A hybrid PET‐MRI: An integrated molecular‐genetic imaging system with HRRT‐PET and 7.0‐T MRI

A PET‐MRI fusion system is developed for molecular‐genetic imaging. The purpose of the system is to obtain images of the in‐vivo human brain using two high‐end imaging devices, an advanced PET and an ultrahigh‐field MRI. These are the HRRT‐PET, a high‐resolution research tomograph dedicated to brain imaging on the molecular level, and the 7.0‐T MRI, an ultrahigh field version used for morphological imaging. HRRT‐PET delivers high‐resolution molecular imaging with a resolution down to 2.5 mm FWHM, which is currently the highest spatial resolution available for the observation of the human brain's molecular activities, including enzymes and receptors, which are manipulated genetically, such as reporter genes and probes. The 7.0‐T MRI began to reveal submillimeter resolution images of the cortical as well as deep brain areas, down to 250 μm, which allows us to visualize the fine details of the cortical and brainstem areas, including the line of Gennari in the visual cortex and the corticospinal tracts in the pontine area. The current PET‐MRI fusion imaging system produces the highest quality images of molecular and genetic activities of the human brain in vivo. It is starting to provide many answers to the key questions about the neurological diseases. Some of these start providing answers to many cognitive neuroscience problems with clear molecular and genetic bases. There is great potential in the PET‐MRI for early diagnosis of cancers as well as other neurological diseases, which we were previously unable to diagnose, such as microscopic molecular changes that occur in Parkinson's and Alzheimer's diseases. © 2007 Wiley Periodicals, Inc. Int J Imaging Syst Technol, 17, 252–265, 2007     

Non‐iterative reconstruction with a prior for undersampled radial MRI data

This paper develops an FBP‐MAP (filtered backprojection, maximum a posteriori) algorithm to reconstruct MRI images from undersampled data. An objective function is first set up for the MRI reconstruction problem with a data fidelity term and a Bayesian term. The Bayesian term is a constraint in the temporal dimension. This objective function is minimized using the calculus of variations. The proposed algorithm is non‐iterative. Undersampled dynamic myocardial perfusion MRI data were used to test the feasibility of the proposed technique. It is shown that the non‐iterative Fourier–Bayesian reconstruction method effectively incorporates the temporal constraint and significantly reduces the angular aliasing artifacts caused by undersampling. A significant advantage of the proposed non‐iterative Fourier–Bayesian technique over the iterative techniques is its fast computation time and its ability to reach the optimal solution. © 2013 Wiley Periodicals, Inc. Int J Imaging Syst Technol, 23, 53–58, 2013.     

Magnetic resonance imaging reconstruction via non‐convex total variation regularization

Magnetic resonance imaging (MRI) reconstruction model based on total variation (TV) regularization can deal with problems such as incomplete reconstruction, blurred boundary, and residual noise. In this article, a non‐convex isotropic TV regularization reconstruction model is proposed to overcome the drawback. Moreau envelope and minmax‐concave penalty are firstly used to construct the non‐convex regularization of L₂ norm, then it is applied into the TV regularization to construct the sparse reconstruction model. The proposed model can extract the edge contour of the target effectively since it can avoid the underestimation of larger nonzero elements in convex regularization. In addition, the global convexity of the cost function can be guaranteed under certain conditions. Then, an efficient algorithm such as alternating direction method of multipliers is proposed to solve the new cost function. Experimental results show that, compared with several typical image reconstruction methods, the proposed model performs better. Both the relative error and the peak signal‐to‐noise ratio are significantly improved, and the reconstructed images also show better visual effects. The competitive experimental results indicate that the proposed approach is not limited to MRI reconstruction, but it is general enough to be used in other fields with natural images.     

