Intraoperative imaging during Mohs surgery with reflectance confocal microscopy: initial clinical experience

Aluminium in dermatology - Inside story of an innocuous metal

Aluminium, the third most abundant element in the earth's crust, was long considered virtually innocuous to humans but has gained importance in the recent past. Aluminium is ubiquitous in the environment, with various sources of exposure like cosmetics, the food industry, occupational industries, the medical field, transport and electronics. Aluminium finds its utility in various aspects of dermatology as an effective haemostatic agent, anti-perspirant and astringent. Aluminium has a pivotal role to play in wound healing, calciphylaxis, photodynamic therapy and vaccine immunotherapy with diagnostic importance in Finn chamber patch testing and confocal microscopy. The metal also finds significance in cosmetic procedures like microdermabrasion and as an Nd:YAG laser component. It is important to explore the allergic properties of aluminium, as in contact dermatitis and vaccine granulomas. The controversial role of aluminium in breast cancer and breast cysts also needs to be evaluated by further studies.

A Prospective Double-Blinded Comparison of Reflectance Confocal Microscopy with Conventional Histopathology for In Vivo Assessment in Oral Cancer

PURPOSE

We investigated reflectance confocal microscopy (RCM) as a possible noninvasive approach for the diagnosis of cancer and real-time assessment of surgical margins.

EXPERIMENTAL DESIGN

In a phase I study on 20 patients, we established the RCM imaging morphologic features that distinguish oral squamous cell carcinoma (OSCC) from normal tissue with a newly developed intraoral RCM probe. Our subsequent phase II prospective double-blinded study in 60 patients tested the diagnostic accuracy of RCM against histopathology. Five RCM videos from the tumor and five from normal surrounding mucosa were collected on each patient, followed by a 3-mm punch biopsy of the imaged area. An experienced RCM reader, who was blinded to biopsy location and histologic diagnosis, examined the videos from both regions and classified each as "tumor" or "not tumor" based on RCM features established in phase I. Hematoxylin and eosin slides from the biopsies were read by a pathologist who was blinded to RCM results. Using histology as the gold standard, we calculated the sensitivity and specificity of RCM.

RESULTS

We report a high agreement between the blinded readers (95% for normal tissue and 81.7% for tumors), high specificity (98.3%) and negative predictive values (96.6%) for normal tissue identification, and high sensitivity (90%) and positive predictive values (88.2%) for tumor detection.

CONCLUSIONS

RCM imaging is a promising technology for noninvasive in vivo diagnosis of OSCC and for real-time intraoperative evaluation of mucosal surgical margins. Its inherent constraint, however, stems from the diminished capability to evaluate structures located at more substantial depths within the tissue.

Combining Reflectance Confocal Microscopy, Optical Coherence Tomography and Ex-Vivo Fluorescence Confocal Microscopy for Margin Assessment in Basal Cell Carcinoma Excision

INTRODUCTION

Recent developments of noninvasive, high-resolution imaging techniques, such as reflectance confocal microscopy (RCM) and optical coherence tomography (OCT), have enhanced skin cancer detection and precise tumor excision particularly in highly aggressive and poorly defined basal cell carcinomas (BCCs).

OBJECTIVES

The aim of this pilot study is to assess the feasibility and reproducibility of a systematic clinical workflow combining noninvasive (RCM-OCT) and invasive fluorescence confocal microscopy (FCM) imaging modalities in pre- and intra-surgical evaluations of the lateral and deep margins of BCC.

METHODS

Superficial incisions were made 2 mm beyond the clinical-dermoscopic BCC margins. Lateral margins were then explored with OCT and RCM. In positive margins, a further cut was made 2 mm distal from the previous. A final RCM/OCT-based double-negative margin was drawn around the entire perimeter of the lesion before referring to surgery. The freshly excised specimen was then examined with FCM (ex-vivo) for the evaluation of the deep margin. Histopathologic examination eventually confirmed margin involvement.

RESULTS

The study included 22 lesions from 13 patients. At the end of the study, 146 margins-106 negative (73%) and 40 positive (27%) at RCM/OCT-were collected. The RCM/OCT margin evaluation showed an overall sensitivity of 100% and a specificity of 96.3%. The overall positive margins diagnostic accuracy was 98.2%. Reproducibility was evaluated on recorded images and the raters showed a substantial inter-observer agreement on both RCM (κ = 0.752) and OCT images (κ = 0.724).

CONCLUSIONS

The combined RCM/OCT/FCM ex-vivo approach noninvasively facilitates the presurgical and intrasurgical lateral and deep margin assessment of poorly defined BCCs.

