A novel super-resolution approach to time-resolved volumetric 4DMRI with high spatiotemporal resolution for multi-breathing cycle motion assessment

Publication date: Available online 17 February 2017
Source:International Journal of Radiation Oncology*Biology*Physics
Author(s): Guang Li, Jie Wei, Mo Kadbi, Jason Moody, August Sun, Shirong Zhang, Svetlana Markova, Kristen Zakian, Margie Hunt, Joseph O. Deasy
PurposeTo develop and evaluate a super-resolution approach to reconstruct time-resolved four-dimensional magnetic resonance imaging (TR-4DMRI) with a high spatiotemporal resolution for multi-breathing cycle motion assessment.Methods and MaterialsA super-resolution approach was developed to combine fast 3D cine MRI with low-resolution during free breathing (FB) and high-resolution 3D static MRI during breath hold (BH) using deformable image registration (DIR). A T1-weighted, turbo field echo sequence, coronal 3D cine acquisition, partial Fourier approximation, and SENSE parallel acceleration were employed. The same MRI pulse sequence, field of view, and acceleration techniques were applied in both FB and BH acquisitions; the intensity-based Demons DIR method was used. Under an IRB-approved protocol, seven volunteers were studied with 3D cine FB scan (voxel size:5x5x5mm³) at 2Hz for 40s and a 3D static BH scan (2x2x2mm³). To examine the image fidelity of 3D cine and super-resolution TR-4DMRI, a mobile gel phantom with multi-internal targets was scanned at three velocities and compared with the 3D static image. Image similarity among 3D cine, 4DMRI, and 3D static was evaluated visually using difference image and quantitatively using voxel intensity correlation and Dice index (phantom only). Multi-breathing-cycle waveforms were extracted and compared in both phantom and volunteer images using the 3D cine as the references.ResultsMild imaging artifacts were found in the 3D cine and TR-4DMRI of the mobile gel phantom with a Dice index of >0.95. Among seven volunteers, the super-resolution TR-4DMRI yielded high voxel-intensity correlation (0.92±0.05) and low voxel-intensity difference (<0.05). The detected motion differences between TR-4DMRI and 3D cine were -0.2±0.5mm (phantom) and -0.2±1.9mm (diaphragms).ConclusionSuper-resolution TR-4DMRI has been reconstructed with adequate temporal (2Hz) and spatial (2x2x2mm³) resolutions. Further TR-4DMRI characterization and improvement are necessary before clinical applications. Multi-breathing cycles can be examined, providing patient-specific breathing irregularities and motion statistics for future 4D radiotherapy.

Teaser

This study presents a super-resolution approach to achieve time-resolved 4DMRI over multi-breathing cycles with a clinically-adequate spatiotemporal resolution through deformable image registration from a high-resolution breath-hold 3D static image to low-resolution free-breathing 3D cine images. A mobile phantom and seven volunteer experiments were conducted to validate this new approach. This TR-4DMRI technique can image irregular motion without binning artifacts, show high soft-tissue contrast without radiation, and provide multi-breath motion statistics for future high-precision motion-compensated treatment planning.


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