A new technique which combines the advantages of darkfield microscopy with those of confocal microscopy has been developed. The Massively Parallel Confocal darkfield method implemented on a DMD-based confocal platform allows for detection of non-fluorescing particles with dimensions below the diffraction limit. The lateral resolution and depth discrimination of three dimensional objects are improved relative to conventional darkfield microscopy.
Current laser surgery on vocal chords requires the patient to be under general anaesthesia due to relatively low cutting speed and precision. Even minor surgeries can change vocal properties, requiring lengthy post-operative therapy. To solve this problem and reduce recovery time we propose a laryngoscope capable of performing the surgery while the patient is awake. To realize this, it is necessary for each cut to be made on the shortest time scale with the highest precision possible. It is also important to have high speed feedback to initiate or terminate the cutting process as well as to maintain the proper cutting position. In this laryngoscope we employ a coaxial MHz OCT and laser cutting system with a MEMS galvo scanner combined with a high speed stereo camera set. The MHz OCT is responsible for axial feedback and measuring the depth of cut while the stereo camera set is used to adjust the MEMS scanner for lateral offsets. We have determined the optimal optical layout for the laryngoscope using Zemax and have developed 3D CAD models of the prototype demonstrator prior to fabrication and assembly. This new laryngoscope could make laser cuts up to 50% smaller in width than traditional multimode fiber based cuts, in addition to reducing overall surgery time and increasing the precision of each cut.
Digital Micromirror Device based microscopy combines fast confocal 4D-microscopy along with conventional methods
for light microscopy and new technological approaches to a versatile tool for the observation of in vivo processes in
living biological cells and measurement of technical surfaces. Due to the use of variable size pinholes and adjustable
scan patterns conditions for confocal measurement can easily be optimized to the prerequisites of the sample "on the
fly".
One of the most frequently performed blood tests, measurement of total hemoglobin concentration, requires invasive
blood sampling. We developed an optoacoustic technique for noninvasive monitoring of total hemoglobin concentration
and other blood variables by probing the radial artery or other blood vessels. Recently, we designed and built a focused,
wide-band, polymer-based optoacoustic transducer for blood vessel probing with high, submillimeter lateral resolution
and incorporated it into a highly portable, laser diode-based optoacoustic system. The focused optoacoustic transducer
combines a fiber-optic delivery system and a wide-band piezosensor. First, we experimentally measured transducer
parameters (lateral resolution, sensitivity, focal length). To test the transducer capabilities in measurement of total
hemoglobin concentration and other blood parameters from blood vessels, we prepared a tissue phantom simulating
strongly-scattering tissues with blood vessels of different diameters, spacing, and depths. Optoacoustic signals were
acquired from blood at different hemoglobin concentration and oxygenation during transducer scanning over the
phantom. In vivo experiments were performed from radial arteries and peripheral veins of different size, depth, and
spacing. Submillimeter lateral resolution was obtained in the in vitro and in vivo experiments. The high resolution
combined with the wide-band detection of the optoacoustic waves can be used for monitoring of blood variables in blood
vessels with high accuracy, sensitivity, and specificity.
By two-photon time-resolved confocal 4D-microscopy it is possible to image fluorescent objects at a high spatial and
temporal resolution. The usage of femtosecond-laser light creates a two photon effect and therefore reduces bleaching of
the fluorophore. With this technique 4D-visualization of dynamic processes in living cells is possible.
Cryogenic procedures are fundamental tools in modern biology, e.g. for conservation or purification of biological
materials. The processes occurring in biological cells and tissues during freezing and thawing are subject to ongoing
research. Optimization of cell survival rates demands the development and evaluation of exactly defined temperature
profiles. 4D-DMD-microscopy is capable of imaging these highly dynamic processes with high spatial and temporal
resolution, utilizing well established staining procedures for differentiating structures of interest.
Spectroscopic results with laser induced breakdown spectroscopy (LIBS) in liquids have shown a signal improvement
using double pulse experiments compared to single pulse measurements. A setup of two Q-switched Nd:YAG lasers in
an orthogonal arrangement have led to bright illuminated plasma inside cavitation bubbles. A Nd:YAG laser pulse
focussed by a lens (6 ns@532 nm, 2.9*1019 W/m2) into the center of a water filled cuvette gives rise to a cavitation
bubble. A second tightly focused Nd:YAG laser pulse (5 ns@1064 nm, 3.1*1019 W/m2 ) induces a plasma at
approximately 70 μs delay within the cavitation bubble. These absolutely reliable processes allow to capture image
sequences of plasma filled cavitation bubbles with an ultrafast camera. The optical emission is guided via a quartz fibre
to a Czerny-Turner spectrograph and recorded by an intensified CCD camera. A delay time of more than 1.7 μs between
plasma ignition and spectroscopic data taking is necessary to avoid inverse bremsstrahlung and residual lines arising
from bright plasma emission. Characteristic spectral line intensities of manganese (Mn) and Palladium (Pd) are recorded
and correlated with an internal calibration standard using strontium (Sr) and chromium (Cr) respectively. The LOD of
manganese is 0.3 mg/L.
