Submillimeter lung MRI at 0.55 T using balanced steady‐state free precession with half‐radial dual‐echo readout (bSTAR)

Abstract

PurposeTo demonstrate the feasibility of high‐resolution morphologic lung MRI at 0.55 T using a free‐breathing balanced steady‐state free precession half‐radial dual‐echo imaging technique (bSTAR).MethodsSelf‐gated free‐breathing bSTAR (TE1/TE2/TR of 0.13/1.93/2.14 ms) lung imaging in five healthy volunteers and a patient with granulomatous lung disease was performed using a 0.55 T MR‐scanner. A wobbling Archimedean spiral pole (WASP) trajectory was used to ensure a homogenous coverage of k‐space over multiple breathing cycles. WASP uses short‐duration interleaves randomly tilted by a small polar angle and rotated by a golden angle about the polar axis. Data were acquired continuously over 12:50 min. Respiratory‐resolved images were reconstructed off‐line using compressed sensing and retrospective self‐gating. Reconstructions were performed with a nominal resolution of 0.9 mm and a reduced isotropic resolution of 1.75 mm corresponding to shorter simulated scan times of 8:34 and 4:17 min, respectively. Analysis of apparent SNR was performed in all volunteers and reconstruction settings.ResultsThe technique provided artifact‐free morphologic lung images in all subjects. The short TR of bSTAR in conjunction with a field strength of 0.55 T resulted in a complete mitigation of off‐resonance artifacts in the chest. Mean SNR values in healthy lung parenchyma for the 12:50 min scan were 3.6 ± 0.8 and 24.9 ± 6.2 for 0.9 mm and 1.75 mm reconstructions, respectively.ConclusionThis study demonstrates the feasibility of morphologic lung MRI with a submillimeter isotropic spatial resolution in human subjects with bSTAR at 0.55 T.