Simplified and optimized multispectral imaging for 5-ALA-based fluorescence diagnosis of malignant lesions

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.

Comparison of chlorin-e6 detection efficiency by video systems with excitation wavelengths of 405nm and 635nm

BACKGROUND

Fluorescence diagnostics with two different wide field-of-view imaging systems with fluorescence excitation at 405 nm and 635 nm, respectively, were compared. Both systems include fluorescence quantification and experimental geometry normalization algorithms.

METHODS

A newly developed system with an excitation wavelength of 405 nm was tested on intralipid fluorescent tumor phantoms with chlorin-e6. Both, this new system and a second existing system with an excitation wavelength of 635 nm, were used for fluorescent diagnosis in six patients with basal cell carcinoma and cancer of the oral mucosa. For PDT, a red diode laser with a wavelength of 660 nm was used for all 6 patients. One patient received an additional irradiation using the red LED source of the new system RESULTS: The boundaries of the lesions and the fluorescence intensity were successfully determined by both video systems.

CONCLUSIONS

Both fluorescence imaging approaches showed comparable contrast between diseased and healthy tissues. For oral mucosal cancer, a system with violet fluorescence excitation, bispectral frame analysis, and time-resolved background suppression showed better contrast between the tumor and normal tissue and effective elimination of autofluorescence. Moreover, both systems provided efficient quantification of fluorescence and gave fluorescence indices that were weakly dependent on the distance between the device and the tissue.

Stomach tissue classification using autofluorescence spectroscopy and machine learning

BACKGROUND AND OBJECTIVES

Determination of stomach tumor location and invasion depth requires delineation of gastric histological structure, which has hitherto been widely accomplished by histochemical staining. In recent years, alternative histochemical evaluation methods have been pursued to accelerate intraoperative diagnosis, often by bypassing the time-consuming step of dyeing. Owing to strong endogenous signals from coenzymes, metabolites, and proteins, autofluorescence spectroscopy is a favorable candidate technique to achieve this aim.

MATERIALS AND METHODS

We investigated stomach tissue slices and block specimens using a fast fluorescence imaging scanner. To obtain histological information from broad and structureless fluorescence spectra, we analyzed tens of thousands of spectra with multiple machine-learning algorithms and built a tissue classification model trained with dissected gastric tissues.

RESULTS

A machine-learning-based spectro-histological model was built based on the autofluorescence spectra measured from stomach tissue samples with delineated and validated histological structures. The scores from a principal components analysis were employed as input features, and prediction accuracy was confirmed to be 92.0%, 90.1%, and 91.4% for mucosa, submucosa, and muscularis propria, respectively. We investigated the tissue samples in both sliced and block forms using a fast fluorescence imaging scanner.

CONCLUSION

We successfully demonstrated differentiation of multiple tissue layers of well-defined specimens with the guidance of a histologist. Our spectro-histology classification model is applicable to histological prediction for both tissue blocks and slices, even though only sliced samples were trained.

5-Aminolevulinic Acid-Induced Protoporphyrin IX Fluorescence Imaging for Tumor Detection: Recent Advances and Challenges

5-Aminolevulinic acid (5-ALA) is a natural amino acid and a precursor of heme and chlorophyll. Exogenously administered 5-ALA is metabolized into protoporphyrin IX (PpIX). PpIX accumulates in cancer cells because of the low activity of ferrochelatase, an enzyme that metabolizes PpIX to heme. High expression of 5-ALA influx transporters, such as peptide transporters 1/2, in cancer cells also enhances PpIX production. Because PpIX radiates red fluorescence when excited with blue/violet light, 5-ALA has been used for the visualization of various tumors. 5-ALA photodynamic diagnosis (PDD) has been shown to improve the tumor removal rate in high-grade gliomas and non-muscular invasive bladder cancers. However, 5-ALA PDD remains a challenge as a diagnostic method because tissue autofluorescence interferes with PpIX signals in cases where tumors emit only weak signals, and non-tumorous lesions, such as inflammatory sites, tend to emit PpIX fluorescence. Here, we review the current outline of 5-ALA PDD and strategies for improving its diagnostic applicability for tumor detection, focusing on optical techniques and 5-ALA metabolic pathways in both viable and necrotic tumor tissues.

