The apple BTB protein MdBT2 positively regulates MdCOP1 abundance to repress anthocyanin biosynthesis

The ubiquitin ligase CONSTITUTIVELY PHOTOMORPHOGENIC 1 (COP1) plays a central role in light-induced anthocyanin biosynthesis. However, the upstream regulatory factors of COP1 remain poorly understood, particularly in horticultural plants. Here, we identified an MdCOP1-interacting protein, BROAD-COMPLEX, TRAMTRACK AND BRIC A BRAC2 (MdBT2), in apple (Malus domestica). MdBT2 is a BTB protein that directly interacts with and stabilizes MdCOP1 by inhibiting self-ubiquitination. Fluorescence observation and cell fractionation assays showed that MdBT2 increased the abundance of MdCOP1 in the nucleus. Moreover, a series of phenotypic analyses indicated that MdBT2 promoted MdCOP1-mediated ubiquitination and degradation of the MdMYB1 transcription factor, inhibiting the expression of anthocyanin biosynthesis genes and anthocyanin accumulation. Overall, our findings reveal a molecular mechanism by which MdBT2 positively regulates MdCOP1, providing insight into MdCOP1-mediated anthocyanin biosynthesis.

The VvWRKY37 Regulates Bud Break in Grape Vine Through ABA-Mediated Signaling Pathways

Dormancy is a common survival strategy in plants to temporarily suspend visible growth under unsuitable conditions. The elaborate mechanism underlying bud break in perennial woody plants is gradually illustrated. Here, we identified a grape vine WRKY transcription factor, VvWRKY37, which was highly expressed in dormant buds. It was particularly induced by the application of exogenous abscisic acid, and depressed on exposure to gibberellin and low temperature (4°C) stress at the transcript level. The yeast one-hybrid assay confirmed that VvWRKY37 had a transcriptional activity. Ectopic over-expression of VvWRKY37 significantly delayed bud break of transgenic poplar plants. As an ABA-inducible gene, VvWRKY37 also depressed the expression of ABA catabolic gene CYP707As and enhanced the accumulation of endogenous ABA in transgenic poplar plants. The molecular pieces of evidence showed that VvWRKY37 preferentially recognized and bound W-box 5'-G/CATTGACT/C/G-3' cis-element in vitro. Additionally, VvABI5 and VvABF2 acted as the upstream transcriptional activators of VvWRKY37 via protein-DNA interactions. Taken together, our findings provided valuable insights into a new regulatory mechanism of WRKY TF by which it modulates bud break through ABA-mediated signaling pathways.

Increasing the activity of the Cu/CuAl2O4/Al2O3 catalyst for the RWGS through preserving the Cu2+ ions

Cu-Al spinel oxide is a highly active catalyst for CO₂ conversion to CO. However, it suffers from low surface area. By depositing a silica layer, we protected the catalyst surface and preserved the Cu²⁺ ions during the calcination process. These ions form well-dispersed Cu sites which participate in the reaction.

[Clinical characteristics of acute pulmonary embolism at different altitudes in plateau areas]

Objective: To analyze the clinical characteristics of pulmonary embolism patients from different altitudes in plateau areas. Methods: A retrospective cross-sectional study was used to analyze the patients with acute pulmonary embolism diagnosed definitely by pulmonary angiography or pulmonary artery CT angiography admitted to Tibet Autonomous Region People's Hospital from August 2014 to December 2018. The subjects were divided into 3 groups according to the altitude of long-term residence before onset, i.e. low-altitude group (group 1, 2 700 m ≤ altitude ≤3 700 m, n=44), medium-altitude group (group 2, 3 700 m<altitude ≤4 000 m, n=30) and high altitude group (group 3, 4 000 m<altitude ≤4 800 m, n=32). The clinical data, auxiliary examination and risk stratification of pulmonary embolism patients at different altitudes were compared and analyzed. Results: The incidence of chest pain, dyspnea and lower limb fracture in the three groups were statistically significant (P<0.05). The incidence of chest pain in group 2 (70%) was higher than that in group 1(40.9%), and dyspnea in group 3 (93.8%) was higher than that in group 2(66.7%), while lower limb fracture in group 3 (43.8%) was higher than that in group 1(15.9%). The differences in arterial oxygen partial pressure, hemoglobin and D-dimer among the three groups were statistically significant (P<0.05). The arterial oxygen partial pressure [52(43.5-63.5)mmHg] in group 3 was lower than that in group 1 [60 (53.25-73) mmHg]. The hemoglobin (163.1±43.3 g/L) and D-dimer [5.6(3.7-12.6)mg/L] in group 3 were higher than those in group 1 [143.5±38.9 g/L and 3.8(2.0-7.5)mg/L respectively]. The risk stratification of the three groups of patients was moderate or low, and there was no statistical difference among the three groups. In patients with the same low-risk grade, the D-dimer in group 3 was higher than that in group 1 [5.8(4.2-14.8)mg/L and 3.6(2.3-5.8)mg/L respectively, P<0.05]. In patients with the same moderate risk level, the arterial oxygen partial pressure in group 3 was lower than that in group 1 [47.0(36.0-58.0)mmHg and 59.5(52.3-68.5)mmHg, respectively, P<0.05]. Conclusion: There was no difference in the risk stratification of pulmonary embolism from different altitudes in plateau areas, but patients who lived at higher altitudes for a long time showed more significant hypoxemia and increased hemoglobin and D-dimer levels.