Confocal Microscopy for Diagnosis and Management of Cutaneous Malignancies: Clinical Impacts and Innovation

Cutaneous malignancies are common malignancies worldwide, with rising incidence. Most skin cancers, including melanoma, can be cured if diagnosed correctly at an early stage. Thus, millions of biopsies are performed annually, posing a major economic burden. Non-invasive skin imaging techniques can aid in early diagnosis and save unnecessary benign biopsies. In this review article, we will discuss in vivo and ex vivo confocal microscopy (CM) techniques that are currently being utilized in dermatology clinics for skin cancer diagnosis. We will discuss their current applications and clinical impact. Additionally, we will provide a comprehensive review of the advances in the field of CM, including multi-modal approaches, the integration of fluorescent targeted dyes, and the role of artificial intelligence for improved diagnosis and management.

Non-invasive imaging techniques in presurgical margin assessment of basal cell carcinoma: Current evidence

BACKGROUND

The diagnosis of basal cell carcinoma (BCC) is based on clinical and dermoscopical features. In uncertain cases, innovative imaging techniques, such as reflectance confocal microscopy (RCM) and optical coherence tomography (OCT), have been used. The main limitation of these techniques is the inability to study deep margins. HFUS (high-frequency ultrasound) and the most recent UHFUS (ultra-high-frequency ultrasound) have been used in various applications in dermatology, but they are not yet routinely used in the diagnosis of BCC. A key point in clinical practice is to find an imaging technique that can help to reduce post-surgical recurrences with a careful presurgical assessment of the lesional margins. This technique should show high sensitivity, specificity, reproducibility and simplicity of execution. This concept is very important for the optimal management of patients who are often elderly and have many comorbidities. The aim of the paper is to analyse the characteristics of current imaging techniques and the studies in the literature on this topic.

MATERIALS AND METHODS

The authors independently searched the MEDLINE, PubMed, Embase, Scopus, ScienceDirect and Cochrane Library databases for studies looking for non-invasive imaging techniques for the presurgical margin assessment of BCC.

RESULTS

Preoperative study of the BCC subtype can help to obtain a complete excision with free margins. Different non-invasive imaging techniques have been studied for in vivo evaluation of tumour margins, comparing the histologic evaluation with a radical surgery. The possibility to study the lateral and deep margins would allow a reduction of recurrences and sparing of healthy tissue.

CONCLUSION

HFUS and UHFUS represent the most promising, non-invasive techniques for the pre-operative study of BCC facilitating the characterization of vascularization, deep lateral margins and high-risk subtypes, although they are limited by insufficient literature unlike RCM and OCT.

Deep Learning on Basal Cell Carcinoma In Vivo Reflectance Confocal Microscopy Data

Background: Extended skin malignancies of the head and neck region are among the most common cancer types and are associated with numerous diagnostic and therapeutical problems. The radical resection of skin cancer in the facial area often leads to severe functional and aesthetic impairment, and precise margin assessments can avoid the extensive safety margins. On the other hand, the complete removal of the cancer is essential to minimize the risk of recurrence. Reliable intraoperative assessments of the wound margins could overcome this discrepancy between minimal invasiveness and safety distance in the head and neck region. With the help of reflectance confocal laser microscopy (RCM), cells can be visualized in high resolution intraoperatively. The combination with deep learning and automated algorithms allows an investigator independent and objective interpretation of specific confocal imaging data. Therefore, we aimed to apply a deep learning algorithm to detect malignant areas in images obtained via in vivo confocal microscopy. We investigated basal cell carcinoma (BCC), as one of the most common entities with well-described in vivo RCM diagnostic criteria, within a preliminary feasibility study. Patients and Methods: We included 62 patients with histologically confirmed BCC in the head and neck region. All patients underwent in vivo confocal laser microscope scanning. Approximately 382 images with BCC structures could be obtained, annotated, and proceeded for further deep learning model training. Results: A sensitivity of 46% and a specificity of 85% in detecting BCC regions could be achieved using a convolutional neural network model (“MobileNet”). Conclusion: The preliminary results reveal the potential and limitations of the automated detection of BCC with in vivo RCM. Further studies with a larger number of cases are required to obtain better predictability.

Handheld laser scanning microscope catheter for real-time and in vivo confocal microscopy using a high definition high frame rate Lissajous MEMS mirror

A handheld confocal microscope using a rapid MEMS scanning mirror facilitates real-time optical biopsy for simple cancer diagnosis. Here we report a handheld confocal microscope catheter using high definition and high frame rate (HDHF) Lissajous scanning MEMS mirror. The broad resonant frequency region of the fast axis on the MEMS mirror with a low Q-factor facilitates the flexible selection of scanning frequencies. HDHF Lissajous scanning was achieved by selecting the scanning frequencies with high greatest common divisor (GCD) and high total lobe number. The MEMS mirror was fully packaged into a handheld configuration, which was coupled to a home-built confocal imaging system. The confocal microscope catheter allows fluorescence imaging of in vivo and ex vivo mouse tissues with 30 Hz frame rate and 95.4% fill factor at 256 × 256 pixels image, where the lateral resolution is 4.35 μm and the field-of-view (FOV) is 330 μm × 330 μm. This compact confocal microscope can provide diverse handheld microscopic applications for real-time, on-demand, and in vivo optical biopsy.

