Dual-band high-Q near-perfect absorption by tilted Si-assisted metasurfaces.

All-dielectric metasurface perfect absorbers (MPAs) based on quasibound states in the continuum (QBICs) play a crucial role in optical and photonic devices as they can excite high-Q resonances. These structures require adding back reflectors or placing at least two asymmetric elements in each unit to break the absorption limit of 50%, which will increase the design complexity. In this work, we propose a high-Q monolayer MPA (MMPA) composed of a tilted Si nanocube array. By tuning the tilted angle of the nanocube, dual-QBIC modes at two different wavelengths are excited, which corresponds to magnetic quadrupole (MQ) and toroidal dipole (TD) modes, respectively. The high-reflection but low-Q magnetic dipole (MD) background mode excited by such a dual-band structure can decrease the radiative loss of transmission of MQ and TD modes, enabling the structure to break the absorption limit of 50%. The maximum absorption achieves 94% simultaneously at the wavelength of 933 and 961 nm, with the Q factors of 759 and 986, respectively. Our work provides a simple paradigm for designing dual-band high-Q MMPAs, which would greatly expand their range of applications, such as multiplexed optical nanodevices.

Near-perfect absorption of a honeycomb metasurface through QBICs.

All-dielectric high-Q metasurface absorbers based on quasi-bound states in the continuum (QBICs) are essential for optical and photonic devices. However, achieving perfect absorption requires adding back reflectors at the bottom or placing at least four asymmetric elements in each unit of monolayer metasurfaces, which will increase the design complexity. This work proposes a honeycomb structure with units periodically arranged as a hexagonal lattice. Each unit cell is made of two nanopost elements. By only tuning the radius difference of two elements to break the in-plane symmetry, two orthogonal QBIC modes corresponding to toroidal dipole (TD) and electric dipole (ED) modes are excited, respectively. The maximum absorption reaches 92.3% at 955 nm with a Q factor of 1501, breaking the monolayer limit of 50% by the degenerate critical coupling. Our work may provide a promising route for designing high-Q all-dielectric metasurface absorbers applied in ultrafast optoelectronic devices.

Optimization of Exopolysaccharide Produced by Lactobacillus plantarum R301 and Its Antioxidant and Anti-Inflammatory Activities.

In this study, the yield of exopolysaccharide (EPS) from Lactobacillus plantarum R301 was optimized using a single-factor experiment and response surface methodology (RSM). After optimization, the EPS yield was increased with a fold-change of 0.85. The significant factors affecting EPS production, as determined through a Plackett-Burman design and Central Composite Design (CCD), were MgSO4 concentration, initial pH, and inoculation size. The maximum yield was 97.85 mg/mL under the condition of 0.01% MgSO4, an initial pH 7.4, and 6.4% of the inoculation size. In addition, the EPS exhibited strong antioxidant activity, as demonstrated by its ability to scavenge DPPH, ABTS, and hydroxyl radicals. The scavenging rate was up to 100% at concentrations of 4 mg/mL, 1 mg/mL, and 2 mg/mL, respectively. Moreover, the EPS also exhibited reducing power, which was about 30% that of ascorbic acid when both tended to be stable with the increased concentration. These results suggest that L. plantarum R301 EPS possesses different antioxidant mechanisms and warrants further investigation. In addition to its antioxidant activity, the EPS also demonstrated good anti-inflammatory activity by inhibiting the inflammation induced by lipopolysaccharide (LPS) in RAW 264.7 cells, which could decrease nitric oxide (NO) production and expression of the proinflammatory cytokine Il-6. These findings suggest that L. plantarum R301 EPS could be used as a potential multifunctional food additive in the food industry.

Multi-target bioactive compound screening from the infructescence of Platycarya strobilacea Sieb. et Zucc. by affinity chromatography using immobilized ß2 -adrenoceptor and muscarinic-3 acetylcholine receptor as the stationary phase.

