Comparison of T2 and LASER T2dagger image contrast in a rat model of acute cerebral ischemia

Previous studies have shown that T2(dagger)-weighted magnetic resonance images acquired using localization by adiabatic selective refocusing (LASER) can provide early tissue contrast following ischemia, possibly due to alterations in microscopic susceptibility within the tissue. The purpose of this study was to make a direct in vivo comparison of T2-, T2(dagger)- and diffusion-weighted image contrast during acute ischemia. Acute middle cerebral artery (MCA) occlusion was attempted in 14 rats using a modified Tamura approach incorporating electrocoagulation of the left MCA. T2(dagger)-weighted LASER images (Echo Time [TE]=108 ms), T2-weighted Carr-Purcell-Meiboom-Gill (CPMG) images (TE=110 ms) and diffusion-weighted images (b value=105 s/mm(2)) were acquired at 4 T within 1.5 h of ischemia onset. Tissue contrast in the MCA territory was quantified for histologically verified ischemic tissue (n=6) and in sham controls (n=4). T2(dagger)-weighted LASER images demonstrated greater contrast compared to the T2-weighted CPMG images, and more focal contrast compared to the diffusion-weighted images, suggesting different contrast mechanisms were involved.     

Whole-body T2* mapping at 1.5 T

This study investigated the feasibility of an MRI protocol providing whole-body T2* maps at 1.5 T. Seven healthy volunteers (mean age=30.1+/-3.7, three women and four men) and two patients (both male, 53 and 46 years old) affected by transfusion-dependent anemias participated in the study. Coronally oriented images of five subsequent body levels were acquired using a fat-suppressed multiecho 2D gradient-echo sequence (12 echo times ranging from 4.8 to 76.3 ms were selected) and afterwards composed. Parametrical T2* maps of the whole body were reconstructed on a pixel-by-pixel basis. For both, healthy volunteers and patients, representative T2* values were computed from extended regions of interest (ROIs). Good-quality whole-body T2* maps were computed in all volunteers and patients. In healthy volunteers, T2* values were assessed in the cerebral white (58.5+/-4.2 ms) and gray (81.4+/-5.5 ms) matter, liver (34.3+/-7.0 ms), spleen (63.5+/-3.3 ms), kidneys (65.4+/-10.3 ms) and skeletal muscles (~30 ms). The liver presented faster relaxation rates in males as compared to females. One patient (serum ferritin concentration=927 microg/dl) showed shortened T2* values in liver (3.6+/-5.5 ms), spleen (3.1+/-4.8 ms), kidneys (11.1+/-7.1 ms) and muscles (25.1+/-3.4 ms). The second patient (serum ferritin concentration=346 microg/dl) presented reduced T2* values in liver (3.9+/-7.3 ms), spleen (20.1+/-9.8 ms) and kidneys (24.6+/-7.7 ms). The presented technique may find clinical application in the assessment of the iron burden in the entire body, and in monitoring of chelation therapies in patients treated with frequent blood transfusions.     

2H T2rho relaxation dynamics and double-quantum filtered NMR studies

In this study 2H T2rho DQF NMR spectra of water in MCM-41 were measured. The T2rho double-quantum filtered (DQF) NMR signal is generated by applying a radio frequency (RF) field for various durations and then observed after a monitor RF pulse. It was found that the transfer between different quantum coherences by the couplings during long-duration RF fields (i.e., soft pulses) and that residual quadrupolar interaction dominates the signal decay. Knowledge of coherence transfer during long-RF pulses has special significance for the development of sophisticated multi-quantum NMR experiments especially multi-quantum MRI applications.     

The zonal architecture of human articular cartilage described by T2 relaxation time in the presence of Gd-DTPA2-