Time resolved 3D-microscopy using DMD-arrays utilizes the principles of confocal microscopy. Application fitted
patterns optimize optical imaging of reflective, transparent, and fluorescent objects. High spatial resolution is achieved
simultaneously with high temporal resolution due to fast DMD control. This enables to visualize and track processes in
vivo within living biocells.
We developed an optoacoustic technique for noninvasive, accurate, and continuous monitoring of total hemoglobin
concentration and venous oxyhemoglobin saturation by probing specific blood vessels. In this work we report the
development and tests of novel, focused optoacoustic transducers that provide blood vessel probing with sub-millimeter
lateral resolution. The focused transducers were incorporated in our highly portable, laser diode-based optoacoustic
monitoring system for pre-clinical and clinical tests. Our studies demonstrated that: 1) the focused transducer response is
linearly dependent on blood total hemoglobin concentration with a high correlation coefficient; and 2) the sub-millimeter
lateral resolution provided higher specificity of blood vessel probing, in particular, for smaller blood vessels such as the
radial artery (diameter 2-3 mm).
Time resolved 3D-microscopy using DMD-arrays utilizes the principles of confocal microscopy. Application fitted
patterns optimize optical imaging of reflective, transparent, and fluorescent objects. Diffraction limited spatial resolution
is achieved at simultaneously high temporal resolution due to fast DMD controlling. This enables to visualize and track
processes in vivo within living biocells as well as fast structural volume and surface mapping.
Environmental science is concerned about the content of dissolved heavy metals in coastal tidal waters. Fluorescence spectroscopy methods do offer a chance for the detection of dissolved chromium. Due to strong quenching processes in liquids, optical emission spectroscopy often lacks sensitivity. In this study we intended to use subsequent Nd:YAG Q-switched laser pulses to create a plasma directly in front of an optical fiber tip. The plasma emits light at characteristic chromium wavelengths. The emitted fluorescence was recorded using an optical multi-channel analyzer.
Temporal evolution of laser generated cavitation bubbles and shock waves were studied. Q-switched Nd-Yag laser pulses at 1064 nm are focused into the liquid. An Imager 3 CCD camera with multi exposure mode allows recording of 10 images with minimal exposure delay of 100 ns and minimal exposure time of 100 ns. Illumination is provided by xenon flash lamp for single exposure (shock wave recording) and by halogen lamp for multi exposure mode (bubble recording). Distilled water and a retrograde fluid, isooctane, have been under investigation to identify the differences in the cavitation process and shock wave propagation. The calculation of the shock wave velocities in water and isooctane are based on image recording at constant exposure time of 100 ns and using laser differential interferometry. Strong differences of bubble oscillation were observed in water and isooctane. Gilmore's model is used for numerical simulation of bubble dynamics.
Cavitation bubbles generated in water by Tm:YAG laser pulses were studied. Timer-resolved photography was applied to determine volume change with time and surface velocities of expanding and collapsing cavitation bubbles. A new method of determining vapor densities inside bubbles based on reflection changes of a fiber probe placed inside the cavitation bubble has been developed. Density distribution changes with time were measured spatially at 17 points within the bubble. Maximum bubble diameter was about 4.5 mm. Densities measured were compared to the growth of the bubble as shown by ultra fast imaging. Temporal and spatial pressure and temperature distribution will be computed from density distributions based on equilibrium values at maximum bubble extension.
The use of different ultraviolet lasers for fluorescence spectroscopic detection of water pollutants with fiber optical sensors has been studied. Especially detection of small aromatic hydrocarbons via laser induced fluorescence requires short wavelength excitation. Interaction of intense ultraviolet light with the commonly used fused silica fibers leads to a decrease of fiber transmission. Some transmission affecting laser parameters have been studied. A new concept for the use of fiber optic sensors with ultraviolet excitation has been developed. This method is based on transmission of visible laser radiation through the fiber and creation of ultraviolet radiation by optical harmonic generation at the distal end of the fiber. So the unfavorable fiber behavior at short wavelengths can be avoided. Simultaneous coupling of the beam from a single laser source into several optical fibers is interesting for distributed sensor applications. In order to minimize coupling losses for these purposes we developed a new coupling scheme based on a special optical lens array.
Simultaneous coupling of the beam from one laser source into many optical fibers or fiber bundles is of interest for many applications. We developed a coupling scheme based on lens arrays to reduce transmission losses. The laser beam is splitted into focused partial beams. Positioning of an optical fiber near each focus allows multiple fiber coupling with similar efficiency as obtained for a single fiber. A prototype designed for coupling of excimer laser radiation into fiber bundles is presented.
