Optimising the accuracy and reproducibility of aortic root measurements from cardiac MRI data

Abstract

Methods An observational study of 20 consecutive children, (age 11, +/5.5 years) undergoing MRI for aortic root and arch assessment. None had undergone intervention. Imaging used standard true FISP cine sequences and an isotropic, respiratory-navigated, ECG-gated, 3D multi-slab SSFP sequence (allowing reformatting in any 3D-plane). A single, experienced observer measured the maximum diameter from cine images of the LV outflow tract (diastolic phase) and the 3D dataset (diastolic phase), at three aortic root levels and at the diaphragmatic aorta, twice, with one week between measurements. 3D data measurements used true cross-sectional planning, and included planimetered area. Aortic sinus diameter was measured from commissure-to-opposing-cusp (Figure 1). The difference between 2D cine and 3D diameters, and intra-observer variability were compared using Bland-Altman variability analysis Results Though measured in the same phase of the cardiac cycle, 2D cine diameters were smaller than 3D true-cross-sectional diameters (3.6-8.9%). There was no systematic variation with aortic size (Figure 2). The average intraobserver variability at sinus level for 3D data was 1% for diameter, and 5% for area. The variability for 2D cine measurements was 10%. In this best case scenario of repeated measurements, for paediatric aortic roots approximately 30 mm in diameter, a change in aortic sinus diameter would have to exceed 3 mm on 3D data and 6 mm on 2D cine data to be sure the change did not result from measurement variability (Table 1) from 13th Annual SCMR Scientific Sessions Phoenix, AZ, USA. 21-24 January 2010