Analysis of the nonaerated lung volume in combinations of single computed tomography slices – is extrapolation to the entire lung feasible?
© BioMed Central Ltd. 2007
Published: 22 March 2007
The nonaerated lung volume (Vnon) can be quantified from computed tomography (CT) images. Analysis of the CT slices covering the entire lung is time-consuming and thus limits potential clinical and experimental applications. This could be improved by analyzing only a few representative CT slices. The number and anatomical location of CT images required for analyses that are representative for the entire lung, however, is discussed controversially.
The percentage of Vnon (%Vnon) relative to the total lung volume was quantified in CT-image series (n = 21) of sheep with gross anesthesia-induced atelectasis. This was performed for different combinations of number and anatomical location of CT slices and the results were compared with the %Vnon of the entire lung (lung). The combinations were: one juxtadiaphragmatic slice (juxta), three apical, hiliar and juxtadiaphragmatic slices (3 old), and three consecutive juxtadiaphragmatic slices (3 new). The correlation between %Vnon and the arterial oxygen partial pressure (PaO2) was examined for all combinations. The PaO2 was measured at the time of the CT and transformed logarithmically (lnPaO2) to linearize the relation between PaO2 and %Vnon. Linear regression and Bland–Altman plots were used for statistical analysis.
The R-squared (R2) values for the correlation between lnPaO2 and %Vnon of lung and the slice combinations juxta, 3 new and 3 old were 0.61, 0.60, 0.57 and 0.55, respectively. The %Vnon of lung correlated best with the %Vnon of slice combinations juxta and 3 new (R2 = 0.96 and 0.95, respectively). Comparison of these slice combinations with lung also resulted in the least bias in the Bland–Altman analyses (6.3 and 5.9%, respectively). R2 for the correlation between lung and 3 old was 0.93, and the bias for lung vs 3 old in the Bland–Altman analysis was 6.8%.
Depending on the precision required, the use of single juxtadiaphragmatic CT slices can help to speed up the analysis process and thereby propel the clinical implementation of CT-derived information. Our data suggest that juxtadiaphragmatic slices may be better suited than the 'traditional' combination of apical, hiliar and juxtadiaphragmatic slices.