J. Liu, F. Bajraktari, R. Rausch, and P. P. Pott, “3D Reconstruction of Forearm Veins Using NIR-Based Stereovision and Deep Learning,” in
2023 IEEE 36th International Symposium on Computer-Based Medical Systems (CBMS), Jun. 2023, pp. 57–60. doi:
10.1109/CBMS58004.2023.00192.
Zusammenfassung
In this paper, the development of a cost-effective assistance system for venipuncture is presented. The system locates forearm veins through near-infrared imaging, depth estimation, deep learning segmentation, and 3D reconstruction. A single-board computer was integrated with two infrared cameras and two 760 nm near-infrared (NIR) LEDs to capture and process stereo images. The depth estimation was achieved through stereo triangulation. A deep learning model based on the U-Net architecture with an attention mechanism and a training dataset of 900 images from 40 participants was used for vein segmentation. Depth information and segmented veins were combined to enable a 3D visualization of the veins. The results show a Jaccard-Score of 92.80 % for vein segmentation and an average reprojection error of 0.48 pixels for the 3D reconstruction.BibTeX
J. Liu, Ö. Atmaca, and P. P. Pott, “Needle-Based Electrical Impedance Imaging Technology for Needle Navigation,”
Bioengineering, vol. 10, Art. no. 5, 2023, doi:
10.3390/bioengineering10050590.
Zusammenfassung
Needle insertion is a common procedure in modern healthcare practices, such as blood sampling, tissue biopsy, and cancer treatment. Various guidance systems have been developed to reduce the risk of incorrect needle positioning. While ultrasound imaging is considered the gold standard, it has limitations such as a lack of spatial resolution and subjective interpretation of 2D images. As an alternative to conventional imaging techniques, we have developed a needle-based electrical impedance imaging system. The system involves the classification of different tissue types using impedance measurements taken with a modified needle and the visualization in a MATLAB Graphical User Interface (GUI) based on the spatial sensitivity distribution of the needle. The needle was equipped with 12 stainless steel wire electrodes, and the sensitive volumes were determined using Finite Element Method (FEM) simulation. A k-Nearest Neighbors (k-NN) algorithm was used to classify different types of tissue phantoms with an average success rate of 70.56% for individual tissue phantoms. The results showed that the classification of the fat tissue phantom was the most successful (60 out of 60 attempts correct), while the success rate decreased for layered tissue structures. The measurement can be controlled in the GUI, and the identified tissues around the needle are displayed in 3D. The average latency between measurement and visualization was 112.1 ms. This work demonstrates the feasibility of using needle-based electrical impedance imaging as an alternative to conventional imaging techniques. Further improvements to the hardware and the algorithm as well as usability testing are required to evaluate the effectiveness of the needle navigation system.BibTeX
J. Mayer, M. B. Schäfer, J. Liu, G. A. Giacoppo, T. Markert, S. Matich, P. Brunner, and P. P. Pott, “Hand-Held Device for Force Estimation during Tool-Tissue Interaction,” Mannheim, Jun. 2022.
Zusammenfassung
When manipulating tissue during medical interventions, high-accuracy movements are important to avoid injuries. However, feedback is limited and it is hard to establish control loops to ensure correct movements. We propose the use of a novel highly compact 6-axis force / torque sensor (Ø 10.5 mm x 11.0 mm) within a hand piece to determine low forces and torques during various small-scale procedures including gentle tool-tissue interaction. For a first validation of the system, different venepuncture cannulas were connected to the sensor top and driven into skinned fruits (toma-toes and grapes) as well as into a silicone block. During insertion of the needle tips, maximum forces of 74 – 158 mN (tomato) and 51 - 161 mN (grape) were recorded, and steadily increasing forces in the range of 0 – 250 mN when insert-ing needles 7.5 mm into silicone. For a 0.99 g screw nut (9.73 mN), the measured gravitational force was 10.6 ± 1.5 mN during ten measurement sets. During the insertion, needle torques of up to 9.5 mNm were observed. Different cutting phases were seen similar to the phases during needle penetration testing. We conclude that the compact measurement setup used is suitable to measure the low forces and torques occurring when cutting soft, aqueous human tissues with or without skin-like layers.BibTeX
A. Hess, J. Liu, and P. P. Pott, “Analysis of Dielectric Properties of Gelatin-based Tissue Phantoms,”
Current Directions in Biomedical Engineering, vol. 8, Art. no. 2, 2022, doi:
doi:10.1515/cdbme-2022-1087.
