Purpose or Case Report: Three dimensional magnetic resonance angiography (3DMRA) and two-dimensional phase contrast are commonly used for assessment of anatomy and flow in congenital heart disease. Time-resolved, three-dimensional phase contrast MRI (4D flow) provides complete volumetric coverage of the chest with flow assessment in any plane. How the addition of ferumoxytol (Fe), a blood pool contrast, changes 4D flow magnitude image quality relative to extracellular gadolinium-based contrast agents (GB) and non-contrast (NC) exams is unknown. We compare image quality measurements in Fe, GB and NC 4D flow with ECG-gated, respiratory-navigated 3DMRA.
Methods & Materials: 32 patients with Fe 4D flow were age-matched to 33 patients with GB and 13 patients with NC 4D flow. 4D flow image quality was assessed by (1) aortic signal-to-noise ratio (SNR) (2) aortic contrast-to-noise ratio (CNR) (3) qualitative rating by 2 blinded readers. Ascending aorta (Ao), branch pulmonary arteries (PA), right superior vena cava (RSVC), pulmonary veins (PV), endocardial border (EB), and coronary artery origins (CAO) were rated 0=Not included 1=Nondiagnostic 2=Diagnostic. Ascending and descending aorta dimensions (AD, DD) on 4D flow magnitude images were compared to 3DMRA. Agreement between readers was assessed by taking the difference between raters’ scores and performing Wilcoxon rank sum test.
Results: Aortic SNR and CNR was significantly higher in Fe 4D flow (SNR: FE 56±26, GB 35±13, NC 24±12; CNR: FE 19±14, GB -7±15, NC -15±12, p<.001). AD and DD correlated well with 3DMRA for Fe and GBCA but not NC (AD R²: FE .98, GB .94, NC .54; DD R²: FE .96, GB .95, NC .6). All structures were rated diagnostic more often for Fe than GBCA and NC (p<.001). Ao was rated diagnostic on 32(100%) FE, 12(36%) GB, and 3(23%) NC. EB and PV were seen on most Fe studies (63% and 81% respectively); non-diagnostic on all NC and all but 1 GB showing PV. CAO were rarely diagnostic (FE 5(16%), GB 1(3%), no NC). For structures most often seen (Ao, PA, right SVC), interrater agreement was higher in Fe than GB and NC (p<.05).
Conclusions: MRA image quality varies between contrast types. NC 4D flow magnitude images are nondiagnostic for measurements. Qualitatively, Fe image quality is superior to GB and NC, including for detection of the endocardial border and small structures such as pulmonary veins. If 4D flow is to replace 2D-PC and 3D MRA as a single acquisition for vascular and flow assessment, Fe is essential to creating diagnostic magnitude images.