SCMR 22nd Annual Scientific Sessions
Background: Serial imaging is recommended in patients with ascending aortic aneurysms (1). Operative repair is recommended when the aortic dimensions exceed 5.5 cm or the growth rate is greater than 0.5 cm/year (1). Reliable identification of pathological changes requires precise and reproducible measurements of the aortic root and ascending aorta. However, the aortic root and ascending aorta are pulsatile structures and may be affected by cardiac motion. Thus, we hypothesized that implementing ECG-gating into MRA acquisitions would improve vessel sharpness and increase the reproducibility of aortic root and ascending aorta measurements.
Methods: Both ECG-gated and non-gated MRA datasets were acquired in random order in 50 patients during the administration of gadolinium contrast. From the resulting 3D datasets, 2D images were generated at the sinus of Valsalva (SOV), ascending aorta (AAO) at the level of the pulmonary artery bifurcation, and the descending aorta (DAO) at the level of the diaphragm. Two experienced readers, blinded to acquisition type, independently measured vessel diameter, area, and perimeter at these three aortic locations. Each reader made the measurements twice, on two different occasions approximately 6-months apart. Bland-Altman analyses were used to determine inter- and intra-observer reproducibility for the quantification of vessel dimensions at each aortic location (SOV, AAO and DAO) using both ECG-gated and non-gated MRA datasets.
Results: Representative images demonstrating the differences in image quality at the SOV, AAO, and DAO in 2 patients are shown in Figure 1. The use of ECG gating visibly improved vessel sharpness, particularly at the SOV and AAO locations. Table 1 summarizes the quantitative findings of this study, which demonstrate that ECG-gated MRA resulted in improved inter-and intra-observer reproducibility compared to non-ECG gated measurements at the SOV and AAO. Importantly, given that surgical repair is recommended in patients with an aortic aneurysm growth rate greater than 0.5 cm/year, it is noteworthy that the 95% limits of agreement for the non-ECG-gated method were larger than this cutoff (e.g. -0.65 cm, 0.56 for the AAO). However, the 95% limits of agreement were similar with both MRA techniques for measurements of the DAO.
Conclusion: ECG-gated MRA resulted in improved reproducibility for aortic root and ascending aortic measurements. This data suggests that ECG-gating should be performed for the serial assessment of the ascending thoracic aorta.