Figure 1. Schematic Depicting Simulation of Undersampled Multi-echo UTE MRI.

Simulations used modified 3D Shepp-Logan phantoms, augmented with ellipsoids to mimic mouse lung vasculature inside the lung parenchyma. Phantoms were created at three, 3D isotropic matrix sizes: 64³, 96³, and 128³. 3D radial projections generated were generated along golden angle sampling trajectories (a). Tissue-specific ${\mathrm{T}}_2\mathrm{*}$ decay was introduced by adjusting the signal based on an exponential decay (lung parenchyma: ${\mathrm{T}}_2\mathrm{*}=0.4\text{ms}$; lung vasculature ${\mathrm{T}}_2\mathrm{*}=3.16\text{ms}$). K-space data were generated via Fast Fourier Transform (FFT) of decayed images. The corresponding k-space data were sampled to generate Free Induction Decay data (FIDs). Gaussian noise (with mean μ = 0 and standard deviation σ = 50) was added to both the real and imaginary k-space data to produce noisy FIDs to yield parenchymal SNR similar to that observed from in-vivo images (~30) (b). The total radial projections for each matrix size were: 12,868 for 64³, 28,953 for 96³, and 51,472 for 128³. Images were reconstructed at each TE using from noisy FIDs data employing Cartesian re-gridding, iterative density compensation, and FFT (c).