Medical diagnostic system based on simultaneous multispectral fluorescence imaging

Cost-effective device for locating and circumscribing superficial tumors with contrast enhancement and fluorescence quantification

BACKGROUND

Two Bispectral contrast enhancement approaches for the fluorescence diagnosis with chlorine-e6 and a wide field-of-view imaging system with fluorescence excitation at 405 nm and time-resolved background suppression were analyzed and compared.

METHODS

Two techniques for the contrast enhancement of a fluorescent video system (Red/Green (R/G) ratio and Red-Green (R-G)) with time-resolved background suppression for fluorescent diagnosis (FD) were tested in four patients with basal cell carcinoma (BCC).

RESULTS

The results of both contrast enhancement methods were compared for the diagnostic efficiency for FD of BCC. Both techniques successfully determined the boundaries of the lesions and the fluorescence intensity.

CONCLUSIONS

Both contrast enhancement modes have proven effective in identifying tumor borders in cases of low contrast in BCC FD with Ce6. While the Red/Green (R/G) mode provides sharper lesion borders, the Red minus Green (R-G) mode visualizes more fluorescent features and makes it easier to assess the lesion margins.

Types of spectroscopy and microscopy techniques for cancer diagnosis: a review

Cancer is a life-threatening disease that has claimed the lives of many people worldwide. With the current diagnostic methods, it is hard to determine cancer at an early stage, due to its versatile nature and lack of genomic biomarkers. The rapid development of biophotonics has emerged as a potential tool in cancer detection and diagnosis. Using the fluorescence, scattering, and absorption characteristics of cells and tissues, it is possible to detect cancer at an early stage. The diagnostic techniques addressed in this review are highly sensitive to the chemical and morphological changes in the cell and tissue during disease progression. These changes alter the fluorescence signal of the cell/tissue and are detected using spectroscopy and microscopy techniques including confocal and two-photon fluorescence (TPF). Further, second harmonic generation (SHG) microscopy reveals the morphological changes that occurred in non-centrosymmetric structures in the tissue, such as collagen. Again, Raman spectroscopy is a non-destructive method that provides a fingerprinting technique to differentiate benign and malignant tissue based on Raman signal. Photoacoustic microscopy and spectroscopy of tissue allow molecule-specific detection with high spatial resolution and penetration depth. In addition, terahertz spectroscopic studies reveal the variation of tissue water content during disease progression. In this review, we address the applications of spectroscopic and microscopic techniques for cancer detection based on the optical properties of the tissue. The discussed state-of-the-art techniques successfully determines malignancy to its rapid diagnosis.

ZnO nanowire-based fluorometric enzymatic assays for lactate and cholesterol

A rapid fluorometric method is described for the determination of lactate and cholesterol by using ZnO nanowires (ZnO NWs). The assay is based on the detection of the hydrogen peroxide generated during the enzymatic reactions of the oxidation of lactate or cholesterol. Taking advantage of the electrostatic interactions between the enzymes and the ZnO NWs, two bioconjugates were prepared by mixing the nanomaterial and the enzymes, viz. lactate oxidase (LOx) or cholesterol oxidase (ChOx). The enzymatically generated hydrogen peroxide quenches the fluorescence of the ZnO NWs, which have emission peaks at 384 nm and at 520 nm under 330 nm photoexcitation. H₂O₂ quenches the 520 nm band more strongly. Response is linear up to 1.9 μM lactate concentration, and up to 1.1 μM cholesterol concentration. Relative standard deviation was found to be 5%. The detection limits for lactate and cholesterol are 0.54 and 0.24 μM, respectively. Graphical abstractSchematic representation of fluorescence assay based on ZnO nanowires photoluminiscence for lactate and colesterol detection.

Correcting for targeted and control agent signal differences in paired-agent molecular imaging of cancer cell-surface receptors

Paired-agent kinetic modeling protocols provide one means of estimating cancer cell-surface receptors with in vivo molecular imaging. The protocols employ the coadministration of a control imaging agent with one or more targeted imaging agent to account for the nonspecific uptake and retention of the targeted agent. These methods require the targeted and control agent data be converted to equivalent units of concentration, typically requiring specialized equipment and calibration, and/or complex algorithms that raise the barrier to adoption. This work evaluates a kinetic model capable of correcting for targeted and control agent signal differences. This approach was compared with an existing simplified paired-agent model (SPAM), and modified SPAM that accounts for signal differences by early time point normalization of targeted and control signals (SPAMPN). The scaling factor model (SPAMSF) outperformed both SPAM and SPAMPN in terms of accuracy and precision when the scale differences between targeted and imaging agent signals (α) were not equal to 1, and it matched the performance of SPAM for α  =  1. This model could have wide-reaching implications for quantitative cancer receptor imaging using any imaging modalities, or combinations of imaging modalities, capable of concurrent detection of at least two distinct imaging agents (e.g., SPECT, optical, and PET/MR).

