Study: Optical coherence tomography as efficient as histopathologic techniques for basal cell evaluation

October 1, 2007

Study shows the optical coherence tomography (OCT) technique could improve clinical decision-making by allowing for early staging of the depth and pathologic subtype of basal cell cancers.

Scottsdale, Ariz. - Optical coherence tomography (OCT), which offers high-resolution cross-sectional images of basal cell carcinomas (BCC) in real time, can be just as efficient in estimating the superficial thickness of the carcinomas as routine histopathologic techniques, according to a new study.

The pilot study, conducted at the Mayo Clinic here, suggests that, since basal cell carcinomas are thin and superficial, the OCT technique could improve clinical decision-making by allowing for the depth and pathologic subtype of basal cell cancers to be easily staged.

"The most significant benefit for patients would be to improve the triaging of patients to medical management or surgical management, as well as to help determine the most appropriate surgical management: destruction, simple excision or Mohs micrographic surgery," David L. Swanson, M.D., assistant professor of dermatology at the Mayo Clinic, Scottsdale, Ariz., and a lead author on the study, tells Dermatology Times.

Dr. Swanson and his team looked at 20 OCT images of basal cell carcinomas that had been histopathologically confirmed.

The depth of the neoplasms was measured with a computer-generated depth scale and the results were compared with direct measurements of tumor thickness, made with a microscope micrometer.

The results indicated that all 20 sites showed excellent correlation of tissue thickness, to a depth of about 1 mm, whether estimated by optical coherence tomography or routine histopathologic tests.

They also found that the depth correlation was consistent across several different types of basal cell carcinomas that were observed.

OCT scanners specifically work by delivering near-infrared light to the imaging site with single-mode optical fiber. Signals are generated by the interference of the reflected light with a reference beam, and as the incident light scans across the tissue, the interference signals recorded from different depths are processed and displayed in a manner similar to pulse-echo ultrasonography.

The process allows for real-time, in vivo imaging of tissue to depths of 1 mm to 2 mm at a resolution of 3 microns to 15 microns.

"Compared with high-frequency ultrasonography, OCT imaging provides superior visualization of microstructures within the epidermis and upper dermis of normal skin; however, ultrasonography can provide deeper images of the dermal and subdermal layers," the authors write.

In addition, CT imaging has the advantage over confocal laser scanning microscopy of a vertical orientation due to confocal microscopy's limitation to resolution of horizontal cell layers. And the technology has advantages over fluorescence spectroscopy and terahertz pulse imaging, according to the study.

"Most physicians have probably heard of the technology. It is used in ophthalmology to examine retinal pathology in vivo and is being evaluated for the management of Barrett's esophagus," says Dr. Swanson.

Study parameters

For the study, the researchers used an OCT prototype assembled for the study, but they said the device still proved to be beneficial. They were able to see in most scans impressive detail to a depth of 1 mm, despite artifacts related to the design and operation of the probe.

"We observed an image quality that seemed improved over prior reports of OCT images of basal cell cancer, and this difference obviously reflects the technologic advances that are being made in OCT physics," the authors write.

Image quality and depth should only improve as the OCT becomes further refined, and the researchers say they did not find significant discordance between OCT images and processed histopathology specimens, as other studies have reported.

OCT has the potential for use in other clinical applications, including confocal laser scanning microscopy to evaluate basal cell cancer.

"For example, OCT imaging could be used before Mohs micrographic surgery to help define tumor margins. It could be used to assist in the selection of patients for whom chemotherapy with imiquimod or 5-fluorouracil is contemplated," the authors say.

And while there is still uncertainty over OCT's ability to differentiate basal cell carcinoma from actinic keratoses, seborrheic keratoses or other cutaneous neoplasms, the technology has the potential to greatly improve the initial diagnosis of basal cell carcinoma, particularly in conjunction with confocal laser scanning microscopy, Dr. Swanson says.

Into the future

"Based on the quality of the images we have observed to date, we believe that OCT technology compares favorably with other noninvasive technologies, such as ultrasonography, for the evaluation of basal cell cancer.

"I believe that the day will come, however, when user-friendly, noninvasive imaging technologies will allow for the bedside diagnosis of basal carcinoma and other neoplasms with sensitivities and specificities that rival histopathology."