How to measure the right ventricular outflow tract with cardiovascular magnetic resonance imaging: a head-to-head comparison of methods.

INTRODUCTION Structural abnormalities of the right ventricular outflow tract (RVOT) have been described in several clinical conditions. The aim of our study was to prospectively compare the available approaches to measuring the RVOT area and diameter by cardiovascular magnetic resonance imaging (CMR) and establish reference values in healthy volunteers. In addition, we sought to introduce a new algorithm for dedicated RVOT area evaluation determined by the RVOT axis. METHODS In 50 healthy volunteers CMR was performed to measure the RVOT area: 1) on axial images using turbo spin echo imaging (axial TSE), 2) on steady state free precession (axial SSFP), 3) on short axis slices using SSFP (SAX SSFP), and 4) on a plane determined by the RVOT axis using SSFP (RVOT axis SSFP). Additionally, the RVOT diameter was measured on SSFP SAX images. RESULTS RVOT measurements on axial TSE (8.4 ± 1.4 cm(2)) and on RVOT axis SSFP images were comparable (8.4 ± 0.1 cm(2), p=0.99). The axial SSFP (10.2 ± 1.5 cm(2)) and SAX SSFP (11.0 ± 1.9 cm(2)) images resulted in significantly larger RVOT areas than on the axial TSE images (p<0.0001) and on the RVOT axis SSFP images (p<0.0001). The RVOT diameter measured was 22.4 ± 0.3 mm. RVOT assessment on the axial SSFP and RVOT axis SSFP images revealed the best intra- and interobserver reliability. CONCLUSION RVOT area measurements differ significantly in healthy volunteers, depending on the imaging plane and technique. In view of the excellent intra- and interobserver reliability and the precise image plane positioning, we recommend the new RVOT axis approach for dedicated RVOT measurements.