Optical Molecular Imaging Modality Research Articles

Application of machine learning method in optical molecular imaging: a review

Optical molecular imaging (OMI) is an imaging technology that uses an optical signal, such as near-infrared light, to detect biological tissue in organisms. Because of its specific and sensitive imaging performance, it is applied in both preclinical research and clinical surgery. However, it requires heavy data analysis and a complex mathematical model of tomographic imaging. In recent years, machine learning (ML)-based artificial intelligence has been used in different fields because of its ability to perform powerful data processing. Its analytical capability for processing complex and large data provides a feasible scheme for the requirement of OMI. In this paper, we review ML-based methods applied in different OMI modalities.

The image reconstruction for fluorescence molecular tomography via a non-uniform mesh

As an optical molecular imaging modality, fluorescence molecular tomography (FMT) can monitor the activities of organisms in vivo at the molecular and cellular levels. However, the recovered image quality is affected by mesh voxel when the finite element method is utilized to recover the fluorescence probe. The target localization is likely to deviate from the actual target under the coarse mesh, but using the fine mesh will increase the number of unknowns, which makes the computational burden heavier and further aggravate the ill-posedness. To solve the problem, a reconstruction strategy using a non-uniform mesh for FMT is developed in this paper. The numerical experiment and physical experiment validated that the strategy is capable and effective for FMT.

Multispectral bioluminescence tomography-based general iterative shrinkage and threshold algorithm

Bioluminescence tomography (BLT) is a noninvasive optical molecular imaging modality with high sensitivity. The complexity of near-infrared light transmission in biological tissues and the limitation of measurable information place a higher demand on BLT source reconstruction algorithms. In this paper, we present a reconstruction algorithm based on general iterative shrinkage and threshold (GIST), which uses a non-convex smoothly clipped absolute deviation function as the penalty term, and solves a proximal operator problem that has a closed-form solution for the penalty. In addition, we utilize multispectral measurements and an iteratively shrinking permissible region strategy to address the ill-posedness of the BLT inverse problem. To investigate the source location and multi-source resolution abilities of the proposed method, we perform comparisons between three typical sparse reconstruction algorithms based on several groups of simulations and phantom experiments. The reconstruction results demonstrate great advantages of the proposed GIST algorithm in terms of source location accuracy in all considered source settings with different source depths and separations.

Source reconstruction for bioluminescence tomography via L1∕2 regularization

Bioluminescence tomography (BLT) is an important noninvasive optical molecular imaging modality in preclinical research. To improve the image quality, reconstruction algorithms have to deal with the inherent ill-posedness of BLT inverse problem. The sparse characteristic of bioluminescent sources in spatial distribution has been widely explored in BLT and many L1-regularized methods have been investigated due to the sparsity-inducing properties of L1 norm. In this paper, we present a reconstruction method based on L[Formula: see text] regularization to enhance sparsity of BLT solution and solve the nonconvex L[Formula: see text] norm problem by converting it to a series of weighted L1 homotopy minimization problems with iteratively updated weights. To assess the performance of the proposed reconstruction algorithm, simulations on a heterogeneous mouse model are designed to compare it with three representative sparse reconstruction algorithms, including the weighted interior-point, L1 homotopy, and the Stagewise Orthogonal Matching Pursuit algorithm. Simulation results show that the proposed method yield stable reconstruction results under different noise levels. Quantitative comparison results demonstrate that the proposed algorithm outperforms the competitor algorithms in location accuracy, multiple-source resolving and image quality.

Nonlinear Quantitative Photoacoustic Tomography with Two-Photon Absorption

Two-photon photoacoustic tomography (TP-PAT) is a noninvasive optical molecular imaging modality that aims at inferring the two-photon absorption property of heterogeneous media from photoacoustic measurements. In this work, we analyze an inverse problem in quantitative TP-PAT where we intend to reconstruct optical coefficients in a semilinear elliptic PDE, the mathematical model for the propagation of near infrared photons in tissue-like optical media with two-photon absorption, from the internal absorbed energy data. We derive uniqueness and stability results on the reconstructions of single and multiple optical coefficients, and present some numerical reconstruction results based on synthetic data to complement the theoretical analysis.