Accumulation of Uroporphyrin I in Necrotic Tissues of Squamous Cell Carcinoma after Administration of 5-Aminolevulinic Acid

5-aminolevulinic acid (5-ALA)-induced protoporphyrin IX (PpIX) fluorescence is widely used for the intraoperative detection of malignant tumors. However, the fluorescence emission profiles of the accompanying necrotic regions of these tumors have yet to be determined. To address this, we performed fluorescence and high-performance liquid chromatography (HPLC) analyses of necrotic tissues of squamous cancer after 5-ALA administration. In resected human lymph nodes of metastatic squamous cell carcinoma, we found a fluorescence peak at approximately 620 nm in necrotic lesions, which was distinct from the PpIX fluorescence peak at 635 nm for viable cancer lesions. Necrotic lesions obtained from a subcutaneous xenograft model of human B88 oral squamous cancer also emitted the characteristic fluorescence peak at 620 nm after light irradiation: the fluorescence intensity ratio (620 nm/635 nm) increased with the energy of the irradiation light. HPLC analysis revealed a high content ratio of uroporphyrin I (UPI)/total porphyrins in the necrotic cores of murine tumors, indicating that UPI is responsible for the 620 nm peak. UPI accumulation in necrotic tissues after 5-ALA administration was possibly due to the failure of the heme biosynthetic pathway. Taken together, fluorescence imaging of UPI after 5-ALA administration may be applicable for the evaluation of tumor necrosis.

Near-Infrared Molecular Imaging of Glioblastoma by Miltuximab®-IRDye800CW as a Potential Tool for Fluorescence-Guided Surgery

Glioblastoma (GBM) is one of the most aggressive tumors and its 5-year survival is approximately 5%. Fluorescence-guided surgery (FGS) improves the extent of resection and leads to better prognosis. Molecular near-infrared (NIR) imaging appears to outperform conventional FGS, however, novel molecular targets need to be identified in GBM. Proteoglycan glypican-1 (GPC-1) is believed to be such a target as it is highly expressed in GBM and is associated with poor prognosis. We hypothesize that an anti-GPC-1 antibody, Miltuximab^®, conjugated with the NIR dye, IRDye800CW (IR800), can specifically accumulate in a GBM xenograft and provide high-contrast in vivo fluorescent imaging in rodents following systemic administration. Miltuximab^® was conjugated with IR800 and intravenously administered to BALB/c nude mice bearing a subcutaneous U-87 GBM hind leg xenograft. Specific accumulation of Miltuximab^®-IR800 in subcutaneous xenograft tumor was detected 24 h later using an in vivo fluorescence imager. The conjugate did not cause any adverse events in mice and caused strong fluorescence of the tumor with tumor-to-background ratio (TBR) reaching 10.1 ± 2.8. The average TBR over the 10-day period was 5.8 ± 0.6 in mice injected with Miltuximab^®-IR800 versus 2.4 ± 0.1 for the control group injected with IgG-IR800 (p = 0.001). Ex vivo assessment of Miltuximab^®-IR800 biodistribution confirmed its highly specific accumulation in the tumor. The results of this study confirm that Miltuximab^®-IR800 holds promise for intraoperative fluorescence molecular imaging of GBM and warrants further studies.

Machine learning-based prediction of glioma margin from 5-ALA induced PpIX fluorescence spectroscopy

Gliomas are infiltrative brain tumors with a margin difficult to identify. 5-ALA induced PpIX fluorescence measurements are a clinical standard, but expert-based classification models still lack sensitivity and specificity. Here a fully automatic clustering method is proposed to discriminate glioma margin. This is obtained from spectroscopic fluorescent measurements acquired with a recently introduced intraoperative set up. We describe a data-driven selection of best spectral features and show how this improves results of margin prediction from healthy tissue by comparison with the standard biomarker-based prediction. This pilot study based on 10 patients and 50 samples shows promising results with a best performance of 77% of accuracy in healthy tissue prediction from margin tissue.

5-ALA-assistant automated detection of lymph node metastasis in gastric cancer patients

BACKGROUND

5-aminolevulinic acid (5-ALA) has been utilized for cancer diagnosis as a fluorescence probe. We have reported the feasibility of 5-ALA-induced protoporphyrin IX (PpIX) fluorescence for detecting lymph node (LN) metastasis in gastrointestinal malignancies. However, a major barrier to the fluorescence diagnosis has been that the evaluation has been highly dependent on the observers. In this study, we examined the validity of a developed device for automated detection without subjectivity.

METHODS

Gastric cancer patients who received oral administration of 5-ALA (20 mg/kg) prior to surgery were enrolled. For a total of 323 LNs obtained from 64 patients, the diagnostic results of the device were compared to those of conventional histopathological examination based on hematoxylin-and-eosin-stained slides. The accuracy with the device was compared to that of stereoscopic detection with conventional fluorescence microscopy for 211 LNs from 42 patients. We used two types of image processing that we previously developed to eliminate autofluorescence of background tissues: differential and ratio methods.

RESULTS

For detection of metastasis in 323 LNs, the areas under the receiver operating characteristic curves with the differential method and ratio method were 0.921 and 0.909, respectively. The sensitivity, specificity, and accuracy with the differential method were 78.0%, 96.8%, and 94.4%; while those with the ratio method were 78.0%, 96.1%, and 93.8%, respectively. In 211 LN analysis, the diagnostic accuracy with the device was comparable to that of stereoscopic examination.

