Comparison of different methods to define regions of interest for evaluation of regional lung ventilation by EIT

Abstract

The measurement of regional lung ventilation by electrical impedance tomography (EIT) has been evaluated in many experimental studies. However, EIT is not routinely used in a clinical setting, which is attributable to the fact that a convenient concept for how to quantify the EIT data is missing. The definition of region of interest (ROI) is an essential point in the data analysis. To date, there are only limited data available on the different approaches to ROI definition to evaluate regional lung ventilation by EIT. For this survey we examined ten patients (mean age +/- SD: 60 +/- 10 years) under controlled ventilation. Regional tidal volumes were quantified as pixel values of inspiratory-to-expiratory impedance differences and four types of ROIs were subsequently applied. The definition of ROI contours was based on the calculation of the pixel values of (1) standard deviation from each pixel set of impedance data and (2) the regression coefficient from linear regression equations between the individual local (pixel) and average (whole scan) impedance signals. Additionally, arbitrary ROIs (four quadrants and four anteroposterior segments of equal height) were used. Our results indicate that both approaches to ROI definition using statistical parameters are suitable when impedance signals with high sensitivity to ventilation-related phenomena are to be analyzed. The definition of the ROI contour as 20-35% of the maximum standard deviation or regression coefficient is recommended. Simple segmental ROIs are less convenient because of the low ventilation-related signal component in the dorsal region.

Effect of time and body position on ventilation in premature infants

“…The EIT data were band pass filtered to eliminate interference by including the first and second harmonic of the respiratory rate (36). A cut-off mask of 20% of the peak impedance signal was applied (37). As the preterm infant often displays a periodic respiratory pattern, noise-free, regular sections of data were selected for analysis (9).…”

Regional ventilation distribution in the first 6 months of life

“…EIT data were band-pass filtered, inclusive of the first and second harmonics of the respiratory rate [12,17,18], and a cutoff mask at 20% of the peak impedance signal applied [19]. EIT images were generated using the average end-expiratory to end-inspiratory impedance differences for each individual pixel time-course array to describe the magnitude of the regional tidal volume change among individuals.…”

Assessment of Changes in Distribution of Lung Perfusion by Electrical Impedance Tomography

“…5). Using this method, ventilated lung areas can be accurately identified [35]. As lung perfusion is restricted to areas of the scans where lung tissue is present, these lung ROIs were the first step in the definition of the ROIs to be used in the assessment of lung perfusion.…”

“…In the present study, it was used to identify two types of ROIs. The first ROI, which delineated the ventilated lung regions during bilateral ventilation, was defined as those regions within the scan where positive slopes of the filtered EIT signal (breathing rate band) exceeded 20% of the maximum slope, as previously recommended [35]. The second ROI marked the outline of the cardiac ventricular regions and was defined as those regions within the scan where negative slopes of the filtered EIT signal (heart rate band) were found.…”