Research progress of X-ray luminescence optical tomography

Recently, X-ray luminescence optical tomography (XLOT) has been proposed as a promising optical molecular imaging modality. XLOT, or equivalently, X-ray luminescence computed tomography (XLCT), is a tomography imaging technique based on the X-ray excited nanophosphors (NPs). Briefly, when NPs in imaged object are irradiated with X-ray, NPs will emit visible or near infrared (NIR) luminescence. By mathematically modeling the light transportation and solving an inverse problem, the three dimensional (3D) distribution of NPs in imaged object can be recovered. Compared with the conventional optical molecular imaging modalities, XLOT has ability to eliminate the autofluorescence and provide the increased penetration depth in tissues. As a result, the imaging technique is well suited for biomedical researches. Especially, XLOT provides the potential for clinical applications due to the increased penetration depth. Based on the excitation patterns of X-ray beams, the current XLOT imaging systems can be classed into three types, i.e., the pencil-beam system, the fan-beam system, and the cone-beam system. Among these systems, the pencil-beam XLOT has the highest spatial resolution and the lowest time resolution. In contrast, the cone-beam XLOT system, especially the single-view cone-beam XLOT system, has the shortest data acquisition time. But, the imaging quality is relatively lower compared to the pencil-beam system. Hence, there is a tradeoff between the spatial resolution and time resolution for XLOT imaging technique. After acquring the measurement data by the above XLOT system, the 3D distribution of NPs in imaged object can be recovered by the reconstruction methods. For XLOT reconstruction, there are two types of methods, i.e., the filtered back projection (FBP) method and the reconstruction method based on photon migration model. For the pencil-beam XLOT system, the reconstruction is generally performed by FBP method, which is similar to XCT reconstruction method. For the cone-beam XLOT system, the NPs in imaged object are generally resolved by using the method based on photon migration model. It is worth noting that the reconstruction based on migration mode is a high ill-posed problem due to the high scattering of light in biological tissues. To alleviate the ill-posedness, the compressive sensing technique and a priori information method (e.g., excitation a priori information) can be used. In addition, the imaging probes play an important role in XLOT imaging. Currently, the rare-earth nanophosphors have be widely used in XLOT due to their optical properties. Of course, the rare-earth nanophosphors are not sole NPs for XLOT imaging. Other NPs, e.g., quantum dots and gold nanoclusters, have also been used as the imaging probes. Further, with the advances in NPs, more applications would be expected in bio-medical researches. To sum up, for XLOT excellent performances, during the last few years, the continuous research efforts have been made to develop new imaging systems, build robust reconstruction methods, design efficient NPs, and expand the applications of XLOT. This paper reviews the developments of XLOT, including the basic imaging principles, system compositions, and advantages and disadvantages of different XLOT imaging systems. Subsequently, the corresponding reconstruction methods and the imaging probes are classified and summarized. Finally, we discuss the applications of XLOT in the preclinical diagnosis, and the future research direction of XLOT.

Recent Advances in Optical Molecular Imaging and its Applications in Targeted Drug Delivery.

Optical molecular imaging has been frequently used in many preclinical researches including cancer detection, tumor mechanism study, drug efficacy evaluation and targeted drug delivery. Among optical molecular imaging modalities, bioluminescence imaging and fluorescence imaging have acquired certain degree of development and attracted more and more attention in recent years for their high sensitivity and low cost. With the development of optical technology and probe technology, two-photon microscopy imaging and Raman imaging have been widely used in drug evaluation and tumor studies through cell and tissue imaging. This paper focuses on the occurrence and development of optical molecular imaging especially for its imaging method imaging system and its application in target drug delivery. Finally, the existing challenges and brand new applications of optical imaging techniques in drug delivery research are discussed.

