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  • 1
    Abstract: INTRODUCTION: Electrical impedance tomography (EIT) is an emerging clinical tool for monitoring ventilation distribution in mechanically ventilated patients, for which many image reconstruction algorithms have been suggested. We propose an experimental framework to assess such algorithms with respect to their ability to correctly represent well-defined physiological changes. We defined a set of clinically relevant ventilation conditions and induced them experimentally in 8 pigs by controlling three ventilator settings (tidal volume, positive end-expiratory pressure and the fraction of inspired oxygen). In this way, large and discrete shifts in global and regional lung air content were elicited. METHODS: We use the framework to compare twelve 2D EIT reconstruction algorithms, including backprojection (the original and still most frequently used algorithm), GREIT (a more recent consensus algorithm for lung imaging), truncated singular value decomposition (TSVD), several variants of the one-step Gauss-Newton approach and two iterative algorithms. We consider the effects of using a 3D finite element model, assuming non-uniform background conductivity, noise modeling, reconstructing for electrode movement, total variation (TV) reconstruction, robust error norms, smoothing priors, and using difference vs. normalized difference data. RESULTS AND CONCLUSIONS: Our results indicate that, while variation in appearance of images reconstructed from the same data is not negligible, clinically relevant parameters do not vary considerably among the advanced algorithms. Among the analysed algorithms, several advanced algorithms perform well, while some others are significantly worse. Given its vintage and ad-hoc formulation backprojection works surprisingly well, supporting the validity of previous studies in lung EIT.
    Type of Publication: Journal article published
    PubMed ID: 25110887
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  • 2
    Abstract: Validation studies of electrical impedance tomography (EIT) based assessment of regional ventilation under pathological conditions are required to prove that EIT can reliably quantify heterogeneous ventilation distribution with sufficient accuracy. The objective of our study was to validate EIT measurements of regional ventilation through a comparison with xenon-multidetector-row computed tomography (XeCT) in an animal model of sub-lobar lung injury. Nine anesthetized mechanically ventilated supine pigs were examined before and after the induction of lung injury in two adjacent sub-lobar segments of the right lung by saline lavage or endotoxin instillation. Regional ventilation was determined in 32 anteroposterior regions of interest in the right and left lungs and the ventilation change quantified by difference images between injury and control. Six animals were included in the final analysis. Measurements of regional ventilation by EIT and XeCT correlated well before (rs = 0.89 right, rs = 0.90 left lung) and after local injury (rs = 0.79 and 0.92, respectively). No bias and narrow limits of agreement were found during both conditions. The ventilation decrease in the right injured lung was correspondingly measured by both modalities (5.5%+/-1.1% by EIT and 5.4%+/-1.9% by XeCT, p = 0.94). EIT was inferior to clearly separate the exact anatomical location of the regional injuries. Regional ventilation was overestimated (〈2%) in the most ventral and dorsal regions and underestimated (2%) in the middle regions by EIT compared to XeCT. This study shows that EIT is able to reliably discern even small ventilation changes on sub-lobar level.
    Type of Publication: Journal article published
    PubMed ID: 24021927
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  • 3
    Abstract: Purpose: To compare unenhanced lung ventilation-weighted (VW) and perfusion-weighted (QW) imaging based on Fourier decomposition (FD) magnetic resonance (MR) imaging with the clinical reference standard single photon emission computed tomography (SPECT)/computed tomography (CT) in an animal experiment. Materials and Methods: The study was approved by the local animal care committee. Lung ventilation and perfusion was assessed in seven anesthetized pigs by using a 1.5-T MR imager and SPECT/CT. For time-resolved FD MR imaging, sets of lung images were acquired by using an untriggered two-dimensional balanced steady-state free precession sequence (repetition time, 1.9 msec; echo time, 0.8 msec; acquisition time per image, 118 msec; acquisition rate, 3.33 images per second; flip angle, 75 degrees; section thickness, 12 mm; matrix, 128 x 128). Breathing displacement was corrected with nonrigid image registration. Parenchymal signal intensity was analyzed pixelwise with FD to separate periodic changes of proton density induced by respiration and periodic changes of blood flow. Spectral lines representing respiratory and cardiac frequencies were integrated to calculate VW and QW images. Ventilation and perfusion SPECT was performed after inhalation of dispersed technetium 99m ((99m)Tc) and injection of (99m)Tc-labeled macroaggregated albumin. FD MR imaging and SPECT data were independently analyzed by two physicians in consensus. A regional statistical analysis of homogeneity and pathologic signal changes was performed. Results: Images acquired in healthy animals by using FD MR imaging and SPECT showed a homogeneous distribution of VW and QW imaging and pulmonary ventilation and perfusion, respectively. The gravitation-dependent signal distribution of ventilation and perfusion in all animals was similarly observed at FD MR imaging and SPECT. Incidental ventilation and perfusion defects were identically visualized by using both modalities. Conclusion: This animal experiment demonstrated qualitative agreement in the assessment of regional lung ventilation and perfusion between contrast media-free and radiation-free FD MR imaging and conventional SPECT/CT.
    Type of Publication: Journal article published
    PubMed ID: 21586678
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  • 4
  • 5
    ISSN: 1432-1238
    Keywords: Key words Lung injury ; Oleic acid ; Regional ventilation ; Electrical impedance ; Pig
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract Objective: To apply electrical impedance tomography (EIT) and the new evaluation approach (the functional EIT) in monitoring the development of artificial lung injury. Design: Acute experimental trial. Setting: Operating room for animal experimental studies at a university hospital. Subjects: Five pigs (41.3 ± 4.1 kg, mean body weight ± SD). Interventions: The animals were anaesthetised and mechanically ventilated. Sixteen electrodes were attached on the thoracic circumference and used for electrical current injection and surface voltage measurement. Oleic acid was applied sequentially (total dose 0.05 ml/kg body weight) into the left pulmonary artery to produce selective unilateral lung injury. Measurements and results: The presence of lung injury was documented by significant changes of PaCO2 (40.1 mmHg vs control 37.1 mmHg), PaO2 (112.3 mmHg vs 187.5 mmHg), pH (7.35 vs 7.42), mean pulmonary arterial pressure (29.2 mmHg vs 20.8 mmHg) and chest radiography. EIT detected 1) a regional decrease in mean impedance variation over the affected left lung (–41.4 % vs control) and an increase over the intact right lung ( + 20.4 % vs control) indicating reduced ventilation of the affected, and a compensatory augmented ventilation of the unaffected lung and 2) a pronounced fall in local baseline electrical impedance over the injured lung (–20.6 % vs control) with a moderate fall over the intact lung (–10.0 % vs control) indicating the development of lung oedema in the injured lung with a probable atelectasis formation in the contralateral one. Conclusion: The development of the local impairment of pulmonary ventilation and the formation of lung oedema could be followed by EIT in an experimental model of lung injury. This technique may become a useful tool for monitoring local pulmonary ventilation in intensive care patients suffering from pulmonary disorders associated with regionally reduced ventilation, fluid accumulation and/or cell membrane changes.
    Type of Medium: Electronic Resource
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