Bartłomiej Grychtol

GREIT: A unified approach to 2D linear EIT reconstruction of lung images

Electrical impedance tomography (EIT) is an attractive method for clinically monitoring patients during mechanical ventilation, because it can provide a non-invasive continuous image of pulmonary impedance which indicates the distribution of ventilation. However, most clinical and physiological research in lung EIT is done using older and proprietary algorithms; this is an obstacle to interpretation of EIT images because the reconstructed images are not well characterized. To address this issue, we develop a consensus linear reconstruction algorithm for lung EIT, called GREIT (Graz consensus Reconstruction algorithm for EIT). This paper describes the unified approach to linear image reconstruction developed for GREIT. The framework for the linear reconstruction algorithm consists of (1) detailed finite element models of a representative adult and neonatal thorax, (2) consensus on the performance figures of merit for EIT image reconstruction and (3) a systematic approach to optimize a linear reconstruction matrix to desired performance measures. Consensus figures of merit, in order of importance, are (a) uniform amplitude response, (b) small and uniform position error, (c) small ringing artefacts, (d) uniform resolution, (e) limited shape deformation and (f) high resolution. Such figures of merit must be attained while maintaining small noise amplification and small sensitivity to electrode and boundary movement. This approach represents the consensus of a large and representative group of experts in EIT algorithm design and clinical applications for pulmonary monitoring. All software and data to implement and test the algorithm have been made available under an open source license which allows free research and commercial use.

Chest electrical impedance tomography examination, data analysis, terminology, clinical use and recommendations: consensus statement of the TRanslational EIT developmeNt stuDy group

Electrical impedance tomography (EIT) has undergone 30 years of development. Functional chest examinations with this technology are considered clinically relevant, especially for monitoring regional lung ventilation in mechanically ventilated patients and for regional pulmonary function testing in patients with chronic lung diseases. As EIT becomes an established medical technology, it requires consensus examination, nomenclature, data analysis and interpretation schemes. Such consensus is needed to compare, understand and reproduce study findings from and among different research groups, to enable large clinical trials and, ultimately, routine clinical use. Recommendations of how EIT findings can be applied to generate diagnoses and impact clinical decision-making and therapy planning are required. This consensus paper was prepared by an international working group, collaborating on the clinical promotion of EIT called TRanslational EIT developmeNt stuDy group. It addresses the stated needs by providing (1) a new classification of core processes involved in chest EIT examinations and data analysis, (2) focus on clinical applications with structured reviews and outlooks (separately for adult and neonatal/paediatric patients), (3) a structured framework to categorise and understand the relationships among analysis approaches and their clinical roles, (4) consensus, unified terminology with clinical user-friendly definitions and explanations, (5) a review of all major work in thoracic EIT and (6) recommendations for future development (193 pages of online supplements systematically linked with the chief sections of the main document). We expect this information to be useful for clinicians and researchers working with EIT, as well as for industry producers of this technology.

Regional lung volume changes in children with acute respiratory distress syndrome during a derecruitment maneuver.

Objective:Regional differences in lung volume have been described in adults with acute respiratory distress syndrome, but it remains unclear to what extent they occur in children. To quantify regional alveolar collapse that occurred during mechanical ventilation during a standardized suctioning maneuver, we evaluated regional and global relative impedance changes (relative &Dgr;Z) in children with acute respiratory distress syndrome using electrical impedance tomography. Design:Prospective observational trial. Setting:A 30-bed pediatric intensive care unit. Patients:Six children with acute respiratory distress syndrome. Interventions:Standardized suctioning maneuver. Measurements and Main Results:By comparing layers from nondependent (layers 1 and 2) to dependent lung areas (layers 3 and 4), it was demonstrated that the middle layers (2 and 3) had the greatest ventilation-induced change in relative &Dgr;Z; layer 4 showed the least ventilation-induced change in relative &Dgr;Z. During suctioning, layers 1, 2, and 3 showed a negative change in relative &Dgr;Z, whereas layer 4 showed no significant change in relative &Dgr;Z. The derecruitment-induced change in relative &Dgr;Z representing the lung-volume loss was −9.8 (−3.0 mL/kg) during the first suctioning maneuver, −16.1 (−5.4 mL/kg) during the second, and −21.7 (−7.4 mL/kg) during the third. The ventilation-induced change in relative &Dgr;Z during mechanical ventilation remained unchanged after suctioning (mean change in relative &Dgr;Z before vs. after suctioning, 40.1 ± 9.1 vs. 41.4 ± 10.8; p = .30). Dynamic compliance was 11.8 ± 6.1 mL·cm H2O−1 before and 11.8 ± 6.9 mL·cm H2O−1 after the suctioning sequence (p = .90). Conclusions:Considerable regional heterogeneity was present during ventilation and a derecruitment maneuver. Significantly lower change in relative &Dgr;Z in the most dependent lung regions suggests alveolar collapse during ventilation before suctioning.

