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Section: New Results

Optimizing 4D abdominal MRI: Image denoisingusing an iterative back-projection approach

Authors: B Denis de Senneville, C R Cardiet, A J Trotier, E J Ribot, L Lafitte, L Facq, S Miraux. Published in Physics in Medicine and Biology.

4D-MRI is a promising tool for organ exploration, target delineationand treatmentplanning. Intra-scan motion artifacts may be greatly reduced by increasing the imagingframe rate. However, poor signal-to-noise ratios (SNR) are observed when increasingspatial and/or frame number per physiological cycle, in particular inthe abdomen.In the current work, the proposed 4D-MRI method favored spatial resolution, framenumber, isotropic voxels and large field-of-view (FOV) during MR-acquisition. Theconsequential SNR penalty in the reconstructed data is addressed retrospectively usingan iterative back-projection (IBP) algorithm. Practically, after computing individualspatial 3D deformations present in the images using a deformable image registration(DIR) algorithm, each 3D image is individually enhanced by fusing several successiveframes in its local temporal neighborood, these latter being likely tocover commonindependent informations. A tuning parameter allows one to freely readjust the balancebetween temporal resolution and precision of the 4D-MRI.The benefit of the method was quantitatively evaluated on the thorax of 6 miceunder free breathing using a clinically acceptable duration. Improved 4D cardiacimaging was also shown in the heart of 1 mice. Obtained results are comparedto theoretical expectations and discussed. The proposed implementation is easilyparallelizable and optimized 4D-MRI could thereby be obtained with a clinicallyacceptable duration.