| 1. |
- Bayford, Richard H., et al.
(author)
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Locating Functionalized Gold Nanoparticles Using Electrical Impedance Tomography
- 2022
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In: IEEE Transactions on Biomedical Engineering. - : IEEE. - 0018-9294 .- 1558-2531. ; 69:1, s. 494-502
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Journal article (peer-reviewed)abstract
- Objective: An imaging device to locate functionalised nanoparticles, whereby therapeutic agents are transported from the site of administration specifically to diseased tissues, remains a challenge for pharmaceutical research. Here, we show a new method based on electrical impedance tomography (EIT) to provide images of the location of gold nanoparticles (GNPs) and the excitation of GNPs with radio frequencies (RF) to change impedance permitting an estimation of their location in cell models Methods: We have created an imaging system using quantum cluster GNPs as contrast agent, activated with RF fields to heat the functionalized GNPs, which causes a change in impedance in the surrounding region. This change is then identified with EIT. Results: Images of impedance changes of around 80 ± 4% are obtained for a sample of citrate stabilized GNPs in a solution of phosphate-buffered saline. A second quantification was carried out using colorectal cancer cells incubated with culture media, and the internalization of GNPs into the colorectal cancer cells was undertaken to compare them with the EIT images. When the cells were incubated with functionalised GNPs, the change was more apparent, approximately 40 ± 2%. This change was reflected in the EIT image as the cell area was more clearly identifiable from the rest of the area. Significance: EIT can be used as a new method to locate functionalized GNPs in human cells and help in the development of GNP-based drugs in humans to improve their efficacy in the future.
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| 2. |
- Becher, Tobias H., et al.
(author)
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Prolonged Continuous Monitoring of Regional Lung Function in Infants with Respiratory Failure
- 2022
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In: Annals of the American Thoracic Society. - : American Thoracic Society. - 2329-6933 .- 2325-6621. ; 19:6, s. 991-999
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Journal article (peer-reviewed)abstract
- Rationale: Electrical impedance tomography (EIT) allows instantaneous and continuous visualization of regional ventilation and changes in end-expiratory lung volume at the bedside. There is particular interest in using EIT for monitoring in critically ill neonates and young children with respiratory failure. Previous studies have focused only on short-term monitoring in small populations. The feasibility and safety of prolonged monitoring with EIT in neonates and young children have not been demonstrated yet.Objectives: To evaluate the feasibility and safety of long-term EIT monitoring in a routine clinical setting and to describe changes in ventilation distribution and homogeneity over time and with positioning in a multicenter cohort of neonates and young children with respiratory failure.Methods: At four European University hospitals, we conducted an observational study (NCT02962505) on 200 patients with postmenstrual ages (PMA) between 25 weeks and 36 months, at risk for or suffering from respiratory failure. Continuous EIT data were obtained using a novel textile 32-electrode interface and recorded at 48 images/s for up to 72 hours. Clinicians were blinded to EIT images during the recording. EIT parameters and the effects of body position on ventilation distribution were analyzed offline. Results: The average duration of FAT measurements was 53 +/- 20 hours. Skin contact impedance was sufficient to allow image reconstruction for valid ventilation analysis during a median of 92% (interquartile range, 77-98%) of examination time. EIT examinations were well tolerated, with minor skin irritations (temporary redness or imprint) occurring in 10% of patients and no moderate or severe adverse events. Higher ventilation amplitude was found in the dorsal and right lung areas when compared with the ventral and left regions, respectively. Prone positioning resulted in an increase in the ventilation-related EIT signal in the dorsal hemithorax, indicating increased ventilation of the dorsal lung areas. Lateral positioning led to a redistribution of ventilation toward the dependent lung in preterm infants and to the nondependent lung in patients with PMA > 37 weeks.Conclusions: EIT allows continuous long-term monitoring of regional lung function in neonates and young children for up to 72 hours with minimal adverse effects. Our study confirmed the presence of posture-dependent changes in ventilation distribution and their dependency on PMA in a large patient cohort.
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| 3. |
- Dalarsson, Mariana, et al.
(author)
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Absorption and optimal plasmonic resonances for small ellipsoidal particles in lossy media
- 2017
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In: Journal of Physics D. - : Institute of Physics (IOP). - 0022-3727 .- 1361-6463. ; 50:34
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Journal article (peer-reviewed)abstract
- A new simplified formula is derived for the absorption cross section of small dielectric ellipsoidal particles embedded in lossy media. The new expression leads directly to a closed form solution for the optimal conjugate match with respect to the surrounding medium, i.e. the optimal permittivity of the ellipsoidal particle that maximizes the absorption at any given frequency. This defines the optimal plasmonic resonance for the ellipsoid. The optimal conjugate match represents a metamaterial in the sense that the corresponding optimal permittivity function may have negative real part (inductive properties), and can not in general be implemented as a passive material over a given bandwidth. A necessary and sufficient condition is derived for the feasibility of tuning the Drude model to the optimal conjugate match at a single frequency, and it is found that all the prolate spheroids and some of the (not too flat) oblate spheroids can be tuned into optimal plasmonic resonance at any desired center frequency. Numerical examples are given to illustrate the analysis. Except for the general understanding of plasmonic resonances in lossy media, it is also anticipated that the new results can be useful for feasibility studies with e.g. the radiotherapeutic hyperthermia based methods to treat cancer based on electrophoretic heating in gold nanoparticle suspensions using microwave radiation.
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| 4. |
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| 5. |
- Dalarsson, Mariana, et al.
