Selective Inversion Research Articles

Accelerated noncontrast‐enhanced pulmonary vein MRA with distributed compressed sensing

To investigate the efficacy of distributed compressed sensing (CS) to accelerate free-breathing, electrocardiogram (ECG)-triggered noncontrast pulmonary vein (PV) magnetic resonance angiography (MRA). Fully sampled ECG-triggered noncontrast PV MRA, using a spatially selective slab inversion preparation sequence, was acquired on seven healthy adult subjects (27 ± 17 years, range: 19-65 years, 4 women). The k-space data were retrospectively randomly undersampled by factors of 2, 4, 6, 8, and 10 and then reconstructed using distributed CS and coil-by-coil CS methods. The reconstructed images were evaluated by two blinded readers in consensus for assessment of major PV branches as well as the presence of artifacts in left atrium (LA) and elsewhere. Diameters of right inferior and right superior PV branches were measured. Additionally, mean square errors (MSE) of the reconstructions were calculated. Both CS methods resulted in image quality scores similar to the fully sampled reference images at undersampling factors up to 6-fold for distributed CS and 4-fold for coil-by-coil CS reconstructions. There was no difference in the presence of artifacts in LA and freedom from important artifacts elsewhere between the two techniques up to undersampling factors of 10 compared to the fully sampled reconstruction. For the PV diameters, no systematic variation between the reference and the reconstructions were observed for either technique. There were no significant differences in MSE between the two methods when compared at a given rate, but the difference was significant when compared across all rates. The sparsity of noncontrast PV MRA and the joint sparsity of different coil images allow imaging at high undersampling factors (up to 6-fold) when distributed CS is used.

Modified quadruple inversion recovery prepulse for arterial spin labeling angiography without the need of subtraction

Arterial Spin Labeling (ASL) is a well-known technique that allows the non-invasive acquisition of angiograms without the need of a contrast agent [1][2]. ASL angiography is still clinically underused because of several challenges [3]: ASL requires two acquisitions (labeled and non labeled dataset) thereby doubling scan time. The need of subtraction increases the sensitivity to spatial misregistration and the need of the choice of an optimal inversion delay for best blood-to-background contrast introduces some “operator dependence”. An alternative technique not requiring image subtraction has been proposed (Figure ​(Figure1)1) [4]. This approach is based on a double inversion (DIR-ASL) prepulse and provides good background suppression if the surrounding tissues have similar T1 values (Figure ​(Figure1).1). However, DIR-ASL has only one optimal inversion delay and thus there is a trade-off between background suppression and visualized vessel extent. Our goal was to develop an ASL technique with improved background suppression and without the need of subtraction. Figure 1 Double inversion bright-blood MR angiography sequence Methods The proposed method is a modified Quadruple Inversion Recovery [5] sequence (mQIR-ASL), which provides excellent background signal suppression according to our simulations (Figure ​(Figure2).2). The first pair of RF pulses consists of a non-selective inversion RF pulse followed by a selective reinversion pulse and a navigator-restore pulse. The second pair of RF pulses consists of a non-selective inversion pulse followed by a navigator-restore pulse. With this configuration, the upstream labeled blood only “experiences” the second non-selective inversion pulse, while the static tissue “experiences” both non-selective inversion pulses. With the right choice of TI1 and TI2, signal from static tissue can be suppressed over a wide T1 range while maintaining the signal of target blood (Figure ​(Figure2).2). This pre-pulse was implemented on a 3T Achieva Gyroscan MR scanner (Philips Healthcare, Best, NL) and tested in 5 subjects. Figure 2 mQIR-ASL sequence, NS: Adiabatic Non-Selective Inversion Pulse. R: Selective Inversion Pulse, NR: Navigator Restore Pulse, N: Naviagtor, AQ: Acquisition Results Renal arteries including small branches were successfully visualized in all subjects with excellent suppression of background (Figure ​(Figure33,​,4).4). The plan scan and the maximum projection angiogram (MIP) are shown in Figure ​Figure3.3. Improved background suppression was observed with mQIR-ASL compared to DIR-ASL (Figure ​(Figure44). Figure 3 In vivo result with mQIR-ASL (TR/TI1/TI2 = 1000/480/162 ms). A- Planning procedure; B- and C- MIPs of aorta and renal arteries Figure 4 Transverse slice at the renal artery level demonstrating improved background suppression with mQIR-ASL (TW/TI1/TI2 = 480/162 ms) © compared with DIR-ASL (Inversion time (TI) of 300 ms (A) and 600 ms (B)). L=liver; M=muscle; K=kidneys. Conclusions We demonstrate a new ASL approach for non-contrast enhanced MR angiography with excellent background tissue suppression and without the need of subtraction. In comparison to DIR-ASL, mQIR-ASL yielded better background suppression and improved vessel delineation.

