monitoring of key metabolic parameters of tumor models in vivo using optical spectroscopy, which will significantly advance translational cancer research.

Attenuation correction technique for fluorescence analysis of biological tissues with significantly different optical properties

During intraoperative fluorescence navigation to remove various neoplasms and during pharmacokinetic studies of photosensitizers in laboratory animals, in many cases, the ratio of photosensitizer accumulation in the tumor and normal tissue can reach ⩾ 10-fold, which inevitably changes their optical properties. At the same time, the tumor formation process causes various metabolic and structural changes at cellular and tissue levels, which lead to changes in optical properties. A hardware-software complex for the spectral-fluorescence studies of the content of fluorochromes in biological tissues with significantly different optical properties was developed, and it was tested on optical phantoms with various concentrations of photosensitizers, absorbers, and scatterers. To correct the influence of optical properties on the photosensitizer concentration analysis by fluorescence spectroscopy, we propose the spectrum-processing algorithm, which combines empirical and theory-based approaches.

Wide-field optical spectroscopy system integrating reflectance and spatial frequency domain imaging to measure attenuation-corrected intrinsic tissue fluorescence in radical prostatectomy specimens

The development of a multimodal optical imaging system is presented that integrates endogenous fluorescence and diffuse reflectance spectroscopy with single-wavelength spatial frequency domain imaging (SFDI) and surface profilometry. The system images specimens at visible wavelengths with a spatial resolution of 70 µm, a field of view of 25 cm2 and a depth of field of ∼1.5 cm. The results of phantom experiments are presented demonstrating the system retrieves absorption and reduced scattering coefficient maps using SFDI with <6% reconstruction errors. A phase-shifting profilometry technique is implemented and the resulting 3-D surface used to compute a geometric correction ensuring optical properties reconstruction errors are maintained to <6% in curved media with height variations <20 mm. Combining SFDI-computed optical properties with data from diffuse reflectance spectra is shown to correct fluorescence using a model based on light transport in tissue theory. The system is used to image a human prostate, demonstrating its ability to distinguish prostatic tissue (anterior stroma, hyperplasia, peripheral zone) from extra-prostatic tissue (urethra, ejaculatory ducts, peri-prostatic tissue). These techniques could be integrated in robotic-assisted surgical systems to enhance information provided to surgeons and improve procedural accuracy by minimizing the risk of damage to extra-prostatic tissue during radical prostatectomy procedures and eventually detect residual cancer.

Attenuation correction for confocal laser scanning microscopy and its application in chromatography

The applicability of confocal laser scanning microscopy is limited, e.g. by attenuation of the excitation and the fluorescence emission beam. As a prerequisite for further processing and analysis of the obtained microscopic images, a new method is presented for correcting this attenuation. The correction is based on beam modelling and on a differential form of the modified Beer-Lambert law. It turns out that the intensity decay can be modelled as a double convolution of the microscopic image with the intensities of the excitation semibeam and the emission beam. Under weak assumptions made for the intensities of the fluorescent radiation and the detected signal, formulas for the attenuation correction and the attenuation simulation are derived. The method traces back to that one published by Roerdink which is modified concerning a more realistic beam modelling, avoiding the so-called weak attenuation expansion and considering fluorescence excitation throughout the light cone of the excitation beam. The applicability of the method is demonstrated for synthetic examples as well as microscopic images of chromatographic beads. It is shown that the new method can be successfully applied for reconstructing the true fluorophore distribution in specimens even if the microscopic images are affected by strong attenuation. LAY DESCRIPTION: The applicability of confocal laser scanning microscopy is limited by attenuation of the excitation and the fluorescence emission beam. As a prerequisite for further processing and analysis of the obtained microscopic images, a new method is presented for correcting this attenuation. The correction is based on modeling the excitation as well as the emission beam and on a modified Beer-Lambert law for beam attenuation. The applicability of the method is demonstrated for synthetic examples as well as microscopic images of chromatographic beads. It is shown that the new method can be successfully applied for reconstructing the true fluorophore distribution in specimens even if the microscopic images are affected by strong attenuation.

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.

Transdermal fluorescence detection of a dual fluorophore system for noninvasive point-of-care gastrointestinal permeability measurement

The intestinal mucosal barrier prevents macromolecules and pathogens from entering the circulatory stream. Tight junctions in this barrier are compromised in inflammatory bowel diseases, environmental enteropathy, and enteric dysfunction. Dual sugar absorption tests are a standard method for measuring gastrointestinal integrity, however, these are not clinically amenable. Herein, we report on a dual fluorophore system and fluorescence detection instrumentation for which gastrointestinal permeability is determined in a rat small bowel disease model from the longitudinal measured transdermal fluorescence of each fluorophore. This fluorophore technology enables a specimen-free, noninvasive, point-of-care gastrointestinal permeability measurement which should be translatable to human clinical studies.

