Diagnostic potential of autofluorescence for an assisted intraoperative delineation of glioblastoma resection margins

Label-Free Assessment of Key Biological Autofluorophores: Material Characteristics and Opportunities for Clinical Applications

Autofluorophores are endogenous fluorescent compounds that naturally occur in the intra and extracellular spaces of all tissues and organs. Most have vital biological functions - like the metabolic cofactors NAD(P)H and FAD+, as well as the structural protein collagen. Others are considered to be waste products - like lipofuscin and advanced glycation end products - which accumulate with age and are associated with cellular dysfunction. Due to their natural fluorescence, these materials have great utility for enabling non-invasive, label-free assays with direct ties to biological function. Numerous technologies, with different advantages and drawbacks, are applied to their assessment, including fluorescence lifetime imaging microscopy, hyperspectral microscopy, and flow cytometry. Here, the applications of label-free autofluorophore assessment are reviewed for clinical and health-research applications, with specific attention to biomaterials, disease detection, surgical guidance, treatment monitoring, and tissue assessment - fields that greatly benefit from non-invasive methodologies capable of continuous, in vivo characterization.

Miniature fluorescence sensor for quantitative detection of brain tumour

Fluorescence-guided surgery has emerged as a vital tool for tumour resection procedures. As well as intraoperative tumour visualisation, 5-ALA-induced PpIX provides an avenue for quantitative tumour identification based on ratiometric fluorescence measurement. To this end, fluorescence imaging and fibre-based probes have enabled more precise demarcation between the cancerous and healthy tissues. These sensing approaches, which rely on collecting the fluorescence light from the tumour resection site and its "remote" spectral sensing, introduce challenges associated with optical losses. In this work, we demonstrate the viability of tumour detection at the resection site using a miniature fluorescence measurement system. Unlike the current bulky systems, which necessitate remote measurement, we have adopted a millimetre-sized spectral sensor chip for quantitative fluorescence measurements. A reliable measurement at the resection site requires a stable optical window between the tissue and the optoelectronic system. This is achieved using an antifouling diamond window, which provides stable optical transparency. The system achieved a sensitivity of 92.3% and specificity of 98.3% in detecting a surrogate tumour at a resolution of 1 × 1 mm2. As well as addressing losses associated with collecting and coupling fluorescence light in the current 'remote' sensing approaches, the small size of the system introduced in this work paves the way for its direct integration with the tumour resection tools with the aim of more accurate interoperative tumour identification.

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.

In vivo characterization of the human glioblastoma infiltrative edge with label-free intraoperative fluorescence lifetime imaging

Challenges in identifying a glioblastoma's infiltrative edge during neurosurgical procedures result in rapid recurrence. A label-free fluorescence lifetime imaging (FLIm) device was used to evaluate glioblastoma's infiltrative edge in vivo in 15 patients (89 samples). FLIm data were analyzed according to tumor cell density, infiltrating tissue type (gray and white matter), and diagnosis history (new or recurrent). Infiltrations in white matter from new glioblastomas showed decreasing lifetimes and a spectral red shift with increasing tumor cell density. Areas of high versus low tumor cell density were separated through a linear discriminant analysis with a ROC-AUC=0.74. Current results support the feasibility of intraoperative FLIm for real-time in vivo brain measurements and encourage refinement to predict glioblastoma infiltrative edge, underscoring the ability of FLIm to optimize neurosurgical outcomes.

Comparative Study Between a Customized Bimodal Endoscope and a Benchtop Microscope for Quantitative Tissue Diagnosis

Nowadays, surgical removal remains the standard method to treat brain tumors. During surgery, the neurosurgeon may encounter difficulties to delimitate tumor boundaries and the infiltrating areas as they have a similar visual appearance to adjacent healthy zones. These infiltrating residuals increase the tumor recurrence risk, which decreases the patient’s post-operation survival time. To help neurosurgeons improve the surgical act by accurately delimitating healthy from cancerous areas, our team is developing an intraoperative multimodal imaging tool. It consists of a two-photon fluorescence fibered endomicroscope that is intended to provide a fast, real-time, and reliable diagnosis information. In parallel to the instrumental development, a large optical database is currently under construction in order to characterize healthy and tumor brain tissues with their specific optical signature using multimodal analysis of the endogenous fluorescence. Our previous works show that this multimodal analysis could provide a reliable discrimination response between different tissue types based on several optical indicators. Here, our goal is to show that the two-photon fibered endomicroscope is able to provide, based on the same approved indicators in the tissue database, the same reliable response that could be used intraoperatively. We compared the spectrally resolved and time-resolved fluorescence signal, generated by our two-photon bimodal endoscope from 46 fresh brain tissue samples, with a similar signal provided by a standard reference benchtop multiphoton microscope that has been validated for tissue diagnosis. The higher excitation efficiency and collection ability of an endogenous fluorescence signal were shown for the endoscope setup. Similar molecular ratios and fluorescence lifetime distributions were extracted from the two compared setups. Spectral discrimination ability of the bimodal endoscope was validated. As a preliminary step before tackling multimodality, the ability of the developed bimodal fibered endoscope to excite and to collect efficiently as well as to provide a fast exploitable high-quality signal that is reliable to discriminate different types of human brain tissues was validated.

Preliminary Report: Rapid Intraoperative Detection of Residual Glioma Cell in Resection Cavity Walls Using a Compact Fluorescence Microscope

Objective: The surgical eradication of malignant glioma cells is theoretically impossible. Therefore, reducing the number of remaining tumor cells around the brain–tumor interface (BTI) is crucial for achieving satisfactory clinical results. The usefulness of fluorescence–guided resection for the treatment of malignant glioma was recently reported, but the detection of infiltrating tumor cells in the BTI using a surgical microscope is not realistic. Therefore, we have developed an intraoperative rapid fluorescence cytology system, and exploratorily evaluated its clinical feasibility for the management of malignant glioma. Materials and methods: A total of 25 selected patients with malignant glioma (newly diagnosed: 17; recurrent: 8) underwent surgical resection under photodiagnosis using photosensitizer Talaporfin sodium and a semiconductor laser. Intraoperatively, a crush smear preparation was made from a tiny amount of tumor tissue, and the fluorescence emitted upon 620/660 nm excitation was evaluated rapidly using a compact fluorescence microscope in the operating theater. Results: Fluorescence intensities of tumor tissues measured using a surgical microscope correlated with the tumor cell densities of tissues evaluated by measuring the red fluorescence emitted from the cytoplasm of tumor cells using a fluorescence microscope. A “weak fluorescence” indicated a reduction in the tumor cell density, whereas “no fluorescence” did not indicate the complete eradication of the tumor cells, but indicated that few tumor cells were emitting fluorescence. Conclusion: The rapid intraoperative detection of fluorescence from glioma cells using a compact fluorescence microscope was probably useful to evaluate the presence of tumor cells in the resection cavity walls, and could provide surgical implications for the more complete resection of malignant gliomas.

Optical Characterization of Sodium Fluorescein In Vitro and Ex Vivo

Objective

The utilization of fluorescein-guided biopsies and resection has been recently discussed as a suitable strategy to improve and expedite operative techniques for the resection of central nervous system (CNS) tumors. However, little is known about the optical properties of sodium fluorescein (NaFl) in human tumor tissue and their potential impact on ex vivo analyses involving fluorescence-based methods.