Image reconstruction with a shift‐variant filtration in circular cone‐beam CT

It is well known that cone‐beam data acquired with a circular orbit are insufficient for exact image reconstruction. Despite this, because a cone‐beam scanning configuration with a circular orbit is easy to implement in practice, it has been widely employed for data acquisition in, e.g., micro‐CT and CT imaging in radiation therapy. The algorithm developed by Feldkamp, Davis, and Kress (FDK) and its modifications, such as the Tent–FDK (T‐FDK) algorithm, have been used for image reconstruction from circular cone‐beam data. In this work, we present an algorithm with spatially shift‐variant filtration for image reconstruction in circular cone‐beam CT. We performed computer‐simulation studies to compare the proposed and existing algorithms. Numerical results in these studies demonstrated that the proposed algorithm has resolution properties comparable to, and noise properties better than, the FDK algorithm. As compared to the T‐FDK algorithm, our proposed algorithm reconstructs images with an improved in‐plane spatial resolution. © 2005 Wiley Periodicals, Inc. Int J Imaging Syst Technol, 14, 213–221, 2004; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ima.20026     

One‐Step,Room‐Temperature Synthesis of Glutathione‐Capped Iron‐Oxide Nanoparticles and their Application in In Vivo T1‐Weighted Magnetic Resonance Imaging

The room‐temperature, aqueous‐phase synthesis of iron‐oxide nanoparticles (IO NPs) with glutathione (GSH) is reported. The simple, one‐step reduction involves GSH as a capping agent and tetrakis(hydroxymethyl)phosphonium chloride (THPC) as the reducing agent; GSH is an anti‐oxidant that is abundant in the human body while THPC is commonly used in the synthesis of noble‐metal clusters. Due to their low magnetization and good water‐dispersibility, the resulting GSH‐IO NPs, which are 3.72 ± 0.12 nm in diameter, exhibit a low r₂ relaxivity (8.28 mm ^?1s^?1) and r₂/r₁ ratio (2.28)—both of which are critical for T₁ contrast agents. This, together with the excellent biocompatibility, makes these NPs an ideal candidate to be a T₁ contrast agent. Its capability in cellular imaging is illustrated by the high signal intensity in the T₁‐weighted magnetic resonance imaging (MRI) of treated HeLa cells. Surprisingly, the GSH‐IO NPs escape ingestion by the hepatic reticuloendothelial system, enabling strong vascular enhancement at the internal carotid artery and superior sagittal sinus, where detection of the thrombus is critical for diagnosing a stroke. Moreover, serial T₁‐ and T₂‐weighted time‐dependent MR images are resolved for a rat's kidneys, unveiling detailed cortical‐medullary anatomy and renal physiological functions. The newly developed GSH‐IO NPs thus open a new dimension in efforts towards high‐performance, long‐circulating MRI contrast agents that have biotargeting potential.     

Conformal higher‐order remeshing schemes for implicitly defined interface problems

A new higher‐order accurate method is proposed that combines the advantages of the classical p‐version of the FEM on body‐fitted meshes with embedded domain methods. A background mesh composed by higher‐order Lagrange elements is used. Boundaries and interfaces are described implicitly by the level set method and are within elements. In the elements cut by the boundaries or interfaces, an automatic decomposition into higher‐order accurate sub‐elements is realized. Therefore, the zero level sets are detected and meshed in a first step, which is called reconstruction. Then, based on the topological situation in the cut element, higher‐order sub‐elements are mapped to the two sides of the boundary or interface. The quality of the reconstruction and the mapping largely determines the properties of the resulting, automatically generated conforming mesh. It is found that optimal convergence rates are possible although the resulting sub‐elements are not always well‐shaped. Copyright © 2016 John Wiley & Sons, Ltd.     

In‐Plane 2H‐1T′ MoTe2 Homojunctions Synthesized by Flux‐Controlled Phase Engineering

The fabrication of in‐plane 2H‐1T′ MoTe₂ homojunctions by the flux‐controlled, phase‐engineering of few‐layer MoTe₂ from Mo nanoislands is reported. The phase of few‐layer MoTe₂ is controlled by simply changing Te atomic flux controlled by the temperature of the reaction vessel. Few‐layer 2H MoTe₂ is formed with high Te flux, while few‐layer 1T′ MoTe₂ is obtained with low Te flux. With medium flux, few‐layer in‐plane 2H‐1T′ MoTe₂ homojunctions are synthesized. As‐synthesized MoTe₂ is characterized by Raman spectroscopy and X‐ray photoelectron spectroscopy. Kelvin probe force microscopy and Raman mapping confirm that in‐plane 2H‐1T′ MoTe₂ homojunctions have abrupt interfaces between 2H and 1T′ MoTe₂ domains, possessing a potential difference of about 100 mV. It is further shown that this method can be extended to create patterned metal–semiconductor junctions in MoTe₂ in a two‐step lithographic synthesis. The flux‐controlled phase engineering method could be utilized for the large‐scale controlled fabrication of 2D metal–semiconductor junctions for next‐generation electronic and optoelectronic devices.     

