Matija Jezeršek

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

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.

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

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.

Triangulation model taking into account light sheet curvature

This paper examines the problem of systematic measurement errors in optical triangulation when some light sheets that illuminate the measured surface exhibit non-negligible bending (curvature). The problem is demonstrated experimentally by triangulation measurement of two reference bodies whose geometry reveals systematic measurement errors due to light sheet curvature. To correct these errors a triangulation model is developed which assumes parabolic light sheet shape and allows exact solution of system equations. Test measurements show that the model successfully compensates for systematic measurement errors originating from the curvature of light sheets.

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

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 bubbles expansion.

Initial healing rates as predictive factors of venous ulcer healing : The use of a laser-based three-dimensional ulcer measurement

There is a need for practical methods to predict the healing time of venous leg ulcers. In a prospective cohort study of 81 patients with venous leg ulcers, we used a recently described laser‐based three‐dimensional measurement of the ulcers at days 0 and 28 to estimate the predictive power of horizontal (HIHR) and vertical initial healing rates (VIHR) for wound healing by week 24. The rates were calculated by Gilmans equation [(A1−A2)/((p1+p2)/2)(0–4)] and by its modification [(V1−V2)/((A1+A2)/2)(0–4)], respectively. The influence of risk factors on both the initial healing rates was also studied. The HIHR and VIHR are important predictors of healing at 24 weeks. They are not influenced by age, ulcer duration, initial ulcer area, and insufficient sapheno‐femoral junction, and/or calf perforating veins. Together with ulcer duration, they are independent predictors of the 24‐week healing (the area under ROC curve equals to 0.9). VIHR gives us additional information and significantly improves the prediction of 24‐week healing.

High-speed measurements of steel-plate deformations during laser surface processing.

In this paper we present a novel approach to monitoring the deformations of a steel plates surface during various types of laser processing, e.g., engraving, marking, cutting, bending, and welding. The measuring system is based on a laser triangulation principle, where the laser projector generates multiple lines simultaneously. This enables us to measure the shape of the surface with a high sampling rate (80 Hz with our camera) and high accuracy (+/-7 microm). The measurements of steel-plate deformations for plates of different thickness and with different illumination patterns are presented graphically and in an animation.

3D laser measurements of bare and shod feet during walking

This article presents a new system for 3D foot-shape measurements during walking. It is based on the laser-triangulation, multiple-line-illumination and color-modulation techniques. It consists of a walking stage and four measuring modules that simultaneously acquire the foot shape from the top, bottom and side views. The measuring speed is 30 fps. Custom-developed software makes it possible to analyze the foots dimensions at an arbitrary cross-section by means of the width, height, girth and section orientation. Six subjects were measured during bare and shod walking, and the bare foot and the outside dimensions of the footwear during the entire stance phase are presented. The relative measurement repeatability of a single subject is 0.5% for bare foot and 1% for shod foot. This means that it is possible to study the differences between various influences on the foot-shape dynamics, such as a bare/shod foot, different loading conditions and the shoes stiffness condition.

Laser 3-D measuring system and real-time visual feedback for teaching and correcting breathing

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.

Three-dimensional laser based measurement of human foot during walking

Barefoot walking demonstrated a significantly earlier phase shift in sagittal plane ankle and knee kinematics when compared to the VIB and SS (Table 1; Figure 1). There were no temporal differences evident at the hip. All sagittal waveforms showed a high degree of similarity evidenced by CCCs greater than r 0.95. No phase shifts were observed between SS and VIB at these joints in this plane of motion (Table 1). The similarity between waveforms in the frontal plane was particularly weak (r 0.84). At the ankle, although a pronounced phase shift was observed between BF vs SS and BF vs VIB, the 95% CI prevented this from being significant. At the knee however; these were significant.

In vitro study of the erbium:yttrium aluminum garnet laser cleaning of root canal by the use of shadow photography

Abstract. 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.