As a main source for the recognition and identification of lead compounds, traditional Chinese medicine plays a pivotal role in preventing diseases for years. However, screening bioactive compounds from traditional Chinese medicine remains challenging because of the complexity of the systems and the occurrence of the synergic effect of the compounds. The infructescence of Platycarya strobilacea Sieb. et Zucc is prescribed for allergic rhinitis treatment with unknown bioactive compounds and unclear mechanisms. Herein, we immobilized the ß2 -adrenoceptor and muscarine-3 acetylcholine receptor onto the silica gel surface to prepare the stationary phase in a covalent bond through one step. The feasibility of the columns was investigated by the chromatographic method. Ellagic acid and catechin were identified as the bioactive compounds targeting the receptors. The binding constants of ellagic acid were calculated to be (1.56 ± 0.23)×107  M-1 for muscarine-3 acetylcholine receptor and (2.93 ± 0.15)×107  M-1 for ß2 -adrenoceptor by frontal analysis. While catechin can bind with muscarine-3 acetylcholine receptor with an affinity of (3.21 ± 0.05)×105  M-1 . Hydrogen bonds and van der Waals' force were the main driving forces for the two compounds with the receptors. The established method provides an alternative for multi-target bioactive compound screening in complex matrices.

Research on control strategy of vehicle stability based on dynamic stable region regression analysis.

The intervention time of stability control system is determined by stability judgment, which is the basis of vehicle stability control. According to the different working conditions of the vehicle, we construct the phase plane of the vehicle's sideslip angle and sideslip angular velocity, and establish the sample dataset of the stable region of the different phase planes. To reduce the complexity of phase plane stable region division and avoid large amount of data, we established the support vector regression (SVR) model, and realized the automatic regression of dynamic stable region. The testing of the test set shows that the model established in this paper has strong generalization ability. We designed a direct yaw-moment control (DYC) stability controller based on linear time-varying model predictive control (LTV-MPC). The influence of key factors such as centroid position and road adhesion coefficient on the stable region is analyzed through phase diagram. The effectiveness of the stability judgment and control algorithm is verified by simulation tests.

Improve myocardial T1 measurement in rats with a new regression model: application to myocardial infarction and beyond.

PURPOSE: To improve myocardial and blood T1 measurements with a multi-variable T1 fitting model specifically modified for a segmented multi-shot FLASH sequence. METHODS: The proposed method was first evaluated in a series of phantoms simulating realistic tissues, and then in healthy rats (n = 8) and rats with acute myocardial infarction (MI) induced by coronary artery ligation (n = 8). RESULTS: By taking into account the saturation effect caused by sampling α-train pulses, and the longitudinal magnetization recovery between readouts, our model provided more accurate T1 estimate than the conventional three-parameter fit in phantoms under realistic gating procedures (error of -0.42 ± 1.73% versus -3.40 ± 1.46%, respectively, when using the measured inversion efficiency, ß). The baseline myocardial T1 values in healthy rats was 1636.3 ± 23.4 ms at 7 Tesla. One day postligation, the T1 values in the remote and proximal myocardial areas were 1637.5 ± 62.6 ms and 1740.3 ± 70.5 ms, respectively. In rats with acute MI, regional differences in myocardial T1 values were observed both before and after the administration of gadolinium. CONCLUSION: The proposed method has improved T1 estimate as validated in phantoms and could advance applications in rodents using quantitative myocardial T1 mapping.

High-resolution cardiovascular MRI by integrating parallel imaging with low-rank and sparse modeling.

Magnetic resonance imaging (MRI) has long been recognized as a powerful tool for cardiovascular imaging because of its unique potential to measure blood flow, cardiac wall motion, and tissue properties jointly. However, many clinical applications of cardiac MRI have been limited by low imaging speed. In this paper, we present a novel method to accelerate cardiovascular MRI through the integration of parallel imaging, low-rank modeling, and sparse modeling. This method consists of a novel image model and specialized data acquisition. Of particular novelty is the proposed low-rank model component, which is specially adapted to the particular low-rank structure of cardiovascular signals. Simulations and in vivo experiments were performed to evaluate the method, as well as an analysis of the low-rank structure of a numerical cardiovascular phantom. Cardiac imaging experiments were carried out on both human and rat subjects without the use of ECG or respiratory gating and without breath holds. The proposed method reconstructed 2-D human cardiac images up to 22 fps and 1.0 mm × 1.0 mm spatial resolution and 3-D rat cardiac images at 67 fps and 0.65 mm × 0.65 mm × 0.31 mm spatial resolution. These capabilities will enhance the practical utility of cardiovascular MRI.

