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Article ; Online: A novel two-dimensional phantom for electrical impedance tomography using 3D printing.

Creegan, Andrew / Nielsen, Poul M F / Tawhai, Merryn H

2024 Volume 14, Issue 1, Page(s) 2115

Abstract: Electrical impedance tomography (EIT) is an imaging method that can be used to image electrical impedance contrasts within various tissues of the body. To support development of EIT measurement systems, a phantom is required that represents the ... ...

Abstract	Electrical impedance tomography (EIT) is an imaging method that can be used to image electrical impedance contrasts within various tissues of the body. To support development of EIT measurement systems, a phantom is required that represents the electrical characteristics of the imaging domain. No existing type of EIT phantom combines good performance in all three characteristics of resistivity resolution, spatial resolution, and stability. Here, a novel EIT phantom concept is proposed that uses 3D printed conductive material. Resistivity is controlled using the 3D printing infill percentage parameter, allowing arbitrary resistivity contrasts within the domain to be manufactured automatically. The concept of controlling resistivity through infill percentage is validated, and the manufacturing accuracy is quantified. A method for making electrical connections to the 3D printed material is developed. Finally, a prototype phantom is printed, and a sample EIT analysis is performed. The resulting phantom, printed with an Ultimaker S3, has high reported spatial resolution of 6.9 µm, 6.9 µm, and 2.5 µm for X, Y, and Z axis directions, respectively (X and Y being the horizontal axes, and Z the vertical). The number of resistivity levels that are manufacturable by varying infill percentage is 15 (calculated by dividing the available range of resistivities by two times the standard deviation of the manufacturing accuracy). This phantom construction technique will allow assessment of the performance of EIT devices under realistic physiological scenarios.
Language	English
Publishing date	2024-01-24
Publishing country	England
Document type	Journal Article
ZDB-ID	2615211-3
ISSN	2045-2322 ; 2045-2322
ISSN (online)	2045-2322
ISSN	2045-2322
DOI	10.1038/s41598-024-52696-y
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Article ; Online: A Wearable Open-Source electrical impedance tomography device.

Creegan, Andrew / Bradfield, Joshua / Richardson, Samuel / Sims Johns, Llewellyn / Burrowes, Kelly / Kumar, Haribalan / Nielsen, Poul M F / Tawhai, Merryn H

HardwareX

2024 Volume 18, Page(s) e00521

Abstract: Electrical impedance tomography (EIT) is medical imaging technique in which small electrical signals are used to map the electrical impedance distribution within the body. It is safe and non-invasive, which make it attractive for use in continuous ... ...

Abstract	Electrical impedance tomography (EIT) is medical imaging technique in which small electrical signals are used to map the electrical impedance distribution within the body. It is safe and non-invasive, which make it attractive for use in continuous monitoring or outpatient applications, but the high cost of commercial devices is an impediment to its adoption. Over the last 10 years, many research groups have developed their own EIT devices, but few designs for open-source EIT hardware are available. In this work, we present a complete open-source EIT system that is designed to be suitable for monitoring the lungs of free breathing subjects. The device is low-cost, wearable, and is designed to comply with the industry accepted safety standard for EIT. The device has been tested in two regimes: Firstly in terms of measurement uncertainty as a voltage measurement system, and secondly against a set of measures that have been proposed specifically for EIT hardware. The voltage measurement uncertainty of the device was measured to be - 0.7 % ± 0.36 mV. The EIT specific performance was measured in a phantom test designed to be as physiologically representative as practicable, and the device performed similarly to other published devices. This work will contribute to increased accessibility of EIT for study and will contribute to consensus on testing methodology for EIT devices.
Language	English
Publishing date	2024-03-20
Publishing country	England
Document type	Journal Article
ISSN	2468-0672
ISSN (online)	2468-0672
DOI	10.1016/j.ohx.2024.e00521
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Article ; Online: Improved Electrical Impedance Tomography Reconstruction via a Bayesian Approach With an Anatomical Statistical Shape Model.

