|Year : 2021 | Volume
| Issue : 3 | Page : 115-117
Recent advances in noninvasive imaging of the skin – dermoscopy and optical coherence tomography
Li-Wen Chiu1, Stephen Chu-Sung Hu2
1 Department of Dermatology, Kaohsiung Medical University Hospital; Department of Dermatology, College of Medicine, Kaohsiung Medical University, Kaohsiung, Taiwan
2 Department of Dermatology, Kaohsiung Medical University Hospital; Department of Dermatology, College of Medicine, Kaohsiung Medical University; Department of Dermatology, Kaohsiung Municipal Siaogang Hospital, Kaohsiung, Taiwan
|Date of Submission||30-Aug-2021|
|Date of Acceptance||30-Aug-2021|
|Date of Web Publication||20-Sep-2021|
Dr. Stephen Chu-Sung Hu
Department of Dermatology, Kaohsiung Medical University Hospital, No. 100, Tzyou 1st Road, Kaohsiung 807
Source of Support: None, Conflict of Interest: None
|How to cite this article:|
Chiu LW, Hu SC. Recent advances in noninvasive imaging of the skin – dermoscopy and optical coherence tomography. Dermatol Sin 2021;39:115-7
The early diagnosis and management of skin tumors and inflammatory skin diseases are important to improve clinical outcomes. Currently, the gold standard for the diagnosis of skin cancer and many other dermatological disorders is skin biopsy and histopathological examination. However, skin biopsy is an invasive procedure and can only provide histological information for a small area of the skin lesion. In addition, it is often not possible to repeat skin biopsies on the same skin site, so that monitoring of skin changes by skin biopsy after treatment is difficult. Therefore, the development of noninvasive methods (such as dermoscopy and optical coherence tomography [OCT]) for the diagnosis and monitoring of skin lesions is a clinically important field of investigation.
Dermoscopy is a simple, noninvasive instrument which utilizes either polarized or nonpolarized light to observe morphological features (including pigment pattern and vascular structures) which are not visible to the naked eye. The magnification power of a traditional dermoscope usually ranges from ×10 to ×60. It provides a horizontal view of skin lesions. A number of studies have shown that various skin tumors demonstrate characteristic dermoscopic signs. For example, the dermoscopic features of Bowen's disease are characterized by dotted and glomerular vessels. Dermoscopic examination of basal cell carcinoma (BCC) often shows arborizing vessels, ovoid nests, and leaf-like areas [Figure 1]a. Benign melanocytic nevi usually exhibit a regular pigment network under dermoscopy, while malignant melanoma may show an atypical pigment network in association with blue-white veil, irregular streaks, and irregular dots and globules [Figure 1]b. In addition to skin tumors, dermoscopy is a useful tool in the differential diagnosis of inflammatory and infectious skin diseases, hair disorders (trichoscopy), and nail diseases (onychoscopy). Therefore, in combination with clinical examination, dermoscopy can improve the diagnostic accuracy of many skin diseases, and reduce the need for skin biopsy.
|Figure 1: (a) Dermoscopic image showing arborizing vessels in basal cell carcinoma. (b) Dermoscopic image showing atypical pigment network, blue-white veil, and irregular dots and globules in melanoma.|
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As traditional dermoscopes have limitations in magnification, image width, and image storage and analysis functions, new devices have been developed to address these issues. These technological innovations include videodermoscopy, fluorescence-advanced videodermoscopy, and digital dermoscopy. In videodermoscopy, a high-resolution video camera is connected to a computer, which enables zooming up to ×1000 magnification. This facilitates more detailed examination of skin structures, as certain dermoscopic features can only be seen at higher magnifications (for example, the identification of scabies mites). Videodermoscopy also allows simultaneous examination and discussion of dermoscopic images by multiple physicians, and is an optimal tool for dermoscopy training. In fluorescence-advanced videodermoscopy, a monochromatic light source (wavelength: 405 nm) is used, which is absorbed by certain skin molecules (such as melanin and hemoglobin) and leads to emission of fluorescence. This technique is useful in differentiating benign melanocytic tumors from malignant melanoma, and for the assessment of hair and scalp disorders. In digital dermoscopy, the dermoscopic images are recorded and stored on digital cameras, smartphones, or computers. This allows multiple adjacent dermoscopy images from a large skin lesion to be combined into a single image using computer software (also known as wide-area digital dermoscopy image), and also enables the organized storage of dermoscopy images from a single lesion taken at different times for patient follow-up. These advances in dermoscopy techniques facilitate the differential diagnosis and monitoring of various skin, hair, and nail disorders.