Colorectal cancer detection by hyperspectral imaging using fluorescence excitation scanning

Hyperspectral imaging technologies have shown great promise for biomedical applications. These techniques have been especially useful for detection of molecular events and characterization of cell, tissue, and biomaterial composition. Unfortunately, hyperspectral imaging technologies have been slow to translate to clinical devices - likely due to increased cost and complexity of the technology as well as long acquisition times often required to sample a spectral image. We have demonstrated that hyperspectral imaging approaches which scan the fluorescence excitation spectrum can provide increased signal strength and faster imaging, compared to traditional emission-scanning approaches. We have also demonstrated that excitation-scanning approaches may be able to detect spectral differences between colonic adenomas and adenocarcinomas and normal mucosa in flash-frozen tissues. Here, we report feasibility results from using excitation-scanning hyperspectral imaging to screen pairs of fresh tumoral and nontumoral colorectal tissues. Tissues were imaged using a novel hyperspectral imaging fluorescence excitation scanning microscope, sampling a wavelength range of 360-550 nm, at 5 nm increments. Image data were corrected to achieve a NIST-traceable flat spectral response. Image data were then analyzed using a range of supervised and unsupervised classification approaches within ENVI software (Harris Geospatial Solutions). Supervised classification resulted in >99% accuracy for single-patient image data, but only 64% accuracy for multi-patient classification (n=9 to date), with the drop in accuracy due to increased false-positive detection rates. Hence, initial data indicate that this approach may be a viable detection approach, but that larger patient sample sizes need to be evaluated and the effects of inter-patient variability studied.

Vision 20/20: Molecular-guided surgical oncology based upon tumor metabolism or immunologic phenotype: Technological pathways for point of care imaging and intervention

Surgical guidance with fluorescence has been demonstrated in individual clinical trials for decades, but the scientific and commercial conditions exist today for a dramatic increase in clinical value. In the past decade, increased use of indocyanine green based visualization of vascular flow, biliary function, and tissue perfusion has spawned a robust growth in commercial systems that have near-infrared emission imaging and video display capabilities. This recent history combined with major preclinical innovations in fluorescent-labeled molecular probes, has the potential for a shift in surgical practice toward resection guidance based upon molecular information in addition to conventional visual and palpable cues. Most surgical subspecialties already have treatment management decisions partially based upon the immunohistochemical phenotype of the cancer, as assessed from molecular pathology of the biopsy tissue. This phenotyping can inform the surgical resection process by spatial mapping of these features. Further integration of the diagnostic and therapeutic value of tumor metabolism sensing molecules or immune binding agents directly into the surgical process can help this field mature. Maximal value to the patient would come from identifying the spatial patterns of molecular expression in vivo that are well known to exist. However, as each molecular agent is advanced into trials, the performance of the imaging system can have a critical impact on the success. For example, use of pre-existing commercial imaging systems are not well suited to image receptor targeted fluorophores because of the lower concentrations expected, requiring orders of magnitude more sensitivity. Additionally the imaging system needs the appropriate dynamic range and image processing features to view molecular probes or therapeutics that may have nonspecific uptake or pharmacokinetic issues which lead to limitations in contrast. Imaging systems need to be chosen based upon objective performance criteria, and issues around calibration, validation, and interpretation need to be established before a clinical trial starts. Finally, as early phase trials become more established, the costs associated with failures can be crippling to the field, and so judicious use of phase 0 trials with microdose levels of agents is one viable paradigm to help the field advance, but this places high sensitivity requirements on the imaging systems used. Molecular-guided surgery has truly transformative potential, and several key challenges are outlined here with the goal of seeing efficient advancement with ideal choices. The focus of this vision 20/20 paper is on the technological aspects that are needed to be paired with these agents.