Optical Principles of Fluorescence-Guided Brain Tumor Surgery: A Practical Primer for the Neurosurgeon

Fluorescence-guided surgery is a rapidly growing field that has produced some of the most important innovations in surgical oncology in the past decade. These intraoperative imaging technologies provide information distinguishing tumor tissue from normal tissue in real time as the surgery proceeds and without disruption of the workflow. Many of these fluorescent tracers target unique molecular or cellular features of tumors, which offers the opportunity for identifying pathology with high precision to help surgeons achieve their primary objective of a maximal safe resection. As novel fluorophores and fluorescent probes emerge from preclinical development, a practical understanding of the principles of fluorescence remains critical for evaluating the clinical utility of these agents and identifying opportunities for further innovation. In this review, we provide an "in-text glossary" of the fundamental principles of fluorescence with examples of direct applications to fluorescence-guided brain surgery. We offer a detailed discussion of the various advantages and limitations of the most commonly used intraoperative imaging agents, including 5-aminolevulinic acid, indocyanine green, and fluorescein, with a particular focus on the photophysical properties of these specific agents as they provide a framework through which to understand the new agents that are entering clinical trials. To this end, we conclude with a survey of the fluorescent properties of novel agents that are currently undergoing or will soon enter clinical trials for the intraoperative imaging of brain tumors.

Quantitative Wide-Field Imaging Techniques for Fluorescence Guided Neurosurgery

Fluorescence guided surgery (FGS) has fueled the development of novel technologies aimed at maximizing the utility of fluorescence imaging to help clinicians diagnose and in certain cases treat diseases across a breadth of disciplines such as dermatology, gynecology, oncology, ophthalmology, and neurosurgery. In neurosurgery, the goal of FGS technologies is to provide the neurosurgeon with additional information which can serve as a visual aid to better identify tumor tissue and associated margins. Yet, current clinical FGS technologies are qualitative in nature, limiting the ability to make accurate, reliable, and repeatable measurements. To this end, developments in fluorescence quantification are needed to overcome current limitations of FGS. Here we present an overview of the recent developments in quantitative fluorescence guidance technologies and conclude with the most recent developments aimed at wide-field quantitative fluorescence imaging approaches in neurosurgery.

Fluorescence hyperspectral imaging for live monitoring of multiple spheroids in microfluidic chips

Tumor spheroids represent a realistic 3D in vitro cancer model because they provide a missing link between monolayer cell culture and live tissues. While microfluidic chips can easily form and assay thousands of spheroids simultaneously, few commercial instruments are available to analyze this massive amount of data. Available techniques to measure spheroid response to external stimuli, such as confocal imaging and flow cytometry, are either not appropriate for 3D cultures, or destructive. We designed a wide-field hyperspectral imaging system to analyze multiple spheroids trapped in a microfluidic chip in a single acquisition. The system and its fluorescence quantification algorithm were assessed using liquid phantoms mimicking spheroid optical properties. Spectral unmixing was tested on three overlapping spectral entities. Hyperspectral images of co-culture spheroids expressing two fluorophores were compared with confocal microscopy and spheroid growth was measured over time. The system can spectrally analyze multiple fluorescent markers simultaneously and allows multiple time-points assays, providing a fast and versatile solution for analyzing lab on a chip devices.

Concentration of FAD as a marker for cervical precancer detection

We report the ex vivo results of an in-house fabricated portable device based on polarized fluorescence measurements in the clinical environment. This device measures the polarized fluorescence and elastic scattering spectra with 405-nm laser and white light sources, respectively. The dominating fluorophore with 405-nm excitation is flavin adenine dinucleotide (FAD) with a fluorescence peak around 510 nm. The measured spectra are highly modulated by the interplay of scattering and absorption effects. Due to this, valuable information gets masked. To reduce these effects, intrinsic fluorescence was extracted by normalizing polarized fluorescence spectra with polarized elastic scattering spectra obtained. A number of fluorophores contribute to the fluorescence spectra and need to be decoupled to understand their roles in the progression of cancer. Nelder-Mead method has been utilized to fit the spectral profile with Gaussian to decouple the different bands of contributing fluorophores (FAD and porphyrin). The change in concentration of FAD during disease progression manifests in the change in ratio of total area to FWHM of its Gaussian profile. Receiver operating characteristic (ROC) curve analysis has been used to discriminate different grades of cervical precancer by using the ratio as input parameter. The sensitivity and specificity for discrimination of normal samples from CIN I (cervical intraepithelial neoplasia) are 75% and 54%, respectively. Further, the normal samples can be discriminated from CIN II samples with 100% and 82% sensitivity and specificity, respectively, and the CIN I from CIN II samples can also be discriminated with 100% sensitivity and 90% specificity, respectively. The results show that the change in the concentration of (FAD) can be used as a marker to discriminate the different grades of the cancer and biochemical changes at an early stage of the cancer can also be monitored with this technique.

5-aminolevulinic acid induced protoporphyrin IX (ALA-PpIX) fluorescence guidance in meningioma surgery

INTRODUCTION

5-aminolevulinic acid induced protoporphyrin IX (5-ALA-PpIX) fluorescence guidance has emerged as a valuable surgical adjunct for resection of intracranial tumors.

METHODS

Here we present a focused review on 5-ALA-PpIX fluorescence guidance for meningiomas.

RESULTS

We discuss the clinical studies and specific applications to date as well as the two main intraoperative fluorescence technologies applied to meningiomas.

CONCLUSIONS

The use of 5-ALA-PpIX in meningiomas holds promising potential so neurosurgeons can improve surgical outcomes for patients with meningiomas as well as be pioneers in developing improved fluorescence imaging technologies.