Renate Jahn, Andreas Bleckmann, Edwin Duczynski, Hans-Joachim von der Heide, Guenter Huber, Karl-Heinz Jungbluth, Werner Lierse, Walter Neu, Bert Struve
The interaction of various pulsed lasers with meniscus and bone of freshly slaughtered bovines and pigs was examined. Our aim was to find lasers useful for accident surgical operations (e.g. bone or callus dystopy inside joints or nearby important vessels or nerves after fractures). Laser wavelengths of the UV- and infrared spectral range were investigated: XeCl- excimer lasers (wavelength 308 nm, pulse duration 28 ns, 60 ns, 300 ns) Nd:YAG (1.06 micrometers , 400 microsecond(s) ), Tm:YAG (2.01 micrometers , 400 microsecond(s) ), Ho:YAG (2.12 micrometers , 400 microsecond(s) ), CrEr:YSGG (2.79 micrometers , 400 microsecond(s) ), and Er:YAG (2.94 micrometers , 400 microsecond(s) ). The excimer laser radiation was guided by a tapered fused silica fiber, whereas for all other lasers the tissue samples were positioned in the focus of a lens with 100 mm focal length. Ablation rates were determined by perforating samples of defined thickness, and the effects of laser ablation on tissue were controlled macroscopically, by light microscopy and by scanning electron microscopy.
Power transmission of xenon chloride excimer lasers through optical fibers is necessary for medical applications where tissue removal is performed within the human body. The most important application at present is excimer laser coronary angioplasty. Typical levels of energy densities applied by optical fibers for this application cause color center generation in fused silica leading to transmission decrease called photodegradation. This effect depends essentially on the grade of the fused silica. Important parameters are fiber length, pulse duration, energy density, and the irradiated cross sectional area of the optical fiber endface. For a new grade of core material the influence of these parameters on the transmission performance is described. The obtained material improvement leads to a significant reduction of the observable transmission decrease as a function of the number of laser pulses applied. Thus continuous operation of the laser in the region of the typical transmission plateaus at considerably higher and constant energy levels at the distal fiber end becomes feasible. This offers a new option for more reliable dosimetry in medical applications.
Power transmission of excimer laser radiation at 308 nm through waveguides is of growing importance in medical applications. The maximum energy densities achievable at distal fused silica optical fiber ends are limited by the surface damage threshold of fused silica and by photodegradation of the optical fiber material. Limitations due to the surface damage threshold at the front surface can be avoided by applying tapered fiber geometries. In order to minimize photodegradation effects color center formation caused by high energy UV radiation has to be reduced. This involves optimization of the fused silica material properties and the necessity of modifying the manufacturing processes. Measurements on all silica fibers at 308 nm wavelength (XeCl excimer laser) show different influences of core material manufacturing. Not only the overall decrease of transmission but also the dependence of transmission changes on the number of laser pulses and defect annealing are strongly affected. Consequences for improved performance of all silica optical fibers in angioplasty are demonstrated by measurements on specially produced samples.
Ablation of hard biological tissue using XeCl-excimer lasers (wavelength 308 nm) yielded promising results. The 308 nm radiation was guided by tapered quartz fibers with core diameters of 400 - 1000 micrometers . Applying pulse energy of up to 70 mJ (pulse duration 28 ns, 60 ns, 300 ns) at different repetition rates, we found no noticeable thermal damage. The samples were immersed in water during irradiation. Bone specimens cut by the excimer laser did not show any melted hydroxylapatite crystals as described in the CO2-cutting experiments performed by HORCH (4). The gross, histological, and scanning electron microscope examination of cuts and bore holes produced by excimer laser ablation of meniscus and bone tissue will be presented.
Ablation and tissue removal of normal and atherosclerotic arterial tissue by UV excimer-laser radiation were probed by taking photographs with a dye laser as a flash light-source. The ablating pulses were transmitted through a fused silica fiber into a cuvette with the samples exposed to saline solution. The delay time of the probing dye-laser pulse with respect to the ablating excimer-laser pulse was varied in the nanosecond range up to several hundred microseconds. The ablation process and the resulting plume above the tissue surface were recorded with a CCD camera attached to a PC-based image processing system. All samples under investigation were fresh human cadaver aortic and femoral artery specimens which had been shock-frozen for less than 48 hours. The arterial segments showed different types of lipid-rich and calcified plaques. Big cavitation bubbles and small tissue particles emerging from the irradiated area have been recorded.