Inverse agonism of cannabinoid CB1 receptor blocks the adhesion of encephalitogenic T cells in inflamed brain venules by a protein kinase A-dependent mechanism

It is well known that the cannabinoid system has a significant role in the regulation of the immune responses. Cannabinoid receptors CB1 and CB2 are expressed on T lymphocytes and mediate the immunomodulatory effects of cannabinoids on T cell functions. Here we show that the treatment of proteolipid protein (PLP)139–151-specific T cells with SR141716A, a CB1 inverse agonist and prototype of the diarylpyrazoles series, induced a strong inhibition of firm adhesion in inflamed brain venules in intravital microscopy experiments. In contrast, SR144528, a potent CB2 inverse agonist, had no significant effect on both rolling and arrest of activated T cells. In addition, two analogs of SR141716A and CB1 inverse agonists, AM251 and AM281 inhibited encephalitogenic T cell adhesion suggesting that selective CB1 inverse agonism interfere with lymphocyte trafficking in the CNS. Flow cytometry experiments showed that CB1 inverse agonists have no effect on adhesion molecule expression suggesting that CB1 blockade interferes with signal transduction pathways controlling T cell adhesion in inflamed brain venules. In addition, integrin clustering was not altered after treatment with CB1 inverse agonists suggesting that adhesion blockade is not due to the modulation of integrin valency. Notably, the inhibitory effect exerted by AM251 and AM281 on the adhesive interactions was completely reverted in the presence of protein kinase A (PKA) inhibitor H89, suggesting that cAMP and PKA activation play a key role in the adhesion blockade mediated by CB1 inverse agonists. To further strengthen these results and unveil a previously unknown inhibitory role of cAMP on activated T cell adhesion in vivo in the context of CNS inflammation, we showed that intracellular increase of cAMP induced by treatment with Bt2cAMP, a permeable analog of cAMP, and phosphodiesterase (PDE) inhibitor theophylline efficiently blocked the arrest of encephalitogenic T cells in inflamed brain venules. Our data show that modulation of CB1 function has anti-inflammatory effects and suggests that inverse agonism of CB1 block signal transduction mechanisms controlling encephalitogenic T cells adhesion in inflamed brain venules by a PKA-dependent mechanism.

Langmuir monolayers of a cholesterol-armed cyclen complex that can control enantioselectivity of amino acid recognition by surface pressure

The cholesterol-armed cyclen Na(+) complex formed stable Langmuir monolayers at the air-water interface. The π-A isotherm displayed a reasonable limiting molecular area of ∼1.57 nm(2) and the areas expanded when amino acids were dissolved in water, indicating the efficient accommodation in the monolayers. Brewster angle microscopy (BAM) images exhibited almost no defects of the compressed Langmuir monolayers regardless of the presence of amino acids. Based on the idea that the increase in the limiting molecular areas corresponds to the amount of the adsorbed amino acid, the binding constants of three enantiomeric amino acids, namely valine (Val), leucine (Leu), and phenylalanine (Phe), were calculated at different surface pressures. Remarkably, a surface pressure dependent enantioselectivity of amino acid recognition was observed. Upon compression of the monolayers, the binding constants of amino acids increased accompanying an inversion of chiral selectivity from the D- to L-form in the case of Val and, conversely, from L- to D-form in the case of Phe.