Tissue intrinsic fluorescence recovering by an empirical approach based on the PSO algorithm and its application in type 2 diabetes screening

In order to reduce the influence of scattering and absorption on tissue fluorescence spectra, after tissue fluorescence and diffuse reflectance in different tissue optical properties were simulated by the Monte Carlo method, a tissue intrinsic fluorescence recovering algorithm making use of diffuse reflectance spectrum was developed. The empirical parameters in the tissue intrinsic fluorescence recovering algorithm were coded as a particle in the solution domain, the classification performance was defined as the fitness, and then a particle swarm optimization (PSO) algorithm was established for empirical parameters optimization. The skin autofluorescence and diffuse reflectance spectra of 327 subjects were collected in Anhui Provincial Hospital. The skin intrinsic autofluorescence spectra were recovered by using the empirical approach and the integration area of the spectra were calculated as fluorescence intensity. Receiver operating characteristic (ROC) analysis for fluorescence intensity was applied to evaluate the classification performance in type 2 diabetes screening. In addition, a support vector machine (SVM) method was implemented to improve the performance of the classification. The results showed that the sensitivity and specificity were 32% and 76% respectively, and the area under the curve was 0.54 before recovering, while the sensitivity and specificity were 72% and 86% respectively, and the area under the curve was 0.86 after recovering. Furthermore, the sensitivity and specificity increased to 83% and 86% respectively when using linear SVM while 84% and 88%, respectively, when using nonlinear SVM. The results indicate that using the tissue fluorescence spectrum recovery algorithm based on PSO can improve the application of tissue fluorescence spectroscopy effectively.

Intrinsic fluorescence for cervical precancer detection using polarized light based in-house fabricated portable device

An in-house fabricated portable device has been tested to detect cervical precancer through the intrinsic fluorescence from human cervix of the whole uterus in a clinical setting. A previously validated technique based on simultaneously acquired polarized fluorescence and polarized elastic scattering spectra from a turbid medium is used to extract the intrinsic fluorescence. Using a diode laser at 405 nm, intrinsic fluorescence of flavin adenine dinucleotide, which is the dominant fluorophore and other contributing fluorophores in the epithelium of cervical tissue, has been extracted. Different grades of cervical precancer (cervical intraepithelial neoplasia; CIN) have been discriminated using principal component analysis-based Mahalanobis distance and linear discriminant analysis. Normal, CIN I and CIN II samples have been discriminated from one another with high sensitivity and specificity at 95% confidence level. This ex vivo study with cervix of whole uterus samples immediately after hysterectomy in a clinical environment indicates that the in-house fabricated portable device has the potential to be used as a screening tool for in vivo precancer detection using intrinsic fluorescence.

qF-SSOP: real-time optical property corrected fluorescence imaging

Fluorescence imaging is well suited to provide image guidance during resections in oncologic and vascular surgery. However, the distorting effects of tissue optical properties on the emitted fluorescence are poorly compensated for on even the most advanced fluorescence image guidance systems, leading to subjective and inaccurate estimates of tissue fluorophore concentrations. Here we present a novel fluorescence imaging technique that performs real-time (i.e., video rate) optical property corrected fluorescence imaging. We perform full field of view simultaneous imaging of tissue optical properties using Single Snapshot of Optical Properties (SSOP) and fluorescence detection. The estimated optical properties are used to correct the emitted fluorescence with a quantitative fluorescence model to provide quantitative fluorescence-Single Snapshot of Optical Properties (qF-SSOP) images with less than 5% error. The technique is rigorous, fast, and quantitative, enabling ease of integration into the surgical workflow with the potential to improve molecular guidance intraoperatively.

Imaging the pharmacology of nanomaterials by intravital microscopy: Toward understanding their biological behavior

Therapeutic nanoparticles (NPs) can deliver cytotoxic chemotherapeutics and other drugs more safely and efficiently to patients; furthermore, selective delivery to target tissues can theoretically be accomplished actively through coating NPs with molecular ligands, and passively through exploiting physiological "enhanced permeability and retention" features. However, clinical trial results have been mixed in showing improved efficacy with drug nanoencapsulation, largely due to heterogeneous NP accumulation at target sites across patients. Thus, a clear need exists to better understand why many NP strategies fail in vivo and not result in significantly improved tumor uptake or therapeutic response. Multicolor in vivo confocal fluorescence imaging (intravital microscopy; IVM) enables integrated pharmacokinetic and pharmacodynamic (PK/PD) measurement at the single-cell level, and has helped answer key questions regarding the biological mechanisms of in vivo NP behavior. This review summarizes progress to date and also describes useful technical strategies for successful IVM experimentation.

Optical technologies for intraoperative neurosurgical guidance

Biomedical optics is a broadly interdisciplinary field at the interface of optical engineering, biophysics, computer science, medicine, biology, and chemistry, helping us understand light-tissue interactions to create applications with diagnostic and therapeutic value in medicine. Implementation of biomedical optics tools and principles has had a notable scientific and clinical resurgence in recent years in the neurosurgical community. This is in great part due to work in fluorescence-guided surgery of brain tumors leading to reports of significant improvement in maximizing the rates of gross-total resection. Multiple additional optical technologies have been implemented clinically, including diffuse reflectance spectroscopy and imaging, optical coherence tomography, Raman spectroscopy and imaging, and advanced quantitative methods, including quantitative fluorescence and lifetime imaging. Here we present a clinically relevant and technologically informed overview and discussion of some of the major clinical implementations of optical technologies as intraoperative guidance tools in neurosurgery.