Tracking T-cells in vivo with a new nano-sized MRI contrast agent.

Non-invasive in vivo tracking of T-cells by magnetic resonance imaging (MRI) can lead to a better understanding of many pathophysiological situations, including AIDS, cancer, diabetes, graft rejection. However, an efficient MRI contrast agent and a reliable technique to track non-phagocytic T-cells are needed. We report a novel superparamagnetic nano-sized iron-oxide particle, IOPC-NH2 series particles, coated with polyethylene glycol (PEG), with high transverse relaxivity (250 s(-1) mM(-1)), thus useful for MRI studies. IOPC-NH2 particles are the first reported magnetic particles that can label rat and human T-cells with over 90% efficiency, without using transfection agents, HIV-1 transactivator peptide, or electroporation. IOPC-NH2 particles do not cause any measurable effects on T-cell properties. Infiltration of IOPC-NH2-labeled T-cells can be detected in a rat model of heart-lung transplantation by in vivo MRI. IOPC-NH2 is potentially valuable contrast agents for labeling a variety of cells for basic and clinical cellular MRI studies, e.g., cellular therapy. FROM THE CLINICAL EDITOR: In this study, a novel PEG coated superparamagnetic nano-sized iron-oxide particle was investigated as a T-cell labeling agent for MRI studies. The reported particles can label T-cells with over 90% efficiency, without using transfection agents, HIV-1 transactivator peptide, or electroporation, therefore may enable more convenient preclinical call labeling studies.

A new nano-sized iron oxide particle with high sensitivity for cellular magnetic resonance imaging.

PURPOSE: In this study, we investigated the labeling efficiency and magnetic resonance imaging (MRI) signal sensitivity of a newly synthesized, nano-sized iron oxide particle (IOP) coated with polyethylene glycol (PEG), designed by Industrial Technology Research Institute (ITRI). PROCEDURES: Macrophages, bone-marrow-derived dendritic cells, and mesenchymal stem cells (MSCs) were isolated from rats and labeled by incubating with ITRI-IOP, along with three other iron oxide particles in different sizes and coatings as reference. These labeled cells were characterized with transmission electron microscopy (TEM), light and fluorescence microscopy, phantom MRI, and finally in vivo MRI and ex vivo magnetic resonance microscopy (MRM) of transplanted hearts in rats infused with labeled macrophages. RESULTS: The longitudinal (r (1)) and transverse (r (2)) relaxivities of ITRI-IOP are 22.71 and 319.2 s(-1) mM(-1), respectively. TEM and microscopic images indicate the uptake of multiple ITRI-IOP particles per cell for all cell types. ITRI-IOP provides sensitivity comparable or higher than the other three particles shown in phantom MRI. In vivo MRI and ex vivo MRM detect punctate spots of hypointensity in rejecting hearts, most likely caused by the accumulation of macrophages labeled by ITRI-IOP. CONCLUSION: ITRI-IOP, the nano-sized iron oxide particle, shows high efficiency in cell labeling, including both phagocytic and non-phagocytic cells. Furthermore, it provides excellent sensitivity in T(2)*-weighted MRI, and thus can serve as a promising contrast agent for in vivo cellular MRI.

Four-dimensional MR cardiovascular imaging: method and applications.

Magnetic resonance imaging (MRI) has long been recognized as a powerful tool for cardiovascular imaging because of its unique potential to measure blood flow, cardiac wall motion and tissue properties jointly. However, many clinical applications of cardiac MRI have been limited by low imaging speed. Three-dimensional cardiovascular MRI in real-time, or 4D cardiovascular MRI without cardiac and respiratory gating or triggering, remains an important technological goal of the MR cardiovascular research community. In this paper, we present a novel technique to achieve 4D cardiovascular MR imaging in unprecedented spatiotemporal resolution. This breakthrough is made possible through a creative use of sparse sampling theory and parallel imaging with phased array coils and a novel implementation of data acquisition and image reconstruction. We have successfully used the technique to perform 4D cardiovascular imaging on rats, achieving 0.65 mm × 0.65 mm × 0.31 mm spatial resolution with a frame rate of 67 fps. This capability enables simultaneous imaging of cardiac motion, respiratory motion, and first-pass myocardial perfusion. This in turn allows multiple cardiac assessments including measurement of ejection fraction, cardiac output, and myocardial blood flow in a single experiment. We believe that the proposed technique can open up many important applications of cardiovascular imaging and have significant impact on the field.

