We present a laser induced ultrasound and the localization of cavitation bubbles using an optoacoustic spherical Ti/black-TiOx lens. Results demonstrate the possibility to localize cavitiesand secondary ablative effects into the subsurface tissue.
Laser medical treatments trigger thermal effects which can damage the tissue. Results show an estimation of depth temperature distribution by combining surface temperature dynamics with a thermal-diffusion-based model and a data matching algorithm.
Significance: Hyperspectral imaging (HSI) has emerged as a promising optical technique. Besides optical properties of a sample, other sample physical properties also affect the recorded images. They are significantly affected by the sample curvature and sample surface to camera distance. A correction method to reduce the artifacts is necessary to reliably extract sample properties.
Aim: Our aim is to correct hyperspectral images using the three-dimensional (3D) surface data and assess how the correction affects the extracted sample properties.
Approach: We propose the combination of HSI and 3D profilometry to correct the images using the Lambert cosine law. The feasibility of the correction method is presented first on hemispherical tissue phantoms and next on human hands before, during, and after the vascular occlusion test (VOT).
Results: Seven different phantoms with known optical properties were created and imaged with a hyperspectral system. The correction method worked up to 60 deg inclination angle, whereas for uncorrected images the maximum angles were 20 deg. Imaging hands before, during, and after VOT shows good agreement between the expected and extracted skin physiological parameters.
Conclusions: The correction method was successfully applied on the images of tissue phantoms of known optical properties and geometry and VOT. The proposed method could be applied to any reflectance optical imaging technique and should be used whenever the sample parameters need to be extracted from a curved surface sample.
Curvature and height corrections were made on hyperspectral images in order to reduce intensity dependence on distance and inclination. The corrections were made by Lambertian cosine law and measured 3D surface of the sample. Image of homogeneous phantom appeared significantly more homogeneous after correction.
Laser-enhanced irrigation of complex root canals appears to be a very promising technique to improve the outcome of root canal treatment. This applies, in particular, if the technique can be effective at very low laser energies in irrigating not only the main canal but also the small lateral canals. This is important in order to avoid potential undesirable effects at higher laser energies such as temperature increase, dentin ablation, or extrusion of irrigating solution beyond the apical foramen. An improved understanding of the role of laser parameters, such as laser wavelength and pulse duration, in irrigation of lateral canals is therefore desired in order to optimize treatment efficacy. The influence of laser wavelength and pulse duration on cavitation phenomena was studied using shadow photography and a method of measuring fluid flow in lateral canals based on tracking of movements of small air bubbles naturally forming in liquid as a result of laser agitation. A simulated model of a root canal including a narrow lateral canal designed to represent typical root canal morphology was used for the water flow measurements. The following three laser wavelengths with relatively high absorption in water were studied: Er:YAG (2.94 μm), Er,Cr:YSGG (2.73 μm), and Nd:YAP (1.34 μm). Among the three wavelengths studied, the Er:YAG laser wavelength was found to be the most effective in formation of cavitation bubbles and in generating fluid motions within narrow lateral canals. A comparison between the shadow photography and fluid motion data indicates that it is the bubble’s radius and not the bubble’s volume that predominantly influences the fluid motion within lateral canals. Based on the results of our study, it appears that effective minimally invasive laser-assisted irrigation can be performed with low Er:YAG laser pulse energies below 10 mJ.
Erbium lasers are by now an accepted tool for performing ablative medical procedures, especially when minimal invasiveness is desired. Ideally, a minimally invasive laser cutting procedure should be fast and precise, and with minimal pain and thermal side effects. All these characteristics are significantly influenced by laser pulse duration, albeit not in the same manner. For example, high cutting efficacy and low heat deposition are characteristics of short pulses, while vibrations and ejected debris screening are less pronounced at longer pulse durations. We report on a study of ablation characteristics on dental enamel and cementum, of a chopped-pulse Er:YAG [quantum square pulse (QSP)] mode, which was designed to reduce debris screening during an ablation process. It is shown that in comparison to other studied standard Er:YAG and Er,Cr:YSGG laser pulse duration modes, the QSP mode exhibits the highest ablation drilling efficacy with lowest heat deposition and reduced vibrations, demonstrating that debris screening has a considerable influence on the ablation process. By measuring single-pulse ablation depths, we also show that tissue desiccation during the consecutive delivery of laser pulses leads to a significant reduction of the intrinsic ablation efficacy that cannot be fully restored under clinical settings by rehydrating the tooth using an external water spray.
