Abstract
PURPOSE: The stack-of-short-axis volumes (SAX) summation and single-plane area-length (AL) methods are established approaches for right atrial (RA) volume quantification in cardiovascular magnetic resonance (CMR) imaging. However, data regarding the reliability and agreement between these methods are limited. Furthermore, there is no validation on whether to include the right atrial appendage (RAA) in the analysis. This study aims to evaluate the reliability of the single-plane AL and SAX methods for measuring RA volumes and to assess the agreement between these two approaches. METHODS: CMR (3.0T, Siemens) data from 40 healthy volunteers were analyzed to quantify RA volumes, both including and excluding RAA volume, using the SAX and single-plane (4-chamber view) AL methods. RESULTS: The mean age of 40 participants was 33.6 ± 6.1 years (50% male). RA volumes measured by the SAX method were significantly larger than those obtained by the single-plane AL method (maximum RA volume including RAA: 84.9 ± 22.9 vs. 63.7 ± 16.0 ml, p-value < 0.001; minimum RA volume including RAA: 45.3 ± 15.9 vs. 34.7 ± 12.2 ml, p-value < 0.001). RA ejection fraction (RAEF) was the only parameter that showed no statistical difference between the two methods. Bland-Altman plots demonstrated poor agreement between the techniques, with substantial biases and wide limits of agreement. Both methods exhibited excellent reproducibility when the RAA volume was included (ICC = 0.89-0.96). However, reproducibility was reduced when the RAA volume was excluded, particularly in terms of inter-observer agreement (ICC = 0.73-0.96). CONCLUSIONS: The single-plane AL method underestimates RA volumes compared to the SAX method, and the poor agreement between the two techniques suggests they should not be used interchangeably. RA volume measurements should be interpreted using method-specific reference values. Additionally, including the RAA in RA volume quantification-regardless of the method-may improve measurement reproducibility.