Matija Jezeršek

Bio: Matija Jezeršek is an academic researcher from University of Ljubljana. The author has contributed to research in topics: Laser & Materials science. The author has an hindex of 13, co-authored 81 publications receiving 583 citations.

Optodynamic energy-conversion efficiency during an Er:YAG-laser-pulse delivery into a liquid through different fiber-tip geometries

Abstract: 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=294 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

Amplification of pressure waves in laser-assisted endodontics with synchronized delivery of Er:YAG laser pulses

Abstract: When attempting to clean surfaces of dental root canals with laser-induced cavitation bubbles, the resulting cavitation oscillations are significantly prolonged due to friction on the cavity walls and other factors. Consequently, the collapses are less intense and the shock waves that are usually emitted following a bubble’s collapse are diminished or not present at all. A new technique of synchronized laser-pulse delivery intended to enhance the emission of shock waves from collapsed bubbles in fluid-filled endodontic canals is reported. A laser beam deflection probe, a high-speed camera, and shadow photography were used to characterize the induced photoacoustic phenomena during synchronized delivery of Er:YAG laser pulses in a confined volume of water. A shock wave enhancing technique was employed which consists of delivering a second laser pulse at a delay with regard to the first cavitation bubble-forming laser pulse. Influence of the delay between the first and second laser pulses on the generation of pressure and shock waves during the first bubble’s collapse was measured for different laser pulse energies and cavity volumes. Results show that the optimal delay between the two laser pulses is strongly correlated with the cavitation bubble’s oscillation period. Under optimal synchronization conditions, the growth of the second cavitation bubble was observed to accelerate the collapse of the first cavitation bubble, leading to a violent collapse, during which shock waves are emitted. Additionally, shock waves created by the accelerated collapse of the primary cavitation bubble and as well of the accompanying smaller secondary bubbles near the cavity walls were observed. The reported phenomena may have applications in improved laser cleaning of surfaces during laser-assisted dental root canal treatments.

High-speed measurement of foot shape based on multiple-laser-plane triangulation

Abstract: 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.

Measurement of venous leg ulcers with a laser‐based three‐dimensional method: Comparison to computer planimetry with photography

Abstract: A lack of reproducible and practical methods to assess venous leg ulcer healing is a major problem encountered by investigators evaluating various treatments. We aimed to compare a new laser-based three-dimensional (3D) measuring device with computer planimetry with photography for the assessment of venous leg ulcers, and to estimate the reliability of measurements by the methods. Sixty measurements of perimeter and area of 15 venous leg ulcers, < 10 cm in diameter (eight patients; six females; mean age 71 years; range 52-90 years), were made with both methods. Two independent investigators performed the measurements at the first visit and 2-4 weeks later. The precision and accuracy of the methods were determined and compared. The accuracies for computer planimetry with photography in comparison with the laser-based 3D measuring method were 8.4% for perimeter and 16.0% for area measurements. The precisions of ulcer area and perimeter measurements did not differ significantly between the two methods (p=0.993 and 0.201, respectively). The main advantage of the laser-based measuring method is the 3D ulcer measurement with a precision of 7.5%, which also takes into account distortions created by the limb convexity. The system is accurate, inexpensive, user-friendly, and appropriate for everyday practice.

Wound perimeter, area, and volume measurement based on laser 3D and color acquisition

Abstract: Wound measuring serves medical personnel as a tool to assess the effectiveness of a therapy and predict its outcome. Clinically used methods vary from measuring using rules and calipers to sophisticated methods, based on 3D measuring. Our method combines the added value of 3D measuring and well-known segmentation algorithms to enable volume calculation and achieve reliable and operator-independent analysis, as we demonstrate in the paper. Developed 3D measuring system is based on laser triangulation with simultaneous color acquisition. Wound shape analysis is based on the edge-determination, virtual healthy skin approximation over the wound and perimeter, area, and volume calculation. In order to validate the approach, eight operators analyzed four different wounds using proposed method. Measuring bias was assessed by comparing measured values with expected values on an artificially modeled set of wounds. Results indicate that the perimeter, area, and volume are measured with a repeatability of 2.5 mm, 12 mm2, and 30 mm3, respectively, and with a measuring bias of −0.2 mm, −8.6 mm2, 24 mm3, respectively. According to the results of verification and the fact that typical wound analysis takes 20 seconds, the method for wound shape measurement can be clinically used as a precise tool for objectively monitoring the wound healing based on measuring its 3D shape and color.

Wound healing in the 21st century

Abstract: Delayed wound healing is one of the major therapeutic and economic issues in medicine today. Cutaneous wound healing is an extremely well-regulated and complex process basically divided into 3 phases: inflammation, proliferation, and tissue remodeling. Unfortunately, we still do not understand this process precisely enough to give direction effectively to impaired healing processes. There have been many new developments in wound healing that provide fascinating insights and may improve our ability to manage clinical problems. Our goal is to acquaint the reader with selected major novel findings about cutaneous wound healing that have been published since the beginning of the new millennium. We discuss advances in areas such as genetics, proteases, cytokines, chemokines, and regulatory peptides, as well as therapeutic strategies, all set in the framework of the different phases of wound healing.

Apparatuses, systems and methods for three-dimensional printing

Abstract: The present disclosure provides three-dimensional (3D) objects, 3D printing processes, as well as methods, apparatuses and systems for the production of a 3D object. Methods, apparatuses and systems of the present disclosure may reduce or eliminate the need for auxiliary supports. The present disclosure provides three dimensional (3D) objects printed utilizing the printing processes, methods, apparatuses and systems described herein.

The use of 3D surface scanning for the measurement and assessment of the human foot

Abstract: A number of surface scanning systems with the ability to quickly and easily obtain 3D digital representations of the foot are now commercially available. This review aims to present a summary of the reported use of these technologies in footwear development, the design of customised orthotics, and investigations for other ergonomic purposes related to the foot. The PubMed and ScienceDirect databases were searched. Reference lists and experts in the field were also consulted to identify additional articles. Studies in English which had 3D surface scanning of the foot as an integral element of their protocol were included in the review. Thirty-eight articles meeting the search criteria were included. Advantages and disadvantages of using 3D surface scanning systems are highlighted. A meta-analysis of studies using scanners to investigate the changes in foot dimensions during varying levels of weight bearing was carried out. Modern 3D surface scanning systems can obtain accurate and repeatable digital representations of the foot shape and have been successfully used in medical, ergonomic and footwear development applications. The increasing affordability of these systems presents opportunities for researchers investigating the foot and for manufacturers of foot related apparel and devices, particularly those interested in producing items that are customised to the individual. Suggestions are made for future areas of research and for the standardization of the protocols used to produce foot scans.

Accurate three-dimensional printing

Abstract: The present disclosure provides three-dimensional (3D) printing methods, apparatuses, and systems using, inter alia, a controller that regulates formation of at least one 3D object (e.g., in real time during the 3D printing); and a non-transitory computer-readable medium facilitating the same. For example, a controller that regulates a deformation of at least a portion of the 3D object. The control may be in situ control. The control may be real-time control during the 3D printing process. For example, the control may be during a physical-attribute pulse. The present disclosure provides various methods, apparatuses, systems and software for estimating the fundamental length scale of a melt pool, and for various tools that increase the accuracy of the 3D printing.