Combined use of pulsed arterial spin-labeling and susceptibility-weighted imaging in stroke at 3T

Background and Purpose: In acute stroke it is no longer sufficient to detect simply ischemia, but also to try to evaluate reperfusion/recanalization status and predict eventual hemorrhagic transformation. Arterial spin labeling (ASL) perfusion may have advantages over contrast-enhanced perfusion-weighted imaging (cePWI), and susceptibility weighted imaging (SWI) has an intrinsic sensitivity to paramagnetic effects in addition to its ability to detect small areas of bleeding and hemorrhage. We want to determine here if their combined use in acute stroke and stroke follow-up at 3T could bring new insight into the diagnosis and prognosis of stroke leading to eventual improved patient management. Methods: We prospectively examined 41 patients admitted for acute stroke (NIHSS >1). Early imaging was performed between 1 h and 2 weeks. The imaging protocol included ASL, cePWI, SWI, T2 and diffusion tensor imaging (DTI), in addition to standard stroke protocol. Results: We saw four kinds of imaging patterns based on ASL and SWI: patients with either hypoperfusion and hyperperfusion on ASL with or without changes on SWI. Hyperperfusion was observed on ASL in 12/41 cases, with hyperperfusion status that was not evident on conventional cePWI images. Signs of hemorrhage or blood-brain barrier breakdown were visible on SWI in 15/41 cases, not always resulting in poor outcome (2/15 were scored mRS = 0–6). Early SWI changes, together with hypoperfusion, were associated with the occurrence of hemorrhage. Hyperperfusion on ASL, even when associated with hemorrhage detected on SWI, resulted in good outcome. Hyperperfusion predicted a better outcome than hypoperfusion (p = 0.0148). Conclusions: ASL is able to detect acute-stage hyperperfusion corresponding to luxury perfusion previously reported by PET studies. The presence of hyperperfusion on ASL-type perfusion seems indicative of reperfusion/collateral flow that is protective of hemorrhagic transformation and a marker of favorable tissue outcome. The combination of hypoperfusion and changes on SWI seems on the other hand to predict hemorrhage and/or poor outcome.

Varying spin state composition by the choice of capping ligand in a family of molecular chains: detailed analysis of magnetic properties of chromium(III) horseshoes

We report a detailed physical analysis on a family of isolated, antiferro-magnetically (AF) coupled, chromium(III) finite chains, of general formula (Cr(RCO(2))(2)F)(n) where the chain length n = 6 or 7. Additionally, the chains are capped with a selection of possible terminating ligands, including hfac (= 1,1,1,5,5,5-hexafluoropentane-2,4-dionate(1-)), acac (= pentane-2,4-dionate(1-)) or (F)(3). Measurements by inelastic neutron scattering (INS), magnetometery and electron paramagnetic resonance (EPR) spectroscopy have been used to study how the electronic properties are affected by n and capping ligand type. These comparisons allowed the subtle electronic effects the choice of capping ligand makes for odd member spin 3/2 ground state and even membered spin 0 ground state chains to be investigated. For this investigation full characterisation of physical properties have been performed with spin Hamiltonian parameterisation, including the determination of Heisenberg exchange coupling constants and single ion axial and rhombic anisotropy. We reveal how the quantum spin energy levels of odd or even membered chains can be modified by the type of capping ligand terminating the chain. Choice of capping ligands enables Cr-Cr exchange coupling to be adjusted by 0, 4 or 24%, relative to Cr-Cr exchange coupling within the body of the chain, by the substitution of hfac, acac or (F)(3) capping ligands to the ends of the chain, respectively. The manipulation of quantum spin levels via ligands which play no role in super-exchange, is of general interest to the practise of spin Hamilton modelling, where such second order effects are generally not considered of relevance to magnetic properties.

