Cardiac Magnetic Resonance Imaging at Lower Field Strength

OBJECTIVES: This study aimed to compare biventricular cine measurements and quantitative maps of myocardial T1 and T2 relaxation times at field strengths ranging from 0.55T to 1.5T in patients with a clinical indication for cardiac magnetic resonance imaging (CMR). Establishing the feasibility of low-field CMR may improve accessibility due to easier siting and lower cost of the low-field systems. MATERIALS AND METHODS: Thirteen patients underwent same-day comparative CMR at 0.55T and on a commercial scanner at 1.5T. We examined all individuals with breath-held segmented bSSFP cine sequences for volumetric assessment of the left ventricle (LV), right ventricle (RV), and visual assessment of wall motion abnormalities (WMA) and valve pathologies. The quantitative T1 and T2 maps were acquired in 3 short-axis views for tissue characterization. Blinded readers scored the image quality on a 3-point Likert scale. Ten healthy volunteers were additionally examined at 0.55T to obtain reference values for the parametric maps. RESULTS: Functional analysis of both ventricles at low-field CMR has a reasonable correlation (r=0.94 to 0.99) with conventional 1.5T measurements. LV ejection fraction (EF) ( P =0.62) and RV measurements (all P >0.05) were highly reproducible, but LV absolute volumetric measurements were slightly lower at the low-field strength (all P <0.05). T1 and T2 relaxation times correlated strongly between field strengths (r=0.79; P <0.01 and r=0.63; P =0.02). Reference values from the volunteers were 678.6±13.5 ms (T1) and 66.5±4.1 ms (T2). Overall, good image quality was achieved, and visual assessment showed excellent agreement with 1.5T. Trigger artifacts occurred more frequently during 0.55T scans compared with 1.5T. Correct clinical stratification of volumetric parameters, WMA, valve pathologies, and parametric maps was possible in 94% of all cases. CONCLUSIONS: CMR at 0.55T provides a comprehensive assessment of function, structure, and tissue characterization comparable to that of 1.5T. The diagnostic accuracy in this clinical cohort is high. Identification of the specific trigger problems and optimization of the trigger technique could help to overcome the slight inaccuracies in the LV absolute volumetric measurements. Low-field CMR holds promise for expanding access to this valuable diagnostic tool, benefiting patients worldwide and on an individual level.