Parallel Tempering Simulations of Liquid-Phase Adsorption of n-Alkane Mixtures in Zeolite LTA-5A

Adsorption of n-alkane mixtures in the zeolite LTA-5A under liquid-phase conditions has been studied using grand canonical Monte Carlo (GCMC) simulations combined with parallel tempering. Normal GCMC techniques fail for some of these systems due to the preference of linear molecules to coil within a single cage in the zeolite. The narrow zeolite windows severerly restrict interactions of the molecules, making it difficult to simulate cooperative rearrangements necessary to explore configuration space. Because of these reasons, normal GCMC simulations results show poor reproducibility in some cases. These problems were overcome with parallel tempering techniques. Even with parallel tempering, these are very challenging systems for molecular simulation. Similar problems may arise for other zeolites such as CHA, AFX, ERI, KFI, and RHO having cages connected by narrow windows. The simulations capture the complex selectivity behavior observed in experiments such as selectivity inversion and azeotrope formation.

Selective 15N-Labeling and Analysis of 13C−15N J Couplings as an Effective Tool for Studying the Structure and Azide−Tetrazole Equilibrium in a Series of Tetrazolo[1,5-b][1,2,4]triazines and Tetrazolo[1,5-a]pyrimidines

Two general methods for the selective incorporation of an (15)N-label in the azole ring of tetrazolo[1,5-b][1,2,4]triazines and tetrazolo[1,5-a]pyrimidines were developed. The first approach included treatment of azinylhydrazides with (15)N-labeled nitrous acid, and the second approach was based on fusion of the azine ring to [2-(15)N]-5-aminotetrazole. The synthesized compounds were studied by (1)H, (13)C, and (15)N NMR spectroscopy in both DMSO and TFA solution, in which the azide-tetrazole equilibrium is shifted to tetrazole and azide forms, respectively. Incorporation of the (15)N-label led to the appearance of (13)C-(15)N J coupling constants (J(CN)), which can be measured easily using either 1D (13)C spectra with selective (15)N decoupling or with amplitude modulated 1D (13)C spin-echo experiments with selective inversion of the (15)N nuclei. The observed J(CN) patterns permit unambiguous determination of the type of fusion between the azole and azine rings in tetrazolo[1,5-b][1,2,4]triazine derivatives. Joint analysis of J(CN) patterns and (15)N chemical shifts was found to be the most efficient way to study the azido-tetrazole equilibrium.

An Exploratory Study of Endorectal Magnetic Resonance Imaging and Spectroscopy of the Prostate as Preoperative Predictive Biomarkers of Biochemical Relapse After Radical Prostatectomy

Radical prostatectomy has significant side effects. Preoperative information predicting its long-term outcome would be valuable to patients and physicians. We determined whether pretreatment endorectal magnetic resonance imaging/magnetic resonance spectroscopic imaging predicts biochemical recurrence after radical prostatectomy. Of 202 patients who underwent endorectal magnetic resonance imaging/magnetic resonance spectroscopic imaging from January 2000 to December 2002 before radical prostatectomy 130 satisfied study inclusion criteria and were included in analysis. We compared imaging factors with potential predictive capability to biochemical recurrence data, including magnetic resonance imaging risk score based on local disease extent and magnetic resonance spectroscopic imaging index lesion characteristics, such as the number of voxels and degree of metabolic abnormality (magnetic resonance spectroscopic imaging grade). We evaluated associations of these imaging variables with time to biochemical recurrence by Cox proportional hazards regression adjusted for known predictors of biochemical recurrence, such as stage, grade and prostate specific antigen. At a median 68-month followup there were 26 biochemical failures. Risk score, lesion volume and high grade voxels each correlated with time to biochemical recurrence. In a model combining clinical parameters risk score, lesion volume and at least 1 high grade voxel the magnetic resonance spectroscopic imaging variables remained significant but the magnetic resonance imaging score dropped out. Index lesion volume on magnetic resonance spectroscopic imaging and high grade magnetic resonance spectroscopic imaging voxels correlate with time to biochemical recurrence after radical prostatectomy even when adjusted for clinical data. Results suggest the preoperative predictive usefulness of endorectal magnetic resonance imaging/magnetic resonance spectroscopic imaging in patients considering radical prostatectomy.

