Diffusion time dependence of magnetic resonance diffusion signal decays: an investigation of water exchange in human brain in vivo

Object

To understand the behavior of diffusion signal decays of water in white matter of human brain in vivo and to estimate tissue microstructure parameters such as exchange time of diffusing water molecules in human brain.

Materials and methods

Diffusion decays were measured over an extended range of diffusion weightings (b-values) up to a maximum of 12,500?s/mm² and diffusion times between 19.9 and 53.8?ms in eight healthy human subjects using MRI scans. The diffusion signal decays were all Rician noise corrected and then analyzed using multi-component non-negative least squares (NNLS) data analysis.

Results

Three diffusion coefficients including one at (0.930?±?0.003)?×?10^?3 (80?±?1%)?mm²/s, another at (0.067?±?0.002)?×?10^?3 (19?±?1%)?mm²/s and a small contribution at (1.20?±?0.02)?×?10^?2 (1.00?±?0.01%)?mm²/s were observed in the diffusion decay using the highest b-value. The diffusion decays show diffusion time dependence for the slow diffusion coefficient which has not previously been reported.

Conclusion

This study presents the accurate diffusion parameters by the use of very large b-values along with Rician noise correction and multi-component data analysis. The experimental results are consistent with the theoretical predictions used to estimate the exchange time of diffusing water molecules for a model of human brain tissue.     

Magnetic field dependence of the distribution of NMR relaxation times in the living human brain

OBJECTIVE: This study investigates the field dependence of the distribution of in vivo, whole-brain T1 values, and its usefulness for white matter/grey matter segmentation. Results on T1 values are presented on 12 healthy volunteers. T2 and T2* distributions and their field dependence have been measured on the same cohort of volunteers. In this paper, however, only the T2 and T2* results on a single volunteer are presented. The reported field dependence of T2 and T2* values should, therefore, be given less weight than that of T1 times. MATERIALS AND METHODS: Relaxation times were measured in vivo on 12 healthy volunteers, using three nearly identical whole-body scanners, operating at field strengths of 1.5, 3, and 4 T and employing nearly identical software platforms and very similar hardware. T1 mapping was performed using TAPIR, a sequence based on the Look-Locker method. T2* mapping was performed with a multi-slice, multi-echo, gradient echo sequence. A multi-slice, multi-echo T2 mapping sequence based on the Carr-Purcell-Meiboom-Gill (CPMG) method was used to map T2. For each volunteer, the global distribution of T1 relaxation times was described as the superposition of three Gaussian distributions. The field and age-dependence of the centroids and widths of the three Gaussians was investigated. The segmentation of the brain in white and grey matter was performed separately for each field strength. Using the T1 segmentation and the fact that all maps were coregistered, we investigated the distribution of T2 and [Formula: see text] values separately for the white and grey matter and described them with a Gaussian distribution in each case. RESULTS: Multi-slice quantitative maps were produced for the relaxation parameters T1 (near whole-brain coverage with 41 slices), T2* (whole-brain coverage, 55 slices), and T2 (27 slices). A clear age dependence was identified for grey matter T1 values and correlated with similar behaviour observed in a separate study of the brain water content. The increase with field strength of the bulk white and grey matter T1 values was well reproduced by both Bottomley's [1] and Fischer's [2] formulae, with parameters taken from the literature. The separation between the centroids was, however, either overestimated or underestimated by the two formulae. The width of the T1 distributions was found to increase with increasing field. CONCLUSIONS: The study of the field dependence of the NMR relaxation times is expected to allow for better differentiation between regions which are structurally different, provide a better insight into the microscopic structure of the brain and the molecular substrate of its function.     

Effects of partial volume and phase shift between fat and water in gradient-echo magnetic resonance-mammography

The signal modulations caused by partial volume effect and phase shift between fat and water signal in gradient-echo magnetic resonance mammography (GRE MR-mammography) have been calculated. Based on this, the theoretical sensitivity and specificity of GRE MR-mammography has been investigated considering different evaluation methods for the gadolinium-diethylenetriamine penta-acetic acid (Gd-DTPA)-based signal enhancement. The results show that both in- and out-of-phase sequences suffer from partial volume effects in voxels that contain both fat and water. This can decrease sensitivity to Gd-DTPA uptake in small, fat-embedded lesions or in pathology that contains fat interspersed histologically. Additionally, out-of-phase sequences can suffer from phase cancellation effects that can further decrease their sensitivity to Gd-DTPA uptake. In the worst case signal can actually decrease during Gd-DTPA influx. Determination of enhancement relative to the baseline value can decrease the specificity of GRE MR-mammography in the out-of-phase condition and decrease the sensitivity in the in-phase condition. These effects are less pronounced when enhancement is calculated relative to fat. These effects need to be understood since Gd-DTPA uptake is the prime indicator of malignancy in MR-mammography.     