BibTeX
J. Liu, Ö. Atmaca, T. J. Ly, and P. P. Pott, “Numerical Sensitivity Analysis of Microelectrodes for Multi-Local Impedance Measurements on Needles,” in Beiträge des 9. GMM-Workshops 21. – 22.11.2022 in Aachen, 2022, vol. GMM-Fachbericht 105: Mikro-Nano-Integration, pp. 90–94.
BibTeX
J. Liu, F. Bajraktari, Ö. Atmaca, T. J. Ly, and P. P. Pott, “Microscale Sensor Fabrication on Curved Needle Surfaces,”
Current Directions in Biomedical Engineering, vol. 8, Art. no. 2, 2022, doi:
doi:10.1515/cdbme-2022-1161.
BibTeX
J. Liu, M. Heumann, K. W. Stewart, and P. P. Pott, “Development of a Venous Collapse Prevention Device for Blood Draw,”
Current Directions in Biomedical Engineering, vol. 8, Art. no. 2, 2022, doi:
doi:10.1515/cdbme-2022-1055.
BibTeX
F. Bajraktari, J. Liu, and P. P. Pott, “Methods of Contactless Blood Pressure Measurement,”
Current Directions in Biomedical Engineering, vol. 8, Art. no. 2, 2022, doi:
doi:10.1515/cdbme-2022-1112.
BibTeX
J. Liu, C. Goehring, and P. P. Pott, “Integration of a Hollow, Bipolar Needle Electrode into a Handheld Impedance Measurement Device for Tissue Identification,” 13th Biomedical Engineering International Conference (BMEiCON2021), Nov. 2021.
Zusammenfassung
A method for identification of tissue types using a handheld impedance measurement device is proposed. An impedance analyzer chip AD5933, driven by an Arduino Nano, is utilized for measurements of the electrical impedance. The electrodes interfacing the tissue consist of two concentric standard hypodermic needles, separated by an insulating layer of PTFE. The electrical contact is established by two-pole splicing connectors. By a prior determination of the cell constant, the conductivity of the penetrated tissue type can be inferred from impedance values. The cell constant determined for the self-fabricated needle electrode is 3.72 ∙ 10-3 m. For NaCl solutions, percental differences between the conductivities found in this work and literature values are between 0.8 % and 37.7 %. For a test frequency of 100 kHz, only small differences from expected conductivity values (2.1 % for muscle, and 5.8 % for fat) are found in porcine tissue samples, demonstrating the ability to identify unknown tissue types. However, miniaturization of the needle as well as the consideration of the tissue’s permittivity is desired to increase detection quality.BibTeX
C. Goehring, J. Liu, F. Schiele, K. Moeller, and P. P. Pott, “Fabrication and evaluation of simple tissue-mimicking phantoms for electrical impedance sensing,”
6th IEEE-EMBS Conference on Biomedical Engineering and Sciences (IECBES 2020), Mar. 2021, doi:
https://doi.org/10.1109/IECBES48179.2021.9398842.
Zusammenfassung
Venepuncture is one of the most often performed invasive clinical procedure. Nevertheless, complications still occur. One possibility to counteract these complications is to indicate the insertion by electrical impedance measurement, based on the various electrical properties of different tissues. This paper presents the evaluation and reproducible fabrication of simple tissue-mimicking phantoms for investigation of impedance sensing techniques. Three different tissue-mimicking phantoms, representing blood, fat, and skin, were made on water-based recipes, including agar and gelatin as gelling agents. For evaluation of the electrical properties an electrode probe, made of hypodermic needles, was fabricated and characterized using six sodium chloride (NaCl) solutions of defined concentrations. For characterization of the phantoms, conductances were measured over a frequency range from 20 Hz up to 1 MHz using the self-fabricated electrodes. The calculated conductivities of the tissue-mimicking phantoms show sufficient agreement with corresponding electrical literature data of native tissue. However, the method was not suitable for investigation of relative permittivity, which would be required for full electrical characterization.BibTeX
J. Liu, L. Hauser, M. Kappel, C. Goehring, and P. P. Pott, “Simulation and Experimental Investigation of a Hollow, Bipolar Needle Electrode,” Current Directions in Biomedical Engineering, 2021.