A modified POCS‐based reconstruction method for compressively sampled MR imaging

One of the challenging tasks in the application of compressed sensing to magnetic resonance imaging is the reconstruction algorithm that can faithfully recover the MR image from randomly undersampled k‐space data. The nonlinear recovery algorithms based on iterative shrinkage start with a single initial guess and use soft‐thresholding to recover the original MR image from the partial Fourier data. This article presents a novel method based on projection onto convex set (POCS) algorithm but it takes two images and then randomly combines them at each iteration to estimate the original MR image. The performance of the proposed method is validated using the original data taken from the MRI scanner at St. Mary's Hospital, London. The experimental results show that the proposed method can reconstruct the original MR image from variable density undersampling scheme in less number of iterations and exhibits better performance in terms of improved signal‐to‐noise ratio, artifact power, and correlation as compared to the reconstruction through low‐resolution and POCS algorithms. © 2014 Wiley Periodicals, Inc. Int J Imaging Syst Technol, 24, 203–207, 2014     

Stress‐Strength Reliability Analysis with Extreme Values based on q‐Exponential Distribution

When dealing with practical problems of stress–strength reliability, one can work with fatigue life data and make use of the well‐known relation between stress and cycles until failure. For some materials, this kind of data can involve extremely large values. In this context, this paper discusses the problem of estimating the reliability index R = P(Y < X) for stress–strength reliability, where stress Y and strength X are independent q‐exponential random variables. This choice is based on the q‐exponential distribution's capability to model data with extremely large values. We develop the maximum likelihood estimator for the index R and analyze its behavior by means of simulated experiments. Moreover, confidence intervals are developed based on parametric and nonparametric bootstrap. The proposed approach is applied to two case studies involving experimental data: The first one is related to the analysis of high‐cycle fatigue of ductile cast iron, whereas the second one evaluates the specimen size effects on gigacycle fatigue properties of high‐strength steel. The adequacy of the q‐exponential distribution for both case studies and the point and interval estimates based on maximum likelihood estimator of the index R are provided. A comparison between the q‐exponential and both Weibull and exponential distributions shows that the q‐exponential distribution presents better results for fitting both stress and strength experimental data as well as for the estimated R index. Copyright © 2016 John Wiley & Sons, Ltd.     

Ten‐Gram‐Scale Facile Synthesis of Organogadolinium Complex Nanoparticles for Tumor Diagnosis

The market of available contrast agents for clinical magnetic resonance imaging (MRI) has been dominated by gadolinium (Gd) chelates based T₁ contrast agents for decades. However, there are growing concerns about their safety because they are retained in the body and are nephrotoxic, which necessitated a warning by the U.S. Food and Drug Administration against the use of such contrast agents. To ameliorate these problems, it is necessary to improve the MRI efficiency of such contrast agents to allow the administration of much reduced dosages. In this study, a ten‐gram‐scale facile method is developed to synthesize organogadolinium complex nanoparticles (i.e., reductive bovine serum albumin stabilized Gd‐salicylate nanoparticles, GdSalNPs‐rBSA) with high r₁ value of 19.51 mm ^?1 s^?1 and very low r₂/r₁ ratio of 1.21 (B₀ = 1.5 T) for high‐contrast T₁‐weighted MRI of tumors. The GdSalNPs‐rBSA nanoparticles possess more advantages including low synthesis cost (≈0.54 USD per g), long in vivo circulation time (t_1/2 = 6.13 h), almost no Gd³⁺ release, and excellent biosafety. Moreover, the GdSalNPs‐rBSA nanoparticles demonstrate excellent in vivo MRI contrast enhancement (signal‐to‐noise ratio (ΔSNR) ≈ 220%) for tumor diagnosis.     