Quantitative Fluorescence Sensing Through Highly Autofluorescent, Scattering, and Absorbing Media Using Mobile Microscopy

Compact and cost-effective systems for in vivo fluorescence and near-infrared imaging in combination with activatable reporters embedded inside the skin to sample interstitial fluid or blood can enable a variety of biomedical applications. However, the strong autofluorescence of human skin creates an obstacle for fluorescence-based sensing. Here we introduce a method for quantitative fluorescence sensing through highly autofluorescent, scattering, and absorbing media. For this, we created a compact and cost-effective fluorescence microscope weighing <40 g and used it to measure various concentrations of a fluorescent dye embedded inside a tissue phantom, which was designed to mimic the optical characteristics of human skin. We used an elliptical Gaussian beam excitation to digitally separate tissue autofluorescence from target fluorescence, although they severely overlap in both space and optical spectrum. Using ∼10-fold less excitation intensity than the safety limit for skin radiation exposure, we successfully quantified the density of the embedded fluorophores by imaging the skin phantom surface and achieved a detection limit of ∼5 × 10(5) and ∼2.5 × 10(7) fluorophores within ∼0.01 μL sample volume that is positioned 0.5 and 2 mm below the phantom surface, corresponding to a concentration of 105.9 pg/mL and 5.3 ng/mL, respectively. We also confirmed that this approach can track the spatial misalignments of the mobile microscope with respect to the embedded target fluorescent volume. This wearable microscopy platform might be useful for designing implantable biochemical sensors with the capability of spatial multiplexing to continuously monitor a panel of biomarkers and chronic conditions even at patients' home.

Mathematical model to interpret localized reflectance spectra measured in the presence of a strong fluorescence marker

Quantification of multiple fluorescence markers during neurosurgery has the potential to provide complementary contrast mechanisms between normal and malignant tissues, and one potential combination involves fluorescein sodium (FS) and aminolevulinic acid-induced protoporphyrin IX (PpIX). We focus on the interpretation of reflectance spectra containing contributions from elastically scattered (reflected) photons as well as fluorescence emissions from a strong fluorophore (i.e., FS). A model-based approach to extract μa and μ′s in the presence of FS emission is validated in optical phantoms constructed with Intralipid (1% to 2% lipid) and whole blood (1% to 3% volume fraction), over a wide range of FS concentrations (0 to 1000  μg/ml 1000  μg/ml ). The results show that modeling reflectance as a combination of elastically scattered light and attenuation-corrected FS-based emission yielded more accurate tissue parameter estimates when compared with a nonmodified reflectance model, with reduced maximum errors for blood volume (22% versus 90%), microvascular saturation (21% versus 100%), and μs′ (13% versus 207%). Additionally, quantitative PpIX fluorescence sampled in the same phantom as FS showed significant differences depending on the reflectance model used to estimate optical properties (i.e., maximum error 29% versus 86%). These data represent a first step toward using quantitative optical spectroscopy to guide surgeries through simultaneous assessment of FS and PpIX.

Multispectral fluorescence imaging of human ovarian and fallopian tube tissue for early-stage cancer detection

With early detection, 5-year survival rates for ovarian cancer exceed 90%, yet no effective early screening method exists. Emerging consensus suggests over 50% of the most lethal form of the disease originates in the fallopian tube. Twenty-eight women undergoing oophorectomy or debulking surgery provided informed consent for the use of surgical discard tissue samples for multispectral fluorescence imaging. Using multiple ultraviolet and visible excitation wavelengths and emissions bands, 12 fluorescence and 6 reflectance images of 47 ovarian and 31 fallopian tube tissue samples were recorded. After imaging, each sample was fixed, sectioned, and stained for pathological evaluation. Univariate logistic regression showed cancerous tissue samples had significantly lower intensity than noncancerous tissue for 17 image types. The predictive power of multiple image types was evaluated using multivariate logistic regression (MLR) and quadratic discriminant analysis (QDA). Two MLR models each using two image types had receiver operating characteristic curves with area under the curve exceeding 0.9. QDA determined 56 image type combinations with perfect resubstituting using as few as five image types. Adaption of the system for future in vivo fallopian tube and ovary endoscopic imaging is possible, which may enable sensitive detection of ovarian cancer with no exogenous contrast agents.

Computational model of bladder tissue based on its measured optical properties

Urinary bladder diseases are a common problem throughout the world and often difficult to accurately diagnose. Furthermore, they pose a heavy financial burden on health services. Urinary bladder tissue from male pigs was spectrophotometrically measured and the resulting data used to calculate the absorption, transmission, and reflectance parameters, along with the derived coefficients of scattering and absorption. These were employed to create a "generic" computational bladder model based on optical properties, simulating the propagation of photons through the tissue at different wavelengths. Using the Monte-Carlo method and fluorescence spectra of UV and blue excited wavelength, diagnostically important biomarkers were modeled. Additionally, the multifunctional noninvasive diagnostics system "LAKK-M" was used to gather fluorescence data to further provide essential comparisons. The ultimate goal of the study was to successfully simulate the effects of varying excited radiation wavelengths on bladder tissue to determine the effectiveness of photonics diagnostic devices. With increased accuracy, this model could be used to reliably aid in differentiating healthy and pathological tissues within the bladder and potentially other hollow organs.