Two-color widefield fluorescence microendoscopy enables multiplexed molecular imaging in the alveolar space of human lung tissue

We demonstrate a fast two-color widefield fluorescence microendoscopy system capable of simultaneously detecting several disease targets in intact human ex vivo lung tissue. We characterize the system for light throughput from the excitation light emitting diodes, fluorescence collection efficiency, and chromatic focal shifts. We demonstrate the effectiveness of the instrument by imaging bacteria (Pseudomonas aeruginosa) in ex vivo human lung tissue. We describe a mechanism of bacterial detection through the fiber bundle that uses blinking effects of bacteria as they move in front of the fiber core providing detection of objects smaller than the fiber core and cladding (∼3  μm ∼3  μm ). This effectively increases the measured spatial resolution of 4  μm 4  μm . We show simultaneous imaging of neutrophils, monocytes, and fungus (Aspergillus fumigatus) in ex vivo human lung tissue. The instrument has 10 nM and 50 nM sensitivity for fluorescein and Cy5 solutions, respectively. Lung tissue autofluorescence remains visible at up to 200 fps camera acquisition rate. The optical system lends itself to clinical translation due to high-fluorescence sensitivity, simplicity, and the ability to multiplex several pathological molecular imaging targets simultaneously.

Combined fluorescence-Raman spectroscopic setup for the diagnosis of melanocytic lesions

Two optical fibre-based probes for spectroscopic measurements on human tissues were designed and developed. The two probes combine fluorescence and Raman spectroscopy in a multimodal approach. The fluorescence excitation was provided by two laser diodes emitting in the UV (378 nm) and in the visible (445 nm) range, while a third source in the NIR (785 nm) was used for Raman. The device was tested on freshly excised human skin biopsies clinically diagnosed as malignant melanoma, melanocytic nevus, or healthy skin. Discrimination of lesions based on their fluorescence and Raman spectra showed good correlation with the subsequent histological examination.

Pulsed-light imaging for fluorescence guided surgery under normal room lighting

Fluorescence guided surgery (FGS) is an emerging technology that has demonstrated improved surgical outcomes. However, dim lighting conditions required by current FGS systems are disruptive to standard surgical workflow. We present a novel FGS system capable of imaging fluorescence under normal room light by using pulsed excitation and gated acquisition. Images from tissue-simulating phantoms confirm visual detection down to 0.25 μM of protoporphyrin IX under 125 μW/cm2 of ambient light, more than an order of magnitude lower than that measured with the Zeiss Pentero in the dark. Resection of orthotopic brain tumors in mice also suggests that the pulsed-light system provides superior sensitivity in vivo.

Comparison of multispectral wide-field optical imaging modalities to maximize image contrast for objective discrimination of oral neoplasia

Multispectral widefield optical imaging has the potential to improve early detection of oral cancer. The appropriate selection of illumination and collection conditions is required to maximize diagnostic ability. The goals of this study were to (i) evaluate image contrast between oral cancer∕precancer and non-neoplastic mucosa for a variety of imaging modalities and illumination∕collection conditions, and (ii) use classification algorithms to evaluate and compare the diagnostic utility of these modalities to discriminate cancers and precancers from normal tissue. Narrowband reflectance, autofluorescence, and polarized reflectance images were obtained from 61 patients and 11 normal volunteers. Image contrast was compared to identify modalities and conditions yielding greatest contrast. Image features were extracted and used to train and evaluate classification algorithms to discriminate tissue as non-neoplastic, dysplastic, or cancer; results were compared to histologic diagnosis. Autofluorescence imaging at 405-nm excitation provided the greatest image contrast, and the ratio of red-to-green fluorescence intensity computed from these images provided the best classification of dysplasia∕cancer versus non-neoplastic tissue. A sensitivity of 100% and a specificity of 85% were achieved in the validation set. Multispectral widefield images can accurately distinguish neoplastic and non-neoplastic tissue; however, the ability to separate precancerous lesions from cancers with this technique was limited.