A continuous-flow perfusion system for the maintenance and NMR study of small tissue samples in vitro

To describe and evaluate a novel perfusion system developed to maintain excised tissue in a flowing, oxygenated bathing solution during acquisition of nuclear magnetic resonance (NMR) data, and in addition allow precise data to be acquired continuously while altering the composition of the bathing solution surrounding the tissue. A chamber to house the tissue sample was constructed of interlocking sections of polyethylene tubing, and had approximate internal dimensions of 4 mm in diameter and 4 mm in height. Temperature-controlled, physiologically appropriate buffer solution was pumped via an infusion pump through the chamber, entering and exiting by way of small openings on either end. Immediately surrounding the polyethylene chamber was a tight-fitting four-loop solenoid RF coil. Measured proton NMR parameters were found to be fairly insensitive to the flow rate of the buffer if this coil was used only for reception and a larger-volume transmit-only coil was used for excitation. Temperature control of the sample was successfully implemented between 25 and 40°C. The perfusion system was found to be resistant to the effects of flow rate, as well as a useful tool for the administration of drugs or agents to the tissue. Changes in buffer composition could be performed on the fly without the need to reposition the sample each time a change was made. This avoidance of repositioning was found to yield a fivefold improvement in the precision of T₂ spectral parameters (using frog sciatic nerve as a sample).The authors wish to acknowledge the Canadian Institutes of Health Research (CIHR) for funding and the In Vivo NMR Facility of the University of Alberta for infrastructural support     

磁场对组织愈合的影响

关于磁场的生物学效应,国内研究者从不同方面进行了实验研究,研究结果为临床应用提供了理论基础,并促进了磁疗法的临床应用。 磁场对组织愈合影响的研究,是磁场生物学效应的重要方面,且取得了较好的研究结果。为了有利于这方面的发展,现将国内关于磁场对组织愈合影响的研究予以综述与分析。 1 磁场对神经组织愈合的影响 郭瑞华等[1]报告,应用脉冲电磁场强度30mT、频率50Hz、脉宽0.4ms,N、S磁极分别置于双腿内侧,每日1次,每次20分钟,治疗受损伤的坐骨神经(切断坐骨神经后原位吻合)分别于术后1/2、1、2月后经麻醉肉眼观察、肌电图检测及…     

Automatic segmentation of human supraclavicular adipose tissue using high-resolution T2-weighted magnetic resonance imaging

Magnetic Resonance Materials in Physics, Biology and Medicine - To achieve efficient segmentation of human supraclavicular adipose tissue (sclavAT) using high-resolution T2-weighted magnetic...     

Segmentation of fascias, fat and muscle from magnetic resonance images in humans: the DISPIMAG software

Segmentation of human limb MR images into muscle, fat and fascias remains a cumbersome task. We have developed a new software (DISPIMAG) that allows automatic and highly reproducible segmentation of lower-limb MR images. Based on a pixel intensity analysis, this software does not need any previous mathematical or statistical assumptions. It displays a histogram with two main signals corresponding to fat and muscle, and permits an accurate quantification of their relative spatial distribution. To allow a systematic discrimination between muscle and fat in any subject, fixed boundaries were first determined manually in a group of 24 patients. Secondly, an entirely automatic process using these boundaries was tested by three operators on four patients and compared to the manual approach, showing a high concordance.     

基于LabVIEW的材料磁性状态随温度变化测量系统

利用程控万用表、LCR测量仪、热电偶、计算机,基于LabVIEW软件搭建了一个测量样品的电感随温度的变化,借以反映其磁性状态随温度的变化的测量系统,并可自动在计算机中保存测量数据,实时显示温度-电感曲线,既便于实验过程中用户对数据的观察又便于后期的使用。实验表明,该系统操作简单,具有测量精确、数据分析直观、节省人力物力等优点。     

Temperature dependence of mechanical deformations in strontium titanate thin film on the sapphire substrate

Abstract

The temperature dependence of the dielectric constant (ε) of SrTiO₃ films on the various dielectric substrates differs radically from ε(T) dependence for bulk single crystal. This difference may be connected with temperature dependence of mechanical stress in the film. XRD measurements suggest the high mechanical deformation (u) of STO film unit cells at room temperature. But there is no experimental data about dependence u(T) nowadays. Present work is devoted to investigation of temperature and electric field dependencies of capacitance (C(U,T), C(Q,T)) of capacitor on the structure STO film/sapphire substrate. It is shown that derivative of inverse capacitance on the temperature is not constant and has a maximum at temperature about 200 K. Position of maximum is not influenced by charge (Q_i) on the capacitor. The mechanical deformations play the dominant role in the formation of maximum. The temperature behavior of macroscopic mechanical deformations in STO thin film on sapphire substrate is discussed.     