High-resolution cardiac MRI using partially separable functions and weighted spatial smoothness regularization.

Imaging of cardiac morphology and functions in high spatiotemporal resolution using MRI is a challenging problem due to limited imaging speed and the inherent tradeoff between spatial resolution, temporal resolution, and signal-to-noise ratio (SNR). The partially separable function (PSF) model has been shown to achieve high spatiotemporal resolution but can lead to noisy reconstructions. This paper proposes a method to improve the SNR and reduce artifacts in PSF-based reconstructions through the use of anatomical constraints. These anatomical constraints are obtained from a high-SNR image of composite (k, t)-space data (summed along the time axis) and used to regularize the PSF reconstruction. The method has been evaluated on experimental data of rat hearts to achieve 390 εm in-plane resolution and 15 ms temporal resolution.

First-pass perfusion cardiac MRI using the Partially Separable Functions model with generalized support.

Dynamic imaging methods based on the Partially Separable Functions (PSF) model have been used to perform ungated cardiac MRI, and the critical parameter determining the quality of the reconstructed images is the order, L, of the PSF model. This work extends previous methods by increasing L in the cardiac region to improve the ability of the PSF model to represent complex spatiotemporal signals. The resulting higher order PSF model is fit to sparse (k, t)-space data using spatial-spectral support, spatial-eigenbasis support, and spectral sparsity constraints. This new method is demonstrated in the context of 2D first-pass perfusion MRI in a healthy rat heart.

Improvement of hyperemic myocardial oxygen extraction fraction estimation by a diffusion-prepared sequence.

Myocardial oxygen extraction fraction (OEF) during hyperemia can be estimated using a double-inversion-recovery-prepared T(2)-weighted black-blood sequence. Severe irregular electrocardiogram (ECG) triggering due to elevated heart rate and/or arrhythmias may render it difficult to adequately suppress the flowing left ventricle blood signal and thus potentially cause errors in the estimates of myocardial OEF. Thus, the goal of this study was to evaluate another black-blood technique, a diffusion-weighted-prepared turbo spin echo sequence for its ability to determine regional myocardial OEF during hyperemia. Control dogs and dogs with acute coronary artery stenosis were imaged with both the double-inversion-recovery- and diffusion-weighted-prepared turbo spin echo sequences at rest and during either dipyridamole or dobutamine hyperemia. Validation of MRI OEF estimates was performed using blood sampling from the artery and coronary sinus in control dogs. The two methods showed comparable correlations with blood sampling results (R(2) = 0.9). Similar OEF estimations for all dogs were observed, except for the group of dogs with severe coronary stenosis during dobutamine stress. In these dogs, the diffusion-weighted method provided more physiologically reasonable OEF (hyperemic OEF = 0.75 +/- 0.08 versus resting OEF of 0.6) than the double-inversion-recovery method (hyperemic OEF = 0.56 +/- 0.10). Diffusion-weighted preparation may be a valuable alternative for more accurate oxygenation measurements during irregular ECG-triggering.

Real-time cardiac MRI using prior spatial-spectral information.

Cardiac MRI performed while the patient is breathing is typically achieved using non-real-time techniques such as ECG triggering with respiratory gating; however, modern dynamic imaging techniques are beginning to enable this type of imaging in real-time. One of these dynamic imaging techniques is based on forming a Partially Separable Function (PSF) model of the data, but the model fitting process is known to be sensitive even when truncated SVD regularization is used. As a result, physiologically meaningless artifacts can appear in the dynamic images when the total number of measurements is limited. To address this issue, the dynamic imaging problem is formulated as a generalized Tikhonov regularization problem with the PSF model as a component of the forward data model, and a penalty function is used to introduce spatial-spectral prior information. This new method both reduces data acquisition requirements and improves stability relative to the original PSF based method when applied to cardiac MRI.