Methods

Tumor tissue was obtained from a study cohort of an observational study on the utilization of fluorescein-guided biopsy and resection (n=5). The optical properties of fluorescein-stained tissue were compared to the optical features of the dye in vitro and in control samples consisting of tumor tissue of high-grade glioma patients (n=3) without intravenous (i.v.) application of NaFl. The dye-exposed tumor tissues were used for optical measurements to confirm the detectability of NaFl emission ex vivo. The tissue samples were fixed in 4%PFA, immersed in 30% sucrose, embedded in Tissue-Tek OCT compound, and cut to 10 μm cryosections. Spatially resolved emission spectra from tumor samples were recorded on representative slides with a Confocal Laser Scanning Microscope FV1000 (Olympus GmbH, Hamburg, Germany) upon excitation with λ_exc = 488 nm.

Results

Optical measurements of fluorescein in 0.9% sodium chloride (NaCl) under in vitro conditions showed an absorption maximum of λ_{max abs} = 479 nm as detected with spectrophotometer Specord 200 and an emission peak at λ_{max em} = 538 nm recorded with the emCCD detection system of a custom-made microscope-based single particle setup using a 500 nm long-pass filter. Further measurements revealed pH- and concentration-dependent emission spectra of NaFl. Under ex vivo conditions, confocal laser scanning microscopy of fluorescein tumor samples revealed a slight bathochromic shift and a broadening of the emission band.

Conclusion

Tumor uptake of NaFl leads to changes in the optical properties – a bathochromic shift and broadening of the emission band – possibly caused by the dye’s high pH sensitivity and concentration-dependent reabsorption acting as an inner filter of the dye’s emission, particularly in the short wavelength region of the emission spectrum where absorption and fluorescence overlap. Understanding the ex vivo optical properties of fluorescein is crucial for testing and validating its further applicability as an optical probe for intravital microscopy, immunofluorescence localization studies, and flow cytometry analysis.

Combined autofluorescence and diffuse reflectance for brain tumour surgical guidance: initial ex vivo study results

This ex vivo study was conducted to assess the potential of using a fibre optic probe system based on autofluorescence and diffuse reflectance for tissue differentiation in the brain. A total of 180 optical measurements were acquired from 28 brain specimens (five patients) with eight excitation and emission wavelengths spanning from 300 to 700 nm. Partial least square-linear discriminant analysis (PLS-LDA) was used for tissue discrimination. Leave-one-out cross validation (LOOCV) was then used to evaluate the performance of the classification model. Grey matter was differentiated from tumour tissue with sensitivity of 89.3% and specificity of 92.5%. The variable importance in projection (VIP) derived from the PLS regression was applied to wavelengths selection, and identified the biochemical sources of the detected signals. The initial results of the study were promising and point the way towards a cost-effective, miniaturized hand-held probe for real time and label-free surgical guidance.

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.

In Vivo Real-Time Discrimination Among Glioma, Infiltration Zone, and Normal Brain Tissue via Autofluorescence Technology

BACKGROUND

Surgery is the first-line therapy for glioblastoma. There is evidence that extent of resection is significantly associated with patient survival. Unfortunately, optimal surgical resection is usually limited because of the difficulty in discriminating tumor-infiltrated region and normal brain tissue. This study aimed to develop a tool to distinguish between infiltration zone and normal tissue in real time during glioma surgery.

METHODS

In an in vivo study, C6 glioma cells were implanted into the left cerebral hemispheres of 6 rats to mimic tumorigenesis. A newly designed optical fiber-embedded needle probe was used to measure the autofluorescence of both cerebral hemispheres at various depths 5 days after the implantation. These rats were then sacrificed, and both cerebral hemispheres were removed for histopathologic analysis.

RESULTS

Comparative analyses of corresponding areas by histopathology and autofluorescence revealed highly significant (P < 0.001) differences among the normal tissue, infiltration zone, tumors, and the contralateral cerebral hemispheres. The area of the receiver operating characteristic curve was 0.978, and the sensitivity and specificity of tumor delineation were 93.9% and 94.4%, respectively.

CONCLUSIONS

The newly designed in vivo fiber-optic probe can distinguish tumor-infiltration zones from normal brain tissue in this in vivo study. Therefore, it may help neurosurgeons to increase extent of resection without damaging normal brain tissue and thus potentially improve the patients' survival and quality of life.

Ex vivo classification of spinal cord tumors using autofluorescence spectroscopy and immunohistochemical indexes

Spinal cord tumors are complicated and infrequent, which poses a major challenge to surgeons during neurosurgery. Currently, the intraoperative identification of the tissues' pathological properties is usually difficult for surgeons. This issue influences the decision-making in treatment planning. Traditional pathological diagnoses can facilitate judging the tissues' properties, but the diagnosis process is complex and time-consuming. In this study, we evaluated the potential of autofluorescence spectroscopy for the fast pathological diagnosis of specific spinal cord tumors. The spectral properties of six types of spinal cord tumors were acquired ex vivo. Several peak intensity ratios were calculated for classification and then associated with the pathological immunohistochemical indexes. Our results revealed the spectral properties of three types of intramedullary tumors different from those of the other three types of extramedullary tumors. Furthermore, some peak intensity ratios revealed a high correlation with the immunohistochemical index of glial fibrillary acidic protein (GFAP). Thus, we believe that autofluorescence spectroscopy has the potential to provide real-time pathological information of spinal cord tumors and help surgeons validate tumor types and perform precise tumor resection.

Autofluorescence-based optical biopsy: An effective diagnostic tool in hepatology

Autofluorescence emission of liver tissue depends on the presence of endogenous biomolecules able to fluoresce under suitable light excitation. Overall autofluorescence emission contains much information of diagnostic value because it is the sum of individual autofluorescence contributions from fluorophores involved in metabolism, for example, NAD(P)H, flavins, lipofuscins, retinoids, porphyrins, bilirubin and lipids, or in structural architecture, for example, fibrous proteins, in close relationship with normal, altered or diseased conditions of the liver. Since the 1950s, hepatocytes and liver have been historical models to study NAD(P)H and flavins as in situ, real-time autofluorescence biomarkers of energy metabolism and redox state. Later investigations designed to monitor organ responses to ischaemia/reperfusion were able to predict the risk of dysfunction in surgery and transplantation or support the development of procedures to ameliorate the liver outcome. Subsequently, fluorescent fatty acids, lipofuscin-like lipopigments and collagen were characterized as optical biomarkers of liver steatosis, oxidative stress damage, fibrosis and disease progression. Currently, serum AF is being investigated to improve non-invasive optical diagnosis of liver disease. Validation of endogenous fluorophores and in situ discrimination of cancerous from non-cancerous tissue belong to the few studies on liver in human subjects. These reports along with other optical techniques and the huge work performed on animal models suggest many optically based applications in hepatology. Optical diagnosis is currently offering beneficial outcomes in clinical fields ranging from the respiratory and gastrointestinal tracts, to dermatology and ophthalmology. Accordingly, this review aims to promote an effective bench to bedside transfer in hepatology.