Fluoromodule-based reporter/probes designed for in vivo fluorescence imaging

Optical imaging of whole, living animals has proven to be a powerful tool in multiple areas of preclinical research and has allowed noninvasive monitoring of immune responses, tumor and pathogen growth, and treatment responses in longitudinal studies. However, fluorescence-based studies in animals are challenging because tissue absorbs and autofluoresces strongly in the visible light spectrum. These optical properties drive development and use of fluorescent labels that absorb and emit at longer wavelengths. Here, we present a far-red absorbing fluoromodule-based reporter/probe system and show that this system can be used for imaging in living mice. The probe we developed is a fluorogenic dye called SC1 that is dark in solution but highly fluorescent when bound to its cognate reporter, Mars1. The reporter/probe complex, or fluoromodule, produced peak emission near 730 nm. Mars1 was able to bind a variety of structurally similar probes that differ in color and membrane permeability. We demonstrated that a tool kit of multiple probes can be used to label extracellular and intracellular reporter-tagged receptor pools with 2 colors. Imaging studies may benefit from this far-red excited reporter/probe system, which features tight coupling between probe fluorescence and reporter binding and offers the option of using an expandable family of fluorogenic probes with a single reporter gene.

Quantitative fluorescence using 5-aminolevulinic acid-induced protoporphyrin IX biomarker as a surgical adjunct in low-grade glioma surgery

OBJECT

Previous studies in high-grade gliomas (HGGs) have indicated that protoporphyrin IX (PpIX) accumulates in higher concentrations in tumor tissue, and, when used to guide surgery, it has enabled improved resection leading to increased progression-free survival. Despite the benefits of complete resection and the advances in fluorescence-guided surgery, few studies have investigated the use of PpIX in low-grade gliomas (LGGs). Here, the authors describe their initial experience with 5-aminolevulinic acid (ALA)-induced PpIX fluorescence in a series of patients with LGG.

METHODS

Twelve patients with presumed LGGs underwent resection of their tumors after receiving 20 mg/kg of ALA approximately 3 hours prior to surgery under an institutional review board-approved protocol. Intraoperative assessments of the resulting PpIX emissions using both qualitative, visible fluorescence and quantitative measurements of PpIX concentration were obtained from tissue locations that were subsequently biopsied and evaluated histopathologically. Mixed models for random effects and receiver operating characteristic curve analysis for diagnostic performance were performed on the fluorescence data relative to the gold-standard histopathology.

RESULTS

Five of the 12 LGGs (1 ganglioglioma, 1 oligoastrocytoma, 1 pleomorphic xanthoastrocytoma, 1 oligodendroglioma, and 1 ependymoma) demonstrated at least 1 instance of visible fluorescence during surgery. Visible fluorescence evaluated on a specimen-by-specimen basis yielded a diagnostic accuracy of 38.0% (cutoff threshold: visible fluorescence score ≥ 1, area under the curve = 0.514). Quantitative fluorescence yielded a diagnostic accuracy of 67% (for a cutoff threshold of the concentration of PpIX [CPpIX] > 0.0056 μg/ml, area under the curve = 0.66). The authors found that 45% (9/20) of nonvisibly fluorescent tumor specimens, which would have otherwise gone undetected, accumulated diagnostically significant levels of CPpIX that were detected quantitatively.

CONCLUSIONS

The authors' initial experience with ALA-induced PpIX fluorescence in LGGs concurs with other literature reports that the resulting visual fluorescence has poor diagnostic accuracy. However, the authors also found that diagnostically significant levels of CPpIX do accumulate in LGGs, and the resulting fluorescence emissions are very often below the detection threshold of current visual fluorescence imaging methods. Indeed, at least in the authors' initial experience reported here, if quantitative detection methods are deployed, the diagnostic performance of ALA-induced PpIX fluorescence in LGGs approaches the accuracy associated with visual fluorescence in HGGs.

A technique for correction of attenuations in synchronous fluorescence spectroscopy

Synchronous fluorescence spectroscopy is an efficient technique for decoupling fluorophores which are masked in fluorescence spectroscopy due to overlapping of dominant fluorophores. By choosing appropriate offsets between excitation and emission wavelengths during signal acquisition from turbid samples, responses of individual fluorophores are highlighted as sharp peaks by using this technique. Some of the peaks may, however, still be missed due to wavelength dependent absorption and scattering effects. In this study a correction technique is used to extract such hidden signatures. The technique is validated using tissue phantoms with known concentrations of fluorophores, absorbers and scatterers. On the basis of validation studies on single and combination of two fluorophores, it is found that lower offsets display better recovery due to minimal influence of absorption by blood. Among the different offsets, 55 nm is found to be optimal for investigation of cervical precancers.

Correction for tissue optical properties enables quantitative skin fluorescence measurements using multi-diameter single fiber reflectance spectroscopy

BACKGROUND AND OBJECTIVE

Fluorescence measurements in the skin are very much affected by absorption and scattering but existing methods to correct for this are not applicable to superficial skin measurements.

