(Thursday, 7/18/2019) 7:30 AM - 9:30 AM
Room: 303
Purpose: 4DMRI are classified as either time-resolved (TR) or respiratory-correlated (RC); the former demonstrates real-time motion but with low spatial-dimensionality, while the latter provides high spatial-dimensionality but only one representative breathing cycle. This study aims to achieve novel time-resolved 4DMRI (TR-4DMRI) with high spatiotemporal resolution using dynamic keyhole (DKH) method with RC-4DMRI image library for motion assessment.
Methods: As a proof-of-concept, fast MRI scanning protocol with parallel imaging was applied on a digital motion phantom (ground truth) to acquire low spatial-resolution (4x4x4mm3) 3D cine (temporal-resolution: 2Hz) and high spatial-resolution (2x2x2mm3) RC-4DMRI library, under free-breathing condition. The RC-4DMRI library was built from 10-state breathing cycle. A super-resolution concept is applied to reconstruct TR-4DMRI by combining high temporal-resolution but low spatial-resolution 3D cine and a high spatial-resolution but only 10-phase library image in k-space. For each frame of the 3D cine, two image matching steps were performed between cine and library images: the first step selected one 3D image (representing one respiratory phase), that best matches internal motion status of the cine, from 10-state RC-4DMRI; the second step normalizes the k-space data intensity, to combine them (a 3D cine + a matched library image) in k-space using DKH to reconstruct TR-4DMRI. The TR-4DMRI image quality was evaluated by comparing it with the ground truth based on mean voxel intensity difference (VID) and voxel intensity correlation (VIC).
Results: TR-4DMRI reconstructed from updating central k-space data demonstrated adequate real-time motion information with fine structure details. Comparing the image quality of reconstructed TR-4DMRI and RC-4DMRI, VID=3% and VIC=0.98.
Conclusion: This study investigates the feasibility of TR-4DMRI reconstruction with dynamic keyhole method using an RC-4DMRI image library. It demonstrates motion continuously with adequate spatiotemporal resolution. Further human subject study is on-going. This technique has great potential to achieve real-time 4DMRI performance with clinically preferable spatiotemporal resolution.
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