A comparative analysis of ECG-gated steady state free precession magnetic resonance imaging versus transthoracic echocardiography for evaluation of aortic root dimensions

Accurate and reproducible measurement of aortic root dimensions is essential to inform clinical decision making. Transthoracic echocardiography (TTE) is the first line test for assessment of the aortic root but has potential limitations due to its limited field of view and restricted acoustic windows. Cardiac magnetic resonance imaging (MRI) is considered the "gold standard" technique for assessment of cardiac morphology and recently MRI reference ranges for aortic root dimensions have been published. The purpose of this study was to retrospectively compare aortic root measurements obtained from TTE with those derived from cardiac MRI.Sixty-eight patients (40 males, 28 females) who had undergone both cardiac MRI and TTE imaging within a 4-month interval (mean 62 days) were included. Steady-state-free precession MRI cine imaging was performed with an acquisition plane perpendicular to the aortic root and through the true cross sectional aortic valve plane. A cusp-commissure dimension from inside wall to inside wall in end-diastole was recorded and compared with standardized TTE derived Valsalva sinus measurements. Pearson correlation coefficients and a paired t-test were used for statistical analysis.Mean aortic root dimension by TTE was 3.2±0.5 cm and MRI was 3.4±0.4 cm with a Pearson correlation coefficient of >0.7. Mean difference between TTE and MRI was 0.2±0.3 (P<0.001) with MRI producing a consistently higher measure. In four patients with a dilated aortic root by MRI the TTE measurement was within the normal reference range. In patients with a dilated aortic root (n=19) the mean difference was 0.2±0.4 cm (P<0.05) with MRI consistently producing the larger measure. In patients with a non-dilated aortic root t (n=49) the mean difference was 0.2±0.3 cm (P<0.05) with MRI consistently producing the larger measure.There is a high level of correlation between TTE and MRI derived aortic root measurements at the Valsalva sinus level. MRI consistently measures the aortic root dimension higher than TTE which may under diagnose patients with a mildly dilated aortic root. Further investigation is required to properly integrate MRI into imaging assessment algorithms.