Biomedical Applications of AgClBr Optical Fibers: Laser Bonding of Tissues. Early Detection of Skin Cancer

Svetlana Basov, Department of Biomedical Engineering.

Work done under the supervision of Prof. Amit Gefen and Prof. Abraham Katzir

Abstract.

Standard optical fibers are completely opaque in the mid-IR in the spectral range 3-30µm. In our group we developed special crystalline fibers, made of silver halide (AgClBr), which are flexible, non-toxic, bio-compatible and highly transparent in the mid-IR.

In this work I participated in the fabrication of these fibers and used them for two completely different applications.

Laser Bonding of Incisions: A system based on silica fibers, AgClBr fibers, an IR laser and a control system, made it possible to heat a spot on tissue under close temperature control. It was found that this may be used for laser soldering of incisions. In this case the approximated edges of an incision are covered by Albumin and they are heated, spot by spot, so that each spot is heated for 60C for 10sec. The bonding is strong and there is almost no scarring.

We successfully laser soldered incisions in the corneas of pigs, in vitro, and then measured the burst pressure P_B needed to break open the bonded incisions. This pressure was quite high. We then carried out experiments on the corneas of mid-size live pigs, that we euthanized after few weeks. These soldered corneas showed strong bonding, with no thermal damage. This proved that laser soldering would be a very promising method for corneal transplantation. This method could be used by less experienced surgeons, reducing the load of the highly skilled ones.

In addition, we integrated our laser soldering system with a robotic system at the lab. of Prof. Nisky at Ben Gurion University. We there carried out robotic laser soldering, where robotic arms moved the distal ends of the fibers for heating spots on the approximated edges of an incisions in skin. The procedure was carried out automatically! This would probably the way laser soldering will be carried out in the future, again, making it possible for less experienced surgeons to obtain excellent retults.

Early Detection of Skin Cancer: Melanoma is a very dangerous skin cancer. If its thickness is d <1mm, when detected, and it is removed – almost all patients survive. If d>1mm, almost all patients die. A dermatologist looking at lesions on the skin must distinguish immediately if a lesion is suspicious and send it to pathology to determine if it is indeed melanoma. This requires many years of experience, and a less experienced dermatologist may miss the suspicious lesions which may lead to serious effect. It seems that there is no approved method for the automatic detection of melanoma.

We developed a system that incorporated AgClBr fibers and made it possible to carry out spectroscopic measurements in the mid-IR on lesions on the skins of patients. Clinical measurements were carried out at the Dermatology Department at the Ichilov Hospital. Expert dermatologists detected suspicious lesions and we carried out measurement on each lesion and on neighboring skin. Measurements were done on 90 patients and only 5 lesions were found to be melanoma (by histopathology). We made a great effort to to analyze the results and to see differences in the mid-IR spectra of the melanoma lesions and the benign lesions. Only lately we found a mathematical algorithm that seems to do the job. However, our statistics is insufficient. We plan to carry out many more measurements in the department of Prof. Scope at the Sheba Hospital. If our algorithm indeed works, it will open the way for an automatic early detection of melanoma, without relying on the skill of the examining dermatologist.