5-ALA fluorescence and laser Doppler flowmetry for guidance in a stereotactic brain tumor biopsy

A fiber optic probe was developed for guidance during stereotactic brain biopsy procedures to target tumor tissue and reduce the risk of hemorrhage. The probe was connected to a setup for the measurement of 5-aminolevulinic acid (5-ALA) induced fluorescence and microvascular blood flow. Along three stereotactic trajectories, fluorescence (n = 109) and laser Doppler flowmetry (LDF) (n = 144) measurements were done in millimeter increments. The recorded signals were compared to histopathology and radiology images. The median ratio of protoporphyrin IX (PpIX) fluorescence and autofluorescence (AF) in the tumor was considerably higher than the marginal zone (17.3 vs 0.9). The blood flow showed two high spots (3%) in total. The proposed setup allows simultaneous and real-time detection of tumor tissue and microvascular blood flow for tracking the vessels.

Multimodal fiber-probe spectroscopy allows detecting epileptogenic focal cortical dysplasia in children

We evaluated the diagnostic capability of a multimodal spectroscopic approach for classifying normal brain tissue and epileptogenic focal cortical dysplasia in children. We employed fluorescence spectroscopy at two excitation wavelengths (378 nm and 445 nm) and Raman spectroscopy (at 785 nm excitation) for acquiring fluorescence and Raman spectra from 10 normal brains, 16 focal cortical dysplasia specimens and 1 cortical tuber tissue sites using a custom-built multimodal optical point spectroscopic system. We used principal component analysis combined with leave-one-sample-out-cross-validation for tissue classification. The study resulted in 100% sensitivity and 90% specificity using the information obtained from fluorescence at two distinct wavelengths and Raman spectroscopy for discriminating normal brain tissue and focal cortical dysplasia. Our results demonstrate that this methodology has the potential to be applied clinically for the detection of focal cortical dysplasia and can help to improve as precise as possible surgical resection of the dysplastic tissue during surgery for epilepsy. Schematic draw of the experimental setup used for fiber-probe spectroscopy.

Multimodal optical analysis discriminates freshly extracted human sample of gliomas, metastases and meningiomas from their appropriate controls

Delineating tumor margins as accurately as possible is of primordial importance in surgical oncology: extent of resection is associated with survival but respect of healthy surrounding tissue is necessary for preserved quality of life. The real-time analysis of the endogeneous fluorescence signal of brain tissues is a promising tool for defining margins of brain tumors. The present study aims to demonstrate the feasibility of multimodal optical analysis to discriminate fresh samples of gliomas, metastases and meningiomas from their appropriate controls. Tumor samples were studied on an optical fibered endoscope using spectral and fluorescence lifetime analysis and then on a multimodal set-up for acquiring spectral, one and two-photon fluorescence images, second harmonic generation signals and two-photon fluorescence lifetime datasets. The obtained data allowed us to differentiate healthy samples from tumor samples. These results confirmed the possible clinical relevance of this real-time multimodal optical analysis. This technique can be easily applied to neurosurgical procedures for a better delineation of surgical margins.

Multimodal optical analysis of meningioma and comparison with histopathology

Meningioma is the most frequent primary central nervous system tumor. The risk of recurrence and the prognosis are correlated with the extent of the resection that ideally encompasses the infiltrated dura mater and, if required, the infiltrated bone. No device can deliver real-time intraoperative histopathological information on the tumor environment to help the neurosurgeon to achieve a gross total removal. This study assessed the abilities of nonlinear microscopy to provide relevant and real-time data to help resection of meningiomas. Nine human meningioma samples (four World Health Organization Grade I, five Grade II) were analyzed using different optical modalities: spectral analysis and imaging, lifetime measurements, fluorescence lifetime imaging microscopy, fluorescence emitted under one- and two-photon excitation and the second-harmonic generation signal imaging using a multimodal setup. Nonlinear microscopy produced images close to histopathology as a gold standard. The second-harmonic generation signal delineated the collagen background and two-photon fluorescence underlined cell cytoplasm. The matching between fluorescence images and Hematoxylin and Eosin staining was possible in all cases. Grade I meningioma emitted less autofluorescence than Grade II meningioma and Grade II meningioma exhibited a distinct lifetime value. Autofluorescence was correlated with the proliferation rates and seemed to explain the observed differences between Grade I and II meningiomas. This preliminary multimodal study focused on human meningioma samples confirms the potential of tissue autofluorescence analysis and nonlinear microscopy in helping intraoperatively neurosurgeons to reach the actual boundaries of the tumor infiltration. Correspondence between H&E staining (top pictures) and the two-photon fluorescence imaging (bottom pictures).

Review of the potential of optical technologies for cancer diagnosis in neurosurgery: a step toward intraoperative neurophotonics

Advances in image-guided therapy enable physicians to obtain real-time information on neurological disorders such as brain tumors to improve resection accuracy. Image guidance data include the location, size, shape, type, and extent of tumors. Recent technological advances in neurophotonic engineering have enabled the development of techniques for minimally invasive neurosurgery. Incorporation of these methods in intraoperative imaging decreases surgical procedure time and allows neurosurgeons to find remaining or hidden tumor or epileptic lesions. This facilitates more complete resection and improved topology information for postsurgical therapy (i.e., radiation). We review the clinical application of recent advances in neurophotonic technologies including Raman spectroscopy, thermal imaging, optical coherence tomography, and fluorescence spectroscopy, highlighting the importance of these technologies in live intraoperative tissue mapping during neurosurgery. While these technologies need further validation in larger clinical trials, they show remarkable promise in their ability to help surgeons to better visualize the areas of abnormality and enable safe and successful removal of malignancies.

Spectroscopic and Imaging Characteristics of Pigmented Non-Melanoma Skin Cancer and Melanoma in Patients with Skin Phototypes III and IV

INTRODUCTION

Non-melanoma skin cancer is the most common malignancy worldwide. Differentiating between malignant and benign skin tumors, however, can be challenging. As a result, various auxiliary tools have been developed to aid in the diagnosis of cutaneous neoplasms. Here, skin tumors were investigated through analysis of their digital image histograms and spectroscopic response under ultraviolet (UV) and white light-emitting diodes (LEDs).

METHODS

Fifty tumoral lesions were spectroscopically and histologically studied. For optical studies, UV at 375 nm and white LEDs were used to illuminate the lesions. Commercial cameras were used for imaging, and a miniature spectrometer with a bifurcated optical fiber was used for spectroscopic measurements.

RESULTS

In this study, the intensity histograms of the images taken under white and UV illumination and the spectroscopic response under white light showed clear differences between pigmented basal cell carcinoma (BCC), intradermal melanocytic nevus (IDN), and melanoma lesions for skin phototypes III and IV. However, there was little difference in their spectroscopic response to the UV LED.

CONCLUSION

We found differences in the intensity and shape of diffuse reflectance spectra of pigmented BCC, IDN, and melanoma lesions in patients with skin phototypes III and IV. Also, images taken under UV and white light were helpful for differentiation of these pigmented lesions. Additional research is needed to ascertain the clinical utility of these tools for skin cancer diagnosis.

