Program Information
Introduction of a Pseudo Force in Demons DIR Algorithm for Improved Image Reconstruction of Time-Resolved 4DMRI
A Sun*, J Moody , G Li , Memorial Sloan Kettering Cancer Center, New York, NY
Presentations
SU-K-FS4-9 (Sunday, July 30, 2017) 4:00 PM - 6:00 PM Room: Four Seasons 4
Purpose: Deformable image registration (DIR) is useful in the reconstruction of super-resolution (SR) time-resolved (TR) volumetric 4DMRI with an adequate spatiotemporal resolution for multi-breath motion simulation. This study aims to improve the accuracy, performance, and deformation range of the Demons DIR algorithm by introducing a pseudo force.
Methods: The SR-DIR approach was introduced for reconstruction of TR-4DMRI with adequate spatiotemporal resolution (2x2x2mm³ and 2Hz) by combining two inferior complementary image sets, one with high temporal resolution and the other with high spatial resolution, using DIR. The Demons diffusion-like deformation force at a voxel with high voxel intensity gradient (VIG) and intensity difference (VID) was extended its closest 124 neighbor voxels within a Gaussian cube (gCube: 5x5x5voxels). The amplitude of the pseudo force generated by a voxel is defined to be proportional to the VID of its neighbor voxels with the coefficient from a Gaussian distribution (σ=1 voxel) within the gCube and the direction of the original force on the voxel. Under an IRB-approved protocol, five volunteers were scanned at full inhalation and full exhalation. In the initial coarse registration, the pseudo force was implemented to accelerate the deformation. However, in the final optimization registration, only the original demons force was employed. With a fixed number of iterations, DIR performance with and without the pseudo force was compared via diaphragm alignment.
Results: Large diaphragm displacement is observed at 41±11mm, ranging from 28 to 56mm. The pseudo force accelerates the deformation of deformed anatomy. After 15 iterations, the pseudo force enhances the deformation three-fold, from 23%±9% to 65%±22%. With the same stopping criterion, the pseudo and non-pseudo DIR registration times are 2.7±1.2min and 2.0±0.8min, respectively, a 26% reduction.
Conclusion: The introduction of the pseudo force enhances DIR performance and deformation range, and therefore, is beneficial in TR-4DMRI image reconstruction for clinical applications.
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