Assessment of right atrium volume by conventional CT or MR techniques: Which modality resembles in vivo reality?

Purpose: Right atrial volume (RAV) is a prognostic factor of the right heart function. This retrospective study evaluates the comparability of computed tomography (CT) and magnetic resonance imaging (MRI) for right atrial volumetry with conventional planimetric and diametric methods.
Material and Methods: 29 retrospectively included patients (18 male, 47±12years) underwent CT and 1.5 Tesla MRI within 17±20days. RAV was measured using biplane and ellipsoid method (MRI and CT) and Simpson's method (CT). For interobserver comparison measurements were carried out by two observers. Pearson's correlation, Lin's concordance coefficient, and Bland-Altman statistics were calculated.
Results: There is a correlation of RAV between CT and MRI, r [ellipsoid]=0.65; r [biplane]=0.64 (p<0.001). MRI volumes were significantly lower than CT volumes, [mean±SD] 43±19ml versus 27±9ml, (p<0.002). There was a close interobserver correlation (CT: r=0.83, MRI: r=0.73; p<0.001) but a relatively wide range in Bland-Altman analysis; limits of agreement from ±13ml up to ±29ml.
Conclusions: Compared to left atrial volumes, a higher variability was found for RAV values both in interobserver statistiscs and in intermodality comparison. Complex shape of the right atrium, artifacts due to contrast material (CT), high venous return in inspiration (CT), high flow contrast media administration (CT) and increased heart rate (MRI) might cause these clinically relevant variations.
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