Designing Heterogeneous Catalysts for Renewable Catalysis Applications Using Metal Oxide Deposition

Heterogeneous catalysis has long been a workhorse for the chemical industry and will likely play a key role in the emerging area of renewable chemistry. However, renewable molecule streams pose unique challenges for heterogeneous catalysis due to their high oxygen content, frequent low volatility and the near constant presence of water. These constraints can often lead to the need for catalyst operation in harsh liquid phase conditions, which has compounded traditional catalyst deactivation issues. Oxygenated molecules are also frequently more reactive than petroleum-derived molecules, which creates a need for highly selective catalysts. Synthetic control over the nanostructured environment of catalytic active sites could facilitate the creation of both more stable and selective catalysts. In this review, we discuss the use of metal oxide deposition as an emerging strategy that can be used to synthesize and/or modify heterogeneous catalysts to introduce tailored nanostructures. Several important applications are reviewed, including the synthesis of high surface area mesoporous metal oxides, the enhancement of catalyst stability, and the improvement of catalyst selectivity.

Functional characterization of WRKY46 in grape and its putative role in the interaction between grape and phylloxera (Daktulosphaira vitifoliae)

WRKY transcription factors are involved in defense responses caused by biotic stresses. Phylloxera (Daktulosphaira vitifoliae Fitch), a pest widespread in viticulture, elicits transcriptional reprogramming of plant defense-associated components, such as regulons related to WRKYs and salicylic acid (SA) signaling. In this study, we characterized WRKY46, a WRKY transcription factor responsible for phylloxera attack, and revealed the molecular mechanism for WRKY-mediated defense responses to phylloxera. qRT-PCR and GUS staining analyses revealed that WRKY46 is induced in response to phylloxera damage and mechanical wounding. VvWRKY46 is a nuclear-localized transcription factor that activates its downstream target VvCHIB by direct protein-DNA interaction. Regulons involved in the SA-mediated defense response were regulated during incompatible interactions between "1103 Paulsen" rootstock and phylloxera. In addition, WRKY46 exhibited a higher transcript abundance in "1103 Paulsen" than in "Crimson Seedless", regardless of whether the plants were infected with phylloxera. Furthermore, the enhanced expression of VvWRKY46 significantly attenuated phylloxera attack and delayed nymph development of composite grape plants. In summary, we demonstrated that WRKY46 plays a role in the SA-mediated defense-regulatory network by directly binding to the downstream structural gene VvCHIB. The phylloxera-responsive gene WRKY46 was identified, which could improve the understanding of the basic mechanism of grapevine in response to phylloxera.

Slowing the Kinetics of Alumina Sol-Gel Chemistry for Controlled Catalyst Overcoating and Improved Catalyst Stability and Selectivity

Catalyst overcoating is an emerging approach to engineer surface functionalities on supported metal catalyst and improve catalyst selectivity and durability. Alumina deposition on high surface area material by sol-gel chemistry is traditionally difficult to control due to the fast hydrolysis kinetics of aluminum-alkoxide precursors. Here, sol-gel chemistry methods are adapted to slow down these kinetics and deposit nanometer-scale alumina overcoats. The alumina overcoats are comparable in conformality and thickness control to overcoats prepared by atomic layer deposition even on high surface area substrates. The strategy relies on regulating the hydrolysis/condensation kinetics of Al(^s BuO)₃ by either adding a chelating agent or using nonhydrolytic sol-gel chemistry. These two approaches produce overcoats with similar chemical properties but distinct physical textures. With chelation chemistry, a mild method compatible with supported base metal catalysts, a conformal yet porous overcoat leads to a highly sintering-resistant Cu catalyst for liquid-phase furfural hydrogenation. With the nonhydrolytic sol-gel route, a denser Al₂ O₃ overcoat can be deposited to create a high density of Lewis acid-metal interface sites over Pt on mesoporous silica. The resulting material has a substantially increased hydrodeoxygenation activity for the conversion of lignin-derived 4-propylguaiacol into propylcyclohexane with up to 87% selectivity.