Myocardial blood volume is associated with myocardial oxygen consumption: an experimental study with cardiac magnetic resonance in a canine model.

Understanding the oxygen consumption of the left ventricular myocardium provides important insight into the relationship between myocardial oxygen supply and demand. In other territories, cardiac magnetic resonance has been utilized to measure myocardial oxygen consumption with a blood level oxygen dependent (BOLD) technique. The BOLD technology requires repetitive sampling of stationary tissues and is frequently implemented in areas such as the brain. A limitation to utilizing BOLD cardiac magnetic resonance techniques in the heart has been cardiac motion. In this study, we document a methodology for acquiring BOLD images in the heart and demonstrate the utility of the technique for identifying associations between myocardial oxygen consumption and blood flow.

Resting myocardial perfusion quantification with CMR arterial spin labeling at 1.5 T and 3.0 T.

BACKGROUND: The magnetic resonance technique of arterial spin labeling (ASL) allows myocardial perfusion to be quantified without the use of a contrast agent. This study aimed to use a modified ASL technique and T1 regression algorithm, previously validated in canine models, to calculate myocardial blood flow (MBF) in normal human subjects and to compare the accuracy and repeatability of this calculation at 1.5 T and 3.0 T. A computer simulation was performed and compared with experimental findings. RESULTS: Eight subjects were imaged, with scans at 3.0 T showing significantly higher T1 values (P < 0.001) and signal-to-noise ratios (SNR) (P < 0.002) than scans at 1.5 T. The average MBF was found to be 0.990 +/- 0.302 mL/g/min at 1.5 T and 1.058 +/- 0.187 mL/g/min at 3.0 T. The repeatability at 3.0 T was improved 43% over that at 1.5 T, although no statistically significant difference was found between the two field strengths. In the simulation, the accuracy and the repeatability of the MBF calculations were 61% and 38% higher, respectively, at 3.0 T than at 1.5 T, but no statistically significant differences were observed. There were no significant differences between the myocardial perfusion data sets obtained from the two independent observers. Additionally, there was a trend toward less variation in the perfusion data from the two observers at 3.0 T as compared to 1.5 T. CONCLUSION: This suggests that this ASL technique can be used, preferably at 3.0 T, to quantify myocardial perfusion in humans and with further development could be useful in the clinical setting as an alternative method of perfusion analysis.

Fast mapping of myocardial blood flow with MR first-pass perfusion imaging.

Accurate and fast quantification of myocardial blood flow (MBF) with MR first-pass perfusion imaging techniques on a pixel-by-pixel basis remains difficult due to relatively long calculation times and noise-sensitive algorithms. In this study, Zierler's central volume principle was used to develop an algorithm for the calculation of MBF with few assumptions on the shapes of residue curves. Simulation was performed to evaluate the accuracy of this algorithm in the determination of MBF. To examine our algorithm in vivo, studies were performed in nine normal dogs. Two first-pass perfusion imaging sessions were performed with the administration of the intravascular contrast agent Gadomer at rest and during dipyridamole-induced vasodilation. Radiolabeled microspheres were injected to measure MBF at the same time. MBF measurements in dogs using MR methods correlated well with the microsphere measurements (R2=0.96, slope=0.9), demonstrating a fair accuracy in the perfusion measurements at rest and during the vasodilation stress. In addition to its accuracy, this method can also be optimized to run relatively fast, providing potential for fast and accurate myocardial perfusion mapping in a clinical setting.

Feasibility study of myocardial perfusion and oxygenation by noncontrast MRI: comparison with PET study in a canine model.