Zusammenfassung
Localized impedance measurements at the needle tip identifying the present tissue type could aid clinicians in needle procedures. To assess the sensitivity field of a hollow, bipolar needle electrode, a 3D finite element approach using COMSOL Multiphysics was chosen. The simulated bipolar needle electrode consists of two hypodermic needles (17 G and 23 G) with an insulating layer of polytetrafluoro-ethylene (PTFE) in between. Impedance values were recorded while steadily increasing the insertion depth of the needle electrode in a layered tissue structure of skin (dermis), fat, and blood. Simulation results reveal a highly local sensitivity volume around the needle tip that can be approximated by half a tri-axial ellipsoid with elliptic radii of 0.735 mm, 2.886 mm, and 1.774 mm. A comparison with simulated and measured impedance values shows great correspondence.BibTeX
J. Liu, C. Goehring, F. Schiele, K. Moeller, and P. P. Pott, “Fabrication and Experimental Evaluation of Simple Tissue-Mimicking Phantoms with Realistic Electrical Properties for Impedance-Based Sensing,” International Journal of Integrated Engineering (IJIE), vol. 13, Art. no. 5, 2021.
Zusammenfassung
Venipuncture is one of the most often performed invasive clinical procedure. Nevertheless, complications still occur. One opportunity to counteract these complications is to indicate the insertion by electrical impedance measurement, which bases on the various electrical properties of different tissues. This paper presents the evaluation and reproducible fabrication of simple tissue-mimicking phantoms for investigation of impedance sensing techniques. Three different tissue-mimicking phantoms, representing blood, fat, and skin, were made on water-based recipes, including agar and gelatin as gelling agents. For evaluation of the electrical properties an electrode probe, made of hypodermic needles, was fabricated and characterized using six sodium chloride (NaCl) solutions of defined concentrations. For characterization of the phantoms, conductances were measured over a frequency range from 20 Hz up to 1 MHz using the self-fabricated electrodes. The calculated conductivities of the tissue-mimicking phantoms showed sufficient agreement with corresponding electrical literature data of native tissue. Tests with a layered tissue structure proved usability for impedance-based venous entry tests. However, the method proposed was not suitable for investigation of relative permittivity, which would be required for full electrical characterization.BibTeX
Zusammenfassung
Venepuncture is one of the most common invasive procedures in medical healthcare worldwide, however failure rates are still relatively high, particularly for paediatric, geriatric, darker skinned, and obese patients. Visualisation of the veins has been shown to decrease failure rates and can be achieved through trans-illumination, near infrared reflectance, or sonography. However, these techniques are either not reliable or very expensive, resulting in them not being commonly used in the clinical workplace. This paper develops a proof of concept low-cost LED vein detection device using photocurrent generated by LEDs in reverse bias. The prototype uses two emitting LEDs and one detecting LED to identify the location of a vein via trans-illuminance and reflectance. Various light intensities and wavelengths of the LEDs are tested in regard to resolution, noise, and signal peaks. A balance between system noise and resolution is identified for each LED in relation to the emitted intensity. No significant difference was observed in relative peak height when different wavelengths were used to identify the same superficial veins. The initial proof of concept proves the LED vein detection method and provides the foundation for further low-cost LED vein detection devices to be developed.BibTeX
D. Rehling, J. Liu, K. W. Stewart, F. Schiele, and P. P. Pott, “Investigation of vibration parameters for needle insertion force reduction,”
Current Directions in Biomedical Engineering, vol. 6, 2020, doi:
10.1515/cdbme-2020-3155.
Zusammenfassung
Many medical interventions in therapy and diagnostics require needle insertion into tissue. Common complications such as increased pain and formation of haematoma are caused by wrong needle positioning. It has been shown that pain experience and needle positioning can be improved by a reduction of insertion force, which can be achieved by vibrating the needle axially. An experimental setup has been designed to investigate the influences of different combinations of vibration frequencies (10, 100, and 200 Hz) and vibration amplitudes (20, 100, and 500 μm) during needle insertion into thin sheets of polyethylene terephthalate (PET). A customary 20 W loudspeaker was used to generate the vibration. The results indicate a maximum reduction of 73 % in puncture force and up to a 100 % reduction in shaft friction force. However, the additional vibration force generated by the vibration movement has to be high enough to generate positive effects in terms of force reduction.BibTeX
M. Engers, K. W. Stewart, J. Liu, and P. P. Pott, “Development of a realistic venepuncture phantom,”
Current Directions in Biomedical Engineering, vol. 6, 2020, doi:
10.1515/cdbme-2020-3104.