Fluorescent Magnetic Fe3O4/Rare Earth Colloidal Nanoparticles for Dual‐Modality Imaging

Fluorescent magnetic colloidal nanoparticles (FMCNPs) are produced by a two‐step, seed emulsifier‐free emulsion polymerization in the presence of oleic acid and sodium undecylenate‐modified Fe₃O₄ nanoparticles (NPs). The Fe₃O₄/poly(St‐co‐GMA) nanoparticles are first synthesized as the seed and Eu(AA)₃Phen is copolymerized with the remaining St and GMA to form the fluorescent polymer shell in the second step. The uniform core–shell structured FMCNPs with a mean diameter of 120 nm exhibit superparamagnetism with saturation magnetization of 1.92 emu/g. Red luminescence from the FMCNPs is confirmed by the salient fluorescence emission peaks of europium ions at 594 and 619 nm as well as 2‐photon confocal scanning laser microscopy. The in vitro cytotoxicity test conducted using the MTT assay shows good cytocompatibility and the T₂ relaxivity of the FMCNPs is 353.86 mM^?1S^?1 suggesting its potential in magnetic resonance imaging (MRI). In vivo MRI studies based on a rat model show significantly enhanced T₂‐weighted images of the liver after administration and prussian blue staining of the liver tissue slice reveals accumulation of FMCNPs in the organ. The cytocompatibility, superparamagnetism, and excellent fluorescent properties of FMCNPs make them suitable for biological imaging probes in MRI and optical imaging.     

Real‐time ballistocardiographic artifact reduction using the k‐teager energy operator detector and multi‐channel referenced adaptive noise cancelling

The simultaneous electroencephalogram (EEG) and functional magnetic resonance imaging (fMRI) recording technique has recently received considerable attention and has been used in many studies on cognition and neurological disease. EEG‐fMRI simultaneous recording has the advantage of enabling the monitoring of brain activity with both high temporal resolution and high spatial resolution in real time. The successful removal of the ballistocardiographic (BCG) artifact from the EEG signal recorded during an MRI is an important prerequisite for real‐time EEG‐fMRI joint analysis. We have developed a new framework dedicated to BCG artifact removal in real‐time. This framework includes a new real‐time R‐peak detection method combining a k‐Teager energy operator, a thresholding detector, and a correlation detector, as well as a real‐time BCG artifact reduction procedure combining average artifact template subtraction and a new multi‐channel referenced adaptive noise cancelling method. Our results demonstrate that this new framework is efficient in the real‐time removal of the BCG artifact. The multi‐channel adaptive noise cancellation (mANC) method performs better than the traditional ANC method in eliminating the BCG residual artifact. In addition, the computational speed of the mANC method fulfills the requirements of real‐time EEG‐fMRI analysis. © 2016 Wiley Periodicals, Inc. Int J Imaging Syst Technol, 26, 209–215, 2016     

Reduced‐bias Moment Approximations in Original Units When Using Multivariate Box–Cox Transformations

Motivated by A‐10 single engine aircraft climb experiments, we demonstrate use of the multivariate Box–Cox power transformations in fitting normal‐theory linear models to a q‐variate response vector Y . As predictions in the original units of the response are often desired, a retransformation of the fitted model back to the original units can be performed. Unfortunately, Jensen's inequality suggests that for a nonlinear transformation, such an approach can induce significant bias into the retransformed values. Further, although the retransformation offers a direct estimate of E ( Y ), it offers no direct estimates for the variances and covariances of Y . An estimate for the variance–covariance matrix can be useful when constructing approximate joint prediction regions on Y . To address these concerns, we consider the class of multivariate Box–Cox transformations and derive a closed‐form approximation to (k _i ,k _j ∈[0,1,...]; i ,j = 1,…,q ), which can then be used to provide reduced‐bias estimates of elements of the mean vector and covariance matrix of the original response Y , given parameter estimates obtained from fitting the model in the transformed domain. Using our approximation, we then construct an approximate 100(1 ? α )% joint prediction ellipsoid on Y . Unlike the prediction ellipsoid offered by ordinary least squares analysis, the proposed prediction ellipsoid can change in both size and orientation, depending on the levels of the experimental factors. Copyright © 2016 John Wiley & Sons, Ltd.     

