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Split-Ring Resonator Sensor Penetration Depth Assessment Using In Vivo Microwave Reflectivity and Ultrasound Measurements for Lower Extremity Trauma Rehabilitation
Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
Amrita Vishwa Vidyapeetham, Amrita Sch Engn, Dept Elect & Commun, Bengaluru 560035, India.
Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
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2018 (English)In: Sensors, E-ISSN 1424-8220, Vol. 18, no 2, article id 636Article in journal (Refereed) Published
Abstract [en]

In recent research, microwave sensors have been used to follow up the recovery of lower extremity trauma patients. This is done mainly by monitoring the changes of dielectric properties of lower limb tissues such as skin, fat, muscle, and bone. As part of the characterization of the microwave sensor, it is crucial to assess the signal penetration in in vivo tissues. This work presents a new approach for investigating the penetration depth of planar microwave sensors based on the Split-Ring Resonator in the in vivo context of the femoral area. This approach is based on the optimization of a 3D simulation model using the platform of CST Microwave Studio and consisting of a sensor of the considered type and a multilayered material representing the femoral area. The geometry of the layered material is built based on information from ultrasound images and includes mainly the thicknesses of skin, fat, and muscle tissues. The optimization target is the measured S-11 parameters at the sensor connector and the fitting parameters are the permittivity of each layer of the material. Four positions in the femoral area (two at distal and two at thigh) in four volunteers are considered for the in vivo study. The penetration depths are finally calculated with the help of the electric field distribution in simulations of the optimized model for each one of the 16 considered positions. The numerical results show that positions at the thigh contribute the highest penetration values of up to 17.5 mm. This finding has a high significance in planning in vitro penetration depth measurements and other tests that are going to be performed in the future.

Place, publisher, year, edition, pages
MDPI , 2018. Vol. 18, no 2, article id 636
Keywords [en]
Microwave measurement, ultrasound measurement, split-ring resonator, penetration depth, human lower extremity, sensor, model optimization, multilayered material, electric field distribution
National Category
Medical Equipment Engineering
Identifiers
URN: urn:nbn:se:uu:diva-352995DOI: 10.3390/s18020636ISI: 000427544000319PubMedID: 29466312OAI: oai:DiVA.org:uu-352995DiVA, id: diva2:1233188
Funder
Swedish Research Council, 2017-04644Available from: 2018-07-16 Created: 2018-07-16 Last updated: 2022-02-10Bibliographically approved
In thesis
1. Prospective Applications of Microwaves in Medicine: Microwave Sensors for Orthopedic Monitoring and Burn Depth Assessment
Open this publication in new window or tab >>Prospective Applications of Microwaves in Medicine: Microwave Sensors for Orthopedic Monitoring and Burn Depth Assessment
2019 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

In recent years, the use of microwave techniques for medical diagnostics has experienced impressive developments. It has demonstrated excellent competencies in various modalities such as using non-ionizing electromagnetic waves, providing non-invasive diagnoses, and having the ability to penetrate human tissues within the GHz range. However, due to anatomical, physiological, and biological variations in the human body, certain obstacles are present. Moreover, there are accuracy problems such as the absence of numerical models and experimental data, difficulty in conducting tests due to safety issues with human subjects, and also practical restrictions in clinical implementation. With the presence of these issues, a better understanding of the microwave technique is essential to further improve its medical application and to introduce alternative diagnostic methods that can detect and monitor various medical conditions in real time.

The first part of this thesis focuses on measurement systems for the microwave technique in terms of sensor design and development, numerical analysis, permittivity measurement, and phantom fabrication. The aim is to investigate the feasibility of flexible systems with different fields of application including a microwave sensor system for measuring the healing progression of bone defects present in lower extremity trauma, bone regeneration in craniotomy for craniosynostosis treatments, and dielectric variation for burn injuries. The microwave sensor which utilizes the contrast in dielectric constant between various tissues was used as the primary sensor for the proposed application. This involved detailed optimization of the sensor for greater sensitivity. The experimental work carried out in the lab environment showed that the microwave sensor was able to detect the contrast in dielectric properties so that it can give an indication of the healing status for actual clinical scenarios.

The second part of the thesis is making a significant step towards its practical implementation by establishing a system that can detect and monitor the rate of healing progression with fast data acquisition speed of microseconds, and developing an efficient user interface to convert raw microwave data into legible clinical information in terms of bone healing and burn injuries. As an extension to this thesis, clinical studies were conducted and ethical approval for conducting tests on human subjects was obtained for the development of a microwave medical system. The results showed a clear difference in healing progressions due to high detection capability in terms of dielectric properties of different human tissues. All of these contributions enable a portable system to complement existing medical applications with the aim of providing more advanced healthcare systems.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2019. p. 96
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 1855
Keywords
Microwave sensors, split ring resonator, biomedical application, orthopedics, lower extremity injuries, craniosynostosis, burn assessment, clinical measurements, tissue dielectric properties, phantom
National Category
Other Electrical Engineering, Electronic Engineering, Information Engineering
Research subject
Engineering Science with specialization in Microwave Technology
Identifiers
urn:nbn:se:uu:diva-393105 (URN)978-91-513-0753-4 (ISBN)
Public defence
2019-11-05, Häggsalen, Ångströmlaboratoriet, Lägerhyddsvägen 1, Uppsala, 09:15 (English)
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Supervisors
Available from: 2019-10-15 Created: 2019-09-17 Last updated: 2019-11-12

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Redzwan, SyaifulVelander, JacobPerez, Mauricio D.Asan, Noor BadariahAugustine, Robin

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