Comparison of spatial and temporal pattern for fMRI obtained with BOLD and arterial spin labeling

Functional magnetic resonance imaging (fMRI) is presently either performed using blood oxygenation level-dependent (BOLD) contrast or using cerebral blood flow (CBF), measured with arterial spin labeling (ASL) technique. The present fMRI study aimed to provide practical hints to favour one method over the other. It involved three different acquisition methods during visual checkerboard stimulation on nine healthy subjects: 1) CBF contrast obtained from ASL, 2) BOLD contrast extracted from ASL and 3) BOLD contrast from Echo planar imaging. Previous findings were replicated; i) no differences between the three measurements were found in the location of the activated region; ii) differences were found in the temporal characteristics of the signals and iii) BOLD has significantly higher sensitivity than ASL perfusion. ASL fMRI was favoured when the investigation demands for perfusion and task related signal changes. BOLD fMRI is more suitable in conjunction with fast event related design.

A Donor-Acceptor Tetrathiafulvalene Ligand Complexed to Iron(II): Synthesis, Electrochemistry, and Spectroscopy of Fe(phen)(2)(TTF-dppz)(PF6)(2)

The synthesis and photophysical properties of the complex Fe(phen)(2)(TTF-dppz)(2+) (TTF-dppz = 4',5'-bis-(propylthio)tetrathiafulvenylidipyrido3,2-a:2',3'-c-phenazine, phen = 1,10-phenanthroline) are described. In this complex, excitation into the metal ligand charge transfer bands results in the population of a high-spin state of iron(II), with a decay lifetime of approximately 1.5 ns, in dichloromethane, at room temperature. An intraligand charge transfer state can also be obtained and has a lifetime of 38 ps. A mechanism for the different states reached is proposed based on transient absorption spectroscopy.

Limits on Spin-Dependent WIMP-Nucleon Cross Sections from 225 Live Days of XENON100 Data

We present new experimental constraints on the elastic, spin-dependent WIMP-nucleon cross section using recent data from the XENON100 experiment, operated in the Laboratori Nazionali del Gran Sasso in Italy. An analysis of 224.6 live days x 34 kg of exposure acquired during 2011 and 2012 revealed no excess signal due to axial-vector WIMP interactions with Xe-129 and Xe-131 nuclei. This leads to the most stringent upper limits on WIMP-neutron cross sections for WIMP masses above 6 GeV/c(2), with a minimum cross section of 3.5 x 10(-40) cm(2) at a WIMP mass of 45 GeV/c(2), at 90% confidence level.

Accurate evaluation of hadronic uncertainties in spin-independent WIMP-nucleon scattering: Disentangling two- and three-flavor effects

We show how to avoid unnecessary and uncontrolled assumptions usually made in the literature about soft SU(3) flavor symmetry breaking in determining the two-flavor nucleon matrix elements relevant for direct detection of weakly interacting massive particles (WIMPs). Based on SU(2) chiral perturbation theory, we provide expressions for the proton and neutron scalar couplings fp,nu and fp,nd with the pion-nucleon σ term as the only free parameter, which should be used in the analysis of direct detection experiments. This approach for the first time allows for an accurate assessment of hadronic uncertainties in spin-independent WIMP-nucleon scattering and for a reliable calculation of isospin-violating effects. We find that the traditional determinations of Vfpu−fnu and fpd−fnd are off by a factor of 2.

High-Spin Molecules: Synthesis, X-ray Characterization, and Magnetic Behavior of Two New Cyano-Bridged Ni II 9 Mo V 6 and Ni II 9 W V 6 Clusters with a S = 12 Ground State