Global analysis of microscopic fluorescence lifetime images using spectral segmentation and a digital micromirror spatial illuminator

Fluorescence lifetime imaging (FLIM) is very demanding from a technical and computational perspective, and the output is usually a compromise between acquisition/processing time and data accuracy and precision. We present a new approach to acquisition, analysis, and reconstruction of microscopic FLIM images by employing a digital micromirror device (DMD) as a spatial illuminator. In the first step, the whole field fluorescence image is collected by a color charge-coupled device (CCD) camera. Further qualitative spectral analysis and sample segmentation are performed to spatially distinguish between spectrally different regions on the sample. Next, the fluorescence of the sample is excited segment by segment, and fluorescence lifetimes are acquired with a photon counting technique. FLIM image reconstruction is performed by either raster scanning the sample or by directly accessing specific regions of interest. The unique features of the DMD illuminator allow the rapid on-line measurement of global good initial parameters (GIP), which are supplied to the first iteration of the fitting algorithm. As a consequence, a decrease of the computation time required to obtain a satisfactory quality-of-fit is achieved without compromising the accuracy and precision of the lifetime measurements.

Tumor selectivity at short times following systemic administration of a liposomal temoporfin formulation in a murine tumor model

Meso-tetra(hydroxyphenyl)chlorin (mTHPC) (INN: Temoporfin) is one of the most potent photodynamically active substances in clinical use. Treatment protocols for Temoporfin-mediated photodynamic therapy often rely on drug-light intervals of several days in order for the photosensitizer to accumulate within the target tissue, though tumor selectivity is limited. Here, the mTHPC localization was studied at 2-8 h following systemic administration of a liposomal Temoporfin formulation (0.15 mg kg(-1) b.w.) in HT29 human colon adenocarcinoma in NMRI nu/nu mice. Photosensitizer distribution within tumor and internal organs was investigated by means of high performance liquid chromatography following chemical extraction, as well as in situ fluorescence imaging and point-monitoring fluorescence spectroscopy. For tumor tissue, the Temoporfin concentrations at 4 h (0.16+/-0.024 ng mg(-1)) and 8 h (0.18+/-0.064 ng mg(-1)) were significantly higher than at 2 h (0.08+/-0.026 ng mg(-1)). The average tumor-to-muscle and the tumor-to-skin selectivity were 6.6 and 2, respectively, and did not vary significantly with time after photosensitizer injection. In plasma, the Temoporfin concentration was low (0.07+/-0.07 ng mg(-1)) and showed no significant variation with time. Our results indicate a rapid biodistribution and clearance from the bloodstream. Within the same type of organ, data from both fluorescence methods generally exhibited a significant correlation with the extraction results.

Bispectral fluorescence imaging of aggressive basal cell carcinoma combined with histopathological mapping: a preliminary study indicating a possible adjunct to Mohs micrographic surgery

BACKGROUND

Fluorescence imaging is an attractive diagnostic technique for skin tumour demarcation with potential to move to clinical use. Bispectral fluorescence imaging combines skin autofluorescence with delta-aminolaevulinic acid-induced fluorescence. To evaluate the technique, fluorescence data must be compared with the histopathological extent of the tumour, which is the purpose of the current study.

OBJECTIVES

To investigate the agreement between bispectral fluorescence images and the histopathological tumour boundary of ill-defined basal cell carcinomas (BCCs). After fluorescence imaging the tumours were removed using Mohs micrographic surgery (MMS) to obtain histopathological maps of the tumour boundaries.

METHODS

Twelve patients with aggressive BCC of mean diameter 16 mm (range 5-32) in the face were included in the study. The patients were subjected to bispectral fluorescence imaging within the 2 months prior to MMS. The fluorescence images and histopathological maps were aligned using image warping.

RESULTS

Five patients (42%) showed good agreement with the histopathological mapping and the remaining seven patients (58%) showed partial agreement. Bispectral investigation combining autofluorescence with protoporphyrin IX (PpIX) fluorescence generally yielded better agreement with the histopathological boundaries of the tumours compared with using only the PpIX fluorescence.

CONCLUSIONS

In this preliminary study the fluorescence has been compared with the histopathological tumour boundaries. The result implies that the technique can be applied as a useful tool for indicating tumour boundary of aggressive BCCs. Further refinement is needed to be able to indicate the exact tumour border.

