Diffusion weighted hyperpolarized 129Xe MRI of the lung with 2D and 3D (FLORET) spiral

Purpose To enable efficient hyperpolarized Xe-129 diffusion imaging using 2D and 3D (Fermat Looped, ORthogonally Encoded Trajectories, FLORET) spiral sequences and demonstrate that Xe-129 ADCs obtained using these sequences are comparable to those obtained using a conventional, 2D gradient-recalled echo (GRE) sequence. Theory and Methods Diffusion-weighted Xe-129 MRI (b-values = 0, 7.5, 15 s/cm(2)) was performed in four healthy volunteers and one subject with lymphangioleiomyomatosis using slice-selective 2D-GRE (scan time = 15 s), slice-selective 2D-Spiral (4 s), and 3D-FLORET (16 s) sequences. Experimental SNRs from b-value = 0 images (SNR0EX$$ SNR{0}_{EX} $$) and mean ADC values were compared across sequences. In two healthy subjects, a second b = 0 image was acquired using the 2D-Spiral sequence to map flip angle and correct RF-induced, hyperpolarized signal decay at the voxel level, thus improving regional ADC estimates. Results Diffusion-weighted images from spiral sequences displayed image quality comparable to 2D-GRE and produced sufficient SNR0EX$$ SNR{0}_{EX} $$ (16.8 +/- 3.8 for 2D-GRE, 21.2 +/- 3.5 for 2D-Spiral, 20.4 +/- 3.5 for FLORET) to accurately calculate ADC. Whole-lung means and SDs of ADC obtained via spiral were not significantly different (P > 0.54) from those obtained via 2D-GRE. Finally, 2D-Spiral images were corrected for signal decay, which resulted in a whole-lung mean ADC decrease of similar to 15%, relative to uncorrected images. Conclusions Relative to GRE, efficient spiral sequences allow Xe-129 diffusion images to be acquired with isotropic lung coverage (3D), higher SNR$$ SNR $$(2D and 3D), and three-fold faster (2D) within a single breath-hold. In turn, shortened breath-holds enable flip-angle mapping, and thus, allow RF-induced signal decay to be corrected, increasing ADC accuracy.