The distribution and species of Ca2+ and subcellular localization of Ca2+ and Ca2+-ATPase in grape leaves of plants treated with fluoroglycofen

Fluoroglycofen, a post-emergence herbicide used in vineyards to eradicate weeds, has previously been shown to turn grape leaves dark green following its use. Therefore, this study evaluates the relationship of dark green leaves with calcium form and subcellular distribution. To do this, we focused on the Ca²⁺ distribution and Ca²⁺-ATPase activity in leaf cells of one-year-old self-rooted Chardonnay grapevines treated with fluoroglycofen. Plants were separated into different treatments when they had seven or eight leaves, and different concentrations of fluoroglycofen were sprayed on the sand. The results showed that all of the soluble calcium content in the grape leaves that were treated with the highest concentration of fluoroglycofen (187.5gaiha^-1) increased significantly. Specifically, the water-soluble organic acid calcium, pectate calcium, and calcium oxalate increased by 18.43%, 17.14%, and 31.05%, respectively, in the upper leaves than in the control. The subcellular distribution of Ca²⁺ in the dark green leaves increased significantly, especially in the cell wall and chloroplast, which increased by 25.54% and 24.10%, respectively. Through the ultrastructure localization of Ca²⁺ and Ca²⁺-ATPase contrasted with the control, the extracellular space and chloroplasts in the mesophyll cells of dark green leaves had large calcium pyroantimonate (Ca-PA) deposits. The extracellular space had fewer Ca²⁺-ATPase precipitation particles, whereas the chloroplasts had more. At the same time, a high concentration of fluoroglycofen decreased Ca²⁺-ATPase activity in grape leaves, which potentially might be due to disrupted regulation of calcium homeostatic mechanisms inside and outside of cells, resulting in a large number of Ca²⁺ accumulation in cells. The Ca²⁺ accumulation not only hindered the various cellular physiological reactions, but also caused leaves to become dark green in color.

Identification of a Novel Alternative Splicing Variant of VvPMA1 in Grape Root under Salinity

It has been well-demonstrated that the control of plasma membrane H⁺-ATPase (PM H⁺-ATPase) activity is important to plant salt tolerance. This study found a significant increase in PM H⁺-ATPase (PMA) activity in grape root exposed to NaCl. Furthermore, 7 Vitis vinifera PM H⁺-ATPase genes (VvPMAs) were identified within the grape genome and the expression response of these VvPMAs in grape root under salinity was analyzed. Two VvPMAs (VvPMA1 and VvPMA3) were expressed more strongly in roots than the other five VvPMAs. Moreover, roots exhibited diverse patterns of gene expression of VvPMA1 and VvPMA3 responses to salt stress. Interestingly, two transcripts of VvPMA1, which were created through alternative splicing (AS), were discovered and isolated from salt stressed root. Comparing the two VvPMA1 cDNA sequences (designated VvPMA1α and VvPMA1β) with the genomic sequence revealed that the second intron was retained in the VvPMA1β cDNA. This intron retention was predicted to generate a novel VvPMA1 through N-terminal truncation because of a 5'- terminal frame shift. Yeast complementation assays of the two splice variants showed that VvPMA1β could enhance the ability to complement Saccharomyces cerevisiae deficient in PM H⁺-ATPase activity. In addition, the expression profiles of VvPMA1α and VvPMA1β differed under salinity. Our data suggests that through AS, the N-terminal length of VvPMA1 may be regulated to accurately modulate PM H⁺-ATPase activity of grape root in salt stress.

Study of Binding Interaction between Pif80 Protein Fragment and Aragonite

Pif is a crucial protein for the formation of the nacreous layer in Pinctada fucata. Three non-acidic peptide fragments of the aragonite-binding domain (Pif80) are selected, which contain multiple copies of the repeat sequence DDRK, to study the interaction between non-acidic peptides and aragonite. The polypeptides DDRKDDRKGGK (Pif80-11) and DDRKDDRKGGKDDRKDDRKGGK (Pif80-22) have similar binding affinity to aragonite. Solid-state NMR data indicate that the backbones of Pif80-11 and Pif80-22 peptides bound on aragonite adopt a random-coil conformation. Pif80-11 is a lot more effective than Pif80-22 in promoting the nucleation of aragonite on the substrate of β-chitin. Our results suggest that the structural arrangement at a protein-mineral interface depends on the surface structure of the mineral substrate and the protein sequence. The side chains of the basic residues, which function as anchors to the aragonite surface, have uniform structures. The role of basic residues as anchors in protein-mineral interaction may play an important role in biomineralization.