Real time optical Biopsy: Time-resolved Fluorescence Spectroscopy instrumentation and validation

The Time-resolved fluorescence spectroscopy (TR-FS) has the potential to differentiate tumor and normal tissue in real time during surgical excision. In this manuscript, we describe the design of a novel TR-FS device, along with preliminary data on detection accuracy for fluorophores in a mixture. The instrument is capable of near real-time fluorescence lifetime acquisition in multiple spectral bands and analysis. It is also able to recover fluorescence lifetime with sub-20ps accuracy as validated with individual organic fluorescence dyes and dye mixtures yielding lifetime values for standard fluorescence dyes that closely match with published data. We also show that TR-FS is able to quantify the relative concentration of fluorescence dyes in a mixture by the unmixing of lifetime decays. We show that the TR-FS prototype is able to identify in near-real time the concentrations of dyes in a complex mixture based on previously trained data. As a result, we demonstrate that in complex mixtures of fluorophores, the relative concentration information is encoded in the fluorescence lifetime across multiple spectral bands. We show for the first time the temporal and spectral measurements of a mixture of fluorochromes and the ability to differentiate relative concentrations of each fluorochrome mixture in real time.

405 nm versus 633 nm for protoporphyrin IX excitation in fluorescence-guided stereotactic biopsy of brain tumors

Fluorescence diagnosis may be used to improve the safety and reliability of stereotactic brain tumor biopsies using biopsy needles with integrated fiber optics. Based on 5-aminolevulinic-acid-induced protoporphyrin IX (PpIX) fluorescence, vital tumor tissue can be localized in vivo during the excision procedure to reduce the number of necessary samples for a reliable diagnosis. In this study, the practical suitability of two different PpIX excitation wavelengths (405 nm, 633 nm) was investigated on optical phantoms. Violet excitation at 405 nm provides a 50-fold higher sensitivity for the bulk tumor; this factor increases up to 100 with decreasing fluorescent volume as shown by ray tracing simulations. Red excitation at 633 nm, however, is noticeably superior with regard to blood layers obscuring the fluorescence. Experimental results on the signal attenuation through blood layers of well-defined thicknesses could be confirmed by ray tracing simulations. Typical interstitial fiber probe measurements were mimicked on agarose-gel phantoms. Even in direct contact, blood layers of 20-40 µm between probe and tissue must be expected, obscuring 405-nm-excited PpIX fluorescence almost completely, but reducing the 633-nm-excited signal only by 25.5%. Thus, 633 nm seems to be the wavelength of choice for PpIX-assisted detection of high-grade gliomas in stereotactic biopsy. PpIX signal attenuation through clinically relevant blood layers for 405 nm (violet) and 633 nm (red) excitation.

New light in flavin autofluorescence

Our attention was captured by the interesting debate on the identification of lipofuscins, lipofuscin-like lipopigments, or flavins as the responsible for intracellular autofluorescence (AF) detected in epithelial cancer stem cells when exciting at 480-490 nm. Evidence was provided leading to ascribe AF emission to flavins accumulating in cytoplasmic structures, bounded to membranes and bearing ATP-dependent ABCG2 transporters. Flavins were then proposed as an intrinsic AF biomarker of cancer stem cells, with advantageous implications on cell invasiveness and chemoresistance investigations. It is however worth recalling the huge amount of literature on flavins and NAD(P)H as AF biomarkers of cell energetic metabolism and redox state, an aspect that should not be overlooked in the renewed course to extend the potential of flavins as AF biomarkers, entailing also a recent proposal of Flavin-based fluorescent proteins as substitutes of Green fluorescent proteins.

Comparing high-resolution microscopy techniques for potential intraoperative use in guiding low-grade glioma resections

BACKGROUND AND OBJECTIVES

Fluorescence image-guided surgery (FIGS), with contrast provided by 5-ALA-induced PpIX, has been shown to enable a higher extent of resection of high-grade gliomas. However, conventional FIGS with low-power microscopy lacks the sensitivity to aid in low-grade glioma (LGG) resection because PpIX signal is weak and sparse in such tissues. Intraoperative high-resolution microscopy of PpIX fluorescence has been proposed as a method to guide LGG resection, where sub-cellular resolution allows for the visualization of sparse and punctate mitochondrial PpIX production in tumor cells. Here, we assess the performance of three potentially portable high-resolution microscopy techniques that may be used for the intraoperative imaging of human LGG tissue samples with PpIX contrast: high-resolution fiber-optic microscopy (HRFM), high-resolution wide-field microscopy (WFM), and dual-axis confocal (DAC) microscopy.

MATERIALS AND METHODS

Thick unsectioned human LGG tissue samples (n = 7) with 5-ALA-induced PpIX contrast were imaged using three imaging techniques (HRFM, WFM, DAC). The average signal-to-background ratio (SBR) was then calculated for each imaging modality (5 images per tissue, per modality).

RESULTS

HRFM provides the ease of use and portability of a flexible fiber bundle, and is simple and inexpensive to build. However, in most cases (6/7), HRFM is not capable of detecting PpIX signal from LGGs due to high autofluorescence, generated by the fiber bundle under laser illumination at 405 nm, which overwhelms the PpIX signal and impedes its visualization. WFM is a camera-based method possessing high lateral resolution but poor axial resolution, resulting in sub-optimal image contrast.

CONCLUSIONS

Consistent successful detection of PpIX signal throughout our human LGG tissue samples (n = 7), with an acceptable image contrast (SBR >2), was only achieved using DAC microscopy, which offers superior image resolution and contrast that is comparable to histology, but requires a laser-scanning mechanism to achieve optical sectioning.

Spectral and lifetime domain measurements of rat brain tumors

During glioblastoma surgery, delineation of the brain tumor margins is difficult because the infiltrated and normal tissues have the same visual appearance. We use a fiber-optical fluorescence probe for spectroscopic and time domain measurements to assist surgeon in differentiating the healthy and the infiltrated tissues. First study was performed on rats that were previously injected with tumorous cells. Measurements of endogenous tissue fluorescence were performed on fresh and fixed rat tumor brain slices. Spectral characteristics, fluorescence redox ratios and fluorescence lifetime measurements were analyzed. The study aimed at defining an optical index that can act as an indicator for discriminating healthy from tumorous tissue.

Autofluorescence spectroscopy and imaging: a tool for biomedical research and diagnosis

Native fluorescence, or autofluorescence (AF), consists in the emission of light in the UV-visible, near-IR spectral range when biological substrates are excited with light at suitable wavelength. This is a well-known phenomenon, and the strict relationship of many endogenous fluorophores with morphofunctional properties of the living systems, influencing their AF emission features, offers an extremely powerful resource for directly monitoring the biological substrate condition. Starting from the last century, the technological progresses in microscopy and spectrofluorometry were convoying attention of the scientific community to this phenomenon. In the future, the interest in the autofluorescence will certainly continue. Current instrumentation and analytical procedures will likely be overcome by the unceasing progress in new devices for AF detection and data interpretation, while a progress is expected in the search and characterization of endogenous fluorophores and their roles as intrinsic biomarkers.

