New tool allows noninvasive screening of skin lesions

In tests with 100 skin cancer lesions and more than 500 benign nevi, the device could distinguish malignant melanoma from benign nevi with 75 percent specificity at 100 percent sensitivity. It could also discriminate between non-melanoma skin cancer and benign nevi with 87 percent specificity at 100 percent sensitivity. Histological examination confirmed all diagnoses. (Åberg P et al. IEEE Trans Biomed Eng. 2004; 51(12): 2097-2102).

Detection rate

How it works

The company's technology relies on the electrical impedance characteristics of skin cells. A pen-shaped probe contains a series of four concentric electrodes that create a current through the skin when applied to its surface. A desktop electrical impedance spectrometer measures cellular opposition to the electrical current. Computer software analyzes the data statistically. Values are compared to a control measurement taken ipsilaterally to the lesion to generate a diagnosis.

Electrical impedance technology is already employed by a handful of other devices. Whole-body electrical bioimpedance measures various body composition parameters such as total body water, body fat and nutritional status. Impedance measurements of teeth have also been studied to detect dental caries. Electrical impedance tomography imaging is used in brain, heart and lung research. Skin conditions also give rise to specific skin impedance characteristics.

Cancer not first target

Dr. Ollmar, who is also associate professor at the Division of Medical Engineering at Karolinska Institutet, didn't think to apply the technology to cancer at first. Over a decade ago, he headed a number of interdisciplinary projects at the Institute's Center for Oral Biology. One of the projects focused on the skin's healing process in response to different drugs.

Dr. Ollmar noticed that various irritants applied to the skin generated unique impedance patterns depending on the physical properties of the cells such as shape, membrane structure and amount of intra- and extracellular water. The observation sparked his interest in skin cancer.

"I surveyed everything I could find about electrical impedance and skin disease," he recalls.

His first paper on the subject was published in 1992.

New probe

Recently the company developed a new type of probe to improve the detection rate. While studies have shown that the existing probe can detect melanoma accurately, there were a few borderline values.

"We want to be sure the system doesn't miss anything," Dr. Ollmar says.

Since melanoma manifests below the stratum corneum, the company fitted the probe tip with small spikes that reach the underlying layers. While the spikes do puncture the skin, they do not penetrate blood vessels or sensory nerves in the dermis and are hence painless.

Preliminary data suggest that the spiked probe eliminates unnecessary information from the stratum corneum and gives a more precise snapshot of the layers below. The non-invasive probe, however, showed superior when examining skin disorders, such as atopic dermatitis, that degrade the barrier function in the stratum corneum.

Ongoing research

Research on the microinvasive probe is ongoing.

"The sample size of malignant melanoma is still too small," according to Dr. Ollmar. "In the clinic there is much more variation."