Fiber optic probes for biomedical optical spectroscopy

Fiber optic probes are a key element for biomedical spectroscopic sensing. We review the use of fiber optic probes for optical spectroscopy, focusing on applications in turbid media, such as tissue. The design of probes for reflectance, polarized reflectance, fluorescence, and Raman spectroscopy is illustrated. We cover universal design principles as well as technologies for beam deflecting and reshaping.

mTHPC-mediated photodynamic diagnosis of malignant brain tumors

Radical tumor resection is the basis for the prolonged survival of patients suffering from malignant brain tumors such as glioblastoma multiforme. We have carried out a phase-II study involving 22 patients with malignant brain tumors to assess the feasibility and the effectiveness of the combination of intraoperative photodynamic diagnosis and fluorescence-guided resection (FGR) mediated by the second-generation photosensitizer meta-tetrahydroxyphenylchlorin (mTHPC). In addition, intraoperative photodynamic therapy (PDT) was performed. Several commercially available fluorescence diagnostic systems were investigated for their applicability in clinical practice. We have adapted and optimized a diagnostic system that includes a surgical microscope, an excitation light source (filtered to 370-440 nm), a video camera detection system and a spectrometer for clear identification of the mTHPC fluorescence emission at 652 nm. Especially in regions of faint fluorescence, it turned out to be essential to maximize the spectral information by optimizing and matching the spectral properties of all components, such as excitation source, camera and color filters. To sum up, on the basis of 138 tissue samples derived from 22 tumor specimens, we have been able to achieve a sensitivity of 87.9% and a specificity of 95.7%. This study demonstrates that mTHPC-mediated intraoperative FGR followed by PDT is a highly promising concept in improving the radicality of tumor resection combined with a therapeutic approach.

Fast and noninvasive fluorescence imaging of biological tissues in vivo using a flying-spot scanner

We have developed a flying-spot scanner (FSS), for fluorescence imaging of tissues in vivo. The FSS is based on the principles of single-pixel illumination and detection via a raster scanning technique. The principal components of the scanner are a laser light source, a pair of horizontal and vertical scanning mirrors to deflect the laser light in these respective directions on the tissue surface, and a photo multiplier tube (PMT) detector. This paper characterizes the performance of the FSS for fluorescence imaging of tissues in vivo. First, a signal-to-noise ratio (SNR) analysis is presented. This is followed by characterization of the experimental SNR, linearity and spatial resolution of the FSS. Finally, the feasibility of tissue fluorescence imaging is demonstrated using an animal model. In summary, the performance of the FSS is comparable to that of fluorescence-imaging systems based on multipixel illumination and detection. The primary advantage of the FSS is the order-of-magnitude reduction in the cost of the light source and detector. However, the primary disadvantage of the FSS its significantly slower frame rate (1 Hz). In applications where high frame rates are not critical, the FSS will represent a low-cost alternative to multichannel fluorescence imaging-systems.

Optical processing of light-induced autofluorescence for characterization of tissue pathology

We describe an optical processing method for characterizing tissue pathology that is based on principal-component analysis of light-induced autofluorescence. A set of optical spectral filters, which are related to the principal-component loading vectors, is designed to process the autofluorescence signal optically and to generate principal-component scores from the autofluorescence spectra. The scores are then correlated with the tissue pathology. An optical processing system is designed that uses the in vivo fluorescence spectra recorded from nasopharyngeal tissues. We demonstrate that the system can differentiate nasopharyngeal carcinoma from normal tissue with a high degree of sensitivity and specificity and that the optical filters used in the system can be manufactured.

Preliminary study of in vivo autofluorescence of nasopharyngeal carcinoma and normal tissue

BACKGROUND AND OBJECTIVE

In nasopharyngeal cancer, conventional white light endoscopy does not provide adequate information to detect the flat/small lesion and identify the margin of observable tumor. In the present study, we evaluate the potential of light-induced fluorescence spectroscopic imaging for the localization of cancerous nasopharyngeal tissue.

STUDY DESIGN/MATERIALS AND METHODS

We built a multiple channel spectrometer specifically for the investigation of fluorescence collected by a conventional endoscopic system. Nasopharyngeal fluorescence were measured in vivo from 27 subjects during the routine endoscopy. The biopsy specimens for histologic analysis were taken from the tissue sites where the fluorescence were measured.

RESULTS

Two algorithms to discriminate the nasopharyngeal carcinoma from normal tissue were created based on the good correlation between the tissue autofluorescence and histologic diagnosis. For the two-wavelength algorithm, carcinoma can be differentiated from normal tissue with a sensitivity and specificity of 93% and 92%, respectively. For the three-wavelength algorithm with compensation of variation of blood content in tissue, a sensitivity of 98% and specificity of 95% were achieved.

