Jin Zhang^{1}, Li Feng^{1}, Ricardo Otazo^{1}, and Sungheon Gene Kim^{1}

It remains challenging to achieve simultaneous high spatial isotropic resolution and high temporal resolution in dynamic contrast enhanced (DCE) MRI of small animals, due to the relatively low signal to noise ratio (SNR) from small voxels. The purpose of this study is to develop a highly accelerated, high-spatial and high-temporal resolution DCE-MRI method for small animal imaging at 7T using 3D ultrashort echo time (UTE) golden-angle radial sampling with a combined compressed sensing and parallel imaging approach based on the GRASP technique. Our preliminary results demonstrate that the proposed UTE-GRASP method has the potential to improve both spatial and temporal resolution.

A 3D UTE pulse sequence
was used to achieve an isotropic spatial resolution and to minimize the *T _{2}^{*}*
effect. As shown in Fig.1, a 3D golden-angle sampling with center-out radial readouts
was implemented using a 2D golden angle approach,

** Data Acquisition:** Six
to eight-week-old C57BL6 mice (

* Image Reconstruction:* The targeted temporal resolution was

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Figure 1. 3D golden angle sampling. (a) modified 3D
radial spokes in *k*-space with azimuth angle *Φ*=2*πmA* and projection length (*Z*) in *k*_{z} direction being the modules one of *mB*, for *m*=1,2,…,102712
spokes with 2D golden angle means, *A*=0.6823 and *B*=0.4656. Distribution of 400
projection tips for the modified (b) and original (c) 3D golden angle sampling.
The green areas are computed Voronoi regions for
*k*-space sampling density compensation.

Figure 2.(a) Reference image (using post-contrast 38,750 spokes
from 50 s to 205 s) with tumor ROI (red), NUFFT reconstruction of the dynamic
datasets (using 1,250 spokes/frame), and GRASP reconstructions with different regularization *λ *(using 1,250 spokes/frame). (b)
Normalized signal enhancement curves of tumor ROI average from NUFFT
reconstruction (assumed to be the reference) and different *λ*s. (c) Sum of
squares between different *λ* reconstructed curves and NUFFT reconstructed
reference.

Figure 3. 3D maximum intensity projection (MIP) rendering of
DCE-MRI dynamics (reconstructed with *T*=5 s and *λ*=1) at different stages: baseline (15 s), AIF peak (35 s), tumor
enhancement peak (75 s), and washout end (405 s).

Figure 4. Pharmacokinetic model parameter color maps of tumor
center slices in coronal/axial/sagittal planes. The coronal/axial/sagittal
images in gray scale were reconstructed with 1,250 spokes/frame and *λ*=1.