Brain tumor demarcation by applying a LAMSTAR neural network to spectroscopy data

The application of optical spectroscopy for intra-operatively delineating brain tumors has been studied in this paper. The classification of tissue as normal, tumor and boundary is done using the LAMSTAR neural network (NN). The objective is to combine both fluorescence and reflectance as attributes to be used for the demarcation, thus giving the identification greater specificity and sensitivity. The input word has seven sub-words, five with autofluorescence parameters and two with reflectance values. The mean and standard deviation for the fluorescence parameters that were used for setting the weights of the NN were obtained from previous work. The reflectance value was used with the fluorescence parameters through a two-step discrimination algorithm. The neural network was trained with 10 sets of each tumor, normal and boundary type of tissue parameters. The network was then tested with 15 complete input sets and 10 incomplete sets for the identification. A 100% success rate was obtained for the complete testing sets and 80% for the incomplete ones. The most significant self-organizing map layers of the network were also identified for each decision. A sensitivity of 97.1% and specificity of 94.73% were achieved, which is much higher than earlier published results of 89 and 76%, respectively.

Fluorescence Lifetime Spectroscopy and Imaging in Neurosurgery

Clinical outcome of patients diagnosed with primary brain tumor has been correlated with the extent of surgical resection. In treating this disease, the neurosurgeon must balance between an aggressive, radical resection and minimizing the loss of healthy, functionally significant brain tissue. Numerous intra-operative methodologies and technological approaches have been explored as a means to improve the accuracy of surgical resection. This paper presents an overview of current conventional techniques and new emerging technologies with potential to impact the area of image-guided surgery of brain tumors. Emphasis is placed on techniques based on endogenous fluorescence lifetime contrast and their potential for intraoperative diagnosis of brain tumors.

Fluorescence lifetime techniques in medical applications

This article presents an overview of time-resolved (lifetime) fluorescence techniques used in biomedical diagnostics. In particular, we review the development of time-resolved fluorescence spectroscopy (TRFS) and fluorescence lifetime imaging (FLIM) instrumentation and associated methodologies which allow in vivo characterization and diagnosis of biological tissues. Emphasis is placed on the translational research potential of these techniques and on evaluating whether intrinsic fluorescence signals provide useful contrast for the diagnosis of human diseases including cancer (gastrointestinal tract, lung, head and neck, and brain), skin and eye diseases, and atherosclerotic cardiovascular disease.

Compact point-detection fluorescence spectroscopy system for quantifying intrinsic fluorescence redox ratio in brain cancer diagnostics

We report the development of a compact point-detection fluorescence spectroscopy system and two data analysis methods to quantify the intrinsic fluorescence redox ratio and diagnose brain cancer in an orthotopic brain tumor rat model. Our system employs one compact cw diode laser (407 nm) to excite two primary endogenous fluorophores, reduced nicotinamide adenine dinucleotide, and flavin adenine dinucleotide. The spectra were first analyzed using a spectral filtering modulation method developed previously to derive the intrinsic fluorescence redox ratio, which has the advantages of insensitivity to optical coupling and rapid data acquisition and analysis. This method represents a convenient and rapid alternative for achieving intrinsic fluorescence-based redox measurements as compared to those complicated model-based methods. It is worth noting that the method can also extract total hemoglobin concentration at the same time but only if the emission path length of fluorescence light, which depends on the illumination and collection geometry of the optical probe, is long enough so that the effect of absorption on fluorescence intensity due to hemoglobin is significant. Then a multivariate method was used to statistically classify normal tissues and tumors. Although the first method offers quantitative tissue metabolism information, the second method provides high overall classification accuracy. The two methods provide complementary capabilities for understanding cancer development and noninvasively diagnosing brain cancer. The results of our study suggest that this portable system can be potentially used to demarcate the elusive boundary between a brain tumor and the surrounding normal tissue during surgical resection.

Fluorescence lifetime spectroscopy for guided therapy of brain tumors

This study evaluates the potential of time-resolved laser induced fluorescence spectroscopy (TR-LIFS) as intra-operative tool for the delineation of brain tumor from normal brain. Forty two patients undergoing glioma (WHO grade I-IV) surgery were enrolled in this study. A TR-LIFS prototype apparatus (gated detection, fast digitizer) was used to induce in-vivo fluorescence using a pulsed N2 laser (337 nm excitation, 0.7 ns pulse width) and to record the time-resolved spectrum (360-550 nm range, 10 nm interval). The sites of TR-LIFS measurement were validated by conventional histopathology (H&E staining). Parameters derived from the TR-LIFS data including intensity values and time-resolved intensity decay features (average fluorescence lifetime and Laguerre coefficients values) were used for tissue characterization and classification. 71 areas of tumor and normal brain were analyzed. Several parameters allowed for the differentiation of distinct tissue types. For example, normal cortex (N=35) and normal white matter (N=12) exhibit a longer-lasting fluorescence emission at 390 nm (τ390=2.12±0.10 ns) when compared with 460 nm (τ460=1.16±0.08 ns). High grade glioma (grades III and IV) samples (N=17) demonstrate emission peaks at 460 nm, with large variation at 390 nm while low grade glioma (I and II) samples (N=7) demonstrated a peak fluorescence emission at 460 nm. A linear discriminant algorithm allowed for the classification of low-grade gliomas with 100% sensitivity and 98% specificity. High-grade glioma demonstrated a high degree of heterogeneity thus reducing the discrimination accuracy of these tumors to 47% sensitivity and 94% specificity. Current findings demonstrate that TR-LIFS holds the potential to diagnose brain tumors intra-operatively and to provide a valuable tool for aiding the neurosurgeon-neuropathologist team in to rapidly distinguish between tumor and normal brain during surgery.

Fluorescence lifetime imaging microscopy for brain tumor image-guided surgery

We demonstrate for the first time the application of an endoscopic fluorescence lifetime imaging microscopy (FLIM) system to the intraoperative diagnosis of glioblastoma multiforme (GBM). The clinically compatible FLIM prototype integrates a gated (down to 0.2 ns) intensifier imaging system with a fiber-bundle (fiber image guide of 0.5 mm diameter, 10,000 fibers with a gradient index lens objective 0.5 NA, and 4 mm field of view) to provide intraoperative access to the surgical field. Experiments conducted in three patients undergoing craniotomy for tumor resection demonstrate that FLIM-derived parameters allow for delineation of tumor from normal cortex. For example, at 460±25-nm wavelength band emission corresponding to NADH/NADPH fluorescence, GBM exhibited a weaker fluorescence intensity (35% less, p-value<0.05) and a longer lifetime τGBM-Amean=1.59±0.24 ns than normal cortex τNC-Amean=1.28±0.04 ns (p-value<0.005). Current results demonstrate the potential use of FLIM as a tool for image-guided surgery of brain tumors.