Page, Mitchell I / Nicholson, Ruanui / Tawhai, Merryn H / Clark, Alys R / Kumar, Haribalan

IEEE transactions on bio-medical engineering

2023 Volume 70, Issue 8, Page(s) 2486–2495

Abstract: Objective: electrical impedance tomography (EIT) is a promising technique for rapid and continuous bedside monitoring of lung function. Accurate and reliable EIT reconstruction of ventilation requires patient-specific shape information. However, this ... ...

Abstract	Objective: electrical impedance tomography (EIT) is a promising technique for rapid and continuous bedside monitoring of lung function. Accurate and reliable EIT reconstruction of ventilation requires patient-specific shape information. However, this shape information is often not available and current EIT reconstruction methods typically have limited spatial fidelity. This study sought to develop a statistical shape model (SSM) of the torso and lungs and evaluate whether patient-specific predictions of torso and lung shape could enhance EIT reconstructions in a Bayesian framework. Methods: torso and lung finite element surface meshes were fitted to computed tomography data from 81 participants, and a SSM was generated using principal component analysis and regression analyses. Predicted shapes were implemented in a Bayesian EIT framework and were quantitatively compared to generic reconstruction methods. Results: Five principal shape modes explained 38% of the cohort variance in lung and torso geometry, and regression analysis yielded nine total anthropometrics and pulmonary function metrics that significantly predicted these shape modes. Incorporation of SSM-derived structural information enhanced the accuracy and reliability of the EIT reconstruction as compared to generic reconstructions, demonstrated by reduced relative error, total variation, and Mahalanobis distance. Conclusion: As compared to deterministic approaches, Bayesian EIT afforded more reliable quantitative and visual interpretation of the reconstructed ventilation distribution. However, no conclusive improvement of reconstruction performance using patient specific structural information was observed as compared to the mean shape of the SSM. Significance: The presented Bayesian framework builds towards a more accurate and reliable method for ventilation monitoring via EIT.
MeSH term(s)	Humans ; Tomography/methods ; Bayes Theorem ; Electric Impedance ; Reproducibility of Results ; Tomography, X-Ray Computed
Language	English
Publishing date	2023-07-18
Publishing country	United States
Document type	Journal Article ; Research Support, Non-U.S. Gov't
ZDB-ID	160429-6
ISSN	1558-2531 ; 0018-9294
ISSN (online)	1558-2531
ISSN	0018-9294
DOI	10.1109/TBME.2023.3250650
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Article ; Online: Integrative Computational Models of Lung Structure-Function Interactions.

Clark, Alys R / Burrowes, Kelly S / Tawhai, Merryn H

Comprehensive Physiology

2021 Volume 11, Issue 1, Page(s) 1501–1530

Abstract: Anatomically based integrative models of the lung and their interaction with other key components of the respiratory system provide unique capabilities for investigating both normal and abnormal lung function. There is substantial regional variability in ...

Abstract	Anatomically based integrative models of the lung and their interaction with other key components of the respiratory system provide unique capabilities for investigating both normal and abnormal lung function. There is substantial regional variability in both structure and function within the normal lung, yet it remains capable of relatively efficient gas exchange by providing close matching of air delivery (ventilation) and blood delivery (perfusion) to regions of gas exchange tissue from the scale of the whole organ to the smallest continuous gas exchange units. This is despite remarkably different mechanisms of air and blood delivery, different fluid properties, and unique scale-dependent anatomical structures through which the blood and air are transported. This inherent heterogeneity can be exacerbated in the presence of disease or when the body is under stress. Current computational power and data availability allow for the construction of sophisticated data-driven integrative models that can mimic respiratory system structure, function, and response to intervention. Computational models do not have the same technical and ethical issues that can limit experimental studies and biomedical imaging, and if they are solidly grounded in physiology and physics they facilitate investigation of the underlying interaction between mechanisms that determine respiratory function and dysfunction, and to estimate otherwise difficult-to-access measures. © 2021 American Physiological Society. Compr Physiol 11:1501-1530, 2021.
MeSH term(s)	Computer Simulation ; Humans ; Lung ; Pulmonary Gas Exchange ; Respiration
Language	English
Publishing date	2021-02-12
Publishing country	United States
Document type	Journal Article ; Research Support, Non-U.S. Gov't
ISSN	2040-4603
ISSN (online)	2040-4603
DOI	10.1002/cphy.c200011
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Article ; Online: Sustained vs. Intratidal Recruitment in the Injured Lung During Airway Pressure Release Ventilation: A Computational Modeling Perspective.