The preparations, X-ray structures, and magnetic characterizations are presented for two new pentadecanuclear cluster compounds:  [NiII{NiII(MeOH)3}8(μ-CN)30{MV(CN)3}6]·xMeOH·yH2O (MV = MoV (1) with x = 17, y = 1; MV = WV (2) with x = 15, y = 0). Both compounds crystallize in the monoclinic space group C2/c, with cell dimensions of a = 28.4957(18) Å, b = 19.2583(10) Å, c = 32.4279(17) Å, β = 113.155(6)°, and Z = 4 for 1 and a = 28.5278(16) Å, b = 19.2008(18) Å, c = 32.4072(17) Å, β = 113.727(6)°, and Z = 4 for 2. The structures of 1 and 2 consist of neutral cluster complexes comprising 15 metal ions, 9 NiII and 6 MV, all linked by μ-cyano ligands. Magnetic susceptibilities and magnetization measurements of compounds 1 and 2 in the crystalline and dissolved state indicate that these clusters have a S = 12 ground state, originating from intracluster ferromagnetic exchange interactions between the μ-cyano-bridged metal ions of the type NiII−NC−MV. Indeed, these data show clearly that the cluster molecules stay intact in solution. Ac magnetic susceptibility measurements reveal that the cluster compounds exhibit magnetic susceptibility relaxation phenomena at low temperatures since, with nonzero dc fields, χ‘ ‘M has a nonzero value that is frequency dependent. However, there appears no out-of-phase (χ‘ ‘M) signal in zero dc field down to 1.8 K, which excludes the expected signature for a single molecule magnet. This finding is confirmed with the small uniaxial magnetic anisotropy value for D of 0.015 cm-1, deduced from the high-field, high-frequency EPR measurement, which distinctly reveals a positive sign in D. Obviously, the overall magnetic anisotropy of the compounds is too low, and this may be a consequence of a small single ion magnetic anisotropy combined with the highly symmetric arrangement of the metal ions in the cluster molecule.

Microscopic theory of cooperative spin crossover: Interaction of molecular modes with phonons

In this article, we present a new microscopic theoretical approach to the description of spin crossover in molecular crystals. The spin crossover crystals under consideration are composed of molecular fragments formed by the spin-crossover metal ion and its nearest ligand surrounding and exhibiting well defined localized (molecular) vibrations. As distinguished from the previous models of this phenomenon, the developed approach takes into account the interaction of spin-crossover ions not only with the phonons but also a strong coupling of the electronic shells with molecular modes. This leads to an effective coupling of the local modes with phonons which is shown to be responsible for the cooperative spin transition accompanied by the structural reorganization. The transition is characterized by the two order parameters representing the mean values of the products of electronic diagonal matrices and the coordinates of the local modes for the high- and low-spin states of the spin crossover complex. Finally, we demonstrate that the approach provides a reasonable explanation of the observed spin transition in the [Fe(ptz)6](BF4)2 crystal. The theory well reproduces the observed abrupt low-spin → high-spin transition and the temperature dependence of the high-spin fraction in a wide temperature range as well as the pronounced hysteresis loop. At the same time within the limiting approximations adopted in the developed model, the evaluated high-spin fraction vs. T shows that the cooperative spin-lattice transition proves to be incomplete in the sense that the high-spin fraction does not reach its maximum value at high temperature.

Experimental and Calculated Spectra of π-Stacked Mild Charge-Transfer Complexes: Jet-Cooled Perylene·(Tetrachloroethene) n , n = 1,2

The S0 ↔ S1 spectra of the mild charge-transfer (CT) complexes perylene·tetrachloroethene (P·4ClE) and perylene·(tetrachloroethene)2 (P·(4ClE)2) are investigated by two-color resonant two-photon ionization (2C-R2PI) and dispersed fluorescence spectroscopy in supersonic jets. The S0 → S1 vibrationless transitions of P·4ClE and P·(4ClE)2 are shifted by δν = −451 and −858 cm–1 relative to perylene, translating to excited-state dissociation energy increases of 5.4 and 10.3 kJ/mol, respectively. The red shift is ∼30% larger than that of perylene·trans-1,2-dichloroethene; therefore, the increase in chlorination increases the excited-state stabilization and CT character of the interaction, but the electronic excitation remains largely confined to the perylene moiety. The 2C-R2PI and fluorescence spectra of P·4ClE exhibit strong progressions in the perylene intramolecular twist (1au) vibration (42 cm–1 in S0 and 55 cm–1 in S1), signaling that perylene deforms along its twist coordinate upon electronic excitation. The intermolecular stretching (Tz) and internal rotation (Rc) vibrations are weak; therefore, the P·4ClE intermolecular potential energy surface (IPES) changes little during the S0 ↔ S1 transition. The minimum-energy structures and inter- and intramolecular vibrational frequencies of P·4ClE and P·(4ClE)2 are calculated with the dispersion-corrected density functional theory (DFT) methods B97-D3, ωB97X-D, M06, and M06-2X and the spin-consistent-scaled (SCS) variant of the approximate second-order coupled-cluster method, SCS-CC2. All methods predict the global minima to be π-stacked centered coplanar structures with the long axis of tetrachloroethene rotated by τ ≈ 60° relative to the perylene long axis. The calculated binding energies are in the range of −D0 = 28–35 kJ/mol. A second minimum is predicted with τ ≈ 25°, with ∼1 kJ/mol smaller binding energy. Although both monomers are achiral, both the P·4ClE and P·(4ClE)2 complexes are chiral. The best agreement for adiabatic excitation energies and vibrational frequencies is observed for the ωB97X-D and M06-2X DFT methods.