[Intervention of systolic pressure and left ventricular hypertrophy in rats under cold stress]

OBJECTIVE

To investigate the effects of different drugs on systolic blood pressure (SBP) and left ventricular hypertrophy (LVH) in spontaneously hypertensive rats under cold stress.

METHODS

A total of 40 male spontaneously hypertensive rats aged 10 weeks (160~200 g) were given adaptive feeding for 7 days at a temperature of 20±1°C and then randomly divided into control group, cold stress group, metoprolol group, amlodipine group, and benazepril group, with 8 rats in each group. SBP, body weight, and heart rate were measured once a week. After the rats were sacrificed by exsanguination, left ventricular weight (LVW) was measured, and left ventricular weight index (LVWI; mg/g) was calculated. Radioimmunoassay was used to measure the concentrations of endothelin-1 (ET-1) and angiotensin-II (Ang-II) in plasma and myocardium, and the chemical method was used to measure the concentrations of nitric oxide (NO) in plasma and myocardium. RT-PCR was used to measure the mRNA expression of endothelin-A receptor.

RESULTS

Compared with the cold stress group, all medication groups showed significant reductions in SBP since week 5 (P<0.05). The cold stress group showed a significant increase in LVWI compared with the control group (3.38±0.27 mg/g vs 2.89±0.19 mg/g, P<0.05). The amlodipine group showed a significant reduction in LVWI compared with the cold stress group (2.98±0.28 mg/g vs 3.38±0.27 mg/g, P<0.05). The cold stress group showed a significant reduction in plasma NO concentration compared with the control group (104.9±19.5 μmol/L vs 129.3±17.8 μmol/L, P<0.05) ; compared with the cold stress group, all the medication groups showed significant increases in blood NO concentration (P<0.05). The cold stress group showed a significant increase in myocardial ET-1 concentration compared with the control group (6.3±1.5 pg/100 mg vs 4.5±1.9 pg/100 mg, P<0.05) ; compared with the cold stress group, the amlodipine group showed a significant reduction in myocardial ET-1 concentration (4.4±1.0 pg/100 mg vs 6.3±1.5 pg/100 mg, P<0.05). The cold stress group had significantly higher mRNA expression of endothelin-A receptor than the control group (0.86±0.23 vs 0.45±0.16, P<0.01) ; compared with the cold stress group, the amlodipine group showed a significant reduction in the mRNA expression of endothelin-A receptor (0.41±0.14 vs 0.86±0.23, P<0.01).

CONCLUSION

Amlodipine can reduce the increase in SBP and inhibit LVH in spontaneously hypertensive rats under cold stress.

[Cadmium accumulation, subcellular distribution, and chemical forms in Vitis vinifera cv. chardonnay grapevine]

A pot culture experiment was conducted to study the Cd absorption, Cd subcellular distribution, and Cd chemical forms in one-year old self-rooted Chardonnay and SO4 rootstock-grafted Chardonnay grapevine after root-irrigating with different concentration CdCl and CaCl2. In the grapevine, the absorbed Cd was mostly distributed in underground organs (root and rhizome). In treatment 4 mmol x L(-1) of CdCl2, 77.1% and 1.4% of the absorbed Cd in self-rooted Chardonnay were accumulated in underground organs and leaves, respectively, while 93.9% and 0.1% of the absorbed Cd in grafted Chardonnay were accumulated in the organs below graft position and in leaves, respectively. 5 mmol L(-1) of CaCl2 decreased the plant Cd absorption and accumulation, while 10 mmol x L(-1) of CaCl2 increased the plant Cd absorption and accumulation significantly. The Cd subcellular distribution in roots and leaves was in the order of cell wall > soluble fraction > organelle, and more than 50% of the Cd was accumulated in cell wall. In the roots, NaCl-extractable Cd had a major proportion, followed by HAc-extractable Cd, and water-extractable Cd. The contents of all the Cd chemical forms varied with the increasing concentration of Cd in the treatments.

[Physiological and biochemical responses of different scion/rootstock combinations grapevine to partial rootzone drought]

By using self-made wooden boxes with two separated zones, the grapevine Vitis vinifera cv. Malvasia (M) grafted on rootstocks 3309C, 420A and 110R, respectively, was planted, and the physiological and biochemical responses of these scion/rootstock combinations to bilateral alternative irrigation (AI) and unilateral irrigation (UI) were studied. The results showed that in treatments AI and UI, the average leaf ABA content of test scion/rootstock combinations increased by 267.5% and 394.7%, respectively, while stomatal conduction and transpiration decreased markedly. In treatment UI, the leaf SOD and CAT activities and Pro content were notably enhanced, with the greatest increment in M/110R and followed by in M/420A and M/3309C; while in treatment AI, the leaf SOD and CAT activities of test scion/rootstock combinations enhanced slightly and Pro content increased markedly. UI induced a remarkable increase of leaf relative electronic conductivity and MDA and H2O2 contents, with the highest increment in M/3309C and the lowest in M/110R. In summary, the drought resistance of different scion/rootstock combinations grapevine mainly depended on the variety of rootstock. 110R had a higher drought-resistance than 420A and 3309C. Comparing with unilateral irrigation, bilateral alternative irrigation had lesser damage to grapevine, being a profitable water-saving irrigation technique.