Review of Neurosurgical Fluorescence Imaging Methodologies

Fluorescence imaging in neurosurgery has a long historical development, with several different biomarkers and biochemical agents being used, and several technological approaches. This review focuses on the different contrast agents, summarizing endogenous fluorescence, exogenously stimulated fluorescence and exogenous contrast agents, and then on tools used for imaging. It ends with a summary of key clinical trials that lead to consensus studies. The practical utility of protoporphyrin IX (PpIX) as stimulated by administration of δ-aminolevulinic acid (ALA) has had substantial pilot clinical studies and basic science research completed. Recently multi-center clinical trials using PpIx fluorescence to guide resection have shown efficacy for improved short term survival. Exogenous agents are being developed and tested pre-clinically, and hopefully hold the potential for long term survival benefit if they provide additional capabilities for resection of micro-invasive disease or certain tumor sub-types that do not produce PpIX or help delineate low grade tumors. The range of technologies used for measurement and imaging ranges widely, with most clinical trials being carried out with either point probes or modified surgical microscopes. At this point in time, optimized probe approaches are showing efficacy in clinical trials, and fully commercialized imaging systems are emerging, which will clearly help lead to adoption into neurosurgical practice.

Intraoperative delineation of primary brain tumors using time-resolved fluorescence spectroscopy

The goal of this study is to determine the potential of time-resolved laser-induced fluorescence spectroscopy (TR-LIFS) as an adjunctive tool for delineation of brain tumor from surrounding normal tissue in order to assist the neurosurgeon in near-complete tumor excision. A time-domain TR-LIFS prototype apparatus (gated photomultiplier detection, fast digitizer) was used for recording tissue autofluorescence in normal cortex (NC), normal white matter (NWM), and various grades of gliomas intraoperatively. Tissue fluorescence was induced with a pulsed nitrogen laser (337 nm, 700 ps), and the intensity decay profiles were recorded in the 360- to 550-nm spectral range (10-nm interval). Histopathological analysis (hematoxylin & eosin) of the biopsy samples taken from the site of TR-LIFS measurements was used for validation of spectroscopic results. Preliminary results on 17 patients demonstrate that normal cortex (N=16) and normal white matter (N=3) show two peaks of fluorescence emission at 390 nm (lifetime=1.8+/-0.3 ns) and 460 nm (lifetime=0.8+/-0.1 ns). The 390-nm emission peak is absent in low-grade glioma (N=5; lifetime=1.1 ns) and reduced in high-grade glioma (N=9; lifetime=1.7+/-0.4 ns). The emission characteristics at 460 nm in all tissues correlated with the nicotinamide adenine dinucleotide fluorescence (peak: 440 to 460 nm; lifetime: 0.8 to 1.0 ns). These findings demonstrate the potential of using TR-LIFS as a tool for enhanced delineation of brain tumors during surgery. In addition, this study evaluates similarities and differences between TR-LIFS signatures of brain tumors obtained in vivo and those previously reported in ex vivo brain tumor specimens.

Laser-induced autofluorescence measurements on brain tissues

It was demonstrated that comparison of the autofluorescence spectra induced with laser radiation in ultraviolet and visible allows the identification of brain tumor tissues and normal tissues as well as the difference between them. The measurements were performed on homogenates to ensure an optimal reproducibility of the results. We conclude that the autofluorescence spectra of the tumor samples are close to those measured for normal tissues, but there are differences between them that allow distinguishing the tumor from the normal tissue. One difference is that for each pair of tumor/normal tissue samples, the peak autofluorescence for the normal tissue is shifted with respect to that for the tumor-typically between 10 and 20 nm; overall autofluorescence intensity is also different for the components of the same pair, the difference being in the range 15%-30%. A parameter that can also be used is the variation of the ratio of some fluorescence intensity peaks between normal and tumor tissue samples. Measurements of this parameter yielded variations ranging between 10% and 40%. Another conclusion of the study is that in vitro experiments show that it is mandatory to use pairs of samples (normal/tumor tissue) taken from the same patient. The results show that, after further experimental in vitro tests, the method may be adapted to real-time intraoperative conditions by measuring the autofluorescence of the tumor and of the adjacent normal tissue.

Intra-operative brain tumor detection using elastic light single-scattering spectroscopy: a feasibility study

We have investigated the potential application of elastic light single-scattering spectroscopy (ELSSS) as an adjunctive tool for intraoperative rapid detection of brain tumors and demarcation of the tumor from the surrounding normal tissue. Measurements were performed on 29 excised tumor specimens from 29 patients. There were 21 instances of low-grade tumors and eight instances of high-grade tumors. Normal gray matter and white matter brain tissue specimens of four epilepsy patients were used as a control group. One low-grade and one high-grade tumor were misclassified as normal brain tissue. Of the low- and high-grade tumors, 20 out of 21 and 7 out of 8 were correctly classified by the ELSSS system, respectively. One normal white matter tissue margin was detected in a high-grade tumor, and three normal tissue margins were detected in three low-grade tumors using spectroscopic data analysis and confirmed by histopathology. The spectral slopes were shown to be positive for normal white matter brain tissue and negative for normal gray matter and tumor tissues. Our results indicate that signs of spectral slopes may enable the discrimination of brain tumors from surrounding normal white matter brain tissue with a sensitivity of 93% and specificity of 100%.

The role of optical spectroscopy in epilepsy surgery in children

OBJECT

Surgery is an important therapeutic modality for pediatric patients with intractable epilepsy. However, existing imaging and diagnostic technologies such as MR imaging and electrocochleography (ECoG) do not always effectively delineate the true resection margin of an epileptic cortical lesion because of limitations in their sensitivity. Optical spectroscopic techniques such as fluorescence and diffuse reflectance spectroscopy provide a nondestructive means of gauging the physiological features of the brain in vivo, including hemodynamics and metabolism. In this study, the authors investigate the feasibility of using combined fluorescence and diffuse reflectance spectroscopy to assist epilepsy surgery in children.

METHODS

In vivo static fluorescence and diffuse reflectance spectra were acquired from the brain in children undergoing epilepsy surgery. Spectral measurements were obtained using a portable spectroscopic system in conjunction with a fiber optic probe. The optical investigations were conducted at the normal and abnormal cortex as defined by intraoperative ECoG and preoperative imaging studies. Biopsy samples were taken from the investigated sites located within the zone of resection. The optical spectra were classified into multiple subsets in accordance with the ECoG and histological study results. The authors used statistical comparisons between 2 given data subsets to identify unique spectral features. Empirical discrimination algorithms were developed using the identified spectral features to determine if the objective of the study was achieved.

RESULTS

Fifteen pediatric patients were enrolled in this pilot study. Elevated diffuse reflectance signals between 500 and 600 nm and/or between 650 and 850 nm were observed commonly in the investigated sites with abnormal ECoG and/or histological features in 10 patients. The appearance of a fluorescent peak at 400 nm was observed in both normal and abnormal cortex of 5 patients. These spectral alterations were attributed to changes in morphological and/or biochemical characteristics of the epileptic cortex. The sensitivities and specificities of the empirical discrimination algorithms, which were constructed using the identified spectral features, were all > 90%.

CONCLUSIONS

The results of this study demonstrate the feasibility of using static fluorescence and diffuse reflectance spectroscopy to differentiate normal from abnormal cortex on the basis of intraoperative assessment of ECoG and histological features. It is therefore possible to use fluorescence and diffuse reflectance spectroscopy as an aid in epilepsy surgery.