Investigation of arterial spin labeling MRI for quantitative cerebral blood flow measurement

Arterial spin labeling (ASL) is a technique for noninvasively measuring cerebral perfusion using magnetic resonance imaging. Clinical applications of ASL include functional activation studies, evaluation of the effect of pharmaceuticals on perfusion, and assessment of cerebrovascular disease, stroke, and brain tumor. The use of ASL in the clinic has been limited by poor image quality when large anatomic coverage is required and the time required for data acquisition and processing. This research sought to address these difficulties by optimizing the ASL acquisition and processing schemes. To improve data acquisition, optimal acquisition parameters were determined through simulations, phantom studies and in vivo measurements. The scan time for ASL data acquisition was limited to fifteen minutes to reduce potential subject motion. A processing scheme was implemented that rapidly produced regional cerebral blood flow (rCBF) maps with minimal user input. To provide a measure of the precision of the rCBF values produced by ASL, bootstrap analysis was performed on a representative data set. The bootstrap analysis of single gray and white matter voxels yielded a coefficient of variation of 6.7% and 29% respectively, implying that the calculated rCBF value is far more precise for gray matter than white matter. Additionally, bootstrap analysis was performed to investigate the sensitivity of the rCBF data to the input parameters and provide a quantitative comparison of several existing perfusion models. This study guided the selection of the optimum perfusion quantification model for further experiments. The optimized ASL acquisition and processing schemes were evaluated with two ASL acquisitions on each of five normal subjects. The gray-to-white matter rCBF ratios for nine of the ten acquisitions were within ±10% of 2.6 and none were statistically different from 2.6, the typical ratio produced by a variety of quantitative perfusion techniques. Overall, this work produced an ASL data acquisition and processing technique for quantitative perfusion and functional activation studies, while revealing the limitations of the technique through bootstrap analysis. ^

Electron spin resonance (ESR) and 14C dating in sediments of Bonaire, Leeward Antilles

The coastal deposits of Bonaire, Leeward Antilles, are among the most studied archives for extreme-wave events (EWEs) in the Caribbean. Here we present more than 400 electron spin resonance (ESR) and radiocarbon data on coarse-clast deposits from Bonaire's eastern and western coasts. The chronological data are compared to the occurrence and age of fine-grained extreme-wave deposits detected in lagoons and floodplains. Both approaches are aimed at the identification of EWEs, the differentiation between extraordinary storms and tsunamis, improving reconstructions of the coastal evolution, and establishing a geochronological framework for the events. Although the combination of different methods and archives contributes to a better understanding of the interplay of coastal and archive-related processes, insufficient separation, superimposition or burying of coarse-clast deposits and restricted dating accuracy limit the use of both fine-grained and coarse-clast geoarchives to unravel decadal- to centennial-scale events. At several locations, distinct landforms are attributed to different coastal flooding events interpreted to be of tsunamigenic origin. Coastal landforms on the western coast have significantly been influenced by (sub)-recent hurricanes, indicating that formation of the coarse-clast deposits on the eastern coast is likely to be related to past events of higher energy.