The first clinical trial of optical coherence tomography (OCT) combined with multiphoton tomography (MPT) and
dermoscopy is reported. State-of-the-art (i) OCT systems for dermatology (e.g. multibeam swept source OCT), (ii) the
femtosecond laser multiphoton tomograph DermaInspectTM, and (iii) digital dermoscopes were applied to 47 patients
with a diversity of skin diseases and disorders such as skin cancer, psoriasis, hemangioma, connective tissue diseases,
pigmented lesions, and autoimmune bullous skin diseases. Dermoscopy, also called 'epiluminescent microscopy',
provides two-dimensional color images of the skin surface. OCT imaging is based on the detection of optical reflections
within the tissue measured interferometrically whereas nonlinear excitation of endogenous fluorophores and the second
harmonic generation are the bases of MPT images. OCT cross sectional "wide field" image provides a typical field of
view of 5 x 2 mm2 and offers fast information on the depth and the volume of the investigated lesion. In comparison,
multiphoton tomography presents 0.36 x 0.36 mm2 horizontal or diagonal sections of the region of interest within
seconds with submicron resolution and down to a tissue depth of 200 μm. The combination of OCT and MPT provides a
synergistic optical imaging modality for early detection of skin cancer and other skin diseases.
The mechanisms involved in infrared laser tissue ablation are studied using a free electron laser (FELIX) in order to clarify whether the increased ablation efficiency reported in literature for certain infrared wavelengths is due to a wavelength effect or to the specific pulse structure of the lasers that are generally used in these studies. Investigations are presented of ablation of vitreous from pigs’ eyes using several techniques including protein gel electrophoresis and ablation plume visualization. The ablation effects of three different infrared wavelengths are compared: 3 mm, which is currently in clinical surgical use, and the wavelengths associated with the amide I and amide II bands, i.e. 6.2 mm and 6.45mm, respectively. The results suggest a different ablation mechanism to be in operation for each studied wavelength, thus indicating that the generally reported increased ablation efficiency in the 6-6.5 micron range is due to the wavelength rather than the typical free electron laser pulse structure.
Polyacrylamide gel electrophoresis is a technique that allows the constituents of complex biological mixtures to be resolved with respect to their molecular weight. This is a technique that has been used to identify protein or nucleic acid fragments, and it is now being applied to allow molecular analysis of laser-tissue ablation products. The hope is to allow for a greater understanding of the ablation process than is currently possible, as the effects of the interaction at a molecular level can be identified directly rather than inferred form other related phenomena such as mechanical, acoustic or thermal measurements. Here the preliminary work using This technique is presented, and plans for further work in the autumn at FELIX are outlined.
The Free Electron Laser for Infrared EXperiments (FELIX) Free Electron Laser Facility provides a continuously tunable source ranging continuously through the 4.5 to 200 micron region. The infrared beam consists of short micropulses, which have a nominal duration of 5 ps and are separated by intervals of either 1 ns or 40 ns of zero intensity. The micropulses form a macropulse train with a duration of up to 15 microseconds. The macropulses are repeated every few hundred ms, with a maximum repetition rate of 10 Hz. Previous studies have shown that the combination of this macro / micro pulse structure, coupled with energy output tuned to the vibrational mode of the Amide- band (? = 6.45 ?m), gives a source well suited to precise tissue ablation. Here the thermal, mechanical and molecular behavior of the ablation was studied. Unlike previous studies, which have concentrated on unconstrained ablation where particles could be ejected from the system at the tissue - air boundary, this experiment simulated the confined ablation necessary during a vitrectomy. It is thought that this is the first study where this has been done, and also the first to study vitreous, which consists of only 2% protein rather than the 20% present in corneal tissue for example.
Profuse bleeding due to retinal tearing represents a common problem when working in the posterior chamber of the diabetic eye. If the traction and vibration associated with traditional vitrectomy tools could be eliminated, then many of their associated problems could also be removed. By investigating the tuning of laser energy in order to target the protein in the vitreous, rather than the bulk fluid, it is proposed that such a cutting device could be manufactured. A series of scans were performed on swine vitreous in order to determine its optical properties. A scanning spectrometer covering the region between 2.5 and 25 micrometers was used to scan both the vitreous and pure water samples. For each collagen scan, the water samples from either side were subtracted to give the absorption due to vitreous alone. It was found that there were several peaks of potential interest in the vitreous samples. As well as the water peak at around 3 micrometers, there was also a series of peaks between 6.2 and 6.5 micrometers. These latter bands represent absorption that is due to the proteins in the vitreous. Targeting these Amide bands could represent a possible method of targeting the laser energy without causing the collateral damage associated with high cutting or liquefaction rates. This could thus allow either higher aspiration rates while working in the center of the eye, or more precise removal of membranes in more delicate regions of the eye without any traction on the retina begin caused.
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