Fig 1.
Acquisition and processing procedure.
I) Volume CTs were recorded for each pig and the contours of thorax, lungs and heart were extracted by radiologists. II) Finite element models were created using no prior information (M1), averaged contours (M2) or individual contours of each animal (M3). These models and optimized reconstruction settings were utilized to calculate the reconstruction matrix of EIT. III) Experimental measurement of 4DCT and EIT as well as reconstruction of EIT image series Z1-3(t) and (IV) extraction of tidal volume images and their ventilation profiles.
Fig 2.
Reconstructed EIT images showing tidal impedance changes (red = high, blue = low) using different settings for GREIT and Gauss Newton. Noise figure controls smoothing of the images, time difference (TD) and normalized time difference (NTD) are voltage reference methods, and weighted reconstruction–in contrast to uniform reconstruction–considers that lungs are less conductive than the surrounding tissue. Images are zeroed at a threshold of 10% to reduce artifacts.
Table 1.
Reconstruction settings.
Fig 3.
Tidal volume images and anteroposterior ventilation distribution for (a-c) EIT from M1-M3, (e) EIT with averaged reconstruction model M2 and lung mask, (f) EIT with individual reconstruction model M3 and lung mask, and (d) the reference 4DCT. Note that relative values for ΔHU are lower due to the higher spatial resolution.
Table 2.
Correlation of different reconstruction settings.
Fig 4.
Boxplots for RMSE values over all pigs (n = 8). The circular model (vd1) showed high variation and high error, whereas RMSE decreased with the addition of anatomical information in vd2, vd2+ and vd3. RMSE was significantly lower after adding further individual anatomical information in vd 3+ (p < 0.03).
Fig 5.
Regional ventilation in 4DCT and EIT.
Comparison of regional ventilation acquired from 4DCT and EIT. a) Calculations based on the circular model M1 without anatomical information and (b) on M3 with individual boundaries and lung mask. For both, pooled Pearson correlation, Bland-Altman and distribution of differences are shown. Different symbols correspond to values from different animals (n = 8), whereby only values of vd greater than zero in at least one of the two compared methods are considered. Since the differences of both methods are not normally distributed, bias and limits of agreement are represented as median and 95% quantile interval, respectively.
Table 3.
Individual root mean square errors.