Preoperative Evaluation through Dermoscopy and Reflectance Confocal Microscopy of the Lateral Excision Margins for Primary Basal Cell Carcinoma

Complete removal of malignant skin lesions with minimal impact on the aesthetic and functional aspects is the ideal of every dermatologic surgeon. Incomplete surgical excisions and tumor recurrences of basal cell carcinomas (BCC) commonly occur due to the subclinical extension of tumor lateral margins. Presently, the lateral excision margins for BCC cannot be objectively assessed preoperatively, dermoscopy proving to be relatively inefficient in this respect. The question is whether BCC lateral excision margins can be precisely determined preoperatively through the use of complementary non-invasive imaging techniques such as dermoscopy and reflectance confocal microscopy (RCM), thus permitting the complete removal of the lesion in a single stage, estimation of the post-excisional defect, and planning an appropriate reconstruction, especially in medical centers where Mohs micrographic surgery is not available. We present the results of a prospective, histopathologically controlled study designed to determine the feasibility of preoperative, non-invasive, in vivo evaluation of the lateral excision margins for primary basal cell carcinoma, through dermoscopy and RCM.

Electronic Pneumatic Injection-Assisted Dermal Drug Delivery Visualized by Ex Vivo Confocal Microscopy

Background and Objectives

Electronic pneumatic injection (EPI) is a technique for dermal drug delivery, which is increasingly being used in clinical practice. However, only few studies have been reported on cutaneous drug distribution and related clinical endpoints. We aimed to visualize the immediate cutaneous drug distribution, changes in skin architecture, and related clinical endpoint of EPI.

Study Design/Materials and Methods

Acridine orange (AO) solution was administered to ex vivo porcine skin by EPI at pressure levels from 4 to 6 bar with a fixed injection volume of 50 µl and nozzle size of 200 µm. Immediate cutaneous distribution was visualized using ex vivo confocal microscopy (EVCM). Changes in skin architecture were visualized using both EVCM and hematoxylin and eosin‐stained cryosections.

Results

The defined immediate endpoint was a clinically visible papule formation on the skin. The pressure threshold to consistently induce a papule was 4 bar, achieving delivery of AO to the deep dermis (2319 µm axial and 5944 µm lateral distribution). Increasing the pressure level to 6 bar did not lead to significant differences in axial and lateral dispersion (P = 0.842, P = 0.905; respectively). A distinctively hemispherical distribution pattern was identified. Disruption of skin architecture occurred independently of pressure level, and consisted of subepidermal clefts, dermal vacuoles, and fragmented collagen.

Conclusions

This is the first study to relate a reproducible clinical endpoint to EPI‐assisted immediate drug delivery using EVCM. An EPI‐induced skin papule indicates dermal drug delivery throughout all layers of the dermis, independent of pressure level settings. Lasers Surg. Med. © 2020 The Authors. Lasers in Surgery and Medicine published by Wiley Periodicals LLC

Dual-Wavelength Optical Polarization Imaging for Detecting Skin Cancer Margins

Treatment of keratinocyte carcinomas requires an assessment of the extent of tumor spread. Visual delineation of tumor margins is error-prone owing to the limited contrast between cancerous and normal skin. In this contribution, we introduce spectrally-encoded optical polarization imaging and evaluate its performance for preoperative demarcation of keratinocyte carcinomas. Subjects with basal or squamous cell carcinoma, scheduled for Mohs surgery, were enrolled. The surgeon outlined the clinical boundary of each lesion preoperatively. Optical images of the lesions were then acquired at 440 and 640 nm. Spectral encoding of the experimental images minimized the impact of background pigmentation and vascularization. The surgeon was blinded to the imaging results. Margin assessments by imaging and by the surgeon were recorded and compared with the intraoperative histopathology. In total, 53 lesions were imaged in vivo. Thirteen cases required more than one Mohs stage. In all these cases, images accurately visualized the tumor. For cases negative following the first Mohs stage, margin assessments correlated with histopathology in 39 out of 40 cases. Imaging demonstrated 100% sensitivity and 98% specificity. Spectrally-encoded optical polarization imaging may prove valuable for real-time noninvasive preoperative delineation of skin cancer.

Superpixel Raman spectroscopy for rapid skin cancer margin assessment

Spontaneous Raman micro-spectroscopy has been demonstrated great potential in delineating tumor margins; however, it is limited by slow acquisition speed. We describe a superpixel acquisition approach that can expedite acquisition between ~×100 and ×10 000, as compared to point-by-point scanning by trading off spatial resolution. We present the first demonstration of superpixel acquisition on rapid discrimination of basal cell carcinoma tumor from eight patients undergoing Mohs micrographic surgery. Results have been demonstrated high discriminant power for tumor vs normal skin based on the biochemical differences between nucleus, collagen, keratin and ceramide. We further perform raster-scanned superpixel Raman imaging on positive and negative margin samples. Our results indicate superpixel acquisition can facilitate the use of Raman microspectroscopy as a rapid and specific tool for tumor margin assessment.