(author)
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TE-wave propagation in a graded waveguide structure
- 2018
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In: 2018 12th International Congress on Artificial Materials for Novel Wave Phenomena (Metamaterials). - : IEEE. - 9781538647028 - 9781538647035 - 9781538647011 ; , s. 93-95
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Conference paper (peer-reviewed)abstract
- We investigate TE-wave propagation in a hollow waveguide with a graded dielectric barrier, using an equivalent model of the waveguide filled with a stratified medium. General formulae for the electric field components of the TE-waves, applicable to hollow waveguides with arbitrary cross sectional shapes, are presented. As an illustration, we obtain the exact analytical results for the electric field components in a rectangular waveguide, as well as the exact analytical results for reflection and transmission coefficients which are valid for waveguides of arbitrary cross sectional shapes.
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| 6. |
- Dalarsson, Mariana, et al.
(author)
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TE-wave propagation in graded waveguide structures
- 2020
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In: OSA Continuum. - : Optical Society of America. - 2578-7519. ; 3:1, s. 67-76
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Journal article (peer-reviewed)abstract
- We investigate TE-wave propagation in a hollow waveguide with a graded dielectric layer, described using a hyperbolic tangent function. General formulae for the electric field components of the TE-waves, applicable to hollow waveguides with arbitrary cross sectional shapes, are presented. We illustrate the exact analytical results for the electric field components in the special case of a rectangular waveguide. Furthermore, we derive exact analytical results for the reflection and transmission coefficients valid for waveguides of arbitrary cross sectional shapes. Finally, we show that the obtained reflection and transmission coefficients are in exact asymptotic agreement with those obtained for a very thin homogeneous dielectric layer using mode-matching and cascading. The proposed method gives analytical results that are directly applicable without the need of mode-matching, and it has the ability to model realistic, smooth transitions. (C) 2020 Optical Society of America under the terms of the OSA Open Access Publishing Agreement
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| 7. |
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| 8. |
- Dalarsson, Mariana, et al.
(author)
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TM-wave propagation in a graded waveguide structure
- 2019
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In: 2019 URSI International Symposium on Electromagnetic Theory (EMTS). - : IEEE. ; , s. 1-4
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Conference paper (peer-reviewed)abstract
- We investigate TM-wave propagation in a hollow waveguide with a graded dielectric layer, described using a hyperbolic tangent function. General formulae for the electric field components of the TM-waves, applicable to hollow waveguides with arbitrary cross sectional shapes, are presented. We derive the analytical results for the reflection and transmission coefficients valid for waveguides of arbitrary cross sectional shapes. Thereby, we show that the obtained reflection and transmission coefficients are in exact asymptotic agreement with those obtained for a very thin homogeneous dielectric layer using mode-matching and cascading. The proposed method is tractable since it gives analytical results that are directly applicable without the need of mode-matching, and it has the ability to model realistic, smooth transitions.
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| 9. |
- Dalarsson, Mariana, et al.
(author)
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Wave propagation in waveguides with graded plasmonic obstacles
- 2021
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In: Journal of the Optical Society of America. B, Optical physics. - : OPTICAL SOC AMER. - 0740-3224 .- 1520-8540. ; 38:1, s. 104-113
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Journal article (peer-reviewed)abstract
- In this paper, wave propagation in a hollow waveguide with a graded dielectric layer is studied. Analytic formulas are derived for the electric field components as well as general analytical results for the reflection and transmission coefficients for propagating waves. These results are all valid for waveguides of arbitrary cross sections, and the derived reflection and transmission coefficients are in exact asymptotic agreement with those obtained for a wry thin homogeneous dielectric layer using cascading and mode-matching techniques. Furthermore, the power transmission, reflection, and absorption coefficients, as functions of frequency and layer width, are studied, showing the expected behavior of these parameters. The method proposed in this paper gives directly applicable results that do not require cascading and mode matching, while at the same time having the ability to model smooth transitions that are more realistic in several applications. (C) 2020 Optical Society of America
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| 10. |
- de Gelidi, S., et al.
(author)
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Torso shape detection to improve lung monitoring
- 2018
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In: Physiological Measurement. - : Institute of Physics Publishing (IOPP). - 0967-3334 .- 1361-6579. ; 39:7
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Journal article (peer-reviewed)abstract
- Objective: Newborns with lung immaturity often require continuous monitoring and treatment of their lung ventilation in intensive care units, especially if born preterm. Recent studies indicate that electrical impedance tomography (EIT) is feasible in newborn infants and children, and can quantitatively identify changes in regional lung aeration and ventilation following alterations to respiratory conditions. Information on the patient-specific shape of the torso and its role in minimizing the artefacts in the reconstructed images can improve the accuracy of the clinical parameters obtained from EIT. Currently, only idealized models or those segmented from CT scans are usually adopted. Approach: This study presents and compares two methodologies that can detect the patient-specific torso shape by means of wearable devices based on (1) previously reported bend sensor technology, and (2) a novel approach based on the use of accelerometers. Main results: The reconstruction of different phantoms, taking into account anatomical asymmetries and different sizes, are produced for comparison. Significance: As a result, the accelerometers are more versatile than bend sensors, which cannot be used on bigger cross-sections. The computational study estimates the optimal number of accelerometers required in order to generate an image reconstruction comparable to the use of a CT scan as the forward model. Furthermore, since the patient position is crucial to monitoring lung ventilation, the orientation of the phantoms is automatically detected by the accelerometer-based method.
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