The relationship between vascular wall shear stress and flow-mediated dilation: endothelial function assessed by phase-contrast magnetic resonance angiography

OBJECTIVES

We sought: 1) to investigate the relationship between vascular wall shear stress and flow-mediated dilation (FMD) in humans, and 2) to investigate whether this relationship could explain why FMD is greater in small arteries.

BACKGROUND

Arterial wall shear stress (WSS) is considered to be the primary stimulus for the endothelial-dependent FMD response. However, the relationship between WSS and FMD has not been investigated in humans. Furthermore, FMD is greater in small arteries, though the reasons for this phenomenon are unclear.

METHODS

Using phase-contrast magnetic resonance angiography (PMRCA), we measured hyperemic WSS and FMD in 18 healthy volunteers. Peak systolic WSS was calculated assuming a blunted parabolic velocity profile. Diameter by PCMRA and by ultrasound was compared in nine subjects.

RESULTS

Flow-mediated dilation was linearly proportional to hyperemic peak systolic WSS (r = 0.79, p = 0.0001). Flow-mediated dilation was inversely related to baseline diameter (r = 0.62, p = 0.006), but the hyperemic peak WSS stimulus was also inversely related to baseline diameter (r = 0.47, p = 0.049). Phase-contrast magnetic resonance angiography and ultrasound diameters were compared in nine subjects and correlated well (r = 0.84, p < 0.0001), but diameter by PCMRA was greater (4.1 +/- 0.7 mm vs. 3.7 +/- 0.5 mm, p = 0.009).

CONCLUSION

Arterial FMD is linearly proportional to peak hyperemic WSS in normal subjects. Thus, the endothelial response is linearly proportional to the stimulus. Furthermore, the greater FMD response in small arteries is accounted for, at least partially, by a greater hyperemic WSS stimulus in small arteries. By allowing the calculation of vascular WSS, which is the stimulus for FMD, and by imaging a fixed arterial cross-section, thus reducing operator dependence, PCMRA enhances the assessment of vascular endothelial function.

A comparison of prospective and retrospective respiratory navigator gating in 3D MR coronary angiography

A comparison between the prospective and retrospective respiratory navigator gating in MR coronary angiography was performed with eight normal subjects. A three-dimensional (3D) ECG-gated fast gradient echo pulse sequence was used for image data acquisition. The results show that the MR coronary angiography obtained using retrospective gating retains a considerable amount of motion artifacts. In this study, the images acquired using prospective navigator gating demonstrated significantly reduced motion artifacts (p = 0.009), improved vessel visibility (p = 0.021) with reduced imaging time (p = 0.013) compared to the images obtained using retrospective navigator gating.

Advanced cardiac MR imaging of ischemic heart disease

Important advances in rapid magnetic resonance (MR) imaging technology and its application to cardiovascular imaging have been made during the past decade. High-field-strength clinical magnets, high-performance gradient hardware, and ultrafast pulse sequence technology are rapidly making the vision of a comprehensive "one-stop shop" cardiac MR imaging examination a reality. This examination is poised to have a significant effect on the management of coronary artery disease by means of assessment of wall motion with tagging and pharmacologic stress testing, evaluation of the coronary microvasculature with perfusion imaging, and direct visualization of the coronary arteries with MR coronary angiography. This article reviews current state-of-the-art pulse sequence technology and its application to the evaluation of ischemic heart disease by means of MR tagging with dobutamine stress testing, MR perfusion imaging, and MR coronary angiography. Cutting edge areas of research in coil design and exciting new areas of metabolic and oxygen level-dependent imaging are also explored.

Function and regulation of cholecystokinin octapeptide, β-endorp hin and gastrin in anorexic infantile rats treated with ErBao Granules

AIM: To study the role of cholecystokinin octapeptide (CCK-8), β-endorphin (β-EP), and gastrin in an anorexic infantile rat model and no subsequent regulation of nose peptides by the Yunpi complex prescription ErBao Granule.

METHODS: We fed infantile rats with special prepared forage. A liquid extract of ErBao Granule was administered to the rats daily for 3 weeks, CCK-8, β-EP, and gastrin concentrations in hypothalamus, gastric antrum, and plasma of the rats were measured by radioimmunoassay, and were compared with controls.