Erbium:yttrium aluminum garnet laser cleaning is a promising technique in endodontic treatment. In our in vitro study, we measured the vapor-bubble dynamics in the root canal by using shadow photography. The canal model was made of a plastic cutout placed between two transparent glass plates. An artificial smear layer was applied to the glass to study cleaning efficiency. In our results, no shock waves have been observed, since the pulp-chamber dimensions have been in the same range as the maximum diameter of the vapor bubble. This leads to the conclusion that shock waves are not the main cleaning mechanism within our model. However, the cleaning effects are also visible in the regions significantly below the bubble. Therefore, it can be concluded that fluid flow induced by the bubble’s oscillations contributes significantly to the canal cleaning. We also proposed a simple theoretical model for cleaning efficiency and used it to evaluate the measured data.
A combined laser tattoo removal treatment, first the ablative fractional resurfacing (AFR) with an Er:YAG laser and then the q-switched (QSW) Nd:YAG laser treatment, was studied. Experiments show that significantly higher fluences can be used for the same tissue damage levels.
When an erbium-laser pulse is directed into water through a small-diameter fiber tip (FT), the absorption of the laser energy superheats the water and its boiling induces a vapor bubble. We present the influence of different FT geometries and pulse parameters on the vapor-bubble dynamics. In our investigation, we use a free-running erbium: yttrium aluminum garnet (Er:YAG) (λ = 2.94 μm) laser that was designed for laser dentistry. Its pulse is directed into the water through FTs with a flat and conical geometry. Our results show that in the case of the conical FT, a spherical bubble is induced, while a channel-like bubble develops for the flat FT. The ratio between the mechanical energy of the liquid medium and the pulse energy, which we call the optodynamic energy-conversion efficiency, is examined using shadow photography. The results indicate that this efficiency is significantly larger when a conical FT is used and it increases with increasing pulse energy and decreasing pulse duration. The spherical bubbles are compared with the Rayleigh model in order to present the influence of the pulse duration on the dynamics of the bubble's expansion.
The goal of this research is to use the information contained in the mechanisms occurring during the laser tattoo removal process. We simultaneously employed a laser-beam deflection probe (LBDP) to measure the shock wave and a camera to detect the plasma radiation, both originating from a high-intensity laser-pulse interaction with a tattoo. The experiments were performed in vitro (skin phantoms), ex vivo (marking tattoos on pig skin), and in vivo (professional and amateur decorative tattoos). The LBDP signal includes the information about the energy released during the interaction and indicates textural changes in the skin, which are specific for different skin and tattoo conditions. Using both sensors, we evaluated a measurement of threshold for skin damage and studied the effect of multiple pulses. In vivo results show that a prepulse reduces the interaction strength and that a single strong pulse produces better removal results.
We present a novel method for real-time 3-D body-shape measurement during breathing based on the laser multiple-line triangulation principle. The laser projector illuminates the measured surface with a pattern of 33 equally inclined light planes. Simultaneously, the camera records the distorted light pattern from a different viewpoint. The acquired images are transferred to a personal computer, where the 3-D surface reconstruction, shape analysis, and display are performed in real time. The measured surface displacements are displayed with a color palette, which enables visual feedback to the patient while breathing is being taught. The measuring range is approximately 400×600×500 mm in width, height, and depth, respectively, and the accuracy of the calibrated apparatus is ±0.7 mm. The system was evaluated by means of its capability to distinguish between different breathing patterns. The accuracy of the measured volumes of chest-wall deformation during breathing was verified using standard methods of volume measurements. The results show that the presented 3-D measuring system with visual feedback has great potential as a diagnostic and training assistance tool when monitoring and evaluating the breathing pattern, because it offers a simple and effective method of graphical communication with the patient.
The goal of this research is to use the information contained in the mechanisms occurring during laser tattoo removal
process. We employed a fast laser beam deflection probe (BDP) to measure the cracking sound that originates from the
dye explosions in the process known as selective photothermolysis. The experiments were performed in vitro (skin
phantoms), ex vivo (marking tattoos on pig skin) and in vivo (professional and amateur decorative tattoos on several
patients). The signal includes the information about the energy released during the interaction, specific for different skin
and tattoo conditions.
KEYWORDS: Chest, Calibration, Laser systems engineering, Cameras, Lung, Projection systems, 3D acquisition, 3D image processing, 3D displays, Data processing
Novel method for monitoring the entire three-dimensional shape of the chest wall in real time is presented. The system is
based on the multiple-line laser triangulation principle. The laser projector generates a light pattern of 33 equally inclined
light planes directed toward the measured surface. The camera records the illuminated surface from a different
viewpoint, and consequently, the light pattern is distorted by the shape of the surface. The acquired images are
transferred in the personal computer, where contour detection, three-dimensional surface reconstruction, shape analysis,
and displaying are performed in real time. Surface displacements are calculated by subtraction of the current measured
surface from the reference one. Differences are displayed with color palette, where the blue represent the inward
(negative) and the red represent the outward (positive) movement. The accuracy of the calibrated apparatus is ±0.5 mm,
which is calculated as a standard deviation between points of the measured and nominal reference surface. The
measuring range is approximately 400×600×500 mm in width, height and depth. The intention of this study was to
evaluate the system by means of its ability to distinguish between different breathing patterns and to verify the accuracy
of measuring chest wall deformation volumes during breathing. The results demonstrate that the presented 3-d measuring
system has a great potential as a diagnostic and training tool in case of monitoring the breathing pattern. We believe that
exact graphical communication with the patient is much more simple and easy to understand than verbal and/or
numerical.