Skin Imaging Using Ultrasound Imaging, Optical Coherence Tomography, Confocal Microscopy, and Two-Photon Microscopy in Cutaneous Oncology

With the recognition of dermoscopy as a new medical technology and its available fee assessment in Korea comes an increased interest in imaging-based dermatological diagnosis. For the dermatologist, who treats benign tumors and malignant skin cancers, imaging-based evaluations can assist with determining the surgical method and future follow-up plans. The identification of the tumor's location and the existence of blood vessels can guide safe treatment and enable the use of minimal incisions. The recent development of high-resolution microscopy based on laser reflection has enabled observation of the skin at the cellular level. Despite the limitation of a shallow imaging depth, non-invasive light-based histopathologic examinations are being investigated as a rapid and pain-free process that would be appreciated by patients and feature reduced time from consultation to treatment. In the United States, the current procedural terminology billing code was established for reflectance confocal microscopy in 2016 and has been used for the skin cancer diagnosis ever since. In this review, we introduce the basic concepts and images of ultrasound imaging, optical coherence tomography, confocal microscopy, and two-photon microscopy and discuss how they can be utilized in the field of dermatological oncology.

Potential of contrast agents to enhance in vivo confocal microscopy and optical coherence tomography in dermatology: A review

Distinction between normal skin and pathology can be a diagnostic challenge. This systematic review summarizes how various contrast agents, either topically delivered or injected into the skin, affect distinction between skin disease and normal skin when imaged by optical coherence tomography (OCT) and confocal microscopy (CM). A systematic review of in vivo OCT and CM studies using exogenous contrast agents on healthy human skin or skin disease was performed. In total, nine CM studies and one OCT study were eligible. Four contrast agents aluminum chloride (AlCl) n = 2, indocyanine green (ICG) n = 3, sodium fluorescein n = 3 and acetic acid n = 1 applied to CM in variety of skin diseases. ICG, acetic acid and AlCl showed promise to increase contrast of tumor nests in keratinocyte carcinomas. Fluorescein and ICG enhanced contrast of keratinocytes and adnexal structures. In OCT of healthy skin gold nanoshells, increased contrast of natural skin openings. Contrast agents may improve delineation and diagnosis of skin cancers; ICG, acetic acid and AlCl have potential in CM and gold nanoshells facilitate visualization of adnexal skin structures in OCT. However, as utility of bedside optical imaging increases, further studies with robust methodological quality are necessary to implement contrast agents into routine dermatological practice.

Slide-free imaging of hematoxylin-eosin stained whole-mount tissues using combined third-harmonic generation and three-photon fluorescence microscopy

Intraoperative margin assessment of surgical tissues during cancer surgery is clinically important, especially in the case of tissue conserving surgery like Mohs micrographic surgery in which minimization of the surgical area is considered crucial. Frozen pathology is the gold standard of assessing excised tissues for signs of remaining cancerous lesions. The current protocol, however, is time-consuming and labor-intensive. Instead of the complex frozen sectioning, staining, and traditional white light microscopy imaging protocol, optically sectioned histopathological imaging of hematoxylin-eosin stained whole-mount skin tissues with a subfemtoliter resolution is demonstrated by using nonlinear microscopy in this study. With our proposed method, the reagents of staining and the contrast of imaging are fully consistent with the current clinical standard of frozen pathology, thus facilitating rapid intraoperative assessment of surgical tissues for future applications. Image: Slide-free nonlinear microscopy imaging of H&E stained whole-mount skin tissue showing the morphology of sweat glands.

Peri-operative delineation of non-melanoma skin cancer margins in vivo with handheld reflectance confocal microscopy and video-mosaicking

BACKGROUND

The surgical removal of non-melanoma skin cancers (NMSCs) is guided by the pathologic examination of margins. However, the preparation of histopathology is time consuming, labour-intensive and requires separate laboratory infrastructure. Furthermore, when histopathology indicates positive margins, patients must return for re-excisions. Reflectance confocal microscopy (RCM) with a new video-mosaicking approach can noninvasively delineate margins directly on patients and potentially guide surgery in real-time, augmenting the traditional approaches of histopathology.

OBJECTIVE

To assess a new peri-operative RCM video-mosaicking approach for comprehensive delineation of NMSC margins on patients in vivo.

METHODS

Thirty-five patients undergoing Mohs micrographic surgery (MMS) in the Mohs surgery unit at Memorial Sloan Kettering Cancer Center, New York, NY were included in the study. RCM imaging was performed before and after the first staged excision by acquiring videos along the surgical margins (epidermal, peripheral and deep dermal) of each wound, which were subsequently processed into video-mosaics. Two RCM evaluators read and assessed video-mosaics, and subsequently compared to the corresponding Mohs frozen histopathology.