Impact of Model Shape Mismatch on Reconstruction Quality in Electrical Impedance Tomography

Electrical impedance tomography (EIT) is a low-cost, noninvasive and radiation free medical imaging modality for monitoring ventilation distribution in the lung. Although such information could be invaluable in preventing ventilator-induced lung injury in mechanically ventilated patients, clinical application of EIT is hindered by difficulties in interpreting the resulting images. One source of this difficulty is the frequent use of simple shapes which do not correspond to the anatomy to reconstruct EIT images. The mismatch between the true body shape and the one used for reconstruction is known to introduce errors, which to date have not been properly characterized. In the present study we, therefore, seek to 1) characterize and quantify the errors resulting from a reconstruction shape mismatch for a number of popular EIT reconstruction algorithms and 2) develop recommendations on the tolerated amount of mismatch for each algorithm. Using real and simulated data, we analyze the performance of four EIT reconstruction algorithms under different degrees of shape mismatch. Results suggest that while slight shape mismatch is well tolerated by all algorithms, using a circular shape severely degrades their performance.

Toward Morphological Thoracic EIT: Major Signal Sources Correspond to Respective Organ Locations in CT

Lung and cardiovascular monitoring applications of electrical impedance tomography (EIT) require localization of relevant functional structures or organs of interest within the reconstructed images. We describe an algorithm for automatic detection of heart and lung regions in a time series of EIT images. Using EIT reconstruction based on anatomical models, candidate regions are identified in the frequency domain and image-based classification techniques applied. The algorithm was validated on a set of simultaneously recorded EIT and CT data in pigs. In all cases, identified regions in EIT images corresponded to those manually segmented in the matched CT image. Results demonstrate the ability of EIT technology to reconstruct relevant impedance changes at their anatomical locations, provided that information about the thoracic boundary shape (and electrode positions) are used for reconstruction.

Differences in regional pulmonary pressure-impedance curves before and after lung injury assessed with a novel algorithm.

Global pressure-volume (PV) curves are an adjunct measure to describe lung characteristics in patients with acute respiratory distress syndrome (ARDS). There is convincing evidence that high peak inspiratory pressures (PIP) cause barotrauma, while optimized positive end-expiratory pressure (PEEP) helps avoid mechanical injury to the lungs by preventing repeated alveolar opening and closing. The optimal values of PIP and PEEP are deduced from the shape of the PV curve by the identification of so-called lower and upper inflection points. However, it has been demonstrated using electrical impedance tomography (EIT) that the inflection points vary across the lung. This study employs a simple curve-fitting technique to automatically define inflection points on both pressure-volume (PV) and pressure-impedance (PI) curves to asses the differences between global PV and regional PI estimates in animals before and after induced lung injury. The results demonstrate a clear increase in lower inflection point (LIP) along the gravitational axis both before and after lung injury. Moreover, it is clear from comparison of the local EIT-derived LIPs with those derived from global PV curves that a ventilation strategy based on the PV curve alone may leave dependent areas of the lung collapsed. EIT-based PI curve analysis may help choosing an optimal ventilation strategy.

Human Behavior Integration Improves Classification Rates in Real-Time BCI

Brain-computer interfaces (BCI) offer potential for individuals with a variety of motor and sensory disabilities to interact with their environment, communicate and control mobility aids. Two key factors which affect the performance of a BCI and its usability are the feedback given to the participant and the subjects motivation. This paper presents the results from a study investigating the effects of feedback and motivation on the performance of the Strathclyde Brain Computer Interface. The paper discusses how the performance of the system can be improved by behavior integration and human-in-the-loop design.

