Confocal microscopy in oral cancer and oral potentially malignant disorders: A systematic review

Enabling high-resolution diagnostic oral confocal laser endomicroscopy in mice

Therapeutic prevention of oral squamous cell carcinoma (OSCC) will avoid significant morbidity and mortality. To observe and measure the in vivo efficacy of therapeutic challenges, microscopic-level diagnosis without animal sacrifice is required. This study introduces a refined diagnostic methodology for non-invasive cellular-level imaging for diagnosis of micro-lesions by utilizing high-resolution scanning-fibre confocal laser endomicroscopy (ViewnVivo) with topical fluorescence imaging agents. We detail the development and standardization of imaging protocols using a fluorescent, cell-permeable cancer-targeting agent (PARPi-FL) as a cancer-targeting agent and a pan-cytoarchitectural (acriflavine) agent in a pre-clinical murine 4-NQO induced OSCC model. We provide comprehensive methodology for the in vivo identification of the progressive stages of oral carcinogenesis from microscopic lesions, supported by an annotated signature guide correlating with conventional histopathology. Our findings demonstrate that in vivo CLE imaging with both PARPi-FL and acriflavine clearly distinguishes between histologically normal and pathological oral tissue. Tissues with histologic dysplasia and carcinoma demonstrated PARPi-FL positivity and an aberrant nuclear staining pattern with acriflavine, compared to the regularly spaced nuclear staining of normal nuclei. Crucially, this methodology detects microscopic changes not visible to the naked eye, but histologically abnormal. Our observation model of progressive oral carcinogenesis has the potential to accelerate standardised interrogation of early molecular diagnostic applications and novel therapeutic efficacy, whilst reducing the need for animal sacrifice. This will result in faster validated translation to human applications, advancing effective early oral cancer detection and prevention.

Optical imaging guidance in oncologic surgery and interventional oncology

Over recent decades, optical imaging (OI) has become an integral part of medical imaging, offering significant advantages over other modalities, such as computed tomography (CT) and magnetic resonance imaging (MRI). OI is distinguished by its real-time imaging capability, cost-effectiveness, portability, absence of ionizing radiation, and high patient acceptability. The introduction of advanced optical dyes (including FDA-approved agents like indocyanine green, Cytalux, and Gleolan) has greatly enhanced its clinical utility. OI has shown clear benefits in the management of patients with cancer, originally by open surgery and now extending to minimally invasive, image-guided interventional procedures. This review highlights recent developments in OI for oncology, emphasizing its benefits for clinicians in guiding surgical and interventional procedures.

Convolutional neural networks for accurate real-time diagnosis of oral epithelial dysplasia and oral squamous cell carcinoma using high-resolution in vivo confocal microscopy

Oral cancer detection is based on biopsy histopathology, however with digital microscopy imaging technology there is real potential for rapid multi-site imaging and simultaneous diagnostic analysis. Fifty-nine patients with oral mucosal abnormalities were imaged in vivo with a confocal laser endomicroscope using the contrast agents acriflavine and fluorescein for the detection of oral epithelial dysplasia and oral cancer. To analyse the 9168 images frames obtained, three tandem applied pre-trained Inception-V3 convolutional neural network (CNN) models were developed using transfer learning in the PyTorch framework. The first CNN was used to filter for image quality, followed by image specific diagnostic triage models for fluorescein and acriflavine, respectively. Images were categorised based on a histopathological diagnosis into 4 categories: no dysplasia, lichenoid lesions, low-grade dysplasia and high-grade dysplasia/oral squamous cell carcinoma (OSCC). The quality filtering model had an accuracy of 89.5%. The acriflavine diagnostic model performed well for identifying lichenoid (AUC = 0.94) and low-grade dysplasia (AUC = 0.91) but poorly for identifying no dysplasia (AUC = 0.44) or high-grade dysplasia/OSCC (AUC = 0.28). In contrast, the fluorescein diagnostic model had high classification performance for all diagnostic classes (AUC range = 0.90-0.96). These models had a rapid classification speed of less than 1/10th of a second per image. Our study suggests that tandem CNNs can provide highly accurate and rapid real-time diagnostic triage for in vivo assessment of high-risk oral mucosal disease.

Ultra-low-cost and high-fidelity NIR-II confocal laser scanning microscope with Bessel beam excitation and SiPM detection

Confocal laser scanning microscopy (CLSM) is one of the most important imaging tools in the biomedical field, and near-infrared-II (NIR-II, 900-1700nm) fluorescence imaging technology has also made fruitful research progress in deep imaging in recent years. The NIR-II based CLSM has problems such as an expensive detector and reduced image resolution caused by long wavelength excitation. Here, by simultaneously using a low-cost silicon photomultiplier (SiPM) as a detector and a Bessel beam as an excitation, we developed an ultra-low-cost and high-fidelity NIR-II confocal laser scanning microscope. The use of SiPM reduces the cost of the NIR-II fluorescence detection module in CLSM, while enabling the detection of ultra-broadband fluorescence signals spanning visible to NIR-II regions. The introduction of the Bessel beam compensates to some extent for the weakening of spatial resolution caused by the increase in the wavelength of light in the NIR region. Experimental results show that the use of the Bessel beam can improve the resolution by 12% when observing thin samples. With the increase of sample thickness, the imaging resolution of the Bessel beam at NIR-II wavelengths is better than that of the Gaussian beam at NIR-I wavelengths at the penetrable depth of the NIR-I light. At deeper depths, the imaging resolution and imaging depth of Bessel beam CLSM is superior to Gaussian beam CLSM at the same excitation power.

