Purpose
Volumetric medical image registration has important clinical significance. Traditional registration methods may be time‐consuming when processing large volumetric data due to their iterative optimizations. In contrast, existing deep learning‐based networks can obtain the registration quickly. However, most of them require independent rigid alignment before deformable registration; these two steps are often performed separately and cannot be end‐to‐end.
Methods
We propose an end‐to‐end joint affine and deformable network for three‐dimensional (3D) medical image registration. The proposed network combines two deformation methods; the first one is for obtaining affine alignment and the second one is a deformable subnetwork for achieving the nonrigid registration. The parameters of the two subnetworks are shared. The global and local similarity measures are used as loss functions for the two subnetworks, respectively. Moreover, an anatomical similarity loss is devised to weakly supervise the training of the whole registration network. Finally, the trained network can perform deformable registration in one forward pass.
Results
The efficacy of our network was extensively evaluated on three public brain MRI datasets including Mindboggle101, LPBA40, and IXI. Experimental results demonstrate our network consistently outperformed several state‐of‐the‐art methods with respect to the metrics of Dice index (DSC), Hausdorff distance (HD), and average symmetric surface distance (ASSD).
Conclusions
The proposed network provides accurate and robust volumetric registration without any pre‐alignment requirement, which facilitates the end‐to‐end deformable registration.
Background.
Fibroblastic reticular cells (FRCs) are a type of stromal cells located in the T zone in secondary lymphoid organs. Previous studies showed that FRCs possess the potential to promote myeloid differentiation. We aim to investigate whether FRCs in lymph nodes (LNs) could induce tolerogenic macrophage generation and further influence T-cell immunity at an early stage of allogeneic hematopoietic stem cell transplantation (allo-HSCT).
Methods.
LNs were assayed to confirm the existence of proliferating macrophages after allo-HSCT. Ex vivo—expanded FRCs and bone marrow cells were cocultured to verify the generation of macrophages. Real-time quantitative PCR and ELISA assays were performed to observe the cytokines expressed by FRC. Transcriptome sequencing was performed to compare the difference between FRC-induced macrophages (FMs) and conventional macrophages. Mixed lymphocyte reaction and the utilization of FMs in acute graft-versus-host disease (aGVHD) mice were used to test the inhibitory function of FMs in T-cell immunity in vitro and in vivo.
Results.
We found a large number of proliferating macrophages near FRCs in LNs with tolerogenic phenotype under allo-HSCT conditions. Neutralizing anti–macrophage colony-stimulating factor receptor antibody abolished FMs generation in vitro. Phenotypic analysis and transcriptome sequencing suggested FMs possessed immunoinhibitory function. Mixed lymphocyte reaction proved that FMs could inhibit T-cell activation and differentiation toward Th1/Tc1 cells. Injection of FMs in aGVHD mice effectively attenuated aGVHD severity and mortality.
Conclusions.
This study has revealed a novel mechanism of immune regulation through the generation of FRC-induced tolerogenic macrophages in LNs at an early stage of allo-HSCT.
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