Femtosecond Laser – One Trillionth of a Second for Melanoma Diagnostics – DERMAforum

The femtosecond laser unlocks the “black box” of melanin. With the laser, malignant melanoma can be diagnosed – and, in the future, could it also be treated?

The role of melanin in skin tissue is often aptly characterized as a double-edged sword: on one hand, it acts as a natural sunscreen through its absorption properties, while on the other hand, melanin is the starting point for tissue degeneration leading to malignant melanoma. “The interest in understanding the mechanisms behind this dual role of melanin has always been high, but despite intensive research, the ‘black box’ of melanin has been difficult to unravel. However, recent years have shown that the femtosecond laser can be an important tool in this regard,” says Dr. Dieter Leupold from the Max Born Institute for Nonlinear Optics and Short-Time Spectroscopy.

As reported in DERMAforum 10/2002, laser physicists from the Max Born Institute in Berlin (Leupold and colleagues) and dermatologists from Ruhr University Bochum (Dr. Klaus Hoffmann and colleagues) succeeded in exciting melanin in skin tissue to emit an ultrastrong fluorescence, which has the potential to form the basis for a new non-invasive early detection method for malignant melanoma: the color—or spectrum—of this melanin fluorescence is significantly different in healthy skin tissue compared to that of malignant melanoma.

New Diagnostic Device for Malignant Skin Cancer

Studies conducted on excised samples from a broad range of other skin diseases and benign skin conditions (basal cell carcinoma, squamous cell carcinoma, seborrheic keratosis, fibroma, keloid) have shown that this fluorescence change occurs exclusively in malignant melanoma. This forms the basis for a new diagnostic device, which, after initial testing as a stationary laboratory version at the Max Born Institute, is now being further developed into a mobile prototype suitable for clinical use under the leadership of LTB Lasertechnik Berlin. The device will be tested later this year at the Bochum Dermatology Clinic.

The femtosecond laser is the core of this device development, as only its ultrashort pulses enable the specific, so-called stepwise two-photon absorption required to trigger melanin fluorescence. “On one hand, this new method requires specific technical parameters from the femtosecond laser; on the other hand, the laser must meet clinical standards for safety, reliability, and user-friendliness—and the entire device should ideally be mobile and, of course, cost-effective,” explains Leupold, acknowledging the requirements for such a device. LTB has found a solution that, under current conditions in the laser market, represents the optimal approach: a laser-plus-amplifier unit based on fiber laser and nitrogen laser. This unit was presented at the Laser Messe in Munich and is now the core of the new melanoma diagnostic device.

Careful Investigations Advised

What lies behind the specific change in fluorescence during malignant progression? The Berlin-Bochum research team can now answer this question with the help of the laser. Through laser fluorescence dynamics studies, it was found that in malignant melanoma, there is a shift in the ratio of eumelanin to pheomelanin in favor of the latter. This non-invasive result supports similar findings in clinical analytics.

Looking to the future: if the new diagnostic device identifies a malignant melanoma, could it also be treated with the laser? “Technically, this is possible, but whether it is medically sensible and, most importantly, free of side effects, requires careful further investigation,” Leupold cautions.

Source: DERMAforum, September 2003