Lung Computed Tomography (CT) images play an important role in the diagnosis and treatment of patients with COVID- 19. However, manually identifying lesions in CT images is very time-consuming and requires specialized medical knowledge. The accuracy and integrity of the existing models are still not ideal due to the reasons such as scattered distribution, small lesions and blurred boundaries. Therefore, we propose a segmentation model based on U-Net architecture by combining Mirror-symmetry Boundary Guided (MBG) module and then adding Spatial Attention Dilation (SAD) convolution Module, called MSU-Net. The SAD module uses spatial attention mechanism and dilated convolution and multi-scale feature extraction strategy to enhance the network’s ability to recognize small lesions. The MBG module further enhances the model’s ability to capture more complex context information and boundary details, making the model more robust and able to effectively deal with the challenges of fuzzy boundaries. The proposed method has shown superior performance in terms of the Dice coefficient, Hausdorff distance, and Sensitivity on the publicly available COVID-19 CT dataset.
Bioluminescence tomography (BLT) is an effective noninvasive molecular imaging modality, it has shown great potential for studying and monitoring disease progression in pre-clinical imaging. As the BLT is an inherent highly ill-posed inverse problem, it is still a challenge to obtain an accurate reconstruction result. Some algorithms have been proposed to solve highly ill posedness of inverse problems. Nevertheless, Existing methods always need to consume large time or have low interpretability. Thus, in this paper, we proposed a novel model-driven deep learning network, which unfolding the Fast Iterative Shrinkage Thresholding Algorithm (FISTA) algorithm into a deep network, named FISTA-Net to overcome the above shortcoming. FISTA-Net is formed from three modules, gradient descent module, proximal mapping module and accelerate module. Key parameters of FISTA-Net including the gradient step size, thresholding value are learned from training data. The experimental results, evaluated both visually and quantitatively, show that the FISTA-Net can achieve a high-quality reconstruction result of BLT.
Bioluminescence tomography (BLT) reconstruction is an ill-posed problem. A class of strategy based on the permissible region (PR) reduces the ill-posed by reducing the space. However, in multi-objective reconstruction, the strategy is challenging to fit the sources of different positions. In this study, a subspace decision (SD) method is proposed, which transforms the traditional single permissible region into multiple spatially continuous subspaces by clustering, and performs spatial shrinkage optimization for each of them. In addition, a plug-and-play sliding single polyline module is introduced to analyze and cluster the reconstruction results each time to obtain the number and distribution of subspaces contained in the results. SD method does not rely on any specific reconstruction or clustering algorithm, so it has great flexibility. Experiment results show that the SD approach can more accurately obtain the spatial distribution information of different numbers of sources distributed in different locations and ensure the quality of multi-source BLT reconstruction. Keywords: Bioluminescence Tomography, Inverse Problem, Subspace, Clustering, Permissible Region.
Bioluminescence tomography (BLT) is a promising optical molecular imaging technique in preclinical research. One key problem for BLT is how to deal with the severe ill-posedness and obtain accurate and stable reconstruction. We propose a penalty method for recovering bioluminescence sources, in which we transform reconstruction of BLT into an L1/2-norm penalty problem and solve it via a nonmonotone proximal gradient method with a suitable penalty parameter update scheme. Simulations and phantom experiments based on multispectral measurements were designed to evaluate the proposed reconstruction method. The encouraging results show that the proposed method has better reconstruction accuracy and image quality than the comparative methods.
Sparse regularization methods have been widely used in fluorescence molecular tomography (FMT) for stable three-dimensional reconstruction. Generally, ℓ1-regularization-based methods allow for utilizing the sparsity nature of the target distribution. However, in addition to sparsity, the spatial structure information should be exploited as well. A joint ℓ1 and Laplacian manifold regularization model is proposed to improve the reconstruction performance, and two algorithms (with and without Barzilai–Borwein strategy) are presented to solve the regularization model. Numerical studies and in vivo experiment demonstrate that the proposed Gradient projection-resolved Laplacian manifold regularization method for the joint model performed better than the comparative algorithm for ℓ1 minimization method in both spatial aggregation and location accuracy.
As an important optical molecular imaging technique, bioluminescence tomography (BLT) offers an inexpensive and
sensitive means for non-invasively imaging a variety of physiological and pathological activities at cellular and
molecular levels in living small animals. The key problem of BLT is to recover the distribution of the internal
bioluminescence sources from limited measurements on the surface. Considering the sparsity of the light source
distribution, we directly formulate the inverse problem of BLT into an l0-norm minimization model and present a
smoothed l0-norm (SL0) based reconstruction algorithm. By approximating the discontinuous l0 norm with a suitable
continuous function, the SL0 norm method solves the problem of intractable computational load of the minimal l0 search as well as high sensitivity of l0-norm to noise. Numerical experiments on a mouse atlas demonstrate that the proposed
SL0 norm based reconstruction method can obtain whole domain reconstruction without any a priori knowledge of the
source permissible region, yielding almost the same reconstruction results to those of l1 norm methods.
The diffusion approximation of the radiative transport equation is the most widely used model in current researches on fluorescence molecular tomography (FMT), which is limited in some low or zero scattering regions. Recently, the simplified spherical harmonics equations (SPN) model has attracted much attention in modeling the light propagation in small tissue geometries at visible and near-infrared wavelengths. In this paper, we report an efficient numerical method for FMT that combines the advantage of SPN model and hp-FEM. For comparison purposes, hp-FEM and h-FEM are respectively applied in the reconstruction process with diffusion model and SPN model. Simulation experiments on a 3D digital mouse atlas are designed to evaluate the reconstruction methods in terms of the location and the reconstructed fluorescent yield. The experimental results demonstrate that hp-FEM with SPN model, yield more accurate results than h-FEM with DA model does. And the reconstructed results show the potential and feasibility of the proposed approach.
As a novel optical molecular imaging modality, Bioluminescence Tomography (BLT) aims at quantitative reconstruction
of the bioluminescent source distribution inside the biological tissue from the optical signals measured on the living
animal surface, which is a highly ill-posed inverse problem. In this paper, with the finite element method solving the
diffusion equation, an iterative regularization algorithm, referred to as least square QR-factorization (LSQR), is applied
to the inverse problem in BLT. The affect of the preconditioning strategy on the LSQR method (PLSQR) for BLT is also
investigated. The Simulations with a heterogeneous mouse chest phantom demonstrate that by incorporating a priori
knowledge of the permissible source region, the LSQR method can reconstruct the source accurately and stably.
Moreover, by employing preconditioning strategy, PLSQR outperforms LSQR in terms of source power density and
convergence speed.
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