Detecting skin cancer could soon become non-invasive. A technique developed by American scientists uses lasers pulsing at a thousand-trillionth of a second to diagnose skin cancers.

If proved 100% effective, this will be another option to biopsy - the present day standard procedure used by physicians in which a small piece of the affected area in the patient's body is cut out for laboratory testing with a microscope.

Though in early days, the non-surgical screening for malignant skin cancers has till now successfully captured three-dimensional images of the chemical and structural changes underway beneath the surface of human skin.

According to Duke University scientists, this is the first approach that can target molecules like hemoglobin and melanin and get microscopic resolution images the equivalent of what a doctor would see if he or she were able to slice down to that particular point.

Warren Warren, director of Duke's new Center for Molecular and Biomedical Imaging, said, "What we're trying to do is find cancer signals we can get to without having to cut out the mole."

The distributions of hemoglobin, a component of red blood cells, and melanin, a skin pigment, serve as early warning signs for skin cancer growth. But because skin scatters light strongly, simple microscopes cannot be used to locate those molecules except right at the surface.

Although laser methods have been developed to probe deeper down for some other molecules that can be made to glow, both melanin and hemoglobin remain dark and inaccessible using those methods.

Dr Ramesh Sarin, consultant, surgical oncology, at Apollo Hospital, said, "Skin cancer is not as common in India because we are of dark complexion and not that exposed to Sun's rays. But a large number of people do suffer from it." She added, "Any tumour in the body needs a biopsy to be sure - whether it's with a needle or by cutting a little part - both for ethical and legal purposes. We need to be sure it is cancer or rule it out. With this non-invasive technology, we might not need a biopsy."

The innovation uses a delicate interplay between two laser beams, each emitting a different colour of light. To keep the skin from overheating in the process, the laser pulses on for only femtoseconds - a thousand trillionth's of a second - at a time.

The glow of the hemoglobin and melanin-bearing structures are then magnified by a microscope outside the skin and manipulated by computers to create cellular-scale images. The technique could enable doctors to see as much as a millimetre below the skin's surface - more than enough for diagnosis.

What this is leading to is for a doctor to be able to touch a mole with a fiberoptic cable and characterise what is going on inside it. "Today, if you visit a dermatologist, he or she will probably see many moles on your body. But the difficulty is trying to figure out which of those, if any, are dangerous," the team said.