CONCLUSION

Fluorescence endoscopic imaging used with the algorithms developed in this report is an efficient method for detecting the nasopharyngeal carcinoma.

Laser-induced fluorescence studies of normal and malignant tumour tissue of rat following intravenous injection of delta-amino levulinic acid

BACKGROUND AND OBJECTIVE

Laser-induced fluorescence was studied in normal and tumour tissue of rat after intravenous injection of delta-amino levulinic acid (ALA). The aim of the study was to investigate the protoporphyrin IX accumulation in different tissue types in rat after systemically administered ALA.

STUDY DESIGN/MATERIAL AND METHODS

A malignant rat tumour and normal tissue from 13 different organs were investigated in eight rats. The rats were injected with two different ALA doses, 30 and 90 mg/kg b.w., and the investigations were performed at 10, 30 and 240 min after the injection. The fluorescence was recorded utilising an optical fibre based fluorosensor at 405 nm excitation.

RESULTS

Fluorescence spectra were recorded in the 400-750 nm wavelength region including the dual-peaked PpIX fluorescence at about 635 and 705 nm, and the tissue autofluorescence peaking at about 500 nm. The maximum tumour build-up of PpIX was achieved already in less than 1 hr after ALA injection. The fluorescence demarcation between tumour and surrounding tissue was a factor of 7-8:1 after 30 min and decreased for longer retention times. The accumulation in 13 different organs was investigated and a particularly high PpIX build-up was found in stomach and intestine.

CONCLUSIONS

Fluorescence detection following i.v. injection of ALA provides attractive diagnostics for the experimental tumour used, indicating clinical usefulness.

Propagation of fluorescent light

BACKGROUND AND OBJECTIVE

In general, the remitted fluorescence spectrum is affected by the scattering and absorption properties of tissue. Other important factors are boundary conditions, geometry of the tissue sample, and the quantum yield of tissue fluorophores. Each of these factors is examined through a series of Monte Carlo simulations.

STUDY DESIGN/MATERIALS AND METHODS

Monte Carlo modeling is used to simulate the propagation of excitation light and the resulting fluorescence. Remitted fluorescence is determined for semi-infinite single and multiple layer geometries and for cubic geometries representing small tissue samples. Monte Carlo results are compared to approximations obtained with a heuristic model.

RESULTS

Remitted fluorescence as a function of (1) the depth of fluorescence generation and (2) radial escape position is presented for semi-infinite single and multiple layer geometries. Fluorescence from a small tissue sample is simulated in terms of a cubic geometry, and losses from the sides and bottom are presented as a function of cube dimensions in terms of optical depth of the excitation wavelength. Monte Carlo results for a homogeneous semi-infinite layer are compared to a simple, fast heuristic model.

CONCLUSION

Both Monte Carlo simulations and the heuristic model clearly detail the volume of tissue interrogated by fluorescence. Since approximately 35-40% of the remitted fluorescence is due to photons originally directed away from the surface, distal layers affect the remitted fluorescence. Fluorescence spectra from small biopsy samples may not produce the correct line shape owing to wavelength dependent losses.

Preliminary evaluation of two fluorescence imaging methods for the detection and the delineation of basal cell carcinomas of the skin

BACKGROUND AND OBJECTIVE

Fluorescence techniques can provide powerful noninvasive means for medical diagnosis, based on the detection of either endogenous or exogenous fluorophores. The fluorescence of delta-aminolevulinic acid (ALA)-induced protoporphyrin IX (PpIX) has already shown promise for the diagnosis of tumors. The aim of the study was to investigate the localization of skin tumors after the topical application of ALA, by detecting the PpIX fluorescence either in the spectral or in the time domain. STUDY DESIGN/MATERIALS N AND METHODS: Two fluorescence imaging systems were used to identify basal cell carcinomas of the skin in humans, after topical application of 20% ALA ointment. Both systems rely on the comparison between the exogenous and the endogenous fluorescence, performed either in the spectral domain or in the time domain. The first system works by using three images acquired through different spectral filters, whereas the second one measures the spatial map of the average fluorescence lifetime of the sample.

RESULTS

A clear demarcation of skin malignancies was successfully performed in vivo noninvasively with both fluorescence imaging systems.

CONCLUSION

The two complementary approaches considered in the present study show promise for skin tumor detection and delineation based on specific fluorescence features.