Zusammenfassung
Venepuncture is one of the most common invasive procedures performed worldwide, however, complications still occur. Currently, commercial single layer silicone phantoms used for venepuncture training do not accurately imitate the geometry and mechanical properties seen in the various patient groups. This paper presents the development of a realistic artificial venepuncture phantom. Three multilayered tissue phantoms are developed simulating venepuncture sites of paediatric, adult and geriatric patients. Silicone materials of different stiffnesses were selected to imitate the epidermis, dermis, subcutaneous fat, muscle and superficial veins. Singleaxis indentation tests were carried out on silicone samples and the multi-layered phantom inserts to characterize the material properties. The measured Young's moduli for the artificial dermis, fat and muscle show sufficient agreement with corresponding literature values. However, characterization of the complete phantom inserts showed stiffnesses four times larger than prior in-vivo studies. Future studies will work on developing a more comparable in-vivo study.BibTeX
S. Da Souza, P. Mühlbauer, S. Janzen, J. Liu, and P. P. Pott, “Series and parallel actuation array of elastic micro-twisted string actuators,” Würzburg, 2019. [Online]. Available:
https://ieeexplore.ieee.org/document/8892425Zusammenfassung
The twisted-string actuation (TSA) principle provides simple, lightweight, silent yet powerful actuators well suited for human-machine interaction. This comprises of not only the use in orthotic and prosthetic systems for lower extremities, arms, and wrists but also exo-skeletons. A TSA consists of a bundle of at least two fiber components and an actuator to twist it along its main axis. This forms a helical structure, which shortens the axial length – given non-elastic behaviour of the material. In practice, an axial bearing compensates for the load force and a linear guide counters the motor torque. In cases where a bi-directional force is required, a passive spring return mechanism can be included. Our work focuses on the integration of the described TSA components into a single elastic tube. Three TSAs are arranged in series and six in parallel such that they form an array that can bend in three dimensions with muscle-like behaviour and elastic properties. By switching motor units on and off, the length and force of the array can be varied between zero and maximum force without the need of an internal feedback loop. A first experiment is carried out to validate the force control. A possible application of this technology is soft medical robots for diagnostic and therapeutic purposes. The first demonstrator consists of three motor units in series. Six of these serial arrangements are combined in parallel forming an array of 18 motors. Each TSA unit consists of a DC motor, a string coupling including the axial bearing, the string made of high-density polyethylene, a cylindrical housing that protects the motor against axial forces, houses the DC motor, and provides the support for the previous unit. The entire TSA unit is encapsulated inside a thermoplastic polyurethane (TPU) tube which takes over the counter-torque, acts as linear bearing, is the return spring, and provides the elastic base for the TSA array. Thus, by using these modular units an infinite chain of TSA can be built and arranged as desired. The TSA units can be current-controlled and independently activated. Experiments showed that a no-load stroke of 18 mm and a maximum pulling force of 11 N can be achieved by a single TSA module. The spatial arrangement of the tubes allows muscle-like use in larger and anthropomorphic systems and also 2-dimensional bending and torsion of the array for soft robotic systems. Further work will comprise the improvement of the module, their miniaturization, simplified axial bearings, and integrated control electronics.BibTeX
J. Liu, M. Reisbeck, and O. Hayden, “Investigation of mechanical and magnetophoretic focusing for magnetic flow cytometry,”
Current Directions in Biomedical Engineering, vol. 5, p. 353––, 2019, doi:
10.1515/cdbme-2019-0089.
Zusammenfassung
As an alternative to optical flow cytometry, magnetic flow cytometry has emerged in recent years for single cell analysis with sheath-less flow conditions. Instead of measuring scattered light, magnetic fields of magneticallylabeled cells are recorded and analyzed. To determine microfluidic opportunities to manipulate cell trajectories for in-situ cell focusing we use mechanical guiding structures and magnetophoretic forces. A 3D-microfluidic particle simulation has been implemented that revealed parameters ensuring the crucial balance between hydrodynamic drag and magnetophoretic forces. Experimental measurements verified the 3D particle tracking simulation.BibTeX
J. Liu, K. W. Stewart, and P. P. Pott, “Towards automated and painless venipuncture – vibratory needle insertion techniques,”
Current Directions in Biomedical Engineering, vol. 5, p. 157––, 2019, doi:
10.1515/cdbme-2019-0040.
Zusammenfassung
The insertion of a needle into soft inhomogeneous tissue is required for many medical procedures. It has been shown that vibratory needle insertion methods have the ability to reduce insertion forces, which are correlated with increased needle placement precision, and reduced frequency and intensity of pain and trauma felt. This paper reviews different vibratory needle insertion methods that have been studied experimentally, addressing vibration generation, vibration frequency and amplitude, and force measurement. Reductions of up to 73 % in peak insertion force (150 Hz), and 37 % in placement error (15 Hz) were reported. Additionally, ultrasonic vibration (84 kHz) reduced the force by up to 28 %. The results of vibratory insertion show promise, specifically in regard to automated needle devices.BibTeX