The depth-wise variation of T(2) relaxation time is known to reflect the collagen network architecture in cartilage, while the delayed Gadolinium Enhanced MRI of Cartilage (dGEMRIC) technique is sensitive to tissue proteoglycan (PG) concentration. As the cartilage PG content varies along the tissue depth, the depth-dependent accumulation of the contrast agent may affect the inherent T(2) of cartilage in a nonconstant manner. Therefore, T(2) and dGEMRIC are typically measured in separate MRI sessions. In the present in vitro MRI study at 9.4 T, depth-wise T(2) profiles and collagenous zone thicknesses as determined from T(2) maps in the absence and presence of Gd-DTPA(2-) (T(2) and T(2Gd), respectively) were compared in samples of intact human articular cartilage (n=65). These T(2) measures were further correlated with birefringence (BF) of polarized light microscopy (PLM) to quantify the ability of MRI to predict the properties of the collagen fibril network. The reproducibility of the T(2) measurement in the current setup was also studied. Typical tri-laminar collagen network architecture was observed both with and without Gd-DTPA(2-). The inverse of BF (1/BF) correlated significantly with both T(2) and T(2Gd) (r=0.91, slope=0.56 and r=0.90, slope=0.63), respectively. The statistically significant linear correlations between zone thicknesses as determined from T(2) and T(2Gd) were r=0.55 (slope=0.49), r=0.74 (slope=0.71) and r=0.95 (slope=0.94) for superficial, middle and deep tissue zones, respectively. Reproducibility of the T(2) measurement was worst for superficial cartilage. Consistent with PLM, T(2) and T(2Gd) measurements reveal highly similar depth-dependent information on collagen network in intact human cartilage. Thus, dGEMRIC and T(2) measurements in one MRI session are feasible for intact articular cartilage in vitro.     

A Comparative Study of Water T1 and T2 Nmr Relaxation Times in Healthy and Pathological Blood Fluid

Water protons T₁ and T₂ relaxation times in samples of whole blood, obtained from healthy people and from patients affected by Macrocytic Anemia on one side and Lymphatic and Myeloid Leukemia on the other, have been measured with the FT NMR technique at 80 Mhz and at 25 °C. No significant difference with respect to the value of the spin lattice relaxation time parameter measured for the healthy control group is experimentally evident in the case of the Macrocytic Anaemia while the spin spin relaxation time increases in magnitude. On the reverse both the leukemic cases present a significant (p < 0.001) increase in the relaxation times with respect to the control group. The experimental relaxation data belonging to the anaemic case show a linear correlation with the red cells volume while that obtained for the two leukaemic cases appear linearly correlated with the total white cell numbers. From the relaxation data an estimate of the amount of water tightly bound to the white cells membrane can be determined which results roughly thirty times lower than that bound to the red cells membrane. In this work is also presented a step by step outline of the water relaxation behavior which starts with the pure water and ends with the water in the whole blood supported by relaxation experiments done on the isolated blood main components.     

Deuterium Nuclear Spin–Lattice Relaxation Times and Quadrupolar Coupling Constants in Isotopically Labeled Saccharides

¹³C and ²H spin–lattice relaxation times have been determined by inversion recovery in a range of site-specific ¹³C- and ²H-labeled saccharides under identical solution conditions, and the data were used to calculate deuterium nuclear quadrupolar coupling constants (²H NQCC) at specific sites within cyclic and acyclic forms in solution. ¹³C T₁ values ranged from 0.6 to 8.2 s, and ²H T₁ values ranged from 79 to 450 ms, depending on molecular structure (0.4 M sugar in 5 mM EDTA (disodium salt) in ²H₂O-depleted H₂O, pH 4.8, 30°C). In addition to providing new information on ¹³C and ²H relaxation behavior of saccharides in solution, the resulting ²H1 NQCC values reveal a dependency on anomeric configuration within aldopyranose rings, whereas ²H NQCC values at other ring sites appear less sensitive to configuration at C1. In contrast, ²H NQCC values at both anomeric and nonanomeric sites within aldofuranose rings appear to be influenced by anomeric configuration. These experimental observations were confirmed by density functional theory (DFT) calculations of ²H NQCC values in model aldopyranosyl and aldofuranosyl rings.     

T2* measurements in human brain at 1.5, 3 and 7 T

Measurements have been carried out in six subjects at magnetic fields of 1.5, 3 and 7 T, with the aim of characterizing the variation of T2* with field strength in human brain. Accurate measurement of T2* in the presence of macroscopic magnetic field inhomogeneity is problematic due to signal decay resulting from through-slice dephasing. The approach employed here allowed the signal decay due to through-slice dephasing to be characterized and removed from data, thus facilitating an accurate measurement of T2* even at ultrahigh field. Using double inversion recovery turbo spin-echo images for tissue classification, an analysis of T2* relaxation times in cortical grey matter and white matter was carried out, along with an evaluation of the variation of T2* with field strength in the caudate nucleus and putamen. The results show an approximately linear increase in relaxation rate R2* with field strength for all tissues, leading to a greater range of relaxation times across tissue types at 7 T that can be exploited in high-resolution T2*-weighted imaging.     

双共价因子在半磁半导体HgS:Co2+光谱中的应用

本文采用一种适用于共价晶体的含双共价因子(N_t≠N_e)的能量矩阵计算方法,研究了Co²⁺离子在HgS中的光学吸收谱,并对结果进行了讨论.研究结果表明,对于共价性强的晶体,Racah参量A对能级跃迁的贡献不能忽略.     

