3.0 Tesla High Spatial Resolution Contrast-Enhanced Magnetic Resonance Angiography (CE-MRA) of the Pulmonary Circulation

Abstract

Purpose: To evaluate the technical feasibility of high spatial resolution contrast-enhanced magnetic resonance angiography (CE-MRA) with highly accelerated parallel acquisition at 3.0 T using a 32-channel phased array coil, and a high relaxivity contrast agent. Materials and Methods: Ten adult healthy volunteers (5 men, 5 women, aged 21–66 years) underwent high spatial resolution CE-MRA of the pulmonary circulation. Imaging was performed at 3 T using a 32-channel phase array coil. After intravenous injection of 1 mL of gadobenate dimeglumine (Gd-BOPTA) at 1.5 mL/s, a timing bolus was used to measure the transit time from the arm vein to the main pulmonary artery. Subsequently following intravenous injection of 0.1 mmol/kg of Gd-BOPTA at the same rate, isotropic high spatial resolution data sets (1 × 1 × 1 mm³) CE-MRA of the entire pulmonary circulation were acquired using a fast gradient-recalled echo sequence (TR/TE 3/1.2 milliseconds, FA 18 degrees) and highly accelerated parallel acquisition (GRAPPA × 6) during a 20-second breath hold. The presence of artifact, noise, and image quality of the pulmonary arterial segments were evaluated independently by 2 radiologists. Phantom measurements were performed to assess the signal-to-noise ratio (SNR). Statistical analysis of data was performed by using Wilcoxon rank sum test and 2-sample Student t test. The interobserver variability was tested by kappa coefficient. Results: All studies were of diagnostic quality as determined by both observers. The pulmonary arteries were routinely identified up to fifth-order branches, with definition in the diagnostic range and excellent interobserver agreement (κ = 0.84, 95% confidence interval 0.77–0.90). Phantom measurements showed significantly lower SNR (P < 0.01) using GRAPPA (17.3 ± 18.8) compared with measurements without parallel acquisition (58 ± 49.4). Conclusion: The described 3 T CE-MRA protocol in addition to high T₁ relaxivity of Gd-BOPTA provides sufficient SNR to support highly accelerated parallel acquisition (GRAPPA × 6), resulting in acquisition of isotopic (1 × 1 × 1 mm³) voxels over the entire pulmonary circulation in 20 seconds.