Evaluation of Different Contrast Agents for Regional Lung Perfusion Measurement Using Electrical Impedance Tomography: An Experimental Pilot Study

Muders, Thomas; Hentze, Benjamin; Leonhardt, Steffen; Putensen, Christian

doi:10.3390/jcm12082751

“…We chose not to employ a fixed proportion for anatomic dead space, as previous authors did [ 11 , 39 ], since most of the strength of EIT-based V′/Q lies in its trending ability [ 36 ], while central compression of EIT reconstructions [ 52 ] and positional bias [ 32 ] devoid of interest the comparison with reference ranges for shunt and dead space fractions. Finally, we do not normally observe major hemodynamic derangements during the 20 s breath hold required for measuring lung perfusion at EIT, but cardiac output measurements could not be simultaneous due to technical reasons (thermodilution bolus is known to affect impedance [ 53 ]) and hence we cannot exclude an influence.…”

Section: Discussionmentioning

confidence: 99%

Absolute values of regional ventilation-perfusion mismatch in patients with ARDS monitored by electrical impedance tomography and the role of dead space and shunt compensation

Leali,

Marongiu,

Spinelli

et al. 2024

Crit Care

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Background Assessment of regional ventilation/perfusion (V′/Q) mismatch using electrical impedance tomography (EIT) represents a promising advancement for personalized management of the acute respiratory distress syndrome (ARDS). However, accuracy is still hindered by the need for invasive monitoring to calibrate ventilation and perfusion. Here, we propose a non-invasive correction that uses only EIT data and characterized patients with more pronounced compensation of V′/Q mismatch. Methods We enrolled twenty-one ARDS patients on controlled mechanical ventilation. Cardiac output was measured invasively, and ventilation and perfusion were assessed by EIT. Relative V′/Q maps by EIT were calibrated to absolute values using the minute ventilation to invasive cardiac output (MV/CO) ratio (V′/Q-ABS), left unadjusted (V′/Q-REL), or corrected by MV/CO ratio derived from EIT data (V′/Q-CORR). The ratio between ventilation to dependent regions and perfusion reaching shunted units ($${\text{V}}_{{\text{D}}}^{\prime }$$ V D ′ /QSHUNT) was calculated as an index of more effective hypoxic pulmonary vasoconstriction. The ratio between perfusion to non-dependent regions and ventilation to dead space units (QND/$${\text{V}}_{{{\text{DS}}}}^{\prime }$$ V DS ′ ) was calculated as an index of hypocapnic pneumoconstriction. Results Our calibration factor correlated with invasive MV/CO (r = 0.65, p < 0.001), showed good accuracy and no apparent bias. Compared to V′/Q-ABS, V′/Q-REL maps overestimated ventilation (p = 0.013) and perfusion (p = 0.002) to low V′/Q units and underestimated ventilation (p = 0.011) and perfusion (p = 0.008) to high V′/Q units. The heterogeneity of ventilation and perfusion reaching different V′/Q compartments was underestimated. V′/Q-CORR maps eliminated all these differences with V′/Q-ABS (p > 0.05). Higher $$V_{D}^{\prime } /Q_{SHUNT}$$ V D ′ / Q SHUNT correlated with higher PaO2/FiO2 (r = 0.49, p = 0.025) and lower shunt fraction (ρ = − 0.59, p = 0.005). Higher $$Q_{ND} /V_{DS}^{\prime }$$ Q ND / V DS ′ correlated with lower PEEP (ρ = − 0.62, p = 0.003) and plateau pressure (ρ = − 0.59, p = 0.005). Lower values of both indexes were associated with less ventilator-free days (p = 0.05 and p = 0.03, respectively). Conclusions Regional V′/Q maps calibrated with a non-invasive EIT-only method closely approximate the ones obtained with invasive monitoring. Higher efficiency of shunt compensation improves oxygenation while compensation of dead space is less needed at lower airway pressure. Patients with more effective compensation mechanisms could have better outcomes.

