Optical Coherence Tomography in Dermatology
Optical coherence tomography (OCT), an emerging noninvasive imaging modality, recently received category III Current Procedural Terminology (CPT) codes from the American Medical Association, enabling tracking of its use in the medical community. In this article, we review OCT imaging and its variant systems, discussing its applications and limitations for clinical use. Future directions of OCT technology and goals for obtaining category I CPT codes and reimbursement also are discussed.
Practice Points
- Optical coherence tomography (OCT) technology has considerable utility in research and clinical settings given its high resolution, wide field of view, moderate penetration depth, straightforward image acquisition, and accessibility to anatomically challenging areas.
- Potential benefits of OCT include its ability to noninvasively diagnose and monitor nonmelanoma skin cancers as well as to delineate presurgical margins and elucidate the course and mechanism of action of skin conditions at the bedside.
- Limitations of OCT include device cost, lack of reimbursement, and training, as well as restricted ability to image advanced deep tumors and differentiate melanocytic lesions.
- Optical coherence tomography recently received 2 category III Current Procedural Terminology (CPT) codes to track its utilization in clinical practice and will hopefully receive category I CPT codes within the next 5 years.
Indications for OCT
Depiction of Healthy Versus Diseased Skin
Optical coherence tomography is a valuable tool in visualizing normal skin morphology including principal skin layers, namely the dermis, epidermis, and dermoepidermal junction, as well as structures such as hair follicles, blood vessels, and glands.2,13 The OCT images show architectural changes of the skin layers and can be used to differentiate abnormal from normal tissue in vivo.2
Diagnosis and Treatment Monitoring of Skin Cancers
Optical coherence tomography is well established for use in the diagnosis and management of nonmelanoma skin cancers and to determine clinical end points of nonsurgical treatment without the need for skin biopsy. Promising diagnostic criteria have been developed for nonmelanoma skin cancers including basal cell carcinoma (BCC) and squamous cell carcinoma, as well as premalignant actinic keratoses using FD-OCT and the newer D-OCT and HD-OCT devices.9-17 For example, FD-OCT offers improved diagnosis of lesions suspicious for BCC, the most common type of skin cancer, showing improved sensitivity (79%–96%) and specificity (75%–96%) when compared with clinical assessment and dermoscopy alone.12,14 Typical OCT features differentiating BCC from other lesions include hyporeflective ovoid nests with a dark rim and an alteration of the dermoepidermal junction. In addition to providing a good diagnostic overview of skin, OCT devices show promise in monitoring the effects of treatment on primary and recurrent lesions.14-16
In Vivo Excision Planning
Additionally, OCT is a helpful tool in delineating tumor margins prior to surgical resection to achieve optimal cosmesis. By detecting subclinical tumor extension, this preoperative technique has been shown to reduce the number of surgical stages. Pomerantz et al17 showed that mapping BCC tumor margins with OCT prior to Mohs micrographic surgery closely approximated the final surgical defects. Alawi et al18 showed that the OCT-defined lateral margins correctly indicated complete removal of tumors. These studies illustrate the ability of OCT to minimize the amount of skin excised without compromising the integrity of tumor-free borders. The use of ex vivo OCT to detect residual tumors is not recommended based on current studies.6,17,18
Diagnosis and Treatment Monitoring of Other Diseases
Further applications of OCT include diagnosis of noncancerous lesions such as nail conditions, scleroderma, psoriatic arthritis, blistering diseases, and vascular lesions, as well as assessment of skin moisture and hydration, burn depth, wound healing, skin atrophy, and UV damage.2 For example, Aldahan et al19 demonstrated the utility of D-OCT to identify structural and vascular features specific to nail psoriasis useful in the diagnosis and treatment monitoring of the condition.
Limitations of OCT
Resolution
Frequency-domain OCT enables the detection of architectural details within tissue, but its image resolution is not sufficient to distinguish individual cells, therefore restricting its use in evaluating pigmented benign and malignant lesions such as dysplastic nevi and melanomas. Higher-resolution RCM is superior for imaging these lesions, as its device can better evaluate microscopic structures. With the advent of D-OCT and HD-OCT, research is being conducted to assess their use in differentiating pigmented lesions.8,20 Schuh et al9 and Gambichler et al20 reported preliminary results indicating the utility of D-OCT and HD-OCT to differentiate dysplastic nevi from melanomas and melanoma in situ, respectively.
Depth Measurement
Another limitation is associated with measuring lesion depth for advanced tumors. Although the typical imaging depth of OCT is significantly deeper than most other noninvasive imaging modalities used on skin, imaging deep tumor margins and invasion is restricted.
Image Interpretation
Diagnostic imaging requires image interpretation leading to potential interobserver and intraobserver variation. Experienced observers in OCT more accurately differentiated normal from lesional skin compared to novices, which suggests that training could improve agreement.21,22
Reimbursement and Device Cost
Other practical limitations to widespread OCT utilization at this time include its initial laser device cost and lack of reimbursement. As such, large academic and research centers remain the primary sites to utilize these devices.
Future Directions
Optical coherence tomography complements other established noninvasive imaging tools allowing for real-time visualization of the skin without interfering with the tissue and offering images with a good balance of depth, resolution, and field of view. Although a single histology cut has superior cellular resolution to any imaging modality, OCT provides additional information that is not provided by a physical biopsy, given the multiple vertical sections of data. Optical coherence tomography is a useful diagnostic technique enabling patients to avoid unnecessary biopsies while increasing early lesion diagnosis. Furthermore, OCT helps to decrease repetitive biopsies throughout nonsurgical treatments. With the availability of newer technology such as D-OCT and HD-OCT, OCT will play an increasing role in patient management. Clinicians and researchers should work to convert from category III to category I CPT codes and obtain reimbursement for imaging, with the ultimate goal of increasing its use in clinical practice and improving patient care.