Comparison of selective arterial spin labeling using 1D and 2D tagging RF pulses

Generic arterial spin labeling (ASL) techniques label all brain feeding arteries. In this work, we used two different selective ASL (SASL) methods to show the perfusion of one single artery. A slice selective inversion of an area including the desired vessel was compared to a multidimensional RF pulse with Gaussian profile to label only the artery of interest. Perfusion images with a resolution of 2 x 2 x 5 mm 3 are shown that were acquired after tagging only the internal carotid artery of healthy volunteers. In addition, both techniques were applied to a patient with an extra-intracranial bypass to illustrate its perfusion territory. These perfusion images are consistent with a standard angiography. SASL imaging with a resolution of 2 x 2 x 5 mm 3 is possible in a total scan time of 5 min. The presented MR techniques may in part replace the assessment of revascularization success by conventional angiography.

NMR Spectroscopic Evidence for the Intermediacy of XeF3− in XeF2/F− Exchange, Attempted Syntheses and Thermochemistry of XeF3− Salts, and Theoretical Studies of the XeF3− Anion

The existence of the trifluoroxenate(II) anion, XeF(3)(-), had been postulated in a prior NMR study of the exchange between fluoride ion and XeF(2) in CH(3)CN solution. The enthalpy of activation for this exchange, ΔH(⧧), has now been determined by use of single selective inversion (19)F NMR spectroscopy to be 74.1 ± 5.0 kJ mol(-1) (0.18 M) and 56.9 ± 6.7 kJ mol(-1) (0.36 M) for equimolar amounts of [N(CH(3))(4)][F] and XeF(2) in CH(3)CN solvent. Although the XeF(3)(-) anion has been observed in the gas phase, attempts to prepare the Cs(+) and N(CH(3))(4)(+) salts of XeF(3)(-) have been unsuccessful, and are attributed to the low fluoride ion affinity of XeF(2) and fluoride ion solvation in CH(3)CN solution. The XeF(3)(-) anion would represent the first example of an AX(3)E(3) valence shell electron pair repulsion (VSEPR) arrangement of electron lone pair and bond pair domains. Fluorine-19 exchange between XeF(2) and the F(-) anion has also been probed computationally using coupled-cluster singles and doubles (CCSD) and density functional theory (DFT; PBE1PBE) methods. The energy-minimized geometry of the ground state shows that the F(-) anion is only weakly coordinated to XeF(2) (F(2)Xe---F(-); a distorted Y-shape possessing C(s) symmetry), while the XeF(3)(-) anion exists as a first-order transition state in the fluoride ion exchange mechanism, and is planar and Y-shaped (C(2v) symmetry). The molecular geometry and bonding of the XeF(3)(-) anion has been described and rationalized in terms of electron localization function (ELF) calculations, as well as the VSEPR model of molecular geometry. Quantum-chemical calculations, using the CCSD method and a continuum solvent model for CH(3)CN, accurately reproduced the transition-state enthalpy observed by (19)F NMR spectroscopy, and showed a negative but negligible enthalpy for the formation of the F(2)Xe---F(-) adduct in this medium.

Rationally engineered double substituted variants of Yarrowia lipolytica lipase with enhanced activity coupled with highly inverted enantioselectivity towards 2‐bromo phenyl acetic acid esters

Inverting enzyme enantioselectivity by protein engineering is still a great challenge. Lip2p lipase from Yarrowia lipolytica, which demonstrates a low S-enantioselectivity (E-value = 5) during the hydrolytic kinetic resolution of 2-bromo-phenyl acetic acid octyl esters (an important class of chemical intermediates in the pharmaceutical industry), was converted, by a rational engineering approach, into a totally R-selective enzyme (E-value > 200). This tremendous change in selectivity is the result of only two amino acid changes. The starting point of our strategy was the prior identification of two key positions, 97 and 232, for enantiomer discrimination. Four single substitution variants were recently identified as exhibiting a low inversion of selectivity coupled to a low-hydrolytic activity. On the basis of these results, six double substituted variants, combining relevant mutations at both 97 and 232 positions, were constructed by site-directed mutagenesis. This work led to the isolation of one double substituted variant (D97A-V232F), which displays a total preference for the R-enantiomer. The highly reversed enantioselectivity of this variant is accompanied by a 4.5-fold enhancement of its activity toward the preferred enantiomer. The molecular docking of the R- and S-enantiomers in the wild-type enzyme and the D97A-V232F variant suggests that V232F mutation provides a more favorable stacking interaction for the phenyl group of the R-enantiomer, that could explain both the enhanced activity and the reversal of enantioselectivity. These results demonstrate the potential of rationally engineered mutations to further enhance enzyme activity and to modulate selectivity.