STUDY DESIGN/MATERIALS AND METHODS

The first use of multiple-diameter single fiber reflectance (MDSFR) and single fiber fluorescence (SFF) spectroscopy in human skin was investigated. MDSFR spectroscopy allows a quantification of the full optical properties in superficial skin (μa, μs' and γ), which can next be used to retrieve the corrected - intrinsic - fluorescence of a fluorophore Qμa,x(f). Our goal was to investigate the importance of such correction for individual patients. We studied this in 22 patients undergoing photodynamic therapy (PDT) for actinic keratosis.

RESULTS

The magnitude of correction of fluorescence was around 4 (for both autofluorescence and protoporphyrin IX). Moreover, it was variable between patients, but also within patients over the course of fractionated aminolevulinic acid PDT (range 2.7-7.5). Patients also varied in the amount of protoporphyrin IX synthesis, photobleaching percentages and resynthesis (>100× difference between the lowest and highest PpIX synthesis). The autofluorescence was lower in actinic keratosis than contralateral normal skin (0.0032 versus 0.0052; P<0.0005).

CONCLUSIONS

Our results clearly demonstrate the importance of correcting the measured fluorescence for optical properties, because these vary considerably between individual patients and also during PDT. Protoporphyrin IX synthesis and photobleaching kinetics allow monitoring clinical PDT which facilitates individual-based PDT dosing and improvement of clinical treatment protocols. Furthermore, the skin autofluorescence can be relevant for diagnostic use in the skin, but it may also be interesting because of its association with several internal diseases.

Macroscopic-imaging technique for subsurface quantification of near-infrared markers during surgery

Obtaining accurate quantitative information on the concentration and distribution of fluorescent markers lying at a depth below the surface of optically turbid media, such as tissue, is a significant challenge. Here, we introduce a fluorescence reconstruction technique based on a diffusion light transport model that can be used during surgery, including guiding resection of brain tumors, for depth-resolved quantitative imaging of near-infrared fluorescent markers. Hyperspectral fluorescence images are used to compute a topographic map of the fluorophore distribution, which yields structural and optical constraints for a three-dimensional subsequent hyperspectral diffuse fluorescence reconstruction algorithm. Using the model fluorophore Alexa Fluor 647 and brain-like tissue phantoms, the technique yielded estimates of fluorophore concentration within ±25% of the true value to depths of 5 to 9 mm, depending on the concentration. The approach is practical for integration into a neurosurgical fluorescence microscope and has potential to further extend fluorescence-guided resection using objective and quantified metrics of the presence of residual tumor tissue.

Optical detection of tracer species in strongly scattering media

A combination of optical absorption and scattering is used to detect tracer species in a strongly scattering medium. An optical setup was developed, consisting of a dual-beam scattering detection scheme in which sample scattering beam overlaps with the characteristic absorption feature of quantum dot tracer species, while the reference scattering beam is outside any absorption features of the tracer. This scheme was successfully tested in engineered breakthrough tests typical of wastewater and subsurface fluid analysis, as well as in batch analysis of oil and gas reservoir fluids and biological samples. Tracers were detected even under highly scattering conditions, conditions in which conventional absorption or fluorescence methods failed.

Detecting cervical cancer progression through extracted intrinsic fluorescence and principal component analysis

Intrinsic fluorescence spectra of the human normal, cervical intraepithelial neoplasia 1 (CIN1), CIN2, and cervical cancer tissue have been extracted by effectively combining the measured polarized fluorescence and polarized elastic scattering spectra. The efficacy of principal component analysis (PCA) to disentangle the collective behavior from smaller correlated clusters in a dimensionally reduced space in conjunction with the intrinsic fluorescence is examined. This combination unambiguously reveals the biochemical changes occurring with the progression of the disease. The differing activities of the dominant fluorophores, collagen, nicotinamide adenine dinucleotide, flavins, and porphyrin of different grades of precancers are clearly identified through a careful examination of the sectorial behavior of the dominant eigenvectors of PCA. To further classify the different grades, the Mahalanobis distance has been calculated using the scores of selected principal components.

5-Aminolevulinic acid-induced protoporphyrin IX fluorescence in meningioma: qualitative and quantitative measurements in vivo

BACKGROUND

The use of 5-aminolevulinic acid (ALA)-induced protoporphyrin IX (PpIX) fluorescence has shown promise as a surgical adjunct for maximizing the extent of surgical resection in gliomas. To date, the clinical utility of 5-ALA in meningiomas is not fully understood, with most descriptive studies using qualitative approaches to 5-ALA-PpIX.

OBJECTIVE

To assess the diagnostic performance of 5-ALA-PpIX fluorescence during surgical resection of meningioma.

METHODS

ALA was administered to 15 patients with meningioma undergoing PpIX fluorescence-guided surgery at our institution. At various points during the procedure, the surgeon performed qualitative, visual assessments of fluorescence by using the surgical microscope, followed by a quantitative fluorescence measurement by using an intraoperative probe. Specimens were collected at each point for subsequent neuropathological analysis. Clustered data analysis of variance was used to ascertain a difference between groups, and receiver operating characteristic analyses were performed to assess diagnostic capabilities.