Level‐cut inhomogeneous filtered Poisson field for two‐phase microstructures

Level‐cut homogeneous filtered Poisson fields developed in (J. Appl. Phys. 2003; 94 (6):3762–3770) to model two‐phase microstructures are defined, and their properties are briefly reviewed. Filtered Poisson fields are sums of randomly scaled and oriented kernels that are centered at the points of homogeneous Poisson fields. The cuts of these fields above specified thresholds are called level‐cut homogeneous filtered Poisson fields. It is shown that an arbitrary inhomogeneous Poisson field becomes homogeneous if observed in new coordinates, and that the mapping relating inhomogeneous and homogeneous Poisson fields can be constructed in a simple manner. This mapping and the model in (J. Appl. Phys. 2003; 94 (6): 3762–3770) provide an efficient algorithm for generating arbitrary inhomogeneous two‐phase microstructures. Developments in (Int. J. Numer. Meth. Engng 2008; DOI: 10.1002/nme.2340 ), using arguments essentially identical to those in (J. Appl. Phys. 2003; 94 (6):3762–3770) to define and generate inhomogeneous Poisson fields, overlook the natural extension of results in (J. Appl. Phys. 2003; 94 (6): 3762–3770) to these fields provided by the mapping constructed in this paper. Copyright © 2008 John Wiley & Sons, Ltd.     

Molecular Modelling of Bone Morphogenetic Protein‐2 (BMP‐2) by 3D‐Rapid Prototyping

Bone morphogenetic proteins (BMP) play a decisive role in bone development and osteogenesis. In the past they have been the subject of widespread research and clinical trials as stimulants of bone growth. Recently BMP‐2 has been chemically immobilized on implant surfaces leading to enhanced bone growth and accelerated integration in sheep. Although the 3D‐structure of BMP‐2 is known the surface topography has not been the subject of a detailed analysis. Therefore we have begun implementing the technique of 3D‐rapid prototyping as a novel method for gaining topographical information on the structure‐function relationship of proteins (Laub et al., 2001, FASEB J. 15, A543). 3D‐rapid prototyping allows the construction of accurate three‐dimensional models of proteins based on their x‐ray crystallographic data. In this way we constructed a 3D scale image of BMP‐2 of the size 140 mm × 70 mm × 50 mm corresponding to a ca. 20 × 10⁶ fold magnification (scale 1 nm = 2 cm). BMP‐2 is a twisted banana‐shaped molecule consisting of a convex and a concave face and has a horn‐like protuberance cross‐turned at 180° (long axis) at each end. In the center of the convex face there is a ca. 1 nm deep crater like pit ca. 1.8 nm in diameter. The concave face is characterized by a 6–7 nm long helical groove 0.8–1.6 nm wide and ca 0.8 nm deep, into which a left‐handed helix with a pitch of 8–9 nm and a helical radius of 0.35–0.45 nm can be fitted. The concave face of BMP‐2 therefore corresponds to an imprint (groove) of a left‐handed helix i. e. to an anti‐helix or anthelix. The possible endogenous ligands and functions of these structures are unknown. These results demonstrate that full scale 3D molecular models of proteins can lead to new perceptions in understanding the interactions between ligands and proteins by macroscopic viewing and in‐hand fitting of the molecules without the aid of a computer.     

Magnetic resonance scan‐time reduction using echo prediction

A linear prediction (LP) filter derived from a complete echo with zero‐phase encoding amplitude is used for recovering anatomical details from a partially acquired echo sequence. The LP filter is shown to reconstruct missing k‐space phase and amplitude information, with errors sufficiently low so as to provide image reconstruction with a contrast‐to‐noise ratio (CNR) ≥ 3. For volume imaging using multislice acquisition, the partial‐echo sequence enables more number of slices to be acquired for a given repetition time period T_R. For such sequences, separate predictors are used for reconstruction of missing k‐space data corresponding to each individual slice in the volume. The proposed filtering scheme is shown to achieve results comparable to other partial k‐space approaches such as singularity function analysis (SFA), when the noise content is less than about 0.4%. For higher noise levels, this technique is recommended as a preprocessing step for SFA to track the singularity locations more accurately. © 2013 Wiley Periodicals, Inc. Int J Imaging Syst Technol, 23, 1–8, 2013     

Three‐Dimensional Shape Reconstruction System Based on Fiber‐Optic Interference Fringe Imaging

In this article, we describe a three‐dimensional shape reconstruction system based on the Mach–Zehnder interferometer structure and Young's double pinhole interference principle, while utilizing Fresnel reflection on fiber end face and interference at the fourth port of 3‐dB coupler to achieve closed‐loop precise control of fringe phase. A root‐mean‐square phase stability of 4 mrad is measured with the system. The shape of the object is determined by analyzing the fringe pattern. A new algorithm called rotating rectangular window autoselection is used as the band‐pass filter. The measuring time of the whole system is less than 200 ms, and the error of system is 0.27 mm. Meanwhile, the overall complexity of the measuring algorithm is O(n log n).     