Regional lung volume changes during high-frequency oscillatory ventilation.

Objective: To investigate regional lung volume changes occurring during an inflation–deflation maneuver using high-frequency oscillatory ventilation. Design: Prospective animal trial. Setting: Animal research laboratory. Subjects: Six Yorkshire swine. Interventions: Electrical impedance tomography was used to quantify regional ventilation during high-frequency oscillatory ventilation. The electrical impedance tomography-derived center of ventilation was used to describe the distribution of regional ventilation, whereas spectral analysis was used to describe regional ventilation-induced impedance changes. Lung injury was induced using surfactant lavage. Animals were transitioned to high-frequency oscillatory ventilation and a slow inflation–deflation maneuver was performed by changing mean airway pressure by 5 cm H2O every 15 mins to a maximum mean airway pressure of 40 cm H2O. Measurements and Main Results: The induction of lung injury was associated with a significant shift of the center of ventilation toward nondependent areas and an increase in shunt fraction (p < .001). During the following inflation–deflation maneuver using high-frequency oscillatory ventilation, inflation was associated with a shift of the center of ventilation from nondependent to dependent areas. Center of ventilation was significantly correlated with the shunt fraction (p < .001). Analyzing different lung layers along the gravitational axis separately, nondependent lung areas showed significantly decreased regional ventilation-induced impedance changes at higher pressures, suggesting overdistension, whereas dependent lung areas showed increased impedance changes, suggesting recruitment. The reverse was observed during deflation (all p < .05). Conclusions: The center of ventilation during high-frequency oscillatory ventilation correlated with oxygenating efficiency as measured by the shunt fraction. Lung recruitment during high-frequency oscillatory ventilation produced a significant shift of regional ventilation toward dependent areas of the lung and led to overdistension of nondependent areas.

An individualized approach to sustained inflation duration at birth improves outcomes in newborn preterm lambs

A sustained first inflation (SI) at birth may aid lung liquid clearance and aeration, but the impact of SI duration relative to the volume-response of the lung is poorly understood. We compared three SI strategies: 1) variable duration defined by attaining volume equilibrium using real-time electrical impedance tomography (EIT; SIplat); 2) 30 s beyond equilibrium (SIlong); 3) short 30-s SI (SI30); and 4) positive pressure ventilation without SI (no-SI) on spatiotemporal aeration and ventilation (EIT), gas exchange, lung mechanics, and regional early markers of injury in preterm lambs. Fifty-nine fetal-instrumented lambs were ventilated for 60 min after applying the allocated first inflation strategy. At study completion molecular and histological markers of lung injury were analyzed. The time to SI volume equilibrium, and resultant volume, were highly variable; mean (SD) 55 (34) s, coefficient of variability 59%. SIplat and SIlong resulted in better lung mechanics, gas exchange and lower ventilator settings than both no-SI and SI30. At 60 min, alveolar-arterial difference in oxygen was a mean (95% confidence interval) 130 (13, 249) higher in SI30 vs. SIlong group (two-way ANOVA). These differences were due to better spatiotemporal aeration and tidal ventilation, although all groups showed redistribution of aeration towards the nondependent lung by 60 min. Histological lung injury scores mirrored spatiotemporal change in aeration and were greatest in SI30 group (P < 0.01, Kruskal-Wallis test). An individualized volume-response approach to SI was effective in optimizing aeration, homogeneous tidal ventilation, and respiratory outcomes, while an inadequate SI duration had no benefit over positive pressure ventilation alone.

The strathclyde brain computer interface

Brain-computer interfaces (BCI) offer potential for individuals with a variety of motor and sensory disabilities to control their environment, communicate, and control mobility aids. However, the key to BCI usability rests in being able to extract relevant time varying signals that can be classified into usable commands in real time. This paper reports the first success of the Strathclyde BCI controlling a wheelchair on-line in Virtual Reality. Surface EEG recorded during wrist movement in two different directions were classified and used to control a wheelchair within a virtual reality environment. While Principal Component Analysis was used for feature vector quantiser distances were used for classification. Classification success rates between 68% and 77% were obtained using these relatively simple methods.