In ophthalmic surgery fs laser pulses are used as a precise and safe cutting tool. At specific processing parameters, however, an interesting phenomenon of unintended periodic structures inside the tissue can be observed. In this study, a transparent polymer served as ocular phantom material for further investigations. A Femtosecond laser with MHz-repetition rate and pulse energies below 200 nJ was used. The size of the durable material change caused by applied fs-single pulses was measured in regard to the pulse energy. Furthermore, lines were cut inside the material with different laser spot distances and laser pulse energies. The creation and enhancement of unintended step-like structures could be related to a decrease of spot distance and further increase of pulse energy. Cutting planes inside the material resulted also in a formation of step like structures. For planes the step-like structures were formed with different orientation in the x-y-plane in regard to the used line distance between two applied lines. A maximum step height of 75 μm was measured using our setup. Those periodic structures are unwanted for any application in the field of laser material processing, ophthalmology or biomedical sectioning. Hence, investigations of the parameters which trigger this phenomenon are of great interest.
Fs-lasers are widely used for microsurgery and micromachining. Due to nonlinear interaction of ultrashort pulses with tissue or matter precisions of a few μm can be achieved. But particularly in the field of surgery this precision can not be obtained as the devices for diagnostics and treatment have to be changed due to separate systems. We show a combined system of a fs-laser and a Fourier-Domain optical coherence tomography (FD-OCT) enabling to cut and image the region of interest alternately. The FD-OCT offers non-invasive imaging at an axial resolution of 6, 2 μm and a transverse resolution of 3 μm in air which is comparable to the interaction zone of the fslaser-pulses. OCT-aided subsurface cutting is successfully demonstrated on biological ex-vito samples of porcine
cornea and larynx. Furthermore it appeared that in situ OCT imaging enables to monitor cuts produced with pulse energies close to the energy threshold. In conclusion, this setup demonstrates the potential of a system combining cutting and OCT imaging within the same optical setup without the need of changing devices.
Due to nonlinear interaction with optical transparent and scattering samples the femtosecond technology is a
very useful tool for high precision micro surgery on biological tissues. At the same time femtosecond lasers are
ideal light sources for imaging methods such as optical coherence tomography (OCT) due to the broad spectrum
of the laser, which is necessary for creating ultra short pulses. Using OCT structures within biological tissues
can be imaged non invasive with a resolution within the low m-range.
The combined use of an ultra short pulse laser for cutting of biological tissues as well as imaging via OCT is a
very interesting tool. It opens up a wide range of new surgery techniques and improves many existing methods
due to high precision and high flexibility of the cutting process.
Therefore we combined a femtosecond cutting system and a fourier domain OCT. In this attempt the OCT is
operated with an SLD and is used alternately to the cutting system. The OCT is integrated into the optical
path which enables in situ imaging of the surgery area before and after treatment.
Due to nonlinear interaction with optical transparent samples the femtosecond technology is a very useful tool
for high precision micro surgery on biological tissues. At the same time femtosecond lasers are ideal light sources
for imaging methods such as optical coherence tomography (OCT) due to the broad spectrum of the laser, which
is necessary for creating ultra short pulses. Using OCT structures within biological tissues can be imaged non
invasive with a resolution within the low μm-range. The combined use of an ultra short pulse laser for cutting of
biological tissues as well as imaging via OCT is a very interesting tool. It opens up a wide range of new surgery
techniques and improves many existing methods due to high precision and high flexibility of the cutting process.
Therefore we combined a femtosecond cutting system and a fourier domain OCT. In a first attempt the OCT is
driven with an SLD and is used alternately to the cutting system. The OCT is integrated into the optical path
which enables in situ imaging of the surgery area.
The laser microtome (LMT) is designed to slice biological tissue and various materials with high precision. The
cutting process is performed by an ultrafast laser, emitting infrared light with high repetition rate of about 10
MHz. Biological Tissue can be sliced without fixation and embedding. Therefore cutting of native tissue is
possible. Due to the non contact procedure further investigations of the material like immuno histological tests
can be performed. At present slices with a thickness of 5 - 100&mgr;m in different biological tissues like cartilage,
kidney, lung and cornea has been shown. In conjunction with a 3D imaging system like optical coherence
tomography, preparation of 3D tissue volumes is possible too.
ELAN is a new method for treating atherosclerotic vessels. Its purpose is to restore wall flexibility by removing arterial wall tissue from the outer arterial layer. This leads to expansion of the narrowed vessel resulting in increased blood flow. We present results of treatment of arteries in vitro. Tissue removal was done by excimer-laser ablation using ns-pulses of 193nm wavelength. We also discuss therapy control. OCT images and light diffusion measurements are presented.
ELAN is a new method for treating atherosclerotic vessels. Its purpose is to restore wall flexibility by removing arterial wall tissue from the outer arterial layer. This leads to expansion of the narrowed vessel resulting in increased blood flow. We generated cuts in dissected arteries of sheep and pigs by photo-ablation with an ArF-Excimer Laser operating at a wavelength of 193 nm. During the cutting process the vessel diameter was monitored by measuring the running time of the laser induced pressure transients with a pressure transducer lying under the artery. A nearly linear increase of the diameter dependent on the residual wall thickness was found with a maximum increase of vessel diameter about 10%. We also observed that the arterial wall maintains stable to very small residual wall thicknesses i.e. deep cutting. To support the experiments and to test different geometries of tissue removal we performed FEM-Analysis. We simulated vessel deformation and the total strain depending on the depth, width and number of cuts in the outer artieral wall. We also found a significant increase of the "lumen" in a model with atherosclerotic shape obtained from a histological section.
Due to the low energy threshold of photodisruption with fs laser pulses, thermal and mechanical side effects are limited to the sub μm range. The neglection of side effects enables the use of ultrashort laser pulses in a broad field of medical applications. Moreover, the interaction process based on nonlinear absorption offers the opportunity to process transparent tissue three dimensionally inside the bulk.
We demonstrate the feasibility of surgical procedures in different fields of medical interest: In ophthalmology intrastromal cutting and preparing of corneal flaps for refractive surgery in living animals is presented. Besides, the very low mechanical side effects enables the use of fs-laser in otoralyngology to treat ocecular bones. Moreover, the precise cutting quality can be used in fields of cardiovascular surgery for the treatment of arteriosclerosis as well as in dentistry to remove caries from dental hard tissue.
Ultrafast lasers have become a promising tool for micromachining and extremely precise ablation of all kinds of materials. Due to the low energy threshold, thermal and mechanical side effects are limited to the bu micrometers range. The neglection of side effects enables the use of ultrashort laser pulses in a broad field of medical applications. Moreover, the interaction process based on nonlinear absorption offers the opportunity to process transparent tissue three dimensionally inside the bulk. We demonstrate the feasibility of surgical procedures in different fields of medical interest: in ophthalmology intrastromal cutting and preparing of cornael flaps for refractive surgery in living animals is presented. Besides, the very low mechanical side effects enables the use of fs- laser in otoralyngology to treat ocecular bones. Moreover, the precise cutting quality can be used in fields of cardiovascular surgery for the treatment of arteriosklerosis as well as in dentistry to remove caries from dental hard tissue.
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