CONCLUSION

Our device for automated detection of LN metastasis using 5-ALA can be a useful tool for intraoperative diagnosis.

First-in-human intraoperative near-infrared fluorescence imaging of glioblastoma using cetuximab-IRDye800

Introduction

Maximizing extent of surgical resection with the least morbidity remains critical for survival in glioblastoma patients, and we hypothesize that it can be improved by enhancements in intraoperative tumor detection. In a clinical study, we determined if therapeutic antibodies could be repurposed for intraoperative imaging during resection.

Methods

Fluorescently labeled cetuximab-IRDye800 was systemically administered to three patients 2 days prior to surgery. Near-infrared fluorescence imaging of tumor and histologically negative peri-tumoral tissue was performed intraoperatively and ex vivo. Fluorescence was measured as mean fluorescence intensity (MFI), and tumor-to-background ratios (TBRs) were calculated by comparing MFIs of tumor and histologically uninvolved tissue.

Results

The mean TBR was significantly higher in tumor tissue of contrast-enhancing (CE) tumors on preoperative imaging (4.0 ± 0.5) compared to non-CE tumors (1.2 ± 0.3; p = 0.02). The TBR was higher at a 100 mg dose than at 50 mg (4.3 vs. 3.6). The smallest detectable tumor volume in a closed-field setting was 70 mg with 50 mg of dye and 10 mg with 100 mg. On sections of paraffin embedded tissues, fluorescence positively correlated with histological evidence of tumor. Sensitivity and specificity of tumor fluorescence for viable tumor detection was calculated and fluorescence was found to be highly sensitive (73.0% for 50 mg dose, 98.2% for 100 mg dose) and specific (66.3% for 50 mg dose, 69.8% for 100 mg dose) for viable tumor tissue in CE tumors while normal peri-tumoral tissue showed minimal fluorescence.

Conclusion

This first-in-human study demonstrates the feasibility and safety of antibody based imaging for CE glioblastomas.

Photodynamic Therapy

Photodynamic therapy is a clinical technique for the treatment of cancers, microbial infections and other medical conditions by means of light-induced generation of reactive oxygen species using photosensitising drugs. The intrinsic fluorescence of many such drugs make them potential theranostic agents for simultaneous diagnosis and therapy. This chapter reviews the basic chemical and biological aspects of photodynamic therapy with an emphasis on its applications in theranostics. The roles of nanotechnology is highlighted, as well as emerging trends such as photoimmunotherapy, image-guided surgery and light- and singlet-oxygen dosimetry.

Efficient fluorescence detection of protoporphyrin IX in metastatic lymph nodes of murine colorectal cancer stained with indigo carmine

Protoporphyrin IX (PpIX), a biochemical converted from 5-aminolevulinc acid (5-ALA) in living cells, is useful for intraoperative fluorescent detection of cancer metastasis in lymph nodes (LNs). However, unknown is whether the fluorescence of PpIX can be detected in the LNs when they coexist with indigo carmine, a blue dye commonly used for identification of sentinel LNs during surgery. To address this issue, we sought to evaluate the diagnostic usefulness of PpIX fluorescence in the presence of indigo carmine in a mouse LN metastasis model of rectal cancer after administration of 5-ALA. Spectral analysis of pure chemicals revealed that the absorption spectrum of indigo carmine widely overlapped with the fluorescence spectrum of PpIX specifically at the peak of 632nm, a common emission wavelength for detecting PpIX, but not at the other peak of 700nm. Due to such spectral overlap, the PpIX fluorescence intensity was significantly attenuated by mixture with indigo carmine at 632nm, but not at 700nm. Accordingly, fluorescent measurements of the mouse metastatic LN revealed more intense presentation of PpIX at 700nm than at 632nm, indicating that the diagnostic usefulness is greater at 700nm than at 632nm for the indigo carmine-dyed LNs after administration of 5-ALA. From these observations, we propose that the fluorescence measurement is more efficient at 700nm than at 632nm for detection of PpIX in metastatic LNs stained with indigo carmine.

The potential of photodynamic therapy (PDT)-Experimental investigations and clinical use

Photodynamic therapy (PDT) is an intensively studied part of medicine based on free radicals. These reactive species, extremely harmful for whole human organism, are used for eradication numerous diseases. Specific structure of ill tissues causes accumulation free radicals inside them without attack remaining healthy tissues. A rapid development of medicine and scientific research has led to extension of PDT towards treatment many diseases such as cancer, herpes, acne and based on antimicrobials. The presented review article is focused on the aforementioned disorders with accurate analysis of the newest available scientific achievements. The discussed cases explicitly indicate on high efficacy of the therapy. In most cases, free radicals turned out to be solution of many afflictions. Photodynamic therapy can be considered as promising treatment with comparable effectiveness but without side effects characteristic for chemotherapy.