RESULTS: Treatment of rats with ErBao Granule inhibited CCK-8 secretion and increased β-EP and gastrin secretion. CCK-8 concentration in hypothalamus and plasma of model control group increased significantly and correlated negatively with food intake of models, respectively. β-EP concentration in gastric antrum and plasma of model control group decreased significantly and showed a positive correlation with food intake of models, respectively. Hypothalamus concentration of β-EP was similar in models and controls. Gastrin concentration in gastric antrum of models was lower than in the blank control group, and correlated positively to food intake of models. Finally, CCK-8 concentrations in plasma of rats showed a positive correlation with plasma β-EP (r = -0.68, P < 0.05).

CONCLUSION: The increased plasma and hypothalamus concentration of CCK-8, decreased gastric antrum and plasma level of β-EP, and decreased gastric antrum concentration of gastrin are associated significantly with the anorexia of infantile anorexic rat models produced by special forage. ErBao Granule can reverse these changes, which may be the major mechanisms of ErBao Granule simulating feeding.

[Effect of ET-1 antisense oligodeoxynucleotide on the hemodynamics of normal and experimental hypertensive rats]

It was previously found that a phosphorothioated antisense oligodeoxynucleotide (ETASODN) significantly inhibits production of endothelin-1 (ET-1). The purpose of the present study was to determine whether intracerebroventricular injection of ETASODN targeted to prepro-ET-1 is capable of exerting the same preventing effect on the aorta narrowing of experimentally modeled hypertensive rats. Radioimmunoassay showed that ET-1 level in the brain stem of hypertensive rats was significantly elevated. In addition to down-regulating the ET-1 level, astisense could also reduce mean arterial pressure (MAP), heart rate and LVSP in model rats. The antisense also down-regulated the ET-1 level in hypothalamus and brain stem, reducing MAP in normal control rats. After treatment with the antisense, the value of delta MAP was markedly lowered in experimental hypertensive rats as compared to the control ones. Thus it appears that (1) ET-1 might play an important role in central cardiovascular regulation in rats and (2) antisense ETASODN might be used in treatment of hypertension via inhibiting ET-1 production.

Optimal design of gradient coils in MR imaging: optimizing coil performance versus minimizing cost functions

The "forward" method of an optimal gradient coil design provides a coil that has the minimal cost function value. It is shown in this study that the solution obtained by minimizing the cost function is directly dependent on the specified cost function and generally results in a deviation from the most desirable coil design. In this paper, a gradient coil design approach for obtaining the best achievable coil performance for pre-determined imaging applications is presented. Through this approach, all intermediate coil performance values calculated during an optimization process, using a simulated annealing algorithm, are stored and presented in a three-dimensional data set. Using this three-dimensional data set, a coil designer is able to make a balance between different coil performance parameters and to select a coil that is the most desirable for the pre-determined imaging applications.

Concomitant magnetic-field-induced artifacts in axial echo planar imaging

When a linear magnetic field gradient is used, spatially higher-order magnetic fields are produced to satisfy the Maxwell equations. It has been observed that the higher-order magnetic field produced by the readout gradient causes axial echo planar images acquired with a horizontal solenoid magnet to shift along the phase-encoding direction and lose image intensities. Both the shift and intensity reduction become increasingly severe as the slice offset from the isocenter increases. These phenomena are quantitatively analyzed, and good correlation between experiments and theory has been established. The analysis also predicts a previously unreported Nyquist ghost on images with very large slice offsets. This ghost has been verified with computer simulations. Based on the analysis, several methods have been developed to eliminate the image shift, the intensity reduction, and the ghost. Selected methods have been implemented on a commercial scanner and proved effective in removing these image artifacts.

Vessel enhancement filtering in three-dimensional MR angiograms using long-range signal correlation

Small vessels in three-dimensional MR angiograms have low visibility in maximum-intensity projection images because of their low contrast. In a previous study, we had two nonlinear filters that appeared to give significant improvement in small vessel detail. In this paper, we report on a generalization of this filter that allows a more general modeling of the vessels and a more complete suppression of background. One implementation of the general filter gave a vessel mean contrast-to-noise ratio that is 2.52 and 3.51 times higher than the vessel mean contrast-to-noise ratio obtained using our previously reported maximum-minimum (max-min) filter and cross-section filter, respectively.