Detection of premalignant oral lesions in hamsters with an endoscopic fluorescence imaging system

BACKGROUND

Various methods of detecting cancer with fluorescence have been developed. One type of fluorescence is based on the tumor-localizing properties of certain dyes. However, the phototoxicity of most known tumor-localizing dyes hinders the safe use of such diagnostic methods. The authors have developed a fluorescence imaging system to detect the distribution of a nontoxic dye, fluorescein, and they have evaluated the feasibility of the system by using it to detect oral dysplastic lesions in hamsters.

METHODS

Dysplasia was induced in the cheek pouches of hamsters by application of the carcinogen 9,10-dimethyl-1,2-benzantracene. Fluorescein was administered to the hamsters either intravenously or orally before the fluorescence examination. The endoscopic fluorescence system produced dye-distribution images of both treated and control pouches. Two fluorescence images in different spectral regions were processed for each dye image. Biopsy material from both pouches was examined histopathologically.

RESULTS

The accumulation of fluorescein was detected in 22 of 23 specimens containing dysplastic lesions.

CONCLUSIONS

These results demonstrate the utility of this fluorescein accumulation method in the detection of dysplasia. The accumulation of fluorescein in dysplastic lesions may point to acidification of interstitial medium in such lesions.

Kinetic fluorescence studies of 5-aminolaevulinic acid-induced protoporphyrin IX accumulation in basal cell carcinomas

Laser-induced fluorescence (LIF) investigations have been performed in connection with photodynamic therapy (PDT) of basal cell carcinomas and adjacent normal skin following topical application of 5-aminolaevulinic acid (ALA) in order to study the kinetics of the protoporphyrin IX (PpIX) build-up. Five superficial and 10 nodular lesions in 15 patients are included in the study. Fluorescence measurements are performed prior to the application of ALA, 2, 4 and 6 h post ALA application, immediately post PDT (60 J cm-2 at 635 nm), and 2 h after the treatment. Hence, the build-up, photobleaching and re-accumulation of PpIX can be followed. Superficial lesions show a maximum PpIX fluorescence 6 h post ALA application, whereas the intensity is already the highest 2-4 h after the application in nodular lesions. Immediately post PDT, the fluorescence contribution at 670 nm from the photoproducts is about 2% of the pre-PDT PpIX fluorescence at 635 nm. Two hours after the treatment, a uniform distribution of PpIX is found in the lesion and surrounding normal tissue. During the whole procedure, the autofluorescence of the lesions and the normal skin does not vary significantly from the values recorded before the application of ALA.

Mathematical model of fluorescence endoscopic image formation

We present a mathematical model that describes the spatial distribution of photons in fluorescence endoscopic images, resulting in expressions for image signal-to-noise ratio and resolution. This model was applied to quantitative analysis of fluorescence images collected from human colonic mucosa with a fiber-optic and an electronic endoscope. It provides a tool for the design of fluorescence endoscopic imaging systems and for extraction of quantitative information about image features. The results apply generally to endoscopic imaging of remote structures in biological and industrial settings, in which light of weak intensity such as fluorescence as well as reflected white light is used.

Tumour visualization in a murine model by time-delayed fluorescence of sulphonated aluminium phthalocyanine

Mice bearing the MS-2 fibrosarcoma were administered 0.25, 0.5 or 1 mg kg(-1) body weight (b.w.) of sulphonated aluminium phthalocyanine (AlS(2)Pc) (with average degree of sulphonation of 2.1), and time-gated fluorescence images were acquired up to 6 h after the injection. Different excitation wavelengths (610, 650 and 670 nm) were tested. Red light excitation and 3 ns delayed detection allow one to minimize natural fluorescence and scattered laser light, respectively. The best conditions for tumour detection are reached under either 650 or 670 nm Excitation, 2-4 h after the administration of either 0.5 or 1 mg kg(-1) b.w. of AlS(2)Pc. In these situations, the average fluorescence contrast between tumour area and surrounding healthy tissue is > 2, providing a clear identification of the pathological region. However, tumour localization is possible even after the injection of 0.25 mg kg(-1) b.w. of sensitizer. In conclusion, under low power excitation (< 100MuW cm(-2)), the technique allows real time detection of an intradermal tumour with good contrast.