Cruz, Andrea F / Herrmann, Jacob / Ramcharran, Harry / Kollisch-Singule, Michaela / Tawhai, Merryn H / Bates, Jason H T / Nieman, Gary F / Kaczka, David W

Military medicine

2023 Volume 188, Issue Suppl 6, Page(s) 141–148

Abstract: Introduction: During mechanical ventilation, cyclic recruitment and derecruitment (R/D) of alveoli result in focal points of heterogeneous stress throughout the lung. In the acutely injured lung, the rates at which alveoli can be recruited or ... ...

Abstract	Introduction: During mechanical ventilation, cyclic recruitment and derecruitment (R/D) of alveoli result in focal points of heterogeneous stress throughout the lung. In the acutely injured lung, the rates at which alveoli can be recruited or derecruited may also be altered, requiring longer times at higher pressure levels to be recruited during inspiration, but shorter times at lower pressure levels to minimize collapse during exhalation. In this study, we used a computational model to simulate the effects of airway pressure release ventilation (APRV) on acinar recruitment, with varying inspiratory pressure levels and durations of exhalation. Materials and methods: The computational model consisted of a ventilator pressure source, a distensible breathing circuit, an endotracheal tube, and a porcine lung consisting of recruited and derecruited zones, as well as a transitional zone capable of intratidal R/D. Lung injury was simulated by modifying each acinus with an inflation-dependent surface tension. APRV was simulated for an inhalation duration (Thigh) of 4.0 seconds, inspiratory pressures (Phigh) of 28 and 40 cmH2O, and exhalation durations (Tlow) ranging from 0.2 to 1.5 seconds. Results: Both sustained acinar recruitment and intratidal R/D within the subtree were consistently higher for Phigh of 40 cmH2O vs. 28 cmH2O, regardless of Tlow. Increasing Tlow was associated with decreasing sustained acinar recruitment, but increasing intratidal R/D, within the subtree. Increasing Tlow was associated with decreasing elastance of both the total respiratory system and transitional subtree of the model. Conclusions: Our computational model demonstrates the confounding effects of cyclic R/D, sustained recruitment, and parenchymal strain stiffening on estimates of total lung elastance during APRV. Increasing inspiratory pressures leads to not only more sustained recruitment of unstable acini but also more intratidal R/D. Our model indicates that higher inspiratory pressures should be used in conjunction with shorter exhalation times, to avoid increasing intratidal R/D.
MeSH term(s)	Animals ; Swine ; Continuous Positive Airway Pressure ; Lung ; Respiration, Artificial/adverse effects ; Lung Compliance ; Computer Simulation
Language	English
Publishing date	2023-11-01
Publishing country	England
Document type	Journal Article ; Research Support, U.S. Gov't, Non-P.H.S.
ZDB-ID	391061-1
ISSN	1930-613X ; 0026-4075
ISSN (online)	1930-613X
ISSN	0026-4075
DOI	10.1093/milmed/usad059
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Article ; Online: Ventilation/Perfusion Matching: Of Myths, Mice, and Men.

Clark, Alys R / Burrowes, Kelly S / Tawhai, Merryn H

Physiology (Bethesda, Md.)

2019 Volume 34, Issue 6, Page(s) 419–429

Abstract: Despite a huge range in lung size between species, there is little measured difference in the ability of the lung to provide a well-matched air flow (ventilation) to blood flow (perfusion) at the gas exchange tissue. Here, we consider the remarkable ... ...

Abstract	Despite a huge range in lung size between species, there is little measured difference in the ability of the lung to provide a well-matched air flow (ventilation) to blood flow (perfusion) at the gas exchange tissue. Here, we consider the remarkable similarities in ventilation/perfusion matching between species through a biophysical lens and consider evidence that matching in large animals is dominated by gravity but in small animals by structure.
MeSH term(s)	Animals ; Gravitation ; Humans ; Lung/physiology ; Mice ; Physiological Phenomena/physiology ; Regional Blood Flow/physiology ; Respiration
Language	English
Publishing date	2019-11-04
Publishing country	United States
Document type	Journal Article ; Research Support, N.I.H., Extramural ; Research Support, Non-U.S. Gov't ; Review
ZDB-ID	2158667-6
ISSN	1548-9221 ; 1548-9213
ISSN (online)	1548-9221
ISSN	1548-9213
DOI	10.1152/physiol.00016.2019
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Article ; Online: Strain, strain rate, and mechanical power: An optimization comparison for oscillatory ventilation.