Studies on the performance of circular and elliptical Z-gradient coils using a simulated annealing algorithm

Elliptical z-gradient coils with different ellipticities are optimized using a simulated annealing algorithm. This study demonstrates that when the coil ellipticity was changed from 1.0 to 1.67, the gradient strength was increased by 21% and the coil inductance was reduced by about 34%. At the same time, the gradient inhomogeneity was increased by a factor between 15 to 47%. In these examples we also observed that when the coil ellipticity was increased from 1.0 to 1.11, the gradient inhomogeneity was reduced by a factor between 16 to 19%. This study provides a quantitative assessment of the advantages and disadvantages in coil performance obtained by using elliptical z-gradient coils.

The effect of image resolution on vessel signal in high-resolution magnetic resonance angiography

In this paper, the theoretical dependence of the signal of flowing fluids is considered in terms of the imaging parameters and the physical condition of the flowing fluid. For the vessel sizes, flow ranges, and imaging conditions studied, it is demonstrated that the fluid signal can be predicted from the solution of Bloch equations. For vessels on the order of the imaging resolution or smaller, the effects of the image resolution must be included

A quantitative study of ramped radio frequency, magnetization transfer, and slab thickness in three-dimensional time-of-flight magnetic resonance angiography in a patient population

RATIONALE AND OBJECTIVES

The authors compare the effectiveness of various magnetic resonance (MR) angiography acquisition strategies in enhancing the visibility of small intracranial vessels.

METHODS

Blood vessel contrast-to-noise ratio (CNR) in time-of-flight MR angiography was studied as a function of vessel size and several selectable imaging parameters. Contrast-to-noise measurements were made on 257 vessel segments ranging in size from 0.3 mm to 4.2 mm in patients who recently had undergone intraarterial cerebral angiography. Imaging parameters studied included magnetization transfer, spatially variable radio frequency (RF) pulse profile (ramped RF), and imaging slab thickness.

RESULTS

The combination of thin slabs (16 slices/slab), ramped RF, and magnetization transfer resulted in the highest CNR for all but the smallest vessel sizes. The smallest vessels (< 0.5 mm) had the highest CNR, using the thick slab (64 slices/slab) with ramped RF and magnetization transfer. Magnetization transfer always improved vessel CNR, but the improvement diminished as the slab thickness was reduced. The CNR increased with a decrease in slab thickness for all but the smallest vessel sizes.

CONCLUSIONS

Overall, the results provide a quantitative demonstration that inflow enhancement of blood is reduced for small vessels. Thus, whereas magnetization transfer is important at all vessel sizes, it becomes the primary factor in improving the visibility of the smallest vessels.

Experimental and theoretical studies of vessel contrast-to-noise ratio in intracranial time-of-flight MR angiography

CNR studies were performed for human intracranial vessels in 3D MRA data sets. The CNR dependency of different imaging parameters, such as flip angle, field of view, echo time, repetition time, and echo readout symmetry, was studied for vessels in the region of the circle of Willis. A theoretical model was developed for MR vascular imaging based on the Bloch equations and Fourier imaging theory. This model predicts the MR image intensity of vessels from basic subject parameters, such as the relaxation times of blood and stationary tissue, vessel dimension, and flow velocity, and the parameters of the imaging technique, such as flip angle, voxel volume, repetition time, and echo time. For most experiments, the model was found to fit the experimental results well. The validity of this model allows the optimization of imaging parameters to maximize vessel CNR in MR angiography.

Evaluation of gradient inhomogeneity in the optimal design of gradient coils

The image distortion caused by gradient inhomogeneity was derived from the image equation of Fourier MR imaging. A measurement of gradient inhomogeneity was proposed based on the amount of image distortion. Using the proposed measurement of gradient inhomogeneity in the optimal design of a z-gradient coil reduced image distortion by 39-45% compared to a previously used figure of merit in gradient coil design.

Abbreviated moment-compensated phase encoding

To achieve correct spatial location of blood vessels, first order gradient moment nulling applied to the phase encoding axes can be used. However, gradient moment nulling prolongs echo time (TE), which may degrade the flow image in regions of complex flow. The fact that abbreviated moment compensated phase-encoding (AMCPE) can be used to apply partial flow compensation to the phase-encoding axes to prevent spatial misregistration of vessels without requiring the use of long echo times or using arbitrary chosen TE is demonstrated. AMCPE defines two cutoff lines in k-space. The flow-induced phase is completely compensated for values between the cutoff lines and partially compensated beyond the cutoff lines. The AMCPE technique has been tested on both a flow phantom and a human volunteer. The AMCPE images from both the in vivo and the in vitro study demonstrate correctly imaged flow. Computer simulations have been performed to analyze the penalty caused by the incomplete flow compensation. The result shows that the ripple artifacts due to the incomplete flow compensation are unobservable when 60%-70% of k-space is completely flow compensated.

