SCMR 22nd Annual Scientific Sessions
3D radial1-4 free-breathing continuous acquisitions, so called free-running, have been recently proposed to reconstruct 3D whole-heart images at different cardiac and respiratory phases. These approaches retrospectively assign the data into different cardiac and respiratory phases using ECG or self-gated cardiac signals and self-gated respiratory signals. Cardiac and respiratory resolved images are then reconstructed exploiting temporal redundancy in both cardiac and respiratory directions5. These approaches have shown promising image quality in reasonable scan times ~10-12min, however they require long reconstruction times due to the non-Cartesian nature of the acquisition and some rely on administration of contrast agent.
Methods: VD-CASPR sampling6,7 with golden angle increment between spirals continuously undersamples the Cartesian ky/kz plane by an acceleration factor L. Depending on L, matrix size and number of spiral rings, after S spirals a fully sampled k-space is reached, i.e. all high-frequency points are sampled at least once whilst low-frequency range is oversampled. This property originates from the variable-density sampling and is a desirable to enable low-frequency high-contrast sampling more frequently. Periodically the center line of k-space is sampled serving as a 1D respiratory self-navigator. T2prep and fat saturation pulses are periodically played out for improving cardiac contrast. Data is retrospectively binned into respiratory and cardiac states based on the self-navigation signal which is extracted via PCA, and ECG. A 3D-PROST7 reconstruction with Gaussian soft-weighting is used to generate high-resolution cardiac and respiratory images. Data was acquired with a bSSFP sequence on a 1.5T MR in three healthy subjects.
Results: Fig.2/3 show cardiac motion-resolved images of two subjects. Images were binned into 2 respiratory and 8 resp. 6 cardiac states illustrating good spatial and temporal resolution. Gating can effectively reduce motion-induced blurring. Sufficient image contrast in the heart is obtained with the periodic interruption of T2prep and fat saturation pulses.
The proposed acquisition provides 3D Cartesian cardiac and respiratory resolved images with high spatial and temporal resolution under free-breathing in ~8min scan time and ~2min/state reconstruction times. Temporal redundancies will be exploited in future work, in addition to patch-based low-rank, to increase the number of cardiac and respiratory phases.