RESULTS

Reflectance confocal microscopy videos and video-mosaics displayed acceptable imaging quality (resolution and contrast), pre-operatively in 32/35 (91%) NMSC lesions and intra-operatively in 29/35 lesions (83%). Pre-operative delineation of margins correlated with the histopathology in 32/35 (91%) lesions. Intra-operative delineation correlated in 10/14 (71%) lesions for the presence of residual tumour and in 18/21 (86%) lesions for absence. Sensitivity/specificity were 71%/86% and 86%/81% for two RCM video-mosaic evaluators, and overall agreement was 80% and 83% with histopathology, with moderate inter-evaluator agreement (k = 0.59, P ≤ 0.0002).

CONCLUSIONS

Peri-operative RCM video-mosaicking of NMSC margins directly on patients may potentially guide surgery in real-time, serve as an adjunct to histopathology, reduce time spent in clinic and reduce the need for re-excisions. Further testing in larger studies is needed.

Rapid pathology of lumpectomy margins with open-top light-sheet (OTLS) microscopy

Open-top light-sheet microscopy is a technique that can potentially enable rapid ex vivo inspection of large tissue surfaces and volumes. Here, we have optimized an open-top light-sheet (OTLS) microscope and image-processing workflow for the comprehensive examination of surgical margin surfaces, and have also developed a novel fluorescent analog of H&E staining that is robust for staining fresh unfixed tissues. Our tissue-staining method can be achieved within 2.5 minutes followed by OTLS microscopy of lumpectomy surfaces at a rate of up to 1.5 cm2/minute. An image atlas is presented to show that OTLS image quality surpasses that of intraoperative frozen sectioning and can approximate that of gold-standard H&E histology of formalin-fixed paraffin-embedded (FFPE) tissues. Qualitative evidence indicates that these intraoperative methods do not interfere with downstream post-operative H&E histology and immunohistochemistry. These results should facilitate the translation of OTLS microscopy for intraoperative guidance of lumpectomy and other surgical oncology procedures.

Diagnostic accuracy of ex vivo fluorescence confocal microscopy in Mohs surgery of basal cell carcinomas: a prospective study on 753 margins

BACKGROUND

Frozen histological sections are used for intraoperative margin assessment during Mohs surgery. Fluorescence confocal microscopy (FCM) is a new tool that offers a promising and faster alternative to frozen histology.

OBJECTIVES

To evaluate prospectively in a clinical setting the accuracy of FCM vs. frozen sections in margin assessment of basal cell carcinoma (BCC).

METHODS

Patients with BCC scheduled for Mohs surgery were prospectively enrolled. Freshly excised surgical specimens were examined by FCM and then frozen sections were evaluated. Permanent sections were obtained, in order to validate the sample technique. A blind re-evaluation was also performed for discordant cases. Sensitivity and specificity levels, as well as positive and negative predictive values (PPV and NPV, respectively), were calculated and receiver-operating characteristic curves generated.

RESULTS

We enrolled 127 BCCs in as many patients (40·2% females). Seven hundred and fifty-three sections were examined. All BCCs were located in the head and neck area. In evaluating the performance of FCM vs. frozen sections, sensitivity was 79·8%, specificity was 95·8%, PPV was 80·5% and NPV was 95·7% [area under the curve 0·88, 95% confidence interval 0·84-0·92 (P < 0·001)]. Forty-nine discordant cases were re-evaluated; 24 were false positive and 25 false negative. The performance of FCM and frozen sections was also evaluated according to the final histopathological assessment.

CONCLUSIONS

We found high levels of accuracy for FCM vs. frozen section evaluation in intraoperative BCC margin assessment during Mohs surgery. Some technical issues prevent the wide use of this technique, but new devices promise to overcome these limitations.

Microscopy with ultraviolet surface excitation for wide-area pathology of breast surgical margins

Intraoperative assessment of breast surgical margins will be of value for reducing the rate of re-excision surgeries for lumpectomy patients. While frozen-section histology is used for intraoperative guidance of certain cancers, it provides limited sampling of the margin surface (typically <1  %   of the margin) and is inferior to gold-standard histology, especially for fatty tissues that do not freeze well, such as breast specimens. Microscopy with ultraviolet surface excitation (MUSE) is a nondestructive superficial optical-sectioning technique that has the potential to enable rapid, high-resolution examination of excised margin surfaces. Here, a MUSE system is developed with fully automated sample translation to image fresh tissue surfaces over large areas and at multiple levels of defocus, at a rate of ∼5  min  /  cm2. Surface extraction is used to improve the comprehensiveness of surface imaging, and 3-D deconvolution is used to improve resolution and contrast. In addition, an improved fluorescent analog of conventional H&E staining is developed to label fresh tissues within ∼5  min for MUSE imaging. We compare the image quality of our MUSE system with both frozen-section and conventional H&E histology, demonstrating the feasibility to provide microscopic visualization of breast margin surfaces at speeds that are relevant for intraoperative use.