Temperature dependence on the contact size of GeSbTe films for phase change memories

In this study, a three-dimensional electro-thermal time-domain simulation is developed for dynamic thermal analysis of Phase change memories (PCMs). The geometry effects of the GeSbTe (GST) materials and the TiN heater are explored through a series of numerical examinations. It is found that the contact size of the GST significantly alters the maximum temperature of the PCMs, compared with the height of the GST films. The heater’s aspect ratio also dominates the maximum temperature of the GST material, and the effect of the heater’s thickness on the temperature is more evident than its height. One conformal bi-layer GST structure with different electric and thermal conductivities on the GST layers is examined for different applied currents to extract the curve of resistances versus applied currents.     

Contrast agent derived determination of the total circulating blood volume using magnetic resonance

Object

Knowledge of the total circulating blood volume (TCBV) is essential for the treatment of a variety of medical conditions and blood disorders. To date, blood volume analysis is rarely carried out due to the disadvantages of available methods. Our aim was to develop a widely available, simple, fast, yet accurate method for the determination of the total circulating blood volume.

Materials and methods

Magnetic resonance (MR) is a well-established, non-invasive technique. In this article, we present a method that uses MR contrast agents for the determination of the blood volume. The dependence of MR relaxation times on the concentration of MR contrast agents allows the calculation of the volume the contrast agent has been diluted in.

Results

In phantom and in vivo experiments we could demonstrate that TCBV can be determined with high accuracy and precision.

Conclusion

This work introduces a novel method for the determination of the total circulating blood volume using magnetic resonance contrast agents as tracers.     

Morning to evening changes of intramyocellular lipid content in dependence on nutrition and physical activity during one single day: a volume selective 1H-MRS study

Object  

Intramyocellular lipids (IMCL) were shown to be metabolically highly active. In order to get insight into short-term regulation of IMCL and to reveal related problems with standardization in metabolic studies using the common signal ratio IMCL/Cr3, relative concentration changes from morning to evening in the same day were examined under four different nutritional and exercise conditions.     

Temperature dependence of the dielectric dispersion and ferroelectric properties of neodymium doped bismuth titanate ceramics

Nd-doped bismuth titanate Bi_{4 − x} Nd _x Ti₃O₁₂ ceramics (x = 0–1.0) were prepared by the solid state reaction method. The temperature dependence of the dielectric dispersion and ferroelectric properties were investigated. With the increase of the Nd substitution for Bi ion, the Curie temperature decreased and the corresponding dielectric constant peak broadened. In addition, the strong low-frequency dielectric dispersions were exhibited. The Nd doping decreases the temperature dependence of the ac conductivity and increases the temperature dependence of the remanent polarization, which is caused by the induced polarization by defects, such as bismuth and oxygen vacancies.     

Wavelet transform of breast tissue fluorescence spectra: a technique for diagnosis of tumors

Polarized fluorescence spectra of malignant, benign, and normal human breast tissues in the emission range of 500-700 nm, with an excitation wavelength of 488 nm, are analyzed through discrete wavelet transform. The multiresolution and localization properties of the wavelets are shown to be ideally suited for identifying characteristic features distinguishing these tissue types. Analysis of a number of data sets, belonging to both parallel and perpendicular polarized spectra, have led to several key distinctions between different tumors and corresponding normal breast tissues, revealing the usefulness of polarized fluorescence in the diagnosis of tumors. Wavelet transform also naturally leads to the dimensional reduction of the data set, in the form of low-pass coefficients, making it amenable for physical modeling.     

Feasibility of quantitative susceptibility mapping (QSM) of the human kidney

Objective

To evaluate the feasibility of in-vivo quantitative susceptibility mapping (QSM) of the human kidney.

Methods

An axial single-breath-hold 3D multi-echo sequence (acquisition time 33 s) was completed on a 3 T-MRI-scanner (Magnetom Prisma, Siemens Healthineers, Erlangen, Germany) in 19 healthy volunteers. Graph-cut-based unwrapping combined with the T₂*-IDEAL approach was performed to remove the chemical shift of fat and to quantify QSM of the upper abdomen. Mean susceptibility values of the entire, renal cortex and medulla in both kidneys and the liver were determined and compared. Five subjects were measured twice to examine the reproducibility. One patient with severe renal fibrosis was included in the study to evaluate the potential clinical relevance of QSM.