Freestanding 1T‐MnxMo1–xS2–ySey and MoFe2S4–zSez Ultrathin Nanosheet‐Structured Electrodes for Highly Efficient Flexible Solid‐State Asymmetric Supercapacitors

Fabrication of hierarchical nanosheet arrays of 1T phase of transition‐metal dichalcogenides is indeed a critical task, but it holds immense potential for energy storage. A single‐step strategy is employed for the fabrication of stable 1T‐Mn_xMo_1–xS_2–ySe_y and MoFe₂S_4–zSe_z hierarchical nanosheet arrays on carbon cloth as positive and negative electrodes, respectively. The flexible asymmetric supercapacitor constructed with these two electrodes exhibits an excellent electrochemical performance (energy density of ≈69 Wh kg^?1 at a power density of 0.985 kW kg^?1) with ultralong cyclic stability of ≈83.5% capacity retention, after 10 000 consecutive cycles. Co‐doping of the metal and nonmetal boosts the charge storage ability of the transition‐metal chalcogenides following enrichment in the metallic 1T phase, improvement in the surface area, and expansion in the interlayer spacing in tandem, which is the key focus of the present study. This study explicitly demonstrates the exponential enhancement of specific capacity of MoS₂ following intercalation and doping of Mn and Se, and Fe₂S₃ following doping of Mo and Se could be an ideal direction for the fabrication of novel energy‐storage materials with high‐energy storage ability.     

A novel numerical method of high‐order accuracy for flow in unsaturated porous media

We construct finite volume schemes of very high order of accuracy in space and time for solving the nonlinear Richards equation (RE). The general scheme is based on a three‐stage predictor–corrector procedure. First, a high‐order weighted essentially non‐oscillatory (WENO) reconstruction procedure is applied to the cell averages at the current time level to guarantee monotonicity in the presence of steep gradients. Second, the temporal evolution of the WENO reconstruction polynomials is computed in a predictor stage by using a global weak form of the governing equations. A global space–time DG FEM is used to obtain a scheme without the parabolic time‐step restriction caused by the presence of the diffusion term in the RE. The resulting nonlinear algebraic system is solved by a Newton–Krylov method, where the generalized minimal residual method algorithm of Saad and Schulz is used to solve the linear subsystems. Finally, as a third step, the cell averages of the finite volume method are updated using a one‐step scheme, on the basis of the solution calculated previously in the space–time predictor stage. Our scheme is validated against analytical, experimental, and other numerical reference solutions in four test cases. A numerical convergence study performed allows us to show that the proposed novel scheme is high order accurate in space and time. Copyright © 2011 John Wiley & Sons, Ltd.     

Brain image segmentation using a combination of expectation‐maximization algorithm and watershed transform

Watershed transformation is an effective segmentation algorithm that originates from the mathematical morphology field. This algorithm is widely used in medical image segmentation because it produces complete division even under poor contrast. However, over‐segmentation is its most significant limitation. Therefore, this article proposes a combination of watershed transformation and the expectation‐maximization (EM) algorithm to segment MR brain images efficiently. The EM algorithm is used to form clusters. Then, the brightest cluster is considered and converted into a binary image. A Sobel operator applied on the binary image generates the initial gradient image. Morphological reconstruction is applied to find the foreground and background markers. The final gradient image is obtained using the minima imposition technique on the initial gradient magnitude along with markers. In addition, watershed segmentation applied on the final gradient magnitude generates effective gray matter and cerebrospinal fluid segmentation. The results are compared with simple marker controlled watershed segmentation, watershed segmentation combined with Otsu multilevel thresholding, and local binary fitting energy model for validation. © 2016 Wiley Periodicals, Inc. Int J Imaging Syst Technol, 26, 225–232, 2016