Optical three-dimensional shape measurement of live objects is becoming an important developing and research tool because of its nonintrusive nature and high measuring speed. The current methods are reaching truly high speed in one view configuration, but in the case of the entire object shape measurement, they are limited due to mutual interference between multiple measuring modules. The proposed method overcomes this limitation by using a laser multiple-line triangulation technique, where each of several measuring modules uses a unique laser wavelength. The measuring modules are positioned so that the entire surface of the foot is digitized. This prevents unwanted overlapping between adjacent light patterns. The calibration procedure for each measuring module and for the entire system is based on measurements of the surface of a reference object. The system parameters are determined using an iterative optimization algorithm. The precision of the system is better than ±0.3 mm. The system is capable of measuring objects in motion. The results of the shape of a foot rising on its toes are given as an example.
We have developed a scanning laser system based on the optical triangulation principle for the shape measurement of
fusion weld surfaces. The system integrates a triangulation module consisting of a laser line projector and a digital video
camera with a mechanical scanning stage and an industrial computer. The system is small and rugged, suitable for
application in industrial environment. The system can sample a weld surface at a rate of up to 30 profiles per second
achieving 0.1mm accuracy. Software was developed which analyses the captured weld surface shape in real time
determining the characteristic shape parameters (length, width, height, cross section, volume, starting position,...) which
are then used for automated classification of the welds into acceptable and unacceptable. The software also detects
surface defects such as undercutting, holes or melt splash, etc. The system has been tested in a robotized welding cell for
automotive parts in an industrial production facility. Weld classification obtained by the system was compared to an
independent classification determined by a trained weld inspector on the basis of visual inspection and to another one
determined on the basis of metallographic analysis of the weld. Using the metallographic based classification as the
reference we find that the developed weld inspection system can achieve better classification reliability than a trained
visual weld inspector.
The paper presents a new method for on-line acquisition of weld-piece surface topography during pulsed laser welding. The method is based on illumination of the weld-piece surface with multi-line laser projector and imaging of the illuminated surface with a digital camera. The acquired image is processed by a personal computer to get the three-dimensional (3D) weld-piece surface topography. The set-up was applied to minimize weld-piece distortion during laser butt-welding of low-carbon thin steel sheets. Methodology based on Taguchi methods was developed enabling optimization of processing parameters. Root-mean-square (RMS) of surface distortion was used as the scalar parameter quantifying the amount of distortion. The results show that laser pulse duration and welding speed have a major influence on RMS distortion.
This contribution presents a new optical system, which allows real-time distortion measurement of weld-pieces on a laser welding machine. The system is based on simultaneous displacement measurement of several thousand points on a weld-piece surface employing rapid (non-scanning) laser profilometry. Weld-piece is illuminated by laser light, structured into multiple light planes and imaged by a digital camera. The position of the optical measuring system is fixed relative to the measured weld-piece. Acquired image is fed into a personal computer where it is processed to obtain the three-dimensional (3D) shape of imaged weld-piece surface. The maximum real-time measurement rate of the presented system is up to 20 surface measurements per second. We have applied the set-up to study the distortion of low-carbon thin steel sheet samples during Nd:YAG laser welding. In this paper we present characteristic evolution of surface distortion and distortion of the welding edges as a function of time. The produced weld-pieces exhibit characteristic V-shaped angular distortion mixed with longitudinal distortion, which bends down the welding edges at the end of weld. In welding edge distortion study we found out that the weld tends to annihilate vertical misalignment. The results show that the developed optical system allows fast and accurate temporally and spatially resolved evaluation of various types of weld-piece distortion. The presented system is scalable - the size of the measurement area can be adapted to the size of weld-piece.
A system for real-time surface deformations control during various types of laser processing is presented. It is based on a laser triangulation principle, where the laser projector generates multiple lines simultaneously. Three dimensional shape measurement of a surface is performed with a high sampling rate (80 Hz) and high accuracy (±7 μm). Results of steel-plate deformations are presented for laser bending, drilling and engraving. Laser based flattening process of previously deformed plate is demonstrated, where the measurement system is used as a feed-back control.
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