NQR, NMR and Crystal Structure Studies of [C(NH2)3]3Sb2Br9

The crystal structure of [C(NH₂)₃]₃Sb₂Br₉ was determined at 143 K: monoclinic, space group C2/c, Z = 4, a = 15.695 (3), b = 9.039(2), c = 18.364(3) Å, β = 96.94(1)°. The structure consists of two crystallographically independent guanidinium ions and two-dimensional corrugated sheets of (Sb₂Br₉ ^3?) _n , in which SbBr₆ octahedra are connected through three bridging Br atoms each other. One of the cations situates in a cavity of the (Sb₂Br₉ ^3?) _n layer with statistical disorder, while the other situates between the layers without disorder. Three ⁸¹Br NQR resonance lines were assignable to terminal Br atoms, while only one line was found for two inequivalent bridging Br atoms. All the ⁸¹Br NQR resonance lines were subjected to fade-out at low temperatures. The temperature dependence curve of ¹H NMR T ₁ showed well defined two minima, which were explained by postulating the C₃ reorientations of two types of cations with very different activation energies. The DTA (DSC) measurement revealed a phase transition of a first-order type at 444 K.     

Feasibility of similarity coefficient map in improving morphological evaluation of T2* weighted MRI for renal cancer

The purpose of this paper is to investigate the feasibility of similarity coefficient map (SCM) in improving morphological evaluation of T₂^* weighted (T₂^*W) magnatic resonance imaging (MRI) for renal cancer. Simulation studies and in vivo 12-echo T₂^*W experiments for renal cancers were performed for this purpose. The results of the first simulation study suggest that SCM can reveal small structures which are hard to be distinguished from the background tissue in T₂^*W images and the corresponding T₂^* map. The capability of improving morphological evaluation is likely due to the improvement in signal to noise ratio (SNR) and carrier to noise ratio (CNR) by SCM technique. Compared with T₂^*W images, SCM can improve SNR by a factor ranging from 1.87 to 2.47. Compared with T₂^* maps, SCM can improve SNR by a factor ranging from 3.85 to 33.31. Compared with T₂^*W images, SCM can improve CNR by a factor raging from 2.09 to 2.43. Compared with T₂^* maps SCM can improve CNR by a factor raging from 1.94 to 8.14. For a given noise level, the improvements of SNR and CNR depend mainly on the original SNRs and CNRs in T₂^*W images, respectively. In vivo experiments confirmed the results of the first simulation study. The results of the second simulation study suggest that more echoes are used to generate SCM, and higher SNR and CNR can be achieved in SCM. In conclusion, SCM can provide improved morphological evaluation of T₂^*W MR images for renal cancer by unveiling fine structures which are ambiguous or invisible in the corresponding T₂^*W MR images and T₂^* maps. What is more, in practical application, for a fixed total sampling time, one should increase the number of echoes as much as possible to achieve SCMs with better SNR and CNR.     

T1–T2 Correlation Spectra Obtained Using a Fast Two-Dimensional Laplace Inversion

Spin relaxation is a sensitive probe of molecular structure and dynamics. Correlation of relaxation time constants, such as T₁ and T₂, conceptually similar to the conventional multidimensional spectroscopy, have been difficult to determine primarily due to the absense of an efficient multidimensional Laplace inversion program. We demonstrate the use of a novel computer algorithm for fast two-dimensional inverse Laplace transformation to obtain T₁–T₂ correlation functions. The algorithm efficiently performs a least-squares fit on two-dimensional data with a nonnegativity constraint. We use a regularization method to find a balance between the residual fitting errors and the known noise amplitude, thus producing a result that is found to be stable in the presence of noise. This algorithm can be extended to include functional forms other than exponential kernels. We demonstrate the performance of the algorithm at different signal-to-noise ratios and with different T₁–T₂ spectral characteristics using several brine-saturated rock samples.     

Muon catalyzed fusion and muon to 3He transfer in solid T2 studied by X-ray and neutron detection

X-ray and neutron measurements were carried out for muon catalyzed fusion and related phenomena in solid T₂. The X-ray originated from the μ^- to α sticking in muon catalyzed fusion; t + t + μ ^- → (μ ^- α) + 2n was measured for the first time, yielding K _α X-ray intensity of (μα) atom and the intensity ratio of K _β to K _α . Utilizing the phenomena of ³He accumulation in solid T₂, the X-ray in the μ^- transfer process from (tμ) to ³He was detected, providing a formation rate and radiative decay branching-ratio of (t ³Heμ) molecule. From fusion neutron measurements, estimated values were obtained for (ttμ) molecular formation rate as well as sticking probability ω_t in ttμ fusion. A possible new insight in t + t fusion reaction process at a low energy limit is also obtained. This revised version was published online in August 2006 with corrections to the Cover Date.     

