Urban Pavlovčič

Optical imaging techniques have shown great potential in medical applications, primarily in disease diagnosis and surgical guidance.¹ When light enters a tissue, it is affected by scattering or absorption in tissue chromophores, such as water, lipid, deoxyhemoglobin, oxyhemoglobin, and melanin.² In diseased tissues, their absorption and scattering properties change, resulting in altered diffuse reflectance spectra compared with healthy tissue.³ Diffuse reflectance spectra can be measured by optical techniques, such as hyperspectral imaging (HSI),⁴ and quantitative information about tissue composition can be extracted from the measured images.

A method for simultaneous laser profilometer and hand–eye calibration in relation to an industrial robot as well as its implementation is presented. In contrast to other methods, the new calibration procedure requires the measurement of only one reference geometry to calculate all the transformation parameters. The reference geometry is measured with a laser profilometer from 15 different poses. The intrinsic parameters of the profilometer, as well as the extrinsic (hand–eye) parameters, are then numerically optimized to achieve the minimum deviation between the reference and the measured geometry. The method was characterized with experiments that revealed a standard deviation of the displacements between the reference geometry after the calibration of less than 0.105 mm in the case of using the robot-arm actuator and 0.046 mm in case of using a 5-axis CNC milling machine. The entire procedure, including measurement and calculation, can be completely automated and lasts less than 10 min. This opens up possibilities for regular on-site recalibration of the entire system.

A measuring system based on laser triangulation for ranging a turbulent water surface in a laboratory environment is presented in this paper. The system is composed of a light detection and ranging (LIDAR) device, serving as a light source, and a high-speed camera. Single-point illumination was chosen to facilitate the introduction of the epipolar line in the image-processing step and thus improve the distinction between primary and other reflections, which increase the uncertainty of the measurement and introduce noise. The system was used to measure the water surface in an open channel confluence, which is composed of main and tributary channels, which join at a 90° angle. The surface was measured for 2.01 s, resulting in 54,682 points measured in 543 profiles. The influence of image process parameters (height and width of filtering kernel and width of area surrounding the epipolar line) on smooth and rough water surface was studied. The results show that the parameters’ influence is at least an order of magnitude smaller than the amplitude of water surface fluctuation.

Background: Measuring wound dimensions is important for monitoring and predicting the healing process. In our paper we propose and validate a handheld measuring system with dedicated software for measuring wound dimensions.Methods: The measuring system comprises a commercial DSLR camera and a light pattern projection system. It is based on triangulation and structured illumination principles which enable handheld measuring. An edge of the wound is detected from the colour information of the measurement. Across the area of the wound, virtual healthy skin is approximated which enables the calculation of the wound volume and area, in addition to the wound circumference, which is calculated from the detected edge.Results: In vitro verification using virtual standards showed that the accuracy of the analysis software is over 95% and 93% for measuring the area and volume respectively. A significant part of the error can be attributed to the inability of approximation to replicate entirely missing features. The accuracy of measuring the volume reduced to about 89% when a 3D measuring step was included in the analysis. When measuring in vivo wounds, the unrepeatability of the system was under 8% for measuring the area, which is a bit lower than comparable systems, and 5% for measuring the volume, which is about 4 times lower.Conclusion: Based on these results and the ease of use, we conclude that the system is suitable to be used in daily clinical practice for measuring wound dimensions.

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.

Knowing the orientation of the head is important in many fields, including medicine. Many methods and measuring systems exist, but usually they use different markers or sensors attached to the subject’s head for head orientation determination. In certain applications these attachments may represent a burden or a distraction to the subject under study which may have an unfavourable impact on the measurement. We propose a non-contact optical method for head-to-trunk orientation measurement that does not require any attachments to the subject under study. An innovative handheld 3D apparatus has been developed for non-invasive and fast 3D shape measurements. It is based on the triangulation principle in combination with fringe projection. The shape of the subject’s upper trunk and head is reconstructed from a single image using the Fourier transform profilometry method. Two shape measurements are required to determine the head-to-trunk orientation angles: one in the reference (neutral) position and the other one in the position of interest. The algorithm for the head-to-trunk orientation angle extraction is based on the separate alignment of the shape of the subject’s upper trunk and head against the corresponding shape in the reference pose. Single factor analysis of variance (ANOVA) was used for statistical characterisation of the method precision. The method and the 3D apparatus were verified in-vitro using a mannequin and a reference orientation tracker. The uncertainty of the calculated orientation was 2°. During the in-vivo test with a human subject diagnosed with cervical dystonia (aged 60), the repeatability of the measurements was 3°. In-vitro and in-vivo comparison was done on the basis of an experiment with the mannequin and a healthy male (aged 29). These results show that only the difference between flexion/extension measured angles was statistically significant. The differences between means were less than 1° for all ranges. The new non-contact method enables the compensation of the movement of the measuring instrument or the subject’s body as a whole, is non-invasive, requires little additional equipment and causes little stress for the subject and operator. We find that it is appropriate for measurements of the head orientation with respect to the trunk for the characterization of the cervical dystonia.