Ventilation Imaging of the Lung at 0.55T With Continuous Slice Cycling

To propose and evaluate a novel method for pulmonary ventilation imaging, offering considerably improved SNR.

A continuous slice cycling (CSC) acquisition scheme is proposed to exclusively capture signal modulations from respiratory motion with increased SNR. To this end, a set of single-shot images is acquired at multiple interleaved slice positions. This scheme offers substantially increased image-to-image time-intervals at every slice position, thus allowing near full longitudinal recovery between repeated acquisitions but without losing scan efficiency. Ventilation images are generated from the registered CSC image time series using the coefficient of variation and compared to conventional functional lung MRI using a time-resolved series of 2D images. Functional lung MRI was performed in 7 volunteers and 11 patients at 0.55T using balanced steady state free precession (bSSFP). Six coronal slices with 100% slice spacing were acquired with an image-to-image interval of 2 s, yielding a total scan time of 3:20 min for 100 cycles.

For the proposed 2 s time-interval at 0.55T, almost full signal recovery can be achieved. As a result, CSC centric imaging yields a more than two-fold SNR increase as compared with contemporary functional lung imaging methods. Excellent agreement was observed between ventilation images from CSC and those from standard functional lung MRI.

CSC holds strong potential for ventilation MRI with improved sensitivity, particularly in diseases marked by reduced local tissue density.