The purpose of this study was to examine the feasibility of quantifying myocardial blood flow (MBF) and rate of myocardial oxygen consumption (MVO(2)) during pharmacologically induced stress without using a contrast agent. The former was measured by the arterial spin labeling (ASL) method and the latter was obtained by measuring the oxygen extraction fraction (OEF) with the magnetic resonance imaging (MRI) blood oxygenation level-dependent effect and Fick's law. The MRI results were compared with the established positron emission tomography (PET) methods. Six mongrel dogs with induced acute moderate left coronary artery stenosis were scanned using a clinical PET and a 1.5-T MRI system, in the same day. Regional MBF, myocardial OEF and MVO(2) were measured with both imaging modalities. Correlation coefficients (R(2)) of the three myocardial indexes (MBF, OEF and MVO(2)) between MRI and PET methods ranged from 0.70 to 0.93. Bland-Altman statistics demonstrated that the estimated precision of the limits of agreement between MRI and PET measurements varied from 18% (OEF) to 37% (MBF) and 45% (MVO(2)). The detected changes in these indexes, at rest and during dobutamine stress, were similar between two image modalities. The proposed noncontrast MRI technique is a promising method to quantitatively assess myocardial perfusion and oxygenation.

Quantification of myocardial blood volume during dipyridamole and doubtamine stress: a perfusion CMR study.

PURPOSE: Myocardial blood volume (MBV) may provide complementary information about myocardial oxygen needs and viability. The aim of this study is to examine a Cardiovascular Magnetic Resonance (CMR) perfusion method to quantify the changes in MBV, in comparison with the radiolabeled 99mTc-Red-Blood-Cell (RBC) method. METHODS: Normal mongrel dogs (n=12) were used in this study. Eight dogs were injected intravenously with dipyridamole, and 4 dogs were given dobutamine during the MR scans. CMR first-pass perfusion imaging was performed at rest and during the pharmacological stress. An intravascular contrast agent, Gadomer (Schering AG, Berlin, Germany), was injected (0.015 mmol/kg) as a bolus during the scans. A perfusion quantification method was applied to obtain MBV maps. Radiolabeled-RBCs were injected at the end of the study to measure reference MBV at rest (n=4), during dipyridamole vasodilation (n=4), and during dobutamine stress (n=4). RESULTS: Myocardial blood flow (MBF) increased approximately 3-fold with both dipyridamole and dobutamine injections. Transmural MBV values measured by CMR were closely correlated with those measured by 99mTc method (CMR:MBV=6.2+/-1.3, 7.2+/-0.8, and 8.3+/-0.5 mL/100 g, at rest, with dipyridamole, and with dobutamine, respectively. 99mTc-RBC: MBV=6.1+/-0.5, 7.0+/-0.9, and 8.6+/-0.7 mL/100 g). Dobutamine stress significantly increased MBV by CMR (33%) and 99mTc methods (35%). During dipyridamole induced vasodilation, MBV increased non-significantly by 14% with the 99mTc method and 1% with CMR method, which agreed well with other reports. CONCLUSION: First-pass perfusion CMR with the injection of intravascular contrast agents is a promising non-invasive approach for the assessment of MBV both at rest and pharmacologically induced stress.

Assessment of myocardial oxygen extraction fraction and perfusion reserve with BOLD imaging in a canine model with coronary artery stenosis.

PURPOSE: To determine the feasibility of T2-weighted BOLD imaging for estimating regional myocardial oxygen extraction fraction (OEF) and approximating perfusion reserve (MPR) simultaneously in a canine model with moderate coronary artery stenosis. MATERIALS AND METHODS: Eight mongrel dogs with moderate coronary artery stenosis underwent BOLD imaging at rest and during dipyridamole-induced hyperemia, using a turbo spin echo (TSE) sequence. Based on a two-compartment model, myocardial OEF(hyperemia) was calculated with the corresponding T2. MPR could be approximated based on Fick's law. RESULTS: During responsive hyperemia, a regional hypointensity was observed in the abnormally perfused myocardium, reflecting a relatively smaller myocardial T2 increase (3.06% +/- 2.74%, in contrast to 10.19% +/- 4.12% in the normal region). The average OEFs in the normally and abnormally perfused myocardial territories were 0.21 +/- 0.11 and 0.43 +/- 0.12, respectively. For the MPR approximated from the BOLD imaging, a strong correlation (R = 0.9) in the normal myocardium and a good correlation (R = 0.6) distal to the stenosis were obtained compared to microsphere results. CONCLUSION: In a canine model with moderate coronary artery stenosis, TSE-based BOLD imaging can quantitatively estimate the regional OEF(hyperemia) and approximate the MPR, and can distinguish segments perfused by defected coronary artery.