RESULTS

Red-pink fluorescence was observed in 80% (12/15) of patients, with visible fluorescence generally demonstrating a strong, homogenous character. Quantitative fluorescence measured diagnostically significant PpIX concentrations (cPpIx) in both visibly and nonvisibly fluorescent tissues, with significantly higher cPpIx in both visibly fluorescent (P < .001) and tumor tissue (P = .002). Receiver operating characteristic analyses also showed diagnostic accuracies up to 90% for differentiating tumor from normal dura.

CONCLUSION

ALA-induced PpIX fluorescence guidance is a potential and promising adjunct in accurately detecting neoplastic tissue during meningioma resective surgery. These results suggest a broader reach for PpIX as a biomarker for meningiomas than was previously noted in the literature.

Attenuation-corrected fluorescence spectra unmixing for spectroscopy and microscopy

In fluorescence measurements, light is often absorbed and scattered by a sample both for excitation and emission, resulting in the measured spectra to be distorted. Conventional linear unmixing methods computationally separate overlapping spectra but do not account for these effects. We propose a new algorithm for fluorescence unmixing that accounts for the attenuation-related distortion effect on fluorescence spectra. Using a matrix representation, we derive forward measurement formation and a corresponding inverse method; the unmixing algorithm is based on nonnegative matrix factorization. We also demonstrate how this method can be extended to a higher-dimensional tensor form, which is useful for unmixing overlapping spectra observed under the attenuation effect in spectral imaging microscopy. We evaluate the proposed methods in simulation and experiments and show that it outperforms a conventional, linear unmixing method when absorption and scattering contributes to the measured signals, as in deep tissue imaging.

Steady-state total diffuse reflectance with an exponential decaying source

The increasing preclinical and clinical utilization of digital cameras for photographic measurements of tissue conditions motivates the study of reflectance measurements obtained with planar illumination. We examine herein a formula that models the total diffuse reflectance measured from a semi-infinite medium using an exponentially decaying source, assuming continuous plane wave epi-illumination. The model is validated with experimental reflectance measurements from tissue mimicking phantoms. The need for adjusting the blood absorption spectrum due to pigment packaging is discussed along with the potential applications of the proposed formulation.

Monitoring hemodynamic and metabolic alterations during severe hemorrhagic shock in rat brains

RATIONALE AND OBJECTIVES

Our long-term goals are to identify imaging biomarkers for hemorrhagic shock and to understand how the preservation of cerebral microcirculation works. We also seek to understand how the damage occurs to the cerebral hemodynamics and the mitochondrial metabolism during severe hemorrhagic shock.

MATERIALS AND METHODS

We used a multimodal cerebral cortex optical imaging system to obtain 4-hour observations of cerebral hemodynamic and metabolic alterations in exposed rat cortexes during severe hemorrhagic shock. We monitored the mean arterial pressure, heart rate, cerebral blood flow (CBF), functional vascular density (FVD), vascular perfusion and diameter, blood oxygenation, and mitochondrial reduced nicotinamide adenine dinucleotide (NADH) signals.

RESULTS

During the rapid bleeding and compensatory stage, cerebral parenchymal circulation was protected by inhibiting the perfusion of dural vessels. During the compensatory stage, although the brain parenchymal CBF and FVD decreased rapidly, the NADH signal did not show a significant increase. During the decompensatory stage, FVD and CBF maintained the same low level and the NADH signal remained unchanged. However, the NADH signal showed a significant increase after the rapid blood infusion. FVD and CBF rebounded to the baseline after the resuscitation and then declined again.

CONCLUSIONS

We present for the first time simultaneous imaging of cerebral hemodynamics and NADH signals in vivo during the process of hemorrhagic shock. This novel multimodal method demonstrated clearly that severe hemorrhagic shock imparts irreversible tissue damage that is not compensated by the autoregulatory mechanism. Hemodynamic and metabolic signatures including CBF, FVD, and NADH may be further developed to provide sensitive biomarkers for stage transitions in hemorrhagic shock.

Towards clinically translatable NIR fluorescence molecular guidance for colonoscopy

White-light surveillance colonoscopy is the standard of care for the detection and removal of premalignant lesions to prevent colorectal cancer, and the main screening recommendation following treatment for recurrence detection. However, it lacks sufficient diagnostic yield, exhibits unacceptable adenoma miss-rates and is not capable of revealing functional and morphological information of the detected lesions. Fluorescence molecular guidance in the near-infrared (NIR) is expected to have outstanding relevance regarding early lesion detection and heterogeneity characterization within and among lesions in these interventional procedures. Thereby, superficial and sub-surface tissue biomarkers can be optimally visualized due to a minimization of tissue attenuation and autofluorescence by comparison with the visible, which simultaneously enhance tissue penetration and assure minimal background. At present, this potential is challenged by the difficulty associated with the clinical propagation of disease-specific contrast agents and the absence of a commercially available endoscope that is capable of acquiring wide-field, NIR fluorescence at video-rates. We propose two alternative flexible endoscopic fluorescence imaging methods, each based on a CE certified commercial, clinical grade endoscope, and the employment of an approved monoclonal antibody labeled with a clinically applicable NIR fluorophore. Pre-clinical validation of these two strategies that aim at bridging NIR fluorescence molecular guidance to clinical translation is demonstrated in this study.

Enhanced visibility of colonic neoplasms using formulaic ratio imaging of native fluorescence

BACKGROUND AND OBJECTIVES

Colonoscopy is the preferred method for colon cancer screening, but can miss polyps and flat neoplasms with low color contrast. The objective was to develop a new autofluorescence method that improves image contrast of colonic neoplasms.

