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Prospective Applications of Microwaves in Medicine: Microwave Sensors for Orthopedic Monitoring and Burn Depth Assessment
Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics. (Microwaves in Medical Engineering Group)ORCID iD: 0000-0002-5796-9838
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 [en]
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: urn:nbn:se:uu:diva-393105ISBN: 978-91-513-0753-4 (print)OAI: oai:DiVA.org:uu-393105DiVA, id: diva2:1352082
Public defence
2019-11-05, Häggsalen, Ångströmlaboratoriet, Lägerhyddsvägen 1, Uppsala, 09:15 (English)
Opponent
Supervisors
Available from: 2019-10-15 Created: 2019-09-17 Last updated: 2019-11-12
List of papers
1. Split-Ring Resonator Sensor Penetration Depth Assessment Using In Vivo Microwave Reflectivity and Ultrasound Measurements for Lower Extremity Trauma Rehabilitation
Open this publication in new window or tab >>Split-Ring Resonator Sensor Penetration Depth Assessment Using In Vivo Microwave Reflectivity and Ultrasound Measurements for Lower Extremity Trauma Rehabilitation
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2018 (English)In: Sensors, ISSN 1424-8220, 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
Keywords
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:nbn:se:uu:diva-352995 (URN)10.3390/s18020636 (DOI)000427544000319 ()29466312 (PubMedID)
Funder
Swedish Research Council, 2017-04644
Available from: 2018-07-16 Created: 2018-07-16 Last updated: 2019-09-17Bibliographically approved
2. COMplex Fracture Orthopedic Rehabilitation (COMFORT) - Real-time visual biofeedback on weight bearing versus standard training methods in the treatment of proximal femur fractures in the elderly: study protocol for a multicenter randomized controlled trial
Open this publication in new window or tab >>COMplex Fracture Orthopedic Rehabilitation (COMFORT) - Real-time visual biofeedback on weight bearing versus standard training methods in the treatment of proximal femur fractures in the elderly: study protocol for a multicenter randomized controlled trial
2018 (English)In: Trials, ISSN 1745-6215, E-ISSN 1745-6215, Vol. 19, article id 220Article in journal (Refereed) Published
Abstract [en]

Background:

Proximal femur fractures are a common injury after low energy trauma in the elderly. Most rehabilitation programs are based on restoring mobility and early resumption of weight-bearing. However, therapy compliance is low in patients following lower extremity fractures. Moreover, little is known about the relevance of gait parameters and how to steer the rehabilitation after proximal femur fractures in the elderly. Therefore, the aim of this prospective, randomized controlled trial is to gain insight in gait parameters and evaluate if real-time visual biofeedback can improve therapy compliance after proximal femur fractures in the elderly.

Methods:

This is a two-arm, parallel-design, prospective, randomized controlled trial. Inclusion criteria are age >= 60 years, a proximal femur fracture following low energy trauma, and unrestricted-weight bearing. Exclusion criteria are cognitive impairment and limited mobility before trauma. Participants are randomized into either the control group, which receives care as usual, or the intervention group, which receives real-time visual biofeedback about weight-bearing during gait in addition to care as usual. Spatiotemporal gait parameters will be measured in 94 participants per group during a 30-m walk with an ambulatory biofeedback system (SensiStep). The progress of rehabilitation will be evaluated by the primary outcome parameters maximum peak load and step duration in relation to the discharge date. Secondary outcome parameters include other spatiotemporal gait parameters in relation to discharge date. Furthermore, the gait parameters will be related to three validated clinical tests: Elderly Mobility Scale; Functional Ambulation Categories; and Visual Analogue Scale. The primary hypothesis is that participants in the intervention group will show improved and faster rehabilitation compared to the control group.

Discussion:

The first aim of this multicenter trial is to investigate the normal gait patterns after proximal femur fractures in the elderly. The use of biofeedback systems during rehabilitation after proximal femur fractures in the elderly is promising; therefore, the second aim is to investigate the effect of real-time visual biofeedback on gait after proximal femur fractures in the elderly. This could lead to improved outcome. In addition, analysis of the population may indicate characteristics of subgroups that benefit from feedback, making a differentiated approach in rehabilitation strategy possible.

Keywords
Proximal femur fracture, Weight-bearing, Biofeedback, Gait analysis, SensiStep, Fracture rehabilitation
National Category
Orthopaedics Engineering and Technology
Identifiers
urn:nbn:se:uu:diva-353203 (URN)10.1186/s13063-018-2612-9 (DOI)000429992800001 ()29650034 (PubMedID)
Available from: 2018-06-13 Created: 2018-06-13 Last updated: 2019-09-17
3. Improved Sensor for Non-invasive Assessment of Burn Injury Depth Using Microwave Reflectometry
Open this publication in new window or tab >>Improved Sensor for Non-invasive Assessment of Burn Injury Depth Using Microwave Reflectometry
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2019 (English)In: 2019 13th European Conference on Antennas and Propagation (EuCAP), 2019Conference paper, Published paper (Refereed)
Abstract [en]