Spectral Identification and Inversion of Composition and Component of Objects with Hyperspectral Remote Sensing

The principal advantage of hyperspectral remote sensing is to identify composition and components in objects and inverse the physical and chemical parameters according to the acquired and rebuilt pixel spectral signatures.This paper reviewed the composition and components of rocks,soils,atmosphere,vegetation,water body and manmade structures that can be recognized with hyperspectral remote sensing,described spectral identification methods and then,discussed some key characteristic techniques comparing with multispectral remote sensing,such as spectral matching,spectral unmixing,endmember selection,and quantitative inversion as well.

Slow Li exchange in a Li3N single crystal measured by 6,7Li NMR selective quadrupole satellite inversion

Slow Li exchange in a Li3N single crystal measured by 6,7Li NMR selective quadrupole satellite inversion

2D-NMR reveals different populations of exposed lysine residues in the apoB-100 protein of electronegative and electropositive fractions of LDL particles

Several potentially atherogenic LDL subfractions present low affinity for the LDL receptor, which result in impaired plasma clearance. Electronegative LDL [LDL(-)] is one of these minor subfractions and the molecular basis for its reduced receptor affinity is not well understood. In the present study, high-resolution 2D-NMR spectroscopy has been employed to characterize the surface-exposed lysine residues of the apolipoprotein (apo)B-100 protein in both LDL(-) and LDL(+) subfractions. LDL(+) showed two populations of lysine residues, similar to those previously described in total LDL. "Normal" Lys have a pk(a) of 10.4 whereas "active" Lys have a pk(a) of 8.8 and have been suggested to be involved in receptor binding. In contrast to LDL(+), the LDL(-) subfraction presented a third type of Lys, named as "intermediate" Lys, with a different microenvironment and higher basicity (pk(a) 10.7). These intermediate Lys cannot be reliably identified by 1D-NMR. Because the abundance of normal Lys is similar in LDL(+) and LDL(-), the intermediate Lys in the apoB-100 molecule of LDL(-) should come from a group of active Lys in LDL(+) particles that have a less basic microenvironment in the LDL(-) particle. These differences between LDL(+) and LDL(-) are indicative of a distinct conformation of apoB-100 that could be related to loss of affinity of LDL(-) for the LDL receptor.

Fast inversion recovery magnetic resonance angiography of the intracranial arteries

Inversion-prepared pulse sequences can be used for noncontrast MR angiography (MRA) but suffer from long scan times when acquired using conventional nonaccelerated techniques. This work proposes a subtraction-based spin-labeling, three-dimensional fast inversion recovery MRA (FIR-MRA) method for imaging the intracranial arteries. FIR-MRA uses alternating cycles of nonselective and slab-selective inversions, leading to dark-blood and bright-blood images, respectively. The signal difference between these images eliminates static background tissue and generates the angiogram. To reduce scan time, segmented fast gradient recalled echo readout and parallel imaging are applied. The inversion recovery with embedded self-calibration method used allows for parallel acceleration at factors of 2 and above. An off-resonance selective inversion provides effective venous suppression, with no detriment to the depiction of arteries. FIR-MRA was compared against conventional three-dimensional time-of-flight angiography at 3 T in eight normal subjects. Results showed that FIR-MRA had superior vessel conspicuity in the distal vessels (P < 0.05), and equal or better vessel continuity and venous suppression. However, FIR-MRA had inferior vessel sharpness (P < 0.05) in four of nine vessel groups. The clinical utility of FIR-MRA was demonstrated in three MRA patients.

A scheme of test data compression based on coding of even bits marking and selective output inversion

A new scheme of test data compression/decompression, namely coding of even bits marking and selective output inversion, is presented. It first uses a special kind of codewords, odd bits of which are used to represent the length of runs and even bits of which are used to represent whether the codewords finish. The characteristic of the codewords make the structure of decompressor simple. It then introduces a structure of selective output inversion to increase the probability of 0s. This scheme can obtain a better compression ratio than some already known schemes, but it only needs a very low hardware overhead. The performance of the scheme is experimentally confirmed on the larger examples of the ISCAS89 benchmark circuits.