Vessel enhancement filtering in three-dimensional MR angiography

For a variety of reasons, small vessels have low signal intensity in magnetic resonance angiography. When the vessel signal intensity is lower than the signal intensity of background tissues, these vessels tend not to be visible on maximum-intensity-projection images. The authors developed a nonlinear second-difference spatial filtering technique that enhances the details of small vessels while suppressing both noise and uniform background tissue. Two similar nonlinear second-difference filters are presented and compared with the linear Laplacian second-difference filter. To evaluate the performance of these filters, they were applied to intracranial three-dimensional time-of-flight MR angiographic data and the results compared with the vessel enhancement obtained with a simple second-difference Laplacian filter and with magnetization transfer contrast (MTC) techniques. The comparisons demonstrated that nonlinear filtering and MTC techniques result in similar improvement in small-vessel visibility and apparent continuity. A quantitative comparison demonstrated that the improvement in the contrast-to-noise ratio is much greater with the nonlinear filters than the Laplacian filter.

Vessel enhancement filtering in three-dimensional MR angiography

For a variety of reasons, small vessels have low signal intensity in magnetic resonance angiography. When the vessel signal intensity is lower than the signal intensity of background tissues, these vessels tend not to be visible on maximum-intensity-projection images. The authors developed a nonlinear second-difference spatial filtering technique that enhances the details of small vessels while suppressing both noise and uniform background tissue. Two similar nonlinear second-difference filters are presented and compared with the linear Laplacian second-difference filter. To evaluate the performance of these filters, they were applied to intracranial three-dimensional time-of-flight MR angiographic data and the results compared with the vessel enhancement obtained with a simple second-difference Laplacian filter and with magnetization transfer contrast (MTC) techniques. The comparisons demonstrated that nonlinear filtering and MTC techniques result in similar improvement in small-vessel visibility and apparent continuity. A quantitative comparison demonstrated that the improvement in the contrast-to-noise ratio is much greater with the nonlinear filters than the Laplacian filter.

The voxel sensitivity function in Fourier transform imaging: applications to magnetic resonance angiography

In this paper the problem of small structure visualization in magnetic resonance imaging (MRI) is considered. The relationship between the structure and the image intensities is defined in terms of the voxel sensitivity function (VSF). Using the VSF, the spatial dependence of the voxel signal for small spheres and cylinders is computed. Although the spatial fluctuation is smaller in the MRI VSF than that which would be obtained from a uniformly sensitive cubical voxel, the deviation still results in significant signal loss near the edges and corners of the voxels. Finally, the VSF formalism is used to demonstrate the improvement in signal uniformity that can be obtained by using zero-filled (band-limited or sinc) interpolation.

Reduction of partial-volume artifacts with zero-filled interpolation in three-dimensional MR angiography

Partial-volume artifacts reduce vessel contrast and continuity (especially in small vessels) in magnetic resonance (MR) angiography. The authors applied zero-filled (band-limited) interpolation to three-dimensional (3D) MR angiograms to reduce partial-volume artifacts. They demonstrated that zero-filled interpolation can also be implemented by means of voxel shifting in real space. Voxel-shifted interpolation is much less computer memory intensive than conventional zero-filled interpolation. They numerically simulated the contrast loss due to partial-volume artifacts and contrast recovery obtained with zero-filled interpolation. Zero-filled interpolation in all three orthogonal directions was applied to 3D MR angiography data sets from 29 human studies. These studies were obtained with the three commonly used 3D MR angiography techniques: 3D time of flight, multislab 3D time of flight, and 3D phase contrast. A substantial improvement in vessel contrast and vessel continuity was observed in all cases.

Effect of cigarette smoking on hypoxic pulmonary vasoconstriction and its relation to animal species and period of smoking

The alteration in hypoxic pulmonary vasoconstriction (HPV) induced by cigarette smoking was studied in Wistar rats, piglets and in humans. The percentage change of pulmonary vascular resistance (delta PVR%) and the amplitude of the systolic wave in impedance pneumorheogram (delta H%) were used to estimate the strength of HPV. It was observed that immediately after acute cigarette smoking, HPV in rats increased (delta PVR% from 55.0 +/- 15.6% to 102.3 +/- 12.4%), which is mainly mediated by leukotrienes (LTs); whereas HPV in piglets decreased (delta PVR% from 65.2 +/- 12.5% to 55.9 +/- 9.8%), which is mainly mediated by beta-adrenergic receptors, and HPV in humans also increased (delta H% from 20.6 +/- 2.6% to 31.1 +/- 4.1%), in which prostaglandins and leukotrienes may play the role of mediators. However, after one-month cigarette smoking, the HPV in rats fell significantly (delta PVR% 11.4 +/- 1.6%). An increase in synthesis of vasodilative prostaglandins and a decrease in leukotrienes synthesis may be the contributing factors to this alteration in HPV.