Herrmann, Jacob / Tawhai, Merryn H / Kaczka, David W

International journal for numerical methods in biomedical engineering

2019 Volume 35, Issue 10, Page(s) e3238

Abstract: The purpose of this study was to assess the potential for optimization of mechanical ventilator waveforms using multiple frequencies of oscillatory flow delivered simultaneously to minimize the risk of ventilator-induced lung injury (VILI) associated ... ...

Abstract	The purpose of this study was to assess the potential for optimization of mechanical ventilator waveforms using multiple frequencies of oscillatory flow delivered simultaneously to minimize the risk of ventilator-induced lung injury (VILI) associated with regional strain, strain rate, and mechanical power. Optimization was performed using simulations of distributed oscillatory flow and gas transport in a computational model of anatomically derived branching airway segments and viscoelastic terminal acini under healthy and injured conditions. Objective functions defined by regional strain or strain rate were minimized by single-frequency ventilation waveforms using the highest or lowest frequencies available, respectively. However, a mechanical power objective function was minimized by a combination of multiple frequencies delivered simultaneously. This simulation study thus demonstrates the potential for multifrequency oscillatory ventilation to reduce regional mechanical power in comparison to single-frequency ventilation, and thereby reduce the risk of VILI.
MeSH term(s)	Computer Simulation ; Humans ; Lung/physiology ; Respiration, Artificial/adverse effects ; Respiratory Mechanics ; Tidal Volume/physiology ; Ventilator-Induced Lung Injury/prevention & control
Language	English
Publishing date	2019-08-06
Publishing country	England
Document type	Journal Article ; Research Support, N.I.H., Extramural ; Research Support, Non-U.S. Gov't ; Research Support, U.S. Gov't, Non-P.H.S.
ZDB-ID	2540968-2
ISSN	2040-7947 ; 2040-7939
ISSN (online)	2040-7947
ISSN	2040-7939
DOI	10.1002/cnm.3238
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Article ; Online: Computational Modeling of Primary Blast Lung Injury: Implications for Ventilator Management.

Herrmann, Jacob / Tawhai, Merryn H / Kaczka, David W

Military medicine

2019 Volume 184, Issue Suppl 1, Page(s) 273–281

Abstract: Primary blast lung injury (PBLI) caused by exposure to high-intensity pressure waves is associated with parenchymal tissue injury and severe ventilation-perfusion mismatch. Although supportive ventilation is often required in patients with PBLI, ... ...

Abstract	Primary blast lung injury (PBLI) caused by exposure to high-intensity pressure waves is associated with parenchymal tissue injury and severe ventilation-perfusion mismatch. Although supportive ventilation is often required in patients with PBLI, maldistribution of gas flow in mechanically heterogeneous lungs may lead to further injury due to increased parenchymal strain and strain rate, which are difficult to predict in vivo. In this study, we developed a computational lung model with mechanical properties consistent with healthy and PBLI conditions. PBLI conditions were simulated with bilateral derecruitment and increased perihilar tissue stiffness. As a result of these tissue abnormalities, airway flow was heterogeneously distributed in the model under PBLI conditions, during both conventional mechanical ventilation (CMV) and high-frequency oscillatory ventilation. PBLI conditions resulted in over three-fold higher parenchymal strains compared to the healthy condition during CMV, with flow distributed according to regional tissue stiffness. During high-frequency oscillatory ventilation, flow distribution became increasingly heterogeneous and frequency-dependent. We conclude that the distribution and rate of parenchymal distension during mechanical ventilation depend on PBLI severity as well as ventilatory modality. These simulations may allow realistic assessment of the risks associated with ventilator-induced lung injury following PBLI, and facilitate the development of alternative lung-protective ventilation modalities.
MeSH term(s)	Acute Lung Injury/physiopathology ; Acute Lung Injury/therapy ; Blast Injuries/physiopathology ; Blast Injuries/therapy ; Computer Simulation ; Explosions ; Humans ; Lung/physiology ; Lung/physiopathology ; Pressure/adverse effects ; Respiration, Artificial/methods ; Respiration, Artificial/trends
Language	English
Publishing date	2019-03-21
Publishing country	England
Document type	Journal Article ; Research Support, N.I.H., Extramural ; Research Support, Non-U.S. Gov't ; Research Support, U.S. Gov't, Non-P.H.S.
ZDB-ID	391061-1
ISSN	1930-613X ; 0026-4075
ISSN (online)	1930-613X
ISSN	0026-4075
DOI	10.1093/milmed/usy305
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Article ; Online: Non-invasive over-distension measurements: data driven vs model-based.

