T1ρ mapping improvement using stretched-type adiabatic locking pulses for assessment of human liver function at 3 T

PurposeThe purpose of this study is to investigate the performance of stretched-type adiabatic spin lock pulses for homogeneous spin locking with a flexible spin lock time (TSL) setting.MethodsT_1ρ values were obtained from 61 patients and five normal volunteers who were categorized using the Child–Pugh classification and scanned using each spin lock pulse type. The pulses used were the block and two kinds of hyperbolic secant (HS); HS8_10, and HS8_5. Visual scoring was categorized using a four point scale (1:Severe, 2:Moderate, 3:Mild and 4:None) to evaluate the homogeneity of the T_1ρ map and the source images obtained by each spin lock pulse. Mean T_1ρ values among the patient groups with different Child–Pugh classification were compared.ResultsThe visual assessment scores were 1.98 ± 1.05 for block pulse locking, 3.87 ± 0.39 for HS8_10 pulse locking, and 3.83 ± 0.45 for HS8_5 pulse locking, respectively. The scores between block pulse and HS8_10 were significantly different (p < 0.001), as were those between block pulse and HS8_5 (p < 0.001).The median T_1ρ values of normal liver function, Child–Pugh A, and Child–Pugh B or C were 37.00 ms, 40.77 ms, and 42.20 ms for block pulse, 46.75 ms, 50.78 ms, and 55.60 ms for HS8_10, and 48.80 ms, 55.42 ms, and 57.80 ms for HS8_5, respectively.ConclusionThe spin locking sequence using stretched-type adiabatic pulses provides homogeneous liver T_1ρ maps with reduced artifact and is necessary for a robust evaluation of liver function using T_1ρ.     

Low field T1ρ imaging of myositis

The purpose of this study was to evaluate 1/T₁ρ in relation to 1/T₁ and 1/T₂ in characterizing normal and diseased muscle. We measured the muscle relaxation rates 1/T₁ and 1/T₂ at 0.1 T and 1/T₁ρ at on-resonance locking fields B₁ between 10 and 160 μT in myositis patients and normal volunteers. 1/T₂ and 1/T₁ρ of muscle were lower in the patients than in the volunteers, whereas there was no difference in the 1/T₁ values. The lower relaxation rates 1/T₂ and 1/T₁ρ in the diseased muscle may be due to fat and connective tissue infiltrations and edema. 1/T₁ρ contrast between muscle and subcutaneous fat was higher than 1/T₂ and 1/T₁ contrast. This may be explained by the different B₁ dispersion behavior of these two tissue types. 1/T₁ρ of fat is B₁ field independent, whereas 1/T₁ρ of muscle decreases clearly with increasing B₁ field. In conclusion, 1/T₁ρ provides a useful tool in manipulating contrast in magnetic resonance imaging of diseased muscle.     

Comparison of α-chloralose,medetomidine and isoflurane anesthesia for functional connectivity mapping in the rat

Functional connectivity measures based upon low-frequency blood-oxygenation-level-dependent functional magnetic resonance imaging (BOLD fMRI) signal fluctuations have become a widely used tool for investigating spontaneous brain activity in humans. Still unknown, however, is the precise relationship between neural activity, the hemodynamic response and fluctuations in the MRI signal. Recent work from several groups had shown that correlated low-frequency fluctuations in the BOLD signal can be detected in the anesthetized rat — a first step toward elucidating this relationship. Building on this preliminary work, through this study, we demonstrate that functional connectivity observed in the rat depends strongly on the type of anesthesia used. Power spectra of spontaneous fluctuations and the cross-correlation-based connectivity maps from rats anesthetized with α-chloralose, medetomidine or isoflurane are presented using a high-temporal-resolution imaging sequence that ensures minimal contamination from physiological noise. The results show less localized correlation in rats anesthetized with isoflurane as compared with rats anesthetized with α-chloralose or medetomidine. These experiments highlight the utility of using different types of anesthesia to explore the fundamental physiological relationships of the BOLD signal and suggest that the mechanisms contributing to functional connectivity involve a complicated relationship between changes in neural activity, neurovascular coupling and vascular reactivity.     