Isolation and Biological Evaluation of 8-epi-Malyngamide C from the Floridian Marine Cyanobacterium Lyngbya majuscula

A new stereoisomer of malyngamide C, 8-epi-malyngamide C (1), and the known compound lyngbic acid [(4E,7S)-7-methoxytetradec-4-enoic acid] were isolated from a sample of Lyngbya majuscula collected near Bush Key, Dry Tortugas, Florida. The structure of 1 was determined by NMR and MS experiments. The absolute configuration of 1 was determined by selective Mitsunobu inversion of C-8 to give malyngamide C, as determined by NMR, MS, and comparison of specific rotation. Both 1 and malyngamide C were found to be cytotoxic to HT29 colon cancer cells (IC(50) 15.4 and 5.2 microM, respectively) and to inhibit bacterial quorum sensing in a reporter gene assay.

Palladium(II)-Catalyzed Oxidative C−H/C−H Cross-Coupling of Heteroarenes

An efficient methodology for the synthesis of unsymmetrical biheteroaryl molecules has been developed via Pd(II)-catalyzed oxidative C-H/C-H cross-coupling of heteroarenes. An inversion in reactivity and selectivity has been achieved successfully to perform the desired heterocoupling. This process allows the heterocoupling of not only electron-rich N-containing heteroarenes (e.g., xanthines, azoles, and indolizines) but also electron-poor pyridine N-oxides with various thiophenes or furans.

Non‐contrast‐enhanced pulmonary vein MRI with a spatially selective slab inversion preparation sequence

We propose a non-contrast-enhanced, three-dimensional, free-breathing, electrocardiogram-gated, gradient recalled echo sequence with a slab-selective inversion for pulmonary vein (PV) MRI. A sagittal inversion slab was applied prior to data acquisition to suppress structures adjacent to the left atrium (LA) and PVs, thereby improving the conspicuity of the PV and LA. Compared with other MR angiography methods using an inversion pulse, the proposed method does not require signal subtraction and the inversion slab is not parallel to the imaging slab. The feasibility of the proposed method was demonstrated in healthy subjects. The inversion slab thickness and inversion time were optimized to be 60 mm and 500 ms, respectively. Compared to conventional gradient recalled echo imaging without inversion, the proposed technique significantly increased the contrast-to-noise ratios between the LA and the right atrium by 20-fold (P < 0.01), increased the contrast-to-noise ratios between the PVs and right atrium by 10-fold (P < 0.03), and increased the contrast-to-noise ratios between the PVs, LA and pulmonary artery by 4-fold (P < 0.01 for both). The signal-to-noise ratios of the PVs and the LA were similar with and without the inversion slab (P > 0.3). The proposed technique greatly enhances the conspicuity of the PVs and LA without significant loss of signal-to-noise ratio.

Simulation of electrokinetics at the nanoscale: inversion of selectivity in a bio-nanochannel

Here we show, combining a simulation and theoretical study, that electrostatic correlations typical of multivalent ions can reverse the selectivity of a biological nanochannel. Our results provide a physical mechanism for a new, experimentally observed phenomenon, namely the inversion of the selectivity of a bacterial porin (the E. Coli OmpF) in presence of divalent and trivalent cations. Also, the differences and similarities between the driving force for this phenomenon and other similar nano and micro-escale electrokinetic effects (e.g. inversion of streaming current in silica nanochannels) are explored.

Parallel Hybrid Preconditioning: Incomplete Factorization with Selective Sparse Approximate Inversion

We consider parallel preconditioning to solve large sparse linear systems $Ax=b$ using conjugate gradients when $A$ is symmetric and positive definite. We develop a preconditioner that can be viewed as a hybrid of incomplete factorization and sparse approximate inversion schemes. Such a hybrid can potentially enable fast and reliable solution through a preconditioner with low memory requirements that allows latency-tolerant construction and application on multiprocessor systems. We propose a parallel hybrid scheme which yields a preconditioner as a tree-structured aggregate of sparse incomplete factors and inverses of selected submatrices. We analyze the computation and communication costs of our hybrid preconditioner and report on its parallel performance on some well-known test matrices. Our results indicate that our hybrid has significant advantages over sparse approximate inverse preconditioners and incomplete Cholesky preconditioners using either drop-threshold or zero-level-of-fill schemes.