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Magnetic Field Strength (magnetic + field_strength)
Selected AbstractsToward portable nuclear magnetic resonance devices using atomic magnetometersCONCEPTS IN MAGNETIC RESONANCE, Issue 2 2009Dindi Yu Abstract The motivation for developing alternative detection techniques for nuclear magnetic resonance (NMR) and magnetic resonance imaging (MRI) is to overcome some of the limitations associated with high-field NMR/MRI instruments. The limitations include poor portability, cryogenic requirements, and high costs. To achieve this goal, a low magnetic field is preferred. Since the sensitivity of inductive detection for conventional NMR and MRI scales linearly with the magnetic field strength, it is not optimal for low-field detection. In this contribution, we describe the concept of using atomic magnetometers as an alternative detection method. Atomic magnetometers possess an ultrahigh sensitivity that is independent of the magnetic field strength, which makes them viable for low-field detection in NMR and MRI. We first introduce the principle of atomic magnetometry and follow this with a discussion of recent progress in the field. To compare the sensitivities of atomic magnetometers of diverse sizes, we define a signal-to-noise ratio for a fixed detection volume to normalize the sensitivity with regard to the cell size. We then focus on two coupling schemes for NMR and MRI detection using atomic magnetometers. Finally, we discuss the challenges involved in implementing this alternative detection technique for NMR and MRI. © 2009 Wiley Periodicals, Inc. Concepts Magn Reson Part A 34A: 124,132, 2009. [source] Biomagnetic fluid flow in a 3D rectangular ductINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN FLUIDS, Issue 12 2004E. E. Tzirtzilakis1 Abstract The laminar, incompressible, three-dimensional, fully developed viscous flow of a non-conducting biomagnetic fluid in a impermeable rectangular duct is numerically studied in the presence of an applied magnetic field. It is assumed that the magnetic field strength is sufficiently strong to saturate the biofluid and the magnetization is given as a function of the magnetic field intensity. The system of the partial differential equations, resulting after the introduction of appropriate non-dimensional variables, is solved applying an efficient numerical technique based on a pressure-linked pseudotransient method on a common grid. Results concerning the existence and the uniqueness of the solution, are also given. The obtained results, for different values for the parameters entering into the problem under consideration, show that the flow is appreciably influenced by the presence of the magnetic field. Copyright © 2004 John Wiley & Sons, Ltd. [source] Synthesis and magnetic properties of novel fully conjugated polymeric complexes containing 1,10-phenanthrolineJOURNAL OF APPLIED POLYMER SCIENCE, Issue 4 2008Renhua Zheng Abstract A novel fully conjugated polymer containing 1,10-phenanthroline (DAPcDOD) was first synthesized by the polycondensation of 2,7-dimethyl-2,4,6-octatriene-1,8-dial with 5,6-diamine-1,10-phenanthroline. Three polymeric complexes were first prepared by the reaction of DAPcDOD with NiSO4, CoCl2, and FeSO4, respectively. The structures of the polymer and the complexes were characterized by IR, 1H-NMR, and elemental analysis. The magnetic behaviors of these complexes were measured as a function of magnetic field strength (0,50 kOe) at 5 K and as a function of temperature (5,300 K) at a magnetic field strength of 30 kOe. The results show that DAPcDOD,Ni2+ and DAPcDOD,Co2+ were soft ferromagnets, whereas DAPcDOD,Fe2+ exhibited the features of an antiferromagnet. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008 [source] Effects of Parasite Attributes and Injected Current Parameters on Electromagnetic Detection of Parasites in Fish MuscleJOURNAL OF FOOD SCIENCE, Issue 9 2002G.S. Choudhury ABSTRACT: We examined the potential of an electromagnetic parasite detection technique to become the basis of an automated commercial system. The effects of parasite orientation and position, presence offish bone, and applied signal strength and frequency on resultant magnetic field strength were determined by scanning a conducting cell containing fish fillet and parasite below a SQUID magnetometer. The parasite orientation affected peak-to-peak voltage of the magnetic dipole. The parasite position with respect to myotome structure seemed to affect the orientation of the dipolar signal. A fish bone was readily detected. The magnetic field strength was independent of the frequency of the injected current and scaled with amplitude=. [source] Magnetic resonance imaging of the elbowJOURNAL OF MAGNETIC RESONANCE IMAGING, Issue 5 2010Kathryn J. Stevens MB Abstract Elbow pain is frequently encountered in clinical practice and can result in significant morbidity, particularly in athletes. Magnetic resonance imaging (MRI) is an excellent diagnostic imaging tool for the evaluation of soft tissue and osteochondral pathology around the elbow. Recent advances in magnetic field strength and coil design have