Dependencies of multi-component T2 and T1ρ relaxation on the anisotropy of collagen fibrils in bovine nasal cartilage

Both NMR spectroscopy and MRI were used to investigate the dependencies of multi-component T2 and T1ρ relaxation on the anisotropy of bovine nasal cartilage (BNC). The non-negative least square (NNLS) method and the multi-exponential fitting method were used to analyze all experimental data. When the collagen fibrils in nasal cartilage were oriented at the magic angle (55°) to the magnetic field B0, both T2 and T1ρ were single component, regardless of the spin-lock field strength or the echo spacing time in the pulse sequences. When the collagen fibrils in nasal cartilage were oriented at 0° to B0, both T2 and T1ρ at a spin-lock field of 500 Hz had two components. When the spin-lock field was increased to 1000 Hz or higher, T1ρ relaxation in nasal cartilage became a single component, even when the specimen orientation was 0°. These results demonstrate that the specimen orientation must be considered for any multi-component analysis, even for nasal cartilage that is commonly considered homogenously structured. Since the rapidly and slowly relaxing components can be attributed to different portions of the water population in tissue, the ability to resolve different relaxation components could be used to quantitatively examine individual molecular components in connective tissues.     

Bi-phase age-related brain gray matter magnetic resonance T1ρ relaxation time change in adults

ObjectivesTo investigate normative value and age-related change of brain magnetic resonance T1ρ relaxation at 1.5 T.MethodsThis study was approved by the local ethical committee with participants' written consent obtained. There were 42 adults healthy volunteers, including 20 males (age: 41 ± 16 (mean ± standard deviation) years, range: 22–68 years,) and 22 females (age: 39 ± 15 years, range: 21–62 years). MRI was performed at 1.5 T using 3D fluid suppressed turbo spin echo sequence. Regions-of-interests (ROIs) were obtained by atlas-based tissue segmentation and T1ρ was calculated by fitting the mean value to mono-exponential model. Correlation between T1ρ relaxation of brain gray matter regions and age was investigated.ResultsA regional difference among individual gray matter areas was noted; the highest values were observed in the hippocampus (98.37 ± 5.37 ms, median: 97.88 ms) and amygdala (94.95 ± 4.34 ms, median: 94.73 ms), while the lowest values were observed in the pallidum (83.81 ± 5.49 ms, median: 83.77 ms) and putamen (83.93 ± 4.76 ms, median: 83.99 ms). Gray matter T1ρ values decreased slowly (mean slope: − 0.256) and significantly (p < 0.05) with age in gray matter for subjects younger than 40 years old, while for subjects older than 40 years old there was no apparent correlation between T1ρ relaxation and age. Global white matter measured T1ρ value of 88.65 ± 3.47 ms (median: 87.86 ms), and the correlation with age was not significant (p = 0.18).ConclusionGray matter T1ρ relaxation demonstrates a bi-phase change with age in adults of 22–68 years.     

Determination of T1ρ values for head and neck tissues at 0.1 T: a comparison to T1 and T2 relaxation times

In order to optimize head and neck magnetic resonance (MR) imaging with the spin-lock (SL) technique, the T₁ρ relaxation times for normal tissues were determined. Furthermore, T₁ρ was compared to T₁ and T₂ relaxation times. Ten healthy volunteers were studied with a 0.1 T clinical MR imager. T₁ρ values were determined by first measuring the tissue signal intensities with different locking pulse durations (TL), and then by fitting the signal intensity values to the equation with the least-squares method. The T₁ρ relaxation times were shortest for the muscle and tongue, intermediate for lymphatic and parotid gland tissue and longest for fat. T₁ρ demonstrated statistically significant differences (p < 0.05) between all tissues, except between muscle and tongue. T₁ρ values measured at locking field strength (B1L) of 35 μT were close to T₂ values, the only exception being fat tissue, which showed T₁ρ values much longer than T₂ values. Determination of tissue relaxation times may be utilized to optimize image contrast, and also to achieve better tissue discrimination potential, by choosing appropriate imaging parameters for the head and neck spin-lock sequences.     

T 1ρ Dispersion in Nuclear Quadrupole Resonance

Russian Physics Journal -     

Distribution and densitometry mapping of L1-CAM Immunoreactivity in the adult mouse brain – light microscopic observation

Background  

The importance of L1 expression in the matured brain is suggested by physiological and behavioral studies showing that L1 is related to hippocampal plasticity and fear conditioning. The distribution of L1 in mouse brain might provide a basis for understanding its role in the brain.     

An average-magnetization analysis of R 1ρ relaxation outside of the fast exchange limit

Approximate expressions for the NMR spin relaxation rate constant in the rotating frame of reference R _1ρ are derived for two-site chemical exchange by consideration of the evolution of the average density operator using the stochastic Liouville equation. R _1ρ is obtained as a linearized approximation to the largest (least negative) eigenvalue of the matrix describing the evolution of the average density operator in the long-term limit. The expressions obtained are more accurate than existing expressions when exchange is not fast and the populations of the exchanging sites are close to equal. The new expressions for R _1ρ facilitate the interpretation of chemical exchange phenomena in proteins and other biological macromolecules.     