Recent advances in bioluminescence tomography: methodology and system as well as application

Optical molecular imaging has been rapidly developed to noninvasively visualize in vivo physiological and pathological processes involved in normal and suffering organisms at the cellular and molecular levels, in which advanced optical imaging technology and modern molecular biology are being combined to provide a state-of-the-art tool for preclinical biomedical research. Among optical molecular imaging modalities, bioluminescence tomography (BLT) has experienced considerable growth and attracted much attention in recent years for its excellent performance, unique advantages, and high cost-effectiveness. This article focuses on the genesis and development of BLT, especially for its computational methodology, imaging system, and biomedical application. An overview of the advantages and challenges of the conventional planar bioluminescence imaging technique is first described in comparison with currently available molecular imaging modalities. The imaging algorithms for inverse source reconstruction are classified and summarized according to different a priori knowledge, followed by a simple depiction of the uniqueness theorems of BLT solution. Diverse imaging systems for obtaining three-dimensional quantitative information of internal bioluminescent sources are then reviewed. The latest application examples of BLT in tumor study and drug discovery are introduced and compared with other mature imaging technologies. Finally, the paper is concluded and an attractive prospect for BLT ispredicted.

Recent advances in bioluminescence tomography: methodology and system as well as application

Optical molecular imaging has been rapidly developed to noninvasively visualize in vivo physiological and pathological processes involved in normal and suffering organisms at the cellular and molecular levels, in which advanced optical imaging technology and modern molecular biology are being combined to provide a state-of-the-art tool for preclinical biomedical research. Among optical molecular imaging modalities, bioluminescence tomography (BLT) has experienced considerable growth and attracted much attention in recent years for its excellent performance, unique advantages, and high cost-effectiveness. This article focuses on the genesis and development of BLT, especially for its computational methodology, imaging system, and biomedical application. An overview of the advantages and challenges of the conventional planar bioluminescence imaging technique is first described in comparison with currently available molecular imaging modalities. The imaging algorithms for inverse source reconstruction are classified and summarized according to different a priori knowledge, followed by a simple depiction of the uniqueness theorems of BLT solution. Diverse imaging systems for obtaining three-dimensional quantitative information of internal bioluminescent sources are then reviewed. The latest application examples of BLT in tumor study and drug discovery are introduced and compared with other mature imaging technologies. Finally, the paper is concluded and an attractive prospect for BLT is predicted.

In vivo quantitative bioluminescence tomography using heterogeneous and homogeneous mouse models

Bioluminescence tomography (BLT) is a new optical molecular imaging modality, which can monitor both physiological and pathological processes by using bioluminescent light-emitting probes in small living animal. Especially, this technology possesses great potential in drug development, early detection, and therapy monitoring in preclinical settings. In the present study, we developed a dual modality BLT prototype system with Micro-computed tomography (MicroCT) registration approach, and improved the quantitative reconstruction algorithm based on adaptive hp finite element method (hp-FEM). Detailed comparisons of source reconstruction between the heterogeneous and homogeneous mouse models were performed. The models include mice with implanted luminescence source and tumor-bearing mice with firefly luciferase report gene. Our data suggest that the reconstruction based on heterogeneous mouse model is more accurate in localization and quantification than the homogeneous mouse model with appropriate optical parameters and that BLT allows super-early tumor detection in vivo based on tomographic reconstruction of heterogeneous mouse model signal.

Multimodality Molecular Imaging

In this article, we reported the progress of our research in molecular imaging. Two types of optical molecular imaging modalities are presented in the Optical Imaging section: fluorescence molecular tomography (FMT) and bioluminescence tomography (BLT). medical imaging and probe studies in molecular imaging are studied in the Nuclide Imaging and Molecular Probe sections, respectively. We discuss the biological applications related to molecular imaging in the Biological Application section and conclusions are drawn in the end.