Production ofψ particles in N-N collisions and largeP T phenomenon

We calculate the yield ofψ (3105) particles in N-N collisions in a model which associates the production of heavy particles with largeP _T phenomenon. Our results show thatψ (3105) has a fairly strong coupling to other hadrons. We propose a criterion in the search for charmed particles and a parametrization for the expected yields of such particles.     

NQR, NMR and Crystal Structure Studies of [C(NH2)3]2HgX4 (X = Br, I)

The crystal structure of [C(NH₂)₃]₂HgBr₄ has been determined at room temperature: monoclinic, space group C2/c, with a = 10.035(2), b = 11.164(2), c = 13.358(3) Å, β = 111.67(3)°, and Z = 4. The crystal consists of planar [C(NH₂)₃]⁺ and distorted tetrahedral [HgBr₄]^2? ions. The Hg atom is located on a two-fold axis such that two sets of inequivalent Br atoms exist in an [HgBr₄]^2? ion. In accordance with the crystal structure, two ⁸¹Br NQR lines widely separated in frequency were observed between 77 and ca. 380 K. [C(NH₂)₃]₂HgI₄ yielded four ¹²⁷I NQR lines ascribable to m = ±1/2 ? ±3/2 transitions, indicating that its crystal structure is different from the bromide complex. The ¹H NMR T ₁ measurements showed a single minimum for the bromide but two minima for the iodide. The analyses based on the C₃ reorientations of the planar [C(NH₂)₃]⁺ ions gave the activation energies of 29.8 kJ mol^?1 for the bromide, and 30.2 and 40.0 kJ mol^?1 for the iodide.     

In vivo multiecho T2 relaxation measurements using variable TR to decrease scan time

Multiecho T2 relaxation measurements to determine geometric mean T2 (GMT2) and myelin water fraction (MWF) are lengthy, resulting in increased motion artefacts from patient discomfort and reduced patient compliance. The goal of this study was to shorten the acquisition time for multiecho T2 measurements without affecting T1 weighting by varying TR across k-space. Six phantoms and 10 healthy volunteers were imaged with both a constant TR and a variable TR multiecho T2 sequence. T1 weighting was determined by TR at the center of k-space; for variable TR measurement, TR was shortened linearly from the center to the edges of k-space. Phantoms showed excellent agreement for proton density and GMT2 between constant and variable TR measurements. No significant differences were found in proton density or MWF for any of the brain structures between the two measurements. The average GMT2 over all structures between the two experiments was not significantly different. In summary, with the variable TR approach, scan time was reduced by >20%, with minimal loss of image resolution and no significant affect on proton density, MWF or GMT2.     

Structural studies and T c dependence in La2−x Dy x Ca y Ba2Cu4+y O z type mixed oxide superconductors

A new series of mixed oxide superconductors with the stoichiometric composition La_2−x Dy _x Ca _y Ba₂Cu_4+y O _z (x=0.0 − 0.5, y=2x) has been studied for structural and superconductiong properties. Our earlier studies on La_2−x (Y/Er) _x Ca _y Ba₂Cu_4+y O _z series, show a strong dependence of T _c on hole concentration (p _sh). In the present work, the results of the analysis of the neutron diffraction measurements at room temprerature on x=0.3 and 0.5 samples are reported. It is interesting to know that Ca substitutes for both La and Ba site with concomitant displacement of La onto Ba site. Superconductivity studies show that maximum T _c is obtained for x=0.5, y=1.0 sample (T _c ∼ 75 K), for La_1.5Dy_0.5Ca₁Ba₂Cu₅O _z (La-2125).     

NMR T1–T2 correlation analysis of molecular absorption inside a hardened cement paste containing silanised silica fume

ABSTRACT

The influence of silanised silica fume addition on the pore size distribution and wettability of white cement paste was investigated using T₁–T₂ correlation nuclear magnetic resonance (NMR) relaxometry. Surface silanisation of silica fume particles was achieved by the hydrolysis reaction of APTES (3-Aminopropyltriethoxysilane) and condensation of the silanol functional groups on the surface. The methods used for characterisation of the silanised silica fume particles were scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FT-IR) and thermogravimetric analysis (TGA). By adding silanised silica fume to the cement paste, the accessibility of water molecules to the porous system becomes restricted, leading to a lower permeability in comparison with the unmodified cement paste. Differential scanning calorimetry (DSC) measurements on the cement pastes saturated with Octamethylcyclotetrasiloxane confirm also that the size of inter-C–S–H and capillary pores is not influenced by the addition of silica fume in a detectable manner.     