STUDY DESIGN/MATERIALS AND METHODS

We selected the three strongest native fluorescence signals and developed a novel method where fluorescence images are processed in a ratiometric formula to represent the likely cellular and structural changes associated with neoplasia. Native fluorescence images of fresh surgical specimens of the colon containing normal mucosa, polypoid and flat adenomas as well as adenocarcinoma were recorded using a prototype multi-spectral imager. Sixteen patients, with a mean age of 62 years (range 28-81) undergoing elective resection for colonic neoplasms were enrolled. High contrast images were seen with fluorescence from tryptophan (Tryp), flavin adenine dinucleotide (FAD) and collagen.

RESULTS

When the image intensity of Tryp was divided pixel by pixel, by the intensities of FAD and collagen, the resulting formulaic ratio (FR) images were of exceptionally high contrast. The FR images of adenomas and adenocarcinomas had increased Weber contrast.

CONCLUSIONS

FR imaging is a novel imaging process that represents the likely metabolic and structural changes in colonic neoplasia that produces images with remarkably high contrast.

Enhanced visibility of colonic neoplasms using formulaic ratio imaging of native fluorescence

BACKGROUND AND OBJECTIVES

Colonoscopy is the preferred method for colon cancer screening, but can miss polyps and flat neoplasms with low color contrast. The objective was to develop a new autofluorescence method that improves image contrast of colonic neoplasms.

STUDY DESIGN/MATERIALS AND METHODS

We selected the three strongest native fluorescence signals and developed a novel method where fluorescence images are processed in a ratiometric formula to represent the likely cellular and structural changes associated with neoplasia. Native fluorescence images of fresh surgical specimens of the colon containing normal mucosa, polypoid and flat adenomas as well as adenocarcinoma were recorded using a prototype multi-spectral imager. Sixteen patients, with a mean age of 62 years (range 28-81) undergoing elective resection for colonic neoplasms were enrolled. High contrast images were seen with fluorescence from tryptophan (Tryp), flavin adenine dinucleotide (FAD) and collagen.

RESULTS

When the image intensity of Tryp was divided pixel by pixel, by the intensities of FAD and collagen, the resulting formulaic ratio (FR) images were of exceptionally high contrast. The FR images of adenomas and adenocarcinomas had increased Weber contrast.

CONCLUSIONS

FR imaging is a novel imaging process that represents the likely metabolic and structural changes in colonic neoplasia that produces images with remarkably high contrast.

Monitoring tissue perfusion, oxygenation, and metabolism in critically ill patients

Alterations in oxygen transport and use are integral to the development of multiple organ failure; therefore, the ultimate goal of resuscitation is to restore effective tissue oxygenation and cellular metabolism. Hemodynamic monitoring is the cornerstone of management to promptly identify and appropriately manage (impending) organ dysfunction. Prospective randomized trials have confirmed outcome benefit when preemptive or early treatment is directed toward maintaining or restoring adequate tissue perfusion. However, treatment end points remain controversial, in large part because of current difficulties in determining what constitutes "optimal." Information gained from global whole-body monitoring may not detect regional organ perfusion abnormalities until they are well advanced. Conversely, the ideal "canary" organ that is readily accessible for monitoring, yet offers an early and sensitive indicator of tissue "unwellness," remains to be firmly identified. This review describes techniques available for real-time monitoring of tissue perfusion and metabolism and highlights novel developments that may complement or even supersede current tools.

System and methods for wide-field quantitative fluorescence imaging during neurosurgery

We report an accurate, precise and sensitive method and system for quantitative fluorescence image-guided neurosurgery. With a low-noise, high-dynamic-range CMOS array, we perform rapid (integration times as low as 50 ms per wavelength) hyperspectral fluorescence and diffuse reflectance detection and apply a correction algorithm to compensate for the distorting effects of tissue absorption and scattering. Using this approach, we generated quantitative wide-field images of fluorescence in tissue-simulating phantoms for the fluorophore PpIX, having concentrations and optical absorption and scattering variations over clinically relevant ranges. The imaging system was tested in a rodent model of glioma, detecting quantitative levels down to 20 ng/ml. The resulting performance is a significant advance on existing wide-field quantitative imaging techniques, and provides performance comparable to a point-spectroscopy probe that has previously demonstrated significant potential for improved detection of malignant brain tumors during surgical resection.

Image-guided cancer surgery using near-infrared fluorescence

Paradigm shifts in surgery arise when surgeons are empowered to perform surgery faster, better and less expensively than current standards. Optical imaging that exploits invisible near-infrared (NIR) fluorescent light (700-900 nm) has the potential to improve cancer surgery outcomes, minimize the time patients are under anaesthesia and lower health-care costs largely by way of its improved contrast and depth of tissue penetration relative to visible light. Accordingly, the past few years have witnessed an explosion of proof-of-concept clinical trials in the field. In this Review, we introduce the concept of NIR fluorescence imaging for cancer surgery, examine the clinical trial literature to date and outline the key issues pertaining to imaging system and contrast agent optimization. Although NIR seems to be superior to many traditional imaging techniques, its incorporation into routine care of patients with cancer depends on rigorous clinical trials and validation studies.