In recent years, the portability of the dermoscope has enabled it to be used in the telemedicine setting, in order to provide dermatology services to people living in rural and remote areas. This has been shown to increase diagnostic accuracy and reduce health-care costs. The dermoscopic images from patients living in rural areas may be captured by mobile phones and uploaded onto a cloud-based platform, and these images may then be interpreted by dermatologists based in city hospitals or clinics. In addition, recent advances in artificial intelligence (AI) and machine learning methods have led to computer-aided diagnosis of skin lesions based on dermoscopic images, which has been shown to exhibit high diagnostic sensitivity and specificity., In one study, a deep learning algorithm has shown superior accuracy compared to human dermatologists in the dermoscopic diagnosis of melanoma. AI-assisted diagnosis of skin lesions based on clinical and dermoscopic images is a rapidly progressive field of investigation, and will likely lead to major changes in the way dermatology is practiced in the future.
Due to its relatively low financial cost and portability, the use of dermoscopy has become commonplace in dermatology clinics. Despite the advantages of dermoscopy, it has several limitations. A disadvantage of dermoscopy is that it can only provide horizontal visualization of superficial skin structures. In addition, the magnification power of the traditional handheld dermoscope is limited, and it cannot achieve resolution at the cellular level in the visualization of skin lesions. Therefore, further developments in noninvasive skin imaging modalities with higher resolution are warranted.
OCT is a recently developed imaging instrument, based on the optical principle of interference of infrared or visible light by skin tissues. It provides noninvasive, real-time, three-dimensional (cross-sectional or en face) imaging of the skin. It is able to achieve high resolution at the cellular level with axial resolution of 1–15 μm, and can penetrate the skin to a depth of about 0.4–2 mm. Compared to dermoscopy, OCT offers the advantage of enabling three-dimensional visualization of the skin at the microscopic level. This recently developed imaging tool can be utilized to visualize superficial structures in the epidermis and upper dermis [Figure 2].
|Figure 2: (a) Optical coherence tomography image showing the different layers of the epidermis and upper dermis. (b) Optical coherence tomography image showing blood vessels in the upper dermis (*).|
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Examination of various skin tumors by OCT has revealed certain characteristic features. OCT has been shown to exhibit high sensitivity and specificity in the diagnosis of BCC.,, The OCT features of BCC include a dark border underneath the tumor, the presence of hypo-reflective nests and ovoid structures, and disruption of the dermal-epidermal junction. OCT has also been used to define tumor margins for BCC prior to surgery, and for monitoring tumor recurrence following treatment. In addition, previous studies have shown that OCT may facilitate the diagnosis of actinic keratosis and cutaneous squamous cell carcinoma. However, currently it has not shown sufficient accuracy in the diagnosis of melanoma. Furthermore, OCT may have potential applications in the differential diagnosis and monitoring of inflammatory skin diseases such as psoriasis, as well as in the evaluation of skin aging, photodamage, scars, folliculitis, onychomycosis, and bullous diseases. The use of OCT in dermatology is still at an early phase, and further studies are required to define the OCT features of various skin diseases.
Angiographic (dynamic) OCT is a special form of OCT which can visualize skin blood vessels and blood flow, and may be used to observe the abnormal vasculature of skin tumors. A previous report applied OCT to evaluate changes in vascular morphology during progression from nevus to melanoma. Angiographic OCT has also been utilized to visualize the abnormal vasculature of inflammatory skin diseases such as psoriasis and chronic wounds, and may be useful for monitoring disease activity and treatment response. Currently, the application of angiographic OCT in skin lesion assessment is an ongoing area of investigation, which is likely to improve the evaluation and follow-up of various dermatological conditions in the future.
Although OCT offers several advantages compared to traditional noninvasive imaging methods such as dermoscopy, it also has certain limitations. The diagnostic accuracy of OCT is highly dependent on operator skill and experience, which requires adequate training. In addition, current OCT instruments are expensive, take time to perform scans, and require a skilled clinician to interpret images. In the future, the development of AI-based methods may facilitate the interpretation of OCT images. Furthermore, despite advances in imaging resolution, current OCT instruments cannot achieve the same resolution as histopathology. Future technological advances are required to overcome these limitations.
In summary, recent advances in noninvasive skin imaging methods such as dermoscopy and OCT have led to improvement in the diagnostic accuracy of various skin tumors and inflammatory skin diseases. In the future, technological improvements in imaging resolution as well as developments in machine learning will likely lead to wider application of these imaging modalities in various clinical settings.
Financial support and sponsorship
This work was supported by grants from NCTU-KMU Joint Research Project (NCTU-KMU-109-BIO-01) and Kaohsiung Medical University Hospital (KMUH-DK(B)110007-4).
Conflicts of interest
There are no conflicts of interest.
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[Figure 1], [Figure 2]