Biophysical basis of skin cancer margin assessment using Raman spectroscopy

Achieving adequate margins during tumor margin resection is critical to minimize the recurrence rate and maximize positive patient outcomes during skin cancer surgery. Although Mohs micrographic surgery is by far the most effective method to treat nonmelanoma skin cancer, it can be limited by its inherent required infrastructure, including time-consuming and expensive on-site histopathology. Previous studies have demonstrated that Raman spectroscopy can accurately detect basal cell carcinoma (BCC) from surrounding normal tissue; however, the biophysical basis of the detection remained unclear. Therefore, we aim to explore the relevant Raman biomarkers to guide BCC margin resection. Raman imaging was performed on skin tissue samples from 30 patients undergoing Mohs surgery. High correlations were found between the histopathology and Raman images for BCC and primary normal structures (including epidermis, dermis, inflamed dermis, hair follicle, hair shaft, sebaceous gland and fat). A previously developed model was used to extract the biochemical changes associated with malignancy. Our results showed that BCC had a significantly different concentration of nucleus, keratin, collagen, triolein and ceramide compared to normal structures. The nucleus accounted for most of the discriminant power (90% sensitivity, 92% specificity - balanced approach). Our findings suggest that Raman spectroscopy is a promising surgical guidance tool for identifying tumors in the resection margins.

Emerging imaging technologies in dermatology: Part II: Applications and limitations

Clinical examination is critical for the diagnosis and identification of response to treatment. It is fortunate that technologies are continuing to evolve, enabling augmentation of classical clinical examination with noninvasive imaging modalities. This article discusses emerging technologies with a focus on digital photographic imaging, confocal microscopy, optical coherence tomography, and high-frequency ultrasound, as well as several additional developing modalities. The most readily adopted technologies to date include total-body digital photography and dermoscopy, with some practitioners beginning to use confocal microscopy. In this article, applications and limitations are addressed. For a detailed discussion of the principles involved in these technologies, please refer to the first part of this review article.

Spectrally encoded coherence tomography and reflectometry: Simultaneous en face and cross-sectional imaging at 2 gigapixels per second

Non-invasive biological imaging is crucial for understanding in vivo structure and function. Optical coherence tomography (OCT) and reflectance confocal microscopy are two of the most widely used optical modalities for exogenous contrast-free, high-resolution, three-dimensional imaging in non-fluorescent scattering tissues. However, sample motion remains a critical barrier to raster-scanned acquisition and reconstruction of wide-field anatomically accurate volumetric datasets. We introduce spectrally encoded coherence tomography and reflectometry (SECTR), a high-speed, multimodality system for simultaneous OCT and spectrally encoded reflectance (SER) imaging. SECTR utilizes a robust system design consisting of shared optical relays, scanning mirrors, swept laser and digitizer to achieve the fastest reported in vivo multimodal imaging rate of 2 gigapixels per second. Our optical design and acquisition scheme enable spatiotemporally co-registered acquisition of OCT cross-sections simultaneously with en face SER images for multivolumetric mosaicking. Complementary axial and lateral translation and rotation are extracted from OCT and SER data, respectively, for full volumetric estimation of sample motion with micron spatial and millisecond temporal resolution.

Spectrally encoded coherence tomography and reflectometry: Simultaneous en face and cross-sectional imaging at 2 gigapixels per second

Non-invasive biological imaging is crucial for understanding in vivo structure and function. Optical coherence tomography (OCT) and reflectance confocal microscopy are two of the most widely used optical modalities for exogenous contrast-free, high-resolution, three-dimensional imaging in non-fluorescent scattering tissues. However, sample motion remains a critical barrier to raster-scanned acquisition and reconstruction of wide-field anatomically accurate volumetric datasets. We introduce spectrally encoded coherence tomography and reflectometry (SECTR), a high-speed, multimodality system for simultaneous OCT and spectrally encoded reflectance (SER) imaging. SECTR utilizes a robust system design consisting of shared optical relays, scanning mirrors, swept laser and digitizer to achieve the fastest reported in vivo multimodal imaging rate of 2 gigapixels per second. Our optical design and acquisition scheme enable spatiotemporally co-registered acquisition of OCT cross-sections simultaneously with en face SER images for multivolumetric mosaicking. Complementary axial and lateral translation and rotation are extracted from OCT and SER data, respectively, for full volumetric estimation of sample motion with micron spatial and millisecond temporal resolution.