Clinical imaging fluorescence apparatus for the endoscopic photodetection of early cancers by use of Photofrin II

A fluorescence imaging device applied to the detection of early cancer is described. The apparatus is based on the imaging of laser-induced fluorescence of a dye that localizes in a tumor with a higher concentration than in the surrounding normal tissue after iv injection. Tests carried out in the upper aerodigestive tract, the tracheobronchial tree, and the esophagus with Photofrin II (1 mg/kg of body weight) as the fluorescent agent are reported as examples. The fluorescence is induced by violet (410-nm) light from a continuous-wave (cw) krypton-ion laser. The fluorescence contrast between tumor and surrounding tissue is enhanced by real-time image processing. This is done by the simultaneous recording of the fluorescence image in two spectral domains (470-600 and 600-720 nm), after which these two images are digitized and manipulated with a mathematical operator (look-up table) at video frequency. Among the 7 photodetections performed in the tracheobronchial tree, 6 were successful, whereas it was the case for only 5 of the 15 lesions investigated in squamous mucosa (upper aerodigestive tract and esophagus). The sources of false positives and false negatives are evaluated in terms of the fluorescent dye, tissue optical properties, and illumination optics.

In vivo fluorescence imaging for tissue diagnostics

Non-invasive fluorescence imaging has the potential to provide in vivo diagnostic information for many clinical specialties. Techniques have been developed over the years for simple ocular observations following UV excitation to sophisticated spectroscopic imaging using advanced equipment. Much of the impetus for research on fluorescence imaging for tissue diagnostics has come from parallel developments in photodynamic therapy of malignant lesions with fluorescent photosensitizers. However, the fluorescence of endogenous molecules (tissue autofluorescence) also plays an important role in most applications. In this paper, the possibilities of imaging tissues using fluorescence spectroscopy as a mean of tissue characterization are discussed. The various imaging techniques for extracting diagnostic information suggested in the literature are reviewed. The development of exogenous fluorophores for this purpose is also presented. Finally, the present status of clinical evaluation and future directions are discussed.

Frequency domain modeling of reradiation in highly scattering media

We present a straightforward procedure for frequency domain modeling of reradiation in a highly scattering medium with an arbitrary, finite three-dimensional geometry. We use a finite difference numerical solver to determine the fluence distribution at the excitation wavelength, which is then coupled to the emission wavelength with an array of equivalent reradiating sources. We then calculate the fluence distribution at the emission wavelength with a second, independent numerical simulation with new optical parameters appropriate to the emission wavelength, using the distributed reradiating sources as the excitation. We compare three-dimensional simulations of a fluorophore distributed in a scattering medium with experimental data. We also compare simulations of the Raman reradiation of small diamonds in a scattering medium with experiment.

Detection of adenocarcinoma in Barrett's oesophagus by means of laser induced fluorescence

PATIENTS

Seven patients with Barrett's metaplastic epithelium and oesophageal adenocarcinoma were investigated by means of laser induced fluorescence after low dose intravenous injection (0.35 mg/kg bw) of Photofrin (QLT, Vancouver, Canada). Laser induced fluorescence measurements were performed immediately after resection of the oesophagus.

METHODS

Laser induced fluorescence spectra were recorded from 15-30 locations in each surgical specimen from normal mucosa, Barrett's epithelium, and tumour tissue. Histological examination was performed on each location to correlate the fluorescence spectral characteristics with histological status of the epithelium (normal, metaplastic or malignant). Measurements were also performed during endoscopy in five patients to test the applicability of the method in a clinical setting. Fluorescence spectra were recorded and evaluated at characteristic wavelengths, and biopsy specimens were collected. Fluorescence ratios were calculated as the quotient of Photofrin fluorescence divided by autofluorescence.

RESULTS

The mean (SD) fluorescence ratio values were 0.10 (0.058) for normal oesophageal mucosa, 0.16 (0.073) for normal gastric mucosa, 0.205 (0.17) for Barrett's epithelium with moderate dysplasia, 0.79 (0.54) for severe dysplasia, and 0.78 (0.56) for adenocarcinoma. The highest fluorescence ratios were obtained for adenocarcinoma tissue, which could generally be distinguished from all nonmalignant tissue. Metaplastic Barrett's epithelium also yielded higher fluorescence ratios than did normal mucosa.

CONCLUSIONS

The results suggest that the technique can be used during endoscopy for real time tissue characterisation in the oesophagus, as an aid in detecting malignant transformation not macroscopically apparent at endoscopy.