Optical spectroscopy for in-vitro differentiation of pediatric neoplastic and epileptogenic brain lesions

The objective of this in vitro tissue study is to investigate the feasibility of using optical spectroscopy to differentiate pediatric neoplastic and epileptogenic brain from normal brain. Specimens are collected from 17 patients with brain tumors, and from 26 patients with intractable epilepsy during surgical resection of epileptogenic cerebral cortex. Fluorescence spectra are measured at excitations of 337, 360, and 440 nm; diffuse reflectance spectra are measured between 400 and 900 nm from each specimen. Pathological analysis is performed to classify abnormalities in brain specimens, and its findings are correlated with spectral data. Statistically significant differences (p<0.01) are found for both raw and normalized diffuse reflectance and fluorescence spectra between 1. neoplastic brain and normal gray matter, 2. epileptogenic brain and normal gray matter, and 3. neoplastic brain and normal white matter. However, no distinct spectral features are identified that effectively separate epileptogenic brain from normal white matter. The outcomes of the study suggest that certain unique compositional and structural characteristics of pediatric neoplastic and epileptogenic brain can be detected using optical spectroscopy in vitro.

Liver autofluorescence properties in animal model under altered nutritional conditions

Autofluorescence spectroscopy is a promising and powerful approach for an in vivo, real time characterization of liver functional properties. In this work, preliminary results on the dependence of liver autofluorescence parameters on the nutritional status are reported, with particular attention to vitamin A and lipid accumulation in liver tissue. Normally fed and 24 h starving rats were used as animal models. Histochemical and autofluorescence analysis showed that lipids and vitamin A colocalize in the liver parenchyma. Fasting condition results in a parallel increase in both lipids and vitamin A. Autofluorescence imaging and microspectrofluorometric analysis carried out on unfixed, unstained tissue sections under 366 nm excitation, evidenced differences in both spectral shape and response to continuous irradiation between liver biopsies from fed and starving rats. As to photobleaching, in particular, fitting analysis evidenced a reduction of about 85% of the signal attributable solely to vitamin A during the first 10 s of irradiation. The tissue whole emission measured in fed and starving rat livers exhibited reductions of about 35% and 52%, respectively, that are closely related to vitamin A contents. The findings open interesting perspectives for the set up of an in situ, real time diagnostic procedure for the assessment of liver lipid accumulation, exploiting the photophysical properties of vitamin A.

Receptor-targeted quantum dots: fluorescent probes for brain tumor diagnosis

The intraoperative diagnosis of brain tumors and the timely evaluation of biomarkers that can guide therapy are hindered by the paucity of rapid adjunctive studies. This study evaluates the feasibility and specificity of using quantum dot-labeled antibodies for rapid visualization of epidermal growth factor receptor (EGFR) expression in human brain tumor cells and in surgical frozen section slides of glioma tissue. Streptavidin-coated quantum dots (QDs) were conjugated to anti-EGFR antibodies and incubated with target cultured tumor cells and tissues. The experiments were conducted first in human glioma tumor cell lines with elevated levels of EGFR expression (SKMG-3, U87) and then in frozen tissue sections of glioblastoma multiforme and of oligodendroglioma. The bioconjugated QDs used in the study were found to bind selectively to brain tumor cells expressing EGFR. QD complexed quickly to the cell membrane (less than 15 min), and binding was highly specific and depended on the expression level of EGFR on the cell membrane. Tissue experiments showed that only tumor specimens expressing EGFR were labeled in less than 30 min by QD complexes. These findings demonstrate that QD-labeled antibodies can provide a quick and accurate method for characterizing the presence or absence of a specific predictive biomarker.

A probability-based spectroscopic diagnostic algorithm for simultaneous discrimination of brain tumor and tumor margins from normal brain tissue

This paper reports the development of a probability-based spectroscopic diagnostic algorithm capable of simultaneously discriminating tumor core and tumor margins from normal human brain tissues. The algorithm uses a nonlinear method for feature extraction based on maximum representation and discrimination feature (MRDF) and a Bayesian method for classification based on sparse multinomial logistic regression (SMLR). Both the autofluorescence and the diffuse-reflectance spectra acquired in vivo from patients undergoing craniotomy or temporal lobectomy at the Vanderbilt University Medical Center were used to train and validate the algorithm. The classification accuracy was observed to be approximately 96%, 80%, and 97% for the tumor, tumor margin, and normal brain tissues, respectively, for the training data set and approximately 96%, 94%, and 100%, respectively, for the corresponding tissue types in an independent validation data set. The inherently multi-class nature of the algorithm facilitates a rapid and simultaneous classification of tissue spectra into various tissue categories without the need for a hierarchical multi-step binary classification scheme. Further, the probabilistic nature of the algorithm makes it possible to quantitatively assess the certainty of the classification and recheck the samples that are classified with higher relative uncertainty.

In vivo optical imaging using quantum dots for the management of brain tumors

The surgical management of brain tumors requires the precise localization of tumor tissues within normal brain parenchyma in order to achieve accurate diagnostic biopsy and complete surgical resection. Quantum dots are optical semiconductor nanocrystals that exhibit stable, bright fluorescence. The intravenous injection of quantum dots is accompanied by reticuloendothelial system and macrophage sequestration. Macrophages infiltrate brain tumors and phagocytize intravenously injected quantum dots, optically labeling the tumors. Macrophage-mediated delivery of quantum dots to brain tumors may represent a novel technique to label tumors preoperatively. Quantum dots within tumors may be detected with optical imaging and optical spectroscopy tools, providing the surgeon with real-time optical feedback during the resection and biopsy of brain tumors.

Autofluorescence properties of rat cerebellum cortex during postnatal development

BACKGROUND AND OBJECTIVES

The multilayered structure of rat neocerebellum cortex (VI-VIII lobules of the vermis) during postnatal development undergoes rearrangements, which in turn are affected by treatment with the anti-tumoral drug cisplatin. The dependence of autofluorescence emission properties on the tissue structural and molecular features has been investigated.

STUDY DESIGN/MATERIALS AND METHODS

Autofluorescence analysis was performed at defined time points of cerebellar histogenesis--11, 17, and 30 postnatal days- under normal conditions or after 5 microg/g body weight cisplatin treatment at 10 postnatal day. Autofluorescence signal was analyzed in vivo at the surface of intact lobules of cerebellum vermis by means of fiber optic spectrofluorometry, or on tissue sections by means of microspectrofluorometry and fluorescence imaging.

RESULTS

In vivo spectroscopy showed changes of autofluorescence signal both during normal histogenesis and after cisplatin treatment. External granular layer (EGL) and molecular layer (ML), that is, the more external layers were found to be interested by structural alterations, and showed the greatest changes in signal amplitude, accounting for the in vivo results. Fitting analysis indicated that changes in spectral shape reflected an increase in oxidative damages induced by cisplatin treatment.

CONCLUSIONS

The results confirm the relationship of the autofluorescence emission properties with histological and biochemical features of biological tissue.