Imaging in cutaneous surgery

Skin cancer is the most commonly diagnosed cancer in the USA. Mohs micrographic surgery is a microscopically controlled surgical technique that excises lateral and deep surgical margins while also sparing function and achieving a good cosmetic outcome. Given the increasing incidence in skin cancer worldwide and its associated treatment costs, techniques are being developed to improve the time and cost efficacy of this procedure. The use of noninvasive imaging, both in vivo and ex vivo, has the potential to increase efficiency of diagnosis and surgical management of skin cancers. These devices are useful in delineating lateral and deep tumor margins prior to surgery in vivo as well as to detect residual tumor ex vivo virtually in real time.

Automated video-mosaicking approach for confocal microscopic imaging in vivo: an approach to address challenges in imaging living tissue and extend field of view

We describe a computer vision-based mosaicking method for in vivo videos of reflectance confocal microscopy (RCM). RCM is a microscopic imaging technique, which enables the users to rapidly examine tissue in vivo. Providing resolution at cellular-level morphology, RCM imaging combined with mosaicking has shown to be highly sensitive and specific for non-invasively guiding skin cancer diagnosis. However, current RCM mosaicking techniques with existing microscopes have been limited to two-dimensional sequences of individual still images, acquired in a highly controlled manner, and along a specific predefined raster path, covering a limited area. The recent advent of smaller handheld microscopes is enabling acquisition of videos, acquired in a relatively uncontrolled manner and along an ad-hoc arbitrarily free-form, non-rastered path. Mosaicking of video-images (video-mosaicking) is necessary to display large areas of tissue. Our video-mosaicking methods addresses this need. The method can handle unique challenges encountered during video capture such as motion blur artifacts due to rapid motion of the microscope over the imaged area, warping in frames due to changes in contact angle and varying resolution with depth. We present test examples of video-mosaics of melanoma and non-melanoma skin cancers, to demonstrate potential clinical utility.

Reflectance confocal microscopy-guided laser ablation of basal cell carcinomas: initial clinical experience

Laser ablation offers a procedure for precise, fast, and minimally invasive removal of superficial and early nodular basal cell carcinomas (BCCs). However, the lack of histopathological confirmation has been a limitation toward widespread use in the clinic. A reflectance confocal microscopy (RCM) imaging-guided approach offers cellular-level histopathology-like feedback directly on the patient, which may then guide and help improve the efficacy of the ablation procedure. Following an ex vivo benchtop study (reported in our earlier papers), we performed an initial study on 44 BCCs on 21 patients in vivo, using a pulsed erbium:ytterbium aluminum garnet laser and a contrast agent (aluminum chloride). In 10 lesions on six patients, the RCM imaging-guided detection of either presence of residual tumor or complete clearance was immediately confirmed with histopathology. Additionally, 34 BCCs on 15 patients were treated with RCM imaging-guided laser ablation, with immediate confirmation for clearance of tumor (no histopathology), followed by longer-term monitoring, currently in progress, with follow-up imaging (again, no histopathology) at 3, 6, and 18 months. Thus far, the imaging resolution appears to be sufficient and consistent for monitoring efficacy of ablation in the wound, both immediately postablation and subsequently during recovery. The efficacy results appear to be promising, with observed clearance in 19 cases of 22 cases with follow-ups ranging from 6 to 21 months. An additional 12 cases with 1 to 3 months of follow-ups has shown clearance of tumor but a longer follow-up time is required to establish conclusive results. Further instrumentation development will be necessary to cover larger areas with a more automatically controlled instrument for more uniform, faster, and deeper imaging of margins.

In Vivo and Ex Vivo Confocal Microscopy for Dermatologic and Mohs Surgeons

Confocal microscopy is a modern imaging device that has been extensively applied in skin oncology. More specifically, for tumor margin assessment, it has been used in two modalities: reflectance mode (in vivo on skin patient) and fluorescence mode (on freshly excised specimen). Although in vivo reflectance confocal microscopy is an add-on tool for lentigo maligna mapping, fluorescence confocal microscopy is far superior for basal cell carcinoma and squamous cell carcinoma margin assessment in the Mohs setting. This article provides a comprehensive overview of the use of confocal microscopy for skin cancer margin evaluation.

Bessel-beam illumination in dual-axis confocal microscopy mitigates resolution degradation caused by refractive heterogeneities

One of the main challenges for laser-scanning microscopy of biological tissues with refractive heterogeneities is the degradation in spatial resolution that occurs as a result of beam steering and distortion. This challenge is particularly significant for dual-axis confocal (DAC) microscopy, which achieves improved spatial-filtering and optical-sectioning performance over traditional confocal microscopy through off-axis illumination and collection of light with low-numerical aperture (NA) beams that must intersect precisely at their foci within tissues. DAC microscope image quality is sensitive to positional changes and distortions of these illumination- and collection-beam foci. Previous studies have shown that Bessel beams display improved positional stability and beam quality than Gaussian beams when propagating through tissues with refractive heterogeneities, which suggests that Bessel-beam illumination may enhance DAC microscopy of such tissues. Here, we utilize both Gaussian and Bessel illumination in a point-scanned DAC microscope and quantify the resultant degradation in resolution when imaging within heterogeneous optical phantoms and fresh tissues. Results indicate that DAC microscopy with Bessel illumination exhibits reduced resolution degradation from microscopic tissue heterogeneities compared to DAC microscopy with conventional Gaussian illumination.