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“…Bear in mind that some CE modalities might, however, be most frequently non-uniformly sampled. This approximation is particularly pertinent for DCE-CT and DCE-EIT as a linear signal-to-concentration conversion is typically applied (O'Connor et al 2011, Muders et al 2023). All the previously detailed effects are showcased in figure 3.…”

Section: Tracer-to Modality-specific Effectsmentioning

confidence: 99%

The gamma-variate in contrast-enhanced imaging: a unified view and method from computed to electrical impedance tomography

Silva,

Leonhardt

2024

Phys. Med. Biol.

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Objective: Modern medical imaging plays a vital role in clinical practice, enabling non-invasive visualization of anatomical structures. Dynamic contrast enhancement (DCE) imaging is a technique that uses contrast agents to visualize blood flow dynamics in a time-resolved manner. It can be applied to different modalities, such as computed tomography (CT) and electrical impedance tomography (EIT). This study aims to develop a common theoretical and practical hemodynamic extraction basis for DCE modelling across modalities, based on the gamma-variate function.Approach: The study introduces a framework to generate time-intensity curves for multiple DCE imaging modalities from user-defined hemodynamic parameters. Thus, extensive datasets were simulated for both DCE-CT and EIT, representing different hemodynamic scenarios. Additionally, gamma-variate extensions to account for several physiological effects were detailed in a modality-agnostic manner, and three corresponding fitting strategies, namely nonlinear, linear, and a novel hybrid approach, were implemented and compared on the basis of accuracy of parameter estimation, first pass reconstruction, speed of computation, and failure rate.Main results: As a result, we found the linear method to be the most modality-dependent, exhibiting the greatest bias, variance and failure rates, although remaining the fastest alternative. The hybrid method at least matches the state-of-the-art nonlinear method's accuracy, while improving its robustness and speed by 10 times. Significance: Our research suggests that the hybrid method may bring noteworthy accuracy and efficiency improvements in handling the high-dimensionality of DCE imaging in general, being a step towards real-time processing. Moreover, our generative model presents a potential asset to produce benchmarking and data augmentation datasets across modalities.

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“…The resulting regional dilution curves are analyzed in individual image pixels to provide regional measures of blood flow. Typically, hypertonic saline solution has been used for contrast-enhanced EIT measurements but new agents are also being investigated [48 ▪ ].…”

Section: How Can Electrical Impedance Tomography Help In Setting Posi...mentioning

confidence: 99%

Setting positive end-expiratory pressure by using electrical impedance tomography

Frerichs,

Schädler,

Becher

2023

Current Opinion in Critical Care

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Purpose of review This review presents the principles and possibilities of setting positive end-expiratory pressure (PEEP) using electrical impedance tomography (EIT). It summarizes the major findings of recent studies where EIT was applied to monitor the effects of PEEP on regional lung function and to guide the selection of individualized PEEP setting. Recent findings The most frequent approach of utilizing EIT for the assessment of PEEP effects and the PEEP setting during the time period from January 2022 till June 2023 was based on the analysis of pixel tidal impedance variation, typically acquired during stepwise incremental and/or decremental PEEP variation. The most common EIT parameters were the fraction of ventilation in various regions of interest, global inhomogeneity index, center of ventilation, silent spaces, and regional compliance of the respiratory system. The studies focused mainly on the spatial and less on the temporal distribution of ventilation. Contrast-enhanced EIT was applied in a few studies for the estimation of ventilation/perfusion matching. Summary The availability of commercial EIT devices resulted in an increase in clinical studies using this bedside imaging technology in neonatal, pediatric and adult critically ill patients. The clinical interest in EIT became evident but the potential of this method in clinical decision-making still needs to be fully exploited.

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Evaluation of Different Contrast Agents for Regional Lung Perfusion Measurement Using Electrical Impedance Tomography: An Experimental Pilot Study

Cited by 7 publications

References 38 publications

Absolute values of regional ventilation-perfusion mismatch in patients with ARDS monitored by electrical impedance tomography and the role of dead space and shunt compensation

Absolute values of regional ventilation-perfusion mismatch in patients with ARDS monitored by electrical impedance tomography and the role of dead space and shunt compensation

The gamma-variate in contrast-enhanced imaging: a unified view and method from computed to electrical impedance tomography

Setting positive end-expiratory pressure by using electrical impedance tomography

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