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

• Enlargement of the right atrium is of prognostic interest, but measurement is challenging.
• Using CT, higher right atrial volumes are measured, potentially due to physiological differences of examinations.
• Different volumetry methods show significantly different volumes. Follow-up needs standardization.

PurposeRight 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 methods29 retrospectively included patients (18 male, 47 ± 12 years) underwent CT and 1.5 Tesla MRI within 17 ± 20 days. 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.ResultsThere 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 ± 19 ml versus 27 ± 9 ml, (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 ±13 ml up to ±29 ml.ConclusionsCompared 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.