Structural and functional 3D mapping of skin tumours with non-invasive multispectral optoacoustic tomography

BACKGROUND

Recent advances in technology have enabled the development of various non-invasive skin imaging tools to aid real-time diagnosis of both benign and malignant skin tumours, minimizing the need for invasive skin biopsy. Multispectral optoacoustic tomography (MSOT) is a recently developed non-invasive imaging tool, which offers the unique capacity for high resolution three dimensional (3D) optical mapping of tissue by further delivering highly specific optical contrast from a depth of several millimetres to centimetres in living tissues. MSOT enables volumetric, spectroscopic differentiation of tissue, both in vivo and in real time, with and without the application of biomarker-specific probes, and is further able of providing spatial maps of skin chromophores, as well as underlying blood vasculature.

METHODS

Three patients with suspicious skin tumours consented to have their lesions imaged with MSOT prior to excision. The histological findings and measurements were compared.

RESULTS

We demonstrated the first in vivo clinical use of MSOT for 3D reconstruction of skin tumours in three patients with good histological correlation.

CONCLUSION

Our findings confirm the potential benefit of the new imaging method in guiding surgical intervention to achieve a more precise excision with better clearance and lower relapse rates. It can also potentially help to shorten the duration of Mohs' micrographic surgery. Further large-scale studies are necessary to ensure correlation between MSOT and histology.

Reflectance confocal microscopy of skin in vivo: From bench to bedside

Following more than two decades of effort, reflectance confocal microscopy (RCM) imaging of skin was granted codes for reimbursement by the US Centers for Medicare and Medicaid Services. Dermatologists in the USA have started billing and receiving reimbursement for the imaging procedure and for the reading and interpretation of images. RCM imaging combined with dermoscopic examination is guiding the triage of lesions into those that appear benign, which are being spared from biopsy, against those that appear suspicious, which are then biopsied. Thus far, a few thousand patients have been spared from biopsy of benign lesions. The journey of RCM imaging from bench to bedside is certainly a success story, but still much more work lies ahead toward wider dissemination, acceptance, and adoption. We present a brief review of RCM imaging and highlight key challenges and opportunities. The success of RCM imaging paves the way for other emerging optical technologies, as well-and our bet for the future is on multimodal approaches. Lasers Surg. Med. 49:7-19, 2017. © 2016 Wiley Periodicals, Inc.

Miniature in vivo MEMS-based line-scanned dual-axis confocal microscope for point-of-care pathology

There is a need for miniature optical-sectioning microscopes to enable in vivo interrogation of tissues as a real-time and noninvasive alternative to gold-standard histopathology. Such devices could have a transformative impact for the early detection of cancer as well as for guiding tumor-resection procedures. Miniature confocal microscopes have been developed by various researchers and corporations to enable optical sectioning of highly scattering tissues, all of which have necessitated various trade-offs in size, speed, depth selectivity, field of view, resolution, image contrast, and sensitivity. In this study, a miniature line-scanned (LS) dual-axis confocal (DAC) microscope, with a 12-mm diameter distal tip, has been developed for clinical point-of-care pathology. The dual-axis architecture has demonstrated an advantage over the conventional single-axis confocal configuration for reducing background noise from out-of-focus and multiply scattered light. The use of line scanning enables fast frame rates (16 frames/sec is demonstrated here, but faster rates are possible), which mitigates motion artifacts of a hand-held device during clinical use. We have developed a method to actively align the illumination and collection beams in a DAC microscope through the use of a pair of rotatable alignment mirrors. Incorporation of a custom objective lens, with a small form factor for in vivo clinical use, enables our device to achieve an optical-sectioning thickness and lateral resolution of 2.0 and 1.1 microns respectively. Validation measurements with reflective targets, as well as in vivo and ex vivo images of tissues, demonstrate the clinical potential of this high-speed optical-sectioning microscopy device.

Combined reflectance confocal microscopy-optical coherence tomography for delineation of basal cell carcinoma margins: an ex vivo study

We present a combined reflectance confocal microscopy (RCM) and optical coherence tomography (OCT) approach, integrated within a single optical layout, for diagnosis of basal cell carcinomas (BCCs) and delineation of margins. While RCM imaging detects BCC presence (diagnoses) and its lateral spreading (margins) with measured resolution of ∼1  μm, OCT imaging delineates BCC depth spreading (margins) with resolution of ∼7  μm. When delineating margins in 20 specimens of superficial and nodular BCCs, depth could be reliably determined down to ∼600  μm, and agreement with histology was within about ±50  μm.