The European project “Senseburn” aims to develop a non-invasive diagnostic instrument for assessing the depth and propagation of human burns in the clinical scenario. This article introduces an improved flexible microwave split-ring resonator-based sensor, as a new development in this project. The excitation system and the fabrication process are the major improvements with respect to its precedent microwave sensor, both based in polydimethylsiloxane (PDMS) and copper. Both improvements are introduced together with the design of the sensor and of the experimental setup. Human tissue emulating phantoms are designed, fabricated, validated, and employed to emulate different burn depths and to validate the conceptual functionality of the proposed sensor. The Keysight dielectric probe 85070E is employed for the phantom validation. The analysis suggests that the sensor could estimate the burn depth. Future works will be carried out with ex vivo human tissues. 

National Category
Other Electrical Engineering, Electronic Engineering, Information Engineering
Research subject
Engineering Science with specialization in Microwave Technology
Identifiers
urn:nbn:se:uu:diva-390800 (URN)000480384702154 ()978-88-907018-8-7 (ISBN)
Conference
2019 13th European Conference on Antennas and Propagation (EuCAP), 31 March-5 April 2019, Krakow, Poland
Available from: 2019-08-14 Created: 2019-08-14 Last updated: 2019-09-25Bibliographically approved
4. Microwave-Sensor-Based Clinical Measurements for Monitoring Post-Craniotomy Bone Development in Pediatric Craniosynostosis Patients
Open this publication in new window or tab >>Microwave-Sensor-Based Clinical Measurements for Monitoring Post-Craniotomy Bone Development in Pediatric Craniosynostosis Patients
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(English)In: Article in journal (Refereed) Submitted
Abstract [en]

The bone density analysis system is a new method to analyze the amount of bone healed in cranial vault defects. Craniotomy creates such defects to treat pediatric patients with craniosynostosis. This method uses the variations in the resonance of a microwave sensor attached to the area under test in the patient. Data were collected from infants treated for craniosynostosis through craniotomy surgery in clinical trials. The data, which consist of resonance parameters (frequency, amplitude, and Q-factor) is collected using a microwave-based biomedical sensor. This sensor could detect changes in the resonance as changes in the permittivity of the various tissues at the ISM band. By observing differences between a reference and target defect points, bone healing over time could be accessed. In this paper, we analyze the validity of a proposed Computational Simulation Technology (CST) based numerical model for the sensor and extend the clinical data analysis from previous works with our bone density analysis system. The validity of the model is analyzed by comparing its outcomes to available measurements from numerical simulations, phantoms mimicking living tissues and clinical trial. In the data analysis, a hypothesis is formulated and tested regarding the healing over time. By deriving a set of parameters for each collected dataset in the clinical trials, a distinct pattern was found which shows visible changes such as edema and tissue thickening over the course of the healing process with this technique. Moreover, we manage to distinguish significant differences between the reference and defect points after the craniosynostosis surgery.

National Category
Other Electrical Engineering, Electronic Engineering, Information Engineering
Research subject
Engineering Science with specialization in Microwave Technology
Identifiers
urn:nbn:se:uu:diva-392809 (URN)
Available from: 2019-09-10 Created: 2019-09-10 Last updated: 2019-09-23
5. Analysis of Thickness Variation in Biological Tissues using Microwave Sensors for Health Monitoring Applications
Open this publication in new window or tab >>Analysis of Thickness Variation in Biological Tissues using Microwave Sensors for Health Monitoring Applications
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2019 (English)In: IEEE Access, E-ISSN 2169-3536, Vol. 7, p. 156033-156043Article in journal (Refereed) Published
Abstract [en]

Microwave sensing technique is a possible and attractive alternative modality to standard Xrays,magnetic resonance imaging, and computed tomography methods for medical diagnostic applications.This technique is beneficial since it uses non-ionizing radiation and that can be potentially used for themicrowave healthcare system. The main purpose of this paper is to present a microwave sensing techniqueto analyze the variations in biological tissue thickness, considering the effect of physiological and biologicalproperties on microwave signals. With this goal, we have developed a two-port non-invasive sensor systemcomposed of two split ring resonators (SRRs) operating at an Industrial, Scientific, and Medical frequencyband of 2.45 GHz. The system is verified using the amplitude and phase of the transmitted signal in ex-vivomodels, representing different tissue thicknesses. Clinical applications such as the diagnosis of muscularatrophy can be benefitted from this study.

National Category
Other Electrical Engineering, Electronic Engineering, Information Engineering
Research subject
Engineering Science with specialization in Microwave Technology
Identifiers
urn:nbn:se:uu:diva-392816 (URN)10.1109/ACCESS.2019.2949179 (DOI)000497165400059 ()
Funder
Vinnova, 2015-04159Swedish Research Council, 2017-04644EU, Horizon 2020, 824984Swedish Foundation for Strategic Research , RIT170020
Available from: 2019-09-10 Created: 2019-09-10 Last updated: 2019-12-06Bibliographically approved

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