Comparison of iterative parametric and indirect deep learning-based reconstruction methods in highly undersampled DCE-MR Imaging of the breast.

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Abstract

To compare the performance of iterative direct and indirect parametric reconstruction methods with indirect deep learning based reconstruction methods in estimating tracer-kinetic parameters from highly undersampled DCE-MR Imaging breast data and provide a systematic comparison of the same.
Estimation of tracer-kinetic parameters using indirect methods from undersampled data requires to reconstruct the anatomical images initially by solving an inverse problem. This reconstructed images gets utilized in turn to estimate the tracer-kinetic parameters. In direct estimation, the parameters are estimated without reconstructing the anatomical images. Both problems are ill-posed and are typically solved using prior based regularization or using deep learning. In this study, for indirect estimation, two deep learning based reconstruction frameworks namely, ISTA-Net+ and MODL, were utilized. For direct and indirect parametric estimation, sparsity inducing priors (L1 and Total-Variation) and limited memory Broyden-Fletcher-Goldfarb-Shanno algorithm as solver was deployed. The performance of these techniques were compared systematically in estimation of vascular permeability (Ktrans ) from undersampled DCE-MRI breast data using Patlak as pharmaco-kinetic model. The experiments involved retrospective undersampling of the data 20x, 50x and 100x and compared the results using PSNR, nRMSE, SSIM and Xydeas metrics. The Ktrans maps estimated from fully sampled data were utilized as ground truth. The developed code was made available as open-source for enthusiastic users.
The reconstruction methods performance was evaluated using ten patients breast data (five patients each for training and testing). Consistent with other studies, the results indicate that direct parametric reconstruction methods provide improved performance compared to indirect parameteric reconstruction methods. The results also indicate that for 20x undersampling, deep learning based methods performs better or at par with direct estimation in terms of PSNR, SSIM and nRMSE. However, for higher undersampling rates (50x and 100x) direct estimation performs better in all metrics. For all undersampling rates, direct reconstruction performed better in terms of Xydeas metric, which indicated fidelity in magnitude and orientation of edges.
Deep learning based indirect techniques perform at par with direct estimation techniques for lower undersampling rates in the breast DCE-MR imaging. At higher undersampling rates, they are not able to provided much needed generalization. Direct estimation techniques are able to provide more accurate results than both deep learning and parametric based indirect methods in these high undersampling scenarios.
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