Results

QSM was successful in 17 volunteers and the patient with renal fibrosis. Anatomical structures in the abdomen were clearly distinguishable by QSM and the susceptibility values obtained in the liver were comparable to those found in the literature. The results showed a good reproducibility. Besides, the mean renal QSM values obtained in healthy volunteers (0.04?±?0.07 ppm for the right and ? 0.06?±?0.19 ppm for the left kidney) were substantially higher than that measured in the investigated fibrotic kidney (? 0.43?±?? 0.02 ppm).

Conclusion

QSM of the human kidney could be a promising approach for the assessment of information about microscopic renal tissue structure. Therefore, it might further improve functional renal MR imaging.

     

Slice acquisition order and blood oxygenation level dependent frequency content: an event-related functional magnetic resonance imaging study

Many event-related functional magnetic resonance imaging paradigms performed so far have been designed to study a limited part of the brain with high temporal resolution. However, event-related paradigms can be exploratory, therefore requiring whole brain scans and so repetition times (TR) of several seconds. For these large TR values, the slice acquisition order may have an important effect on the detection of event-related activation. Indeed, when the scanning is interleaved, the temporal delay between the acquisition of two contiguous slices can reach a few seconds. During this time, the subject is likely to move, and the haemodynamic response will vary significantly. In this case, the interpolation applied between contiguous slices for motion correction induces a temporal smoothing between voxels that are spatially close but temporally sampled a few seconds apart. This should modify the frequency structure of the response and may impair the detection of short events. We, therefore tested the effect of three acquisition schemes (sequential, sequential with gap and interleaved. INT) at two repetition times (TR = 3 and 6 s on six and seven subjects, respectively) on activation detection and frequency content in a visual motion event-related paradigm. Unexpectedly, tor large TR (6 s), results were found in favour of the INT acquisition scheme(P <0.05). For smaller TR. no strong bias could be found. Generally, intra-subject variability (across acquisition schemes) is found to be much smaller than inter-subject variability, confirming the importance of multi-subjects analyses. Our study also shows that important physiological information is carried by high frequency components that should not be filtered out.     

A study of the loss characteristics of the amorphous magnetic material under nonsinusoidal wave magnetic flux

This paper presents a study on iron loss characteristics of an amorphous magnetic material under nonsinusoidal wave magnetic flux. The iron loss characteristics of the amorphous magnetic material have been compared to those of grain‐oriented magnetic steel sheets. Measurements of the iron loss have been carried out by means of an SST. It was found that the ratio of the iron loss increase of the amorphous magnetic material under the excitation by distorted waveforms and symmetric PWM waveforms is lower than that of grain‐oriented magnetic steel sheets. On the other hand, the ratio of the iron loss increase of the amorphous magnetic material under the excitation by asymmetric PWM waveforms is higher than that of grain‐oriented magnetic steel sheets. © 2004 Wiley Periodicals, Inc. Electr Eng Jpn, 150(3): 11–18, 2005; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.20004     

Quantitative breast MRI: 2D histogram analysis of diffusion tensor parameters in normal tissue

Object

Diffusion tensor imaging (DTI) of the breast may provide a powerful new approach for the detection of intraductal processes. The aim of this investigation was to characterize the relation between diffusion tensor parameters [fractional anisotropy (FA), mean diffusivity (MD)] in normal breast tissue to obtain information on the microenvironment of the diffusing water molecules and to provide a systematic approach for DTI analysis.

Materials and methods

Seven female, healthy volunteers underwent prospective double-spin-echo prepared echo-planar diffusion-weighted sequence (TR/TE 8,250 ms/74 ms, b values 0 and 500 s/mm (2), six encoding directions, 12 averages, 35 slices) in 4 consecutive weeks (3.0 T). Quantitative maps of diffusion tensor parameters were computed offline with custom routines. The interdependence of MD and FA in different voxels was analysed by linear and exponential regression.

Results

All MD and FA maps were of excellent quality. A consistent pattern was observed in that lower fractional anisotropy values were more likely associated with higher mean diffusivity values. The dependence exhibited an exponential behavior with a correlation coefficient R = 0.60 (R linear = 0.57).

Conclusion

The likelihood with which FA and MD values are observed in a voxel within normal breast tissue is characterized by a specific pattern, which can be described by an exponential model. Moreover, we could show that the proposed technique does not depend on the menstrual cycle.