Phantom-based evaluation of isotropic reconstruction of 4-D MRI volumes using super-resolution

This article investigates the feasibility of isotropic super-resolution reconstruction on 4-D (3-D + time) thoracic MRI data. 4-D MRI sequences generally have high temporal resolution to characterize dynamic phenomena but poor spatial resolution, creating highly anisotropic voxels elongated in the slice-select dimension. Isotropic post-acquisition reconstruction can be obtained using super-resolution algorithms. A new MRI compatible phantom design that simulates lung tumour motion is introduced to evaluate the feasibility and performance of the proposed super-resolution algorithm in the context of 4-D MRI. Several orthogonal low-resolution acquisitions of the phantom are performed through time using a fast true 3-D gradient echo based sequence. The acquired volumes are then registered and combined using a total-variation based regularizer super-resolution algorithm to obtain the high-resolution volume. The quality of the reconstruction is evaluated by measuring the mutual information between the reconstructed volume and a direct isotropic 3-D acquisition. Subjective and objective evaluations show the superiority of our approach compared to the averaging method. This article also discusses the influence of various parameters such as the number of low-resolution scans used and the influence of automatic motion estimation versus known displacement.