Sun, Qianhui / Chase, J Geoffrey / Zhou, Cong / Tawhai, Merryn H / Knopp, Jennifer L / Möller, Knut / Shaw, Geoffrey M

Journal of clinical monitoring and computing

2022 Volume 37, Issue 2, Page(s) 389–398

Abstract: Clinical measurements offer bedside monitoring aiming to minimise unintended over-distension, but have limitations and cannot be predicted for changes in mechanical ventilation (MV) settings and are only available in certain MV modes. This study ... ...

Abstract	Clinical measurements offer bedside monitoring aiming to minimise unintended over-distension, but have limitations and cannot be predicted for changes in mechanical ventilation (MV) settings and are only available in certain MV modes. This study introduces a non-invasive, real-time over-distension measurement, which is robust, predictable, and more intuitive than current methods. The proposed over-distension measurement, denoted as OD, is compared with the clinically proven stress index (SI). Correlation is analysed via R
MeSH term(s)	Humans ; Positive-Pressure Respiration/methods ; Respiration, Artificial/methods ; Lung ; Respiratory Distress Syndrome/therapy ; Ventilators, Mechanical ; Respiratory Mechanics
Language	English
Publishing date	2022-08-03
Publishing country	Netherlands
Document type	Journal Article ; Research Support, Non-U.S. Gov't
ZDB-ID	1418733-4
ISSN	1573-2614 ; 1387-1307 ; 0748-1977
ISSN (online)	1573-2614
ISSN	1387-1307 ; 0748-1977
DOI	10.1007/s10877-022-00900-7
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Zs.A 2054: Show issues

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Article ; Online: Simulating Multi-Scale Pulmonary Vascular Function by Coupling Computational Fluid Dynamics With an Anatomic Network Model.

Ebrahimi, Behdad Shaarbaf / Kumar, Haribalan / Tawhai, Merryn H / Burrowes, Kelly S / Hoffman, Eric A / Clark, Alys R

Frontiers in network physiology

2022 Volume 2, Page(s) 867551

Abstract: The function of the pulmonary circulation is truly multi-scale, with blood transported through vessels from centimeter to micron scale. There are scale-dependent mechanisms that govern the flow in the pulmonary vascular system. However, very few ... ...

Abstract	The function of the pulmonary circulation is truly multi-scale, with blood transported through vessels from centimeter to micron scale. There are scale-dependent mechanisms that govern the flow in the pulmonary vascular system. However, very few computational models of pulmonary hemodynamics capture the physics of pulmonary perfusion across the spatial scales of functional importance in the lung. Here we present a multi-scale model that incorporates the 3-dimensional (3D) complexities of pulmonary blood flow in the major vessels, coupled to an anatomically-based vascular network model incorporating the multiple contributing factors to capillary perfusion, including gravity. Using the model we demonstrate how we can predict the impact of vascular remodeling and occlusion on both macro-scale functional drivers (flow distribution between lungs, and wall shear stress) and micro-scale contributors to gas exchange. The model predicts interactions between 3D and 1D models that lead to a redistribution of blood between postures, both on a macro- and a micro-scale. This allows us to estimate the effect of posture on left and right pulmonary artery wall shear stress, with predictions varying by 0.75-1.35 dyne/cm
Language	English
Publishing date	2022-04-25
Publishing country	Switzerland
Document type	Journal Article
ISSN	2674-0109
ISSN (online)	2674-0109
DOI	10.3389/fnetp.2022.867551
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