Optical imaging for screening and early cancer diagnosis in low-resource settings

Low-cost optical imaging technologies have the potential to reduce inequalities in healthcare by improving the detection of pre-cancer or early cancer and enabling more effective and less invasive treatment. In this Review, we summarise technologies for in vivo widefield, multi-spectral, endoscopic, and high-resolution optical imaging that could offer affordable approaches to improve cancer screening and early detection at the point-of-care. Additionally, we discuss approaches to slide-free microscopy, including confocal imaging, lightsheet microscopy, and phase modulation techniques that can reduce the infrastructure and expertise needed for definitive cancer diagnosis. We also evaluate how machine learning-based algorithms can improve the accuracy and accessibility of optical imaging systems and provide real-time image analysis. To achieve the potential of optical technologies, developers must ensure that devices are easy to use; the optical technologies must be evaluated in multi-institutional, prospective clinical tests in the intended setting; and the barriers to commercial scale-up in under-resourced markets must be overcome. Therefore, test developers should view the production of simple and effective diagnostic tools that are accessible and affordable for all countries and settings as a central goal of their profession.

Personalized Medicine in Oral Oncology: Imaging Methods and Biological Markers to Support Diagnosis of Oral Squamous Cell Carcinoma (OSCC): A Narrative Literature Review

For decades, oral squamous cell carcinoma (OSCC) has been one of the most prevalent and mortal cancers worldwide. The gold standard for OSCC diagnosis is still histopathology but this narrative multidisciplinary review has the aim to explore the literature about conventional OSCC prognostic indicators related to the pTNM stage at the diagnosis such as the depth of invasion and the lymphovascular invasion associated with distant metastasis as indicators of poor life expectancy. Despite its multifactorial nature and recognizable precursors, its diagnosis at the early stages is still challenging. We wanted to highlight the importance of the screening as a primary weapon that a stomatologist should consider, intercepting all at-risk conditions and lesions associated with OSCC and its early stages. This narrative review also overviews the most promising imaging techniques, such as CT, MRI, and US-echography, and their application related to clinical and surgical practice, but also the most-investigated prognostic and diagnostic tissue and salivary biomarkers helpful in OSCC diagnosis and prognostic assessment. Our work highlighted remarkable potential biomarkers that could have a leading role in the future. However, we are still far from defining an appropriate and concrete protocol to apply in clinical practice. The hope is that the present and future research will overcome these limitations to benefit patients, clinicians, and welfare.

Acquisition and annotation in high resolution in vivo digital biopsy by confocal microscopy for diagnosis in oral precancer and cancer

Introduction

Scanned fibre endomicroscopes are full point-scanning confocal microscopes with submicron lateral resolution with an optical slice thickness thin enough to isolate individual cell layers, allow active positioning of the optical slice in the z-axis and collection of megapixel images. Here we present descriptive findings and a brief atlas of an acquisition and annotation protocol high resolution in vivo capture of oral mucosal pathology including oral squamous cell carcinoma and dysplasia using a fluorescence scanned fibre endomicroscope with 3 topical fluorescent imaging agents: fluorescein, acriflavine and PARPi-FL.

Methods

Digital biopsy was successfully performed via an acquisition protocol in seventy-one patients presenting for investigation of oral mucosal abnormalities using a miniaturized, handheld scanned fibre endoscope. Multiple imaging agents were utilized and multiple time points sampled. Fifty-nine patients had a matched histopathology correlating in location with imaging. The images were annotated back to macrographic location using a purpose-built software, MouthMap™.

Results

Acquisition and annotation of cellular level resolved images was demonstrated with all 3 topical agents. Descriptive observations between clinically or histologically normal oral mucosa showed regular intranuclear distance, a regular nuclear profile and fluorescent homogeneity. This was dependent on the intraoral location and type of epithelium being observed. Key features of malignancy were a loss of intranuclear distance, disordered nuclear clustering and irregular nuclear fluorescence intensity and size. Perinuclear fluorescent granules were seen in the absence of irregular nuclear features in lichenoid inflammation.

Discussion

High resolution oral biopsy allows for painless and rapid capture of multiple mucosal sites, resulting in more data points to increase diagnostic precision. High resolution digital micrographs can be easily compared serially across multiple time points utilizing an annotation software. In the present study we have demonstrated realization of a high-resolution digital biopsy protocol of the oral mucosa for utility in the diagnosis of oral cancer and precancer..

Recent progress of second near-infrared (NIR-II) fluorescence microscopy in bioimaging

Visualizing biological tissues in vivo at a cellular or subcellular resolution to explore molecular signaling and cell behaviors is a crucial direction for research into biological processes. In vivo imaging can provide quantitative and dynamic visualization/mapping in biology and immunology. New microscopy techniques combined with near-infrared region fluorophores provide additional avenues for further progress in vivo bioimaging. Based on the development of chemical materials and physical optoelectronics, new NIR-II microscopy techniques are emerging, such as confocal and multiphoton microscopy, light-sheet fluorescence microscopy (LSFM), and wide-field microscopy. In this review, we introduce the characteristics of in vivo imaging using NIR-II fluorescence microscopy. We also cover the recent advances in NIR-II fluorescence microscopy techniques in bioimaging and the potential for overcoming current challenges.