In vivo monitoring the changes of interstitial pH and FAD/NADH ratio by fluorescence spectroscopy in healing skin wounds

The aim of our study was to evaluate the changes of interstitial pH and flavin adenine dinucleotide (FAD)/reduced nicotinamide adenine dinucleotide (NADH) ratio in healing skin wounds using fluorescence spectroscopy in Sprague Dawley rats. In the experiment, excisional and incisional models of wound healing were used. The florescein as the pH-sensitive probe using excitation spectra (lambda(Em) = 535 nm) was used for the measurement of pH changes, and synchronous fluorescence spectra (Deltalambda = 60 nm) for the monitoring of FAD/NADH ratio changes were measured from the surfaces of healing wounds. Increase of interstitial pH and FAD/NADH ratio was recorded during the time interval from the 15th to the 65th minute after surgery. The decrease of pH between the 48th and the 72nd hour after surgery as well as the increase of FAD/NADH ratio between the 72nd and the 96th hour of wound healing were recorded. The results indicate that the use of fluorescence spectroscopy may be considered as a valuable tool for noninvasive in vivo monitoring of selected redox parameters in the early phases of wound healing.

Distinction of brain tissue, low grade and high grade glioma with time-resolved fluorescence spectroscopy

Neuropathology frozen section diagnoses are difficult in part because of the small tissue samples and the paucity of adjunctive rapid intraoperative stains. This study aims to explore the use of time-resolved laser-induced fluorescence spectroscopy as a rapid adjunctive tool for the diagnosis of glioma specimens and for distinction of glioma from normal tissues intraoperatively. Ten low grade gliomas, 15 high grade gliomas without necrosis, 6 high grade gliomas with necrosis and/or radiation effect, and 14 histologically uninvolved "normal" brain specimens are spectroscopicaly analyzed and contrasted. Tissue autofluorescence was induced with a pulsed Nitrogen laser (337 nm, 1.2 ns) and the transient intensity decay profiles were recorded in the 370-500 nm spectral range with a fast digitized (0.2 ns time resolution). Spectral intensities and time-dependent parameters derived from the time-resolved spectra of each site were used for tissue characterization. A linear discriminant analysis diagnostic algorithm was used for tissue classification. Both low and high grade gliomas can be distinguished from histologically uninvolved cerebral cortex and white matter with high accuracy (above 90%). In addition, the presence or absence of treatment effect and/or necrosis can be identified in high grade gliomas. Taking advantage of tissue autofluorescence, this technique facilitates a direct and rapid investigation of surgically obtained tissue.

Diagnosis of meningioma by time-resolved fluorescence spectroscopy

We investigate the use of time-resolved laser-induced fluorescence spectroscopy (TR-LIFS) as an adjunctive tool for the intraoperative rapid evaluation of tumor specimens and delineation of tumor from surrounding normal tissue. Tissue autofluorescence is induced with a pulsed nitrogen laser (337 nm, 1.2 ns) and the intensity decay profiles are recorded in the 370 to 500 nm spectral range with a fast digitizer (0.2 ns resolution). Experiments are conducted on excised specimens (meningioma, dura mater, cerebral cortex) from 26 patients (97 sites). Spectral intensities and time-dependent parameters derived from the time-resolved spectra of each site are used for tissue characterization. A linear discriminant analysis algorithm is used for tissue classification. Our results reveal that meningioma is characterized by unique fluorescence characteristics that enable discrimination of tumor from normal tissue with high sensitivity (>89%) and specificity (100%). The accuracy of classification is found to increase (92.8% cases in the training set and 91.8% in the cross-validated set correctly classified) when parameters from both the spectral and the time domain are used for discrimination. Our findings establish the feasibility of using TR-LIFS as a tool for the identification of meningiomas and enables further development of real-time diagnostic tools for analyzing surgical tissue specimens of meningioma or other brain tumors.

Autofluorescence spectroscopy of rat liver during experimental transplantation procedure. An approach for hepatic metabolism assessment

Ischemia-reperfusion injury, a major cause of organ metabolic alterations and consequent dysfunction in liver transplantation, could be overcome by optimizing organ preservation procedures. The potential of autofluorescence analysis was investigated with the aim to define parameters suitable for in vivo monitoring tissue functionality. Spectrofluorometric analysis was performed on explanted rat livers during cold storage, under standard (4 degrees C University of Wisconsin medium for 20 h) and purposely damaging (4 degrees C Eurocollins medium for 20, 43 and 72 h) preservation conditions, and reperfusion (rewarming-reoxygenation). For both preservation conditions, cold hypoxia caused a signal amplitude increase, mainly attributable to NAD(P)H, and a spectral shape modification, ascribable to changes in the relative contributions of NAD(P)H and flavins, as a result of the tissue reduced state enhancement. Upon rewarming-reoxygenation the autofluorescence signal decreased with a rate depending on the preservation conditions. The time constant changed according to the extent of the liver functionality impairment, as assessed by conventional biochemical and histochemical analyses, thus providing a parameter exploitable for an in situ, real time monitoring of the efficacy of experimental preservation procedures.

Fluorescence lifetime spectroscopy of glioblastoma multiforme

Fluorescence spectroscopy of the endogenous emission of brain tumors has been researched as a potentially important method for the intraoperative localization of brain tumor margins. We investigated the use of time-resolved, laser-induced fluorescence spectroscopy for demarcation of primary brain tumors by studying the time-resolved spectra of gliomas. The fluorescence of human brain samples (glioblastoma multiforme, cortex and white matter: six patients, 23 sites) was induced ex vivo with a pulsed nitrogen laser (337 nm, 3 ns). The time-resolved spectra were detected in a 360-550 nm wavelength range using a fast digitizer and gated detection. Parameters derived from both the spectral- (intensities from narrow spectral bands) and the time domain (average lifetime) measured at 390 and 460 nm were used for tissue characterization. We determined that high-grade gliomas are characterized by fluorescence lifetimes that varied with the emission wavelength (>3 ns at 390 nm, <1 ns at 460 nm) and their emission is overall longer than that of normal brain tissue. Our study demonstrates that the use of fluorescence lifetime not only improves the specificity of fluorescence measurements but also allows a more robust evaluation of data collected from brain tissue. Combined information from both the spectral- and the time domain can enhance the ability of fluorescence-based techniques to diagnose and detect brain tumor margins intraoperatively.

In vivo autofluorescence spectrofluorometry of central serotonin

The autofluorescence properties of serotonin (5-HT) were investigated by light spectrofluorometry in in vitro, ex vivo and in vivo experiments. Ex vivo samples were prepared from rat brain regions containing serotonin (5-HT) i.e. cortex, striatum, hippocampus. Rats were untreated (controls) or previously submitted to chronic behavioural or pharmacological treatments known to affect endogenous 5-HT levels. Autofluorescence analysis (excitation: 366 nm) on hippocampus homogenates supplied with exogenous 5-HT revealed spectral alterations attributable to changes of endogenous 5-HT levels. In vivo, real time fluorescence studies were performed via a 50 microm diameter optic fiber probe stereotaxically implanted into selected brain areas of anaesthetised rats treated with fluoxetine or 5-OH-tryptophan. All autofluorescence data were consistent with those obtained in parallel experiments performed with ex vivo or in vivo voltammetry, confirming that auto-fluorescence spectroscopy is a suitable technique for the direct assessment of fluorescent neurotransmitters. This is a reliable evidence of the in vivo application of spectroscopy together with optic fiber probe for in vivo, in situ and real time measurement of 5-HT in discrete brain areas.