Study of Lamination Characteristics for Rapid Prototyping

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A general strategy for the optimization of Runge–Kutta schemes for wave propagation phenomena

We analyze optimized explicit Runge–Kutta schemes (RK) for computational aeroacoustics, and wave propagation phenomena in general. Exploiting the analysis developed in [S. Pirozzoli, Performance analysis and optimization of finite-difference schemes for wave propagation problems, J. Comput. Phys. 222 (2007) 809–831], we rigorously evaluate the performance of several time integration schemes in terms of appropriate error and cost metrics, and provide a general strategy to design Runge–Kutta methods tailored for specific applications. We present families of optimized second- and third-order Runge–Kutta schemes with up to seven stages, and describe their implementation in the framework of Williamson’s 2N$2N$-storage formulation [J.H. Williamson, Low-storage Runge–Kutta schemes, J. Comput. Phys. 35 (1980) 48–56]. Numerical simulations of the 1D linear advection equation and of the 2D linearized Euler equations are performed to demonstrate the validity of the theory and to quantify the improvement provided by optimized schemes.     

A generalization of the momentum mapping construction for quaternionic Kähler manifolds

We present a method of reduction of any quaternionic Kähler manifold with isometries to another quaternionic Kähler manifold in which the isometries are divided out. Our method is a generalization of the Marsden-Weinstein construction for symplectic manifolds to the non-symplectic geometry of the quaternionic Kähler case. We compare our results with the known construction for Kähler and hyperKähler manifolds. We also discuss the relevance of our results to the physics of supersymmetric non-linear -models and some applications of the method. In particular, we show that the Wolf spaces can be obtained as theU(1) andSU(2) quotients of quaternionic projective spaceH P(n). We also construct an interesting example of compact riemannianV-manifolds(orbifolds) whose metrics are quaternionic Kähler and not symmetric.On leave from the University of Wrocaw, Wrocaw, Poland     

Study of the data taking strategy for a high precision τ mass measurement

To achieve a high precision τ mass measurement at the high luminosity experiment BESIII,Monte Carlo simulation and sampling technique are utilized to simulate various data taking cases for single and multiparameter fits by virtue of which the optimal scheme is determined. The optimized proportion of luminosity distributed at selected points and the relation between precision and luminosity are obtained. In addition,the optimization of the fit scheme is confirmed by scrutinizing a variety of fit possibilities.     

Density functional study of the pressure tensor for inhomogeneous Lennard—Jones fluids

Based on classical density functional theory,an expression of the pressure tensor for inhomogeneous fluids is presented.This takes into account greater correlation between particles,especially for systems that are geometrically confined or involve an interface.The density and pressure components of Lennard-Jones fluids confined in hard and softened nano-cavities are calculated.A comparison between the results of this work and IK expression suggests that the agreement depends on temperature.The interfacial tension for hard sphere fluids agrees well with the Monte Carlo result when the bulk density is not too large.The results of the solid-fluid interfacial tension for Lennard-Jones fluids demonstrate that different types of external potentials modulate the interfacial tension in different manners.     

T1ρ space dependence in rigid polymers by effective radio frequency gradient

An extension of the solid-state nuclear magnetic resonance (NMR) imaging based on magic angle in the rotating frame (MARF) line narrowing approach is presented. The modified magic angle in the rotating frame imaging sequence is able to yield T_1ρ maps of large band polymers with remarkable contrast sensitivity and without contrast parameter alteration referable to the narrowing procedure. This last feature is examined closely in order to outline the actual effectiveness of the method. Further experimental details, especially regarding probe coil design, recently improved, are discussed and some new results are presented.     

Stable computation of the functional variation of the Dirichlet–Neumann operator

This paper presents an accurate and stable numerical scheme for computation of the first variation of the Dirichlet–Neumann operator in the context of Euler’s equations for ideal free-surface fluid flows. The Transformed Field Expansion methodology we use is not only numerically stable, but also employs a spectrally accurate Fourier/Chebyshev collocation method which delivers high-fidelity solutions. This implementation follows directly from the authors’ previous theoretical work on analyticity properties of functional variations of Dirichlet–Neumann operators. These variations can be computed in a number of ways, but we establish, via a variety of computational experiments, the superior effectiveness of our new approach as compared with another popular Boundary Perturbation algorithm (the method of Operator Expansions).     

Microscopic Mechanism of the ω Variation in Moments of Inertia for the Yrast Superdeformed Bands ^194T1（1a,1b）

The variation in moments of inertia(J^(1)and J^(2) with rotational frequency for the superdeformed bands in odd-odd nuclei,194T1(1a,1b),is investigated by using the particle-number conserving method for treating the pairing interaction(monopole and quadrupole),The observed variations ofJ^(1) and J^(2) with ω are reproduced quite well in the calculation and the contributions from each major shell are clearly displayed.