Background: Cardiac magnetic resonance (CMR) is the gold standard for right ventricular (RV) analysis, but special sequences and cardiac segmentation techniques with elaborated measurements are needed for assessment of RV volumes and function by CMR. Although semi- and fully automatic segmentation methods have been developed, these methods are not ubiquitously available and time-consuming manual corrections of imperfect contours are often necessary. 
Aim: This study sought to evaluate a self developed truncated cone and rhomboid pyramid model-based method with the need of only two linear measurements in 4-chamber views for calculation of RV volumes and function by CMR.

Methods: 70 consecutive patients (56±16 years) who were assigned for RV analysis by CMR were included. Image acquisition was performed on a 1.5-T magnetic resonance scanner. Cine steady-state free precession (SSFP) sequences of short axis planes as stack of contiguous slices covering full length of the RV were acquired for measurement of end-diastolic volume index (EDV) and end-systolic volume (ESV) by manually contouring endocardial borders in end-diastole and end-systole as the standard method. Ejection fraction (EF) was calculated as EDV-ESV/EDV.

For simplification of analysis a truncated cone and rhomboid pyramid formula (CPF) for calculation of volumes with geometrical assumptions of the RV based on only measurements of two distances in cine SSFP sequences of the 4-chamber views by CMR was developed (Figure 1). For calculation of RV-EDV (EDV=1.21*Dd²*Ld) and RV-ESV (ESV=1.21*Ds²*Ls) basal diameter at the level of tricuspid valve (Dd and Ds, respectively) as well as baso-apical length from mid tricuspid valve to RV apex in end-diastole and end-systole (Ld and Ls, respectively) were measured (Figure 2).
Results: By standard CMR analysis, RV-EDV index was 81.7±24.1 ml/m², RV-ESV index 44.5±23.2 ml/m² and RV-EF 48.4±13.7%. Based on the CPF method RV-EDV index (86.2±29.4 ml/m²) and RV-ESV index (51.5±22.5 ml/m²) were slightly higher and calculated RV-EF (41.1±13.5%) was lower. There was strong concordance of measurements of RV-EDV index (ΔEDV index=-4.5±19.0 ml/m²; correlation coefficient r=0.765, p<0.0001) as well as RV-ESV index (ΔESV index =-7.0±14.4 ml/m²; correlation coefficient r=0.801, p<0.0001) between both methods. Though smaller RV-EF values calculated by the CPF method, correlation of RV-EF between both methods was still high (ΔRV-EF=7.2±9.6%; correlation coefficient r=0.746, p<0.0001) (Table). 

Conclusions: Calculations of RV volumes and function by a newly developed formula based on geometric assumption of a truncated cone and rhomboid pyramid model with the need of only two linear measurements in 4-chamber views was feasible with strong concordance to measurements by standard CMR analysis.