The method proposed in this paper is based on the detection of resonantly enhanced fluorescence emission induced by a tunable dye laser. First test on anorganic samples exposed to air and to saline solution demonstrate the potential of this technique. A XeCl excimer-laser ((lambda) equals308 nm) pulse, guided by quartz fibers, causes an efficient ablation of the irradiated samples. The specific species to be detected in the ablation plume determines the wavelength of the narrow-band dye-laser radiation. Preferably, it is set to a strong transition of the selected ablation product. Taking into account the formation of the plume, the dye-laser pulse is applied with a certain delay in order to excite resonantly the chosen species in the plume. The resulting resonance fluorescence is then guided by optical fibers to an OMA system. Compared to the broad-band excimer-laser-indiced fluorescence during the ablation process, the resonance fluorescence signal shows a distinct and easily detectable sharp peak. The signal-to-background ratio is improved by one order of magnitude. The achieved increase in sensitivity as well as selectivity is for the benefit of a reliable identification of ablated tissue.
The autofluorescence of human arterial tissue with varying degrees of atherosclerosis was studied in vitro to develop a diagnostic tool for tissue differentiation simultaneously to tissue ablation induced by a XeCl-excimer laser (wavelength 308 nm). Healthy vessel walls and artery segments containing lipid-rich or calcified areas were investigated in air, saline solution (0.9 NaCl), and in blood. The fluorescence spectra in the wavelength range from 320 nm to 650 nm were recorded with an optical multichannel analyzer, and they allowed for a clear discrimination between plaque and healthy vessel wall even in blood. For each single laser shot with an energy density of about 4-5 J/cm2, well above the ablation threshold, a complete spectrum was recorded. The fluorescence spectra were analyzed in terms of their contributions from normal arterial tissue, lipid-rich and calcified plaques. The results clearly show the feasibility of controlling the ablation process by fluorescence spectroscopy in order to avoid vessel-wall perforation which is one of the main drawbacks in laser angioplasty.
Resonantly enhanced fluorescence emission induced by a tunable dye laser can be used for the identification of ablated atherosclerotic tissue. This method has been tested with anorganic samples exposed to air and to saline solution. A XeCl excimer laser pulse ((lambda) = 308 nm), delivered by a fused silica optical fiber, causes an efficient ablation of the irradiated samples. The wavelength of the narrow-band dye laser radiation is set to a strong transition of a specific species to be detected in the ablation plume. Taking into account the formation of the plume, the dye laser pulse is applied with a certain delay in order to excite resonantly the selected species in the plume. The resulting resonance fluorescence then is guided by optical fibers to an optical multi-channel analyzer system. Compared to the broad-band fluorescence during excimer laser ablation the resonance fluorescence signal shows a distinct and easily detectable sharp peak. The signal-to-background ratio is improved by one order of magnitude.
Ablation and tissue removal of normal and atherosclerotic arterial wall by pulses of λ = 308 nm laser radiation have been probed by visible pulsed dye laser radiation. Photographs have been taken where the samples are irradiated in saline solution. The pulsewidth of the ablating XeCl excimer laser is about Δτ = 30 ns FWHM. The pulses have been transmitted through a fused silica fiber with a core diameter of 600 micrometers . The pulse energy was set to 20 mJ at the distal end of the fiber corresponding to a fluence of 7.5 J/cm2, which is well above the ablation threshold. Visible radiation of a dye laser operated at a wavelength of λ = 580 nm (Δτ ~ 10 ns FWHM) is used to illuminate the tissue surface and the ablation plume. The delay time of the probing pulses with respect to the 308 nm pulses is varied in the nanosecond range up to several hundred microseconds. The ablation process and the resulting plume above the tissue surface are recorded with a CCD camera attached to a PC-based image-processing system. All samples under investigation were fresh human cadaver aortic and femoral artery specimens (less than or equal to 48 h), which had been shock-frozen. The arterial segments showed different types of lipid rich and calcified plaques.
In order to optimize bone and cartilage ablation, various excimer laser systems at 308 nm wavelength (pulse width 28 ns, 60 ns, 300 ns) and tapered fibers (core diameter 400 micrometers , 600 micrometers , 1000 micrometers ) were combined. By varying the major parameters such as fluence, pulselength, repetition rate, fiber diameter, medium, manner of application (drilling, cutting); analysis was made of the interaction of the excimer laser beam with different organic material (meniscus, bone tissue). More than 300 cuts and drillings have been realized with different parameters. The ablation rate mainly depends on fluence, repetition rate and pulse duration. The achieved ablation rate was 3 micrometers /pulse in bone. The drilling speed of the meniscus was 6 mm/s. The samples showed no carbonization at all, when being cut or drilled in liquid medium. This might be a breakthrough in fiber guided excimer laser surgery. From these and further experiments the authors obtained the dosimetry, which will be the basis for the elaboration of necessary operation guidelines for accident surgery.
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