Effect of Field Strengths on Magnetic Resonance Angiography

Abstract

We sought to compare the intravascular enhancement of an ultrasmall superparamagnetic iron oxide (USPIO) blood-pool contrast agent to gadopentetate dimeglumine for contrast-enhanced magnetic resonance angiography (CE-MRA) at field strengths of 1.5 and 3.0 T in rabbits.CE-MRA at 1.5 and 3.0 T was performed at several time points (50 seconds and 5, 10, 20, and 30 minutes) after the manual intravenous injection of 40 micromol Fe/kg body weight of an USPIO (SH U 555 C; Schering AG, Berlin, Germany) and 100 micromol/kg body weight gadopentetate dimeglumine (Magnevist; Schering AG, Berlin, Germany). MRA was performed with comparable acquisition parameters at both field strengths (Turbo-gradient sequence; 1.5 T: TR/TE/alpha: 5.5/1.7 milliseconds/40 degrees ; 3.0 T: TR/TE/alpha: 5.1/1.8 milliseconds/40 degrees ) on clinical imaging systems (both: Gyroscan Intera, Philips Medical Systems, Best, The Netherlands). At either field strength, 6 rabbits were studied with both contrast agents (n = 24 in total). Signal-to-noise ratio (SNR) and contrast-to-noise ratio (CNR) were calculated from signal intensity measurements in the abdominal aorta.Compared with 1.5 T, the SNR and CNR of gadopentetate dimeglumine significantly increased at 3.0 T by a factor of 2.2 and 2.3, respectively (P or= 0.05). At both field strength and either time point, CNR and SNR of SH U 555 C were significantly higher compared with gadopentetate dimeglumine at 3.0 T (P <or= 0.01).SNR and CNR of gadopentetate dimeglumine significantly increased with increasing field strength. No SNR or CNR gain was observed for SH U 555 C. However, blood-pool MRA with SH U 555 C is feasible at 3.0 T. Compared with gadopentetate dimeglumine, SNR and CNR of SH U 555 C were significantly higher from 5 to 30 minutes at both field strengths (P <or= 0.01).