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Objective:
Contrast-enhanced 3D MRA (CE-MRA) is commonly used to evaluate the aorta and is considered the reference standard for imaging vessels in congenital heart disease (CHD). However, recent studies have shown noncontrast MRA (NC-MRA) to be as effective as CE-MRA. NC-MRA has many advantages over CE-MRA, including the avoidance of gadolinium-based contrast agents and IV placement. There is limited data on the patient characteristics that predict if NC-MRA can replace CE-MRA. This information can be used to determine the optimal patients for NC-MRA and lead to better utilization of resources. We aim to determine the patient population in which NC-MRA has replaced CE-MRA in current clinical practice.

Materials and Methods:
Patients with CHD who underwent an outpatient MRA chest without sedation or general anesthesia for aorta-related indications (bicuspid aortic valve, coarctation, connective tissue disease, Marfan syndrome, and Turner syndrome) from January 1, 2018 to December 31, 2022 were included. Patient demographics, examination date, dimensions of the aortic root and ascending aorta, and amount of aortic regurgitation and stenosis were collected from the imaging report. Wilcoxon rank-sum tests and chi-squared tests were used to compare NC-MRA and CE-MRA groups. Logistic regression was also performed to determine the effects of the above factors on the likelihood of a successful NC-MRA.

Results:
We identified 298 NC-MRA and 102 CE-MRA examinations. Ages were similar between the two groups (p = 0.948). Height was significantly higher and more men were present in the NC-MRA group (both p < 0.001). The aortic root average diameter was significantly larger in the NC-MRA group (p = 0.021), while aortic peak velocity was higher in the CE-MRA group (p = 0.025). The logistic regression model showed that the odds of NC-MRA grew each year, and increasing height was associated with an increased likelihood of NC-MRA (p = 0.036). Men were also more likely to have NC-MRA (p = 0.001), with and without Turner patients in the model. Patients with Turner syndrome were significantly shorter than all other patients (p < 0.001); however, there was no significant difference in the odds of NC-MRA when compared to other indications. Aortic dimensions were not significant in multivariate models when height was included. Moderate aortic regurgitation was associated with decreased likelihood of NC-MRA (p = 0.006).

Conclusion:
Although there are statistically significant differences between NC-MRA and CE-MRA groups, these differences do not appear to be clinically significant in determining a favorable patient population for NC-MRA. With optimization of NC-MRA in clinical practice, the proportion of NC-MRA examinations is increasing across all preoperative indications and may be suitable for all patients. Institutional preferences likely play an important role in the decision to obtain a NC-MRA versus CE-MRA. Further studies can expand to include other nonaorta indications and additional parameters of interest.