First-principles study of elastic and thermo-physical properties of kesterite-type Cu2ZnSnS4

The lattice constants and elastic constants of the kesterite-type Cu₂ZnSnS₄ have been calculated using density-functional theory (DFT). The calculated lattice constants are in good agreement with the experimental data. The calculated elastic constants indicate that the bonding strength along the [1 0 0] and [0 1 0] directions is as strong as the one along the [0 0 1] direction. The high B/G ratio shows that the kesterite-type Cu₂ZnSnS₄ compound has ductile behavior. Finally, using the Debye model, the volume, bulk modulus and heat capacity as a function of temperature for the kesterite-type CZTS have been estimated at different pressures. The Debye temperature and Gruneisen parameter are 157 K and 2.28 at 300 K temperature, respectively. The present results can give some information for the design of the kesterite-type CZTS compounds, and these can also be used to stimulate future experimental and theoretical work.     

A comparative study at 3 T of sequence dependence of T2 quantitation in the knee

Objective

T₂ mapping has been used widely in detecting cartilage degeneration in osteoarthritis. Several scanning sequences have been developed in the determination of T₂ relaxation times of tissues. However, the derivation of these times may vary from sequence to sequence. This study seeks to evaluate the sequence-dependent differences in T₂ quantitation of cartilage, muscle, fat and bone marrow in the knee joint at 3 T.

Methods

Three commercial phantoms and 10 healthy volunteers were studied using 3 T MR. T₂ relaxation times of the phantoms, cartilage, muscle, subcutaneous fat and marrow were derived using spin echo (SE), multiecho SE (MESE), fast SE (FSE) with varying echo train length (ETL), spiral and spoiler gradient (SPGR) sequences. The differences between these times were then evaluated using Student's t test. In addition, the signal-to-noise ratio (SNR) efficiency and coefficient of variation of T₂ from each sequence were calculated.

Results

The average T₂ relaxation time was 36.38±5.76 ms in cartilage and 34.08±6.55 ms in muscle, ranging from 27 to 45 ms in both tissues. The times for subcutaneous fat and marrow were longer and more varying, ranging from 41 to 143 ms and from 42 to 160 ms, respectively. In FSE acquisition, relaxation time significantly increases as ETL increases (P<.05). In cartilage, the SE acquisition yields the lowest T₂ values (27.52±3.10 ms), which is significantly lower than those obtained from other sequences (P<.002). T₂ values obtained from spiral acquisition (38.27±6.45 ms) were higher than those obtained from MESE (34.35±5.62 ms) and SPGR acquisition (31.64±4.53 ms). These differences, however, were not significant (P>.05).

Conclusion

T₂ quantification can be a valuable tool for the diagnosis of degenerative disease. Several different sequences exist to quantify the relaxation times of tissues. Sequences range in scan time, SNR efficiency, reproducibility and two- or three-dimensional mapping. However, when choosing a sequence for quantitation, it is important to realize that several factors affect the measured T₂ relaxation time.     

The effect of varying echo spacing within a multiecho acquisition: better characterization of long T2 components

A 48-echo pulse sequence with five different echo-spacing combinations was examined to determine how one can most effectively measure the T2 relaxation characteristics of cerebral tissue containing a long T2 component. For each scan, the first 32 echoes had an echo spacing of 10 ms, while the spacing for Echoes 33-48 (DeltaTE2) was 10, 20, 30, 40 or 50 ms. In an in vivo study using 10 normal volunteers, it was found that the resolution of T2 distribution peaks for both myelin water (approximately 20 ms) and intracellular/extracellular (IE) water (approximately 80 ms) improved as DeltaTE2 increased. The geometric mean T2 values of the main peak agreed within the error for all DeltaTE2 values. A phantom study simulated T2 relaxation distributions that are expected in the brains of patients with demyelinating diseases. For phantoms in which the T2 values of the IE and lesion (200-500 ms) water compartments were separated by at least a factor of 3, each compartment in the distribution was better resolved when DeltaTE2=40 or 50 ms. On the basis of these results, we recommend the use of extended DeltaTE2 values for imaging patients with lesions, without the risk of losing valuable short T2 information.