lead to improved spatial resolution and superior soft tissue contrast, making it ideal for visualization of complex joint anatomy. This article describes the normal imaging appearances of anatomy around the elbow and reviews commonly occurring ligamentous, myotendinous, neural, and bursal pathology around the elbow. J. Magn. Reson. Imaging 2010;31:1036,1053. © 2010 Wiley-Liss, Inc. [source] Absolute quantification of cerebral blood flow in normal volunteers: Correlation between Xe-133 SPECT and dynamic susceptibility contrast MRIJOURNAL OF MAGNETIC RESONANCE IMAGING, Issue 4 2007Linda Knutsson PhD Abstract Purpose To compare absolute cerebral blood flow (CBF) estimates obtained by dynamic susceptibility contrast MRI (DSC-MRI) and Xe-133 SPECT. Materials and Methods CBF was measured in 20 healthy volunteers using DSC-MRI at 3T and Xe-133 SPECT. DSC-MRI was accomplished by gradient-echo EPI and CBF was calculated using a time-shift-insensitive deconvolution algorithm and regional arterial input functions (AIFs). To improve the reproducibility of AIF registration the time integral was rescaled by use of a venous output function. In the Xe-133 SPECT experiment, Xe-133 gas was inhaled over 8 minutes and CBF was calculated using a biexponential analysis. Results The average whole-brain CBF estimates obtained by DSC-MRI and Xe-133 SPECT were 85 ± 23 mL/(min 100 g) and 40 ± 8 mL/(min 100 g), respectively (mean ± SD, n = 20). The linear CBF relationship between the two modalities showed a correlation coefficient of r = 0.76 and was described by the equation CBF(MRI) = 2.4 · CBF(Xe),7.9 (CBF in units of mL/(min 100 g)). Conclusion A reasonable positive linear correlation between MRI-based and SPECT-based CBF estimates was observed after AIF time-integral correction. The use of DSC-MRI typically results in overestimated absolute perfusion estimates and the present study indicates that this trend is further enhanced by the use of high magnetic field strength (3T). J. Magn. Reson. Imaging 2007;26:913,920. © 2007 Wiley-Liss, Inc. [source] Microneurography of human median nerveJOURNAL OF MAGNETIC RESONANCE IMAGING, Issue 6 2005Mehmet Bilgen PhD Abstract Purpose To examine the possibility of performing high-resolution MRI (microneurography) on peripheral nerves. Materials and Methods A specific radio frequency (RF) coil was developed to probe the human median nerve at a magnetic field strength of 9.4 T and tested on three excised samples by acquiring microneurograms. Results The microneurograms revealed neuronal tissue constituents at subfascicular level. The contrast features on proton-density and T1- and T2-weighted images were described and compared. The microscopic water movement was quantified using diffusion weighting parallel and orthogonal to the neuronal fiber orientation. The characteristics of anisotropic diffusion in the median nerve were comparable to those reported from other biological tissues (white matter and kidney). Conclusion The results overall suggest that microneurography might provide new noninvasive insights into microscopic gross anatomy of the peripheral nerve, injury evaluation, and efficacy of repair, although the feasibility at current clinically relevant field strengths is yet to be determined. J. Magn. Reson. Imaging 2005;21:826,830. © 2005 Wiley-Liss, Inc. [source] Effects of Abstinence From Alcohol on the Broad Phospholipid Signal in Human Brain: An In Vivo 31P Magnetic Resonance Spectroscopy StudyALCOHOLISM, Issue 8 2001M. R. Estilaei Background: In vivo phosphorus magnetic resonance spectroscopy (31P MRS) at a magnetic field strength of 1.5 T allows measurement of fairly mobile membrane phospholipids in the human brain. We previously showed that subjects who are heavy drinkers had a smaller signal and a shorter transverse relaxation time (T2) of white matter phospholipids than light drinkers, which suggested lower concentrations and molecular mobility of phospholipids in heavy drinkers. The purpose of the present study was to measure if such chronic alcohol-induced white matter tissue changes are persistent in long-term abstinent alcoholics. Methods: Fourteen abstinent alcoholics (mean age 45 years, seven men and seven women) were studied by localized 31P MRS in the centrum semiovale and were compared with 13 male, alcohol-dependent, heavy drinkers and 23 nondependent light drinkers (17 men, 6 women) of similar age. Methods for measurements of the broad membrane phospholipid signal and its relaxation time were described previously. Results: Phospholipid concentrations and relaxation times in alcoholics abstinent for an average of 31 months were not significantly different from those measured in light drinkers. The contribution of fast and slowly relaxing signal components to the broad phospholipid signal, however, was still different in abstinent alcoholics compared with light drinkers. No effects of sex or of family history of alcoholism were noted on any of our spectroscopic measures within the light-drinking or abstinent groups. Conclusions: Most of our results suggest at least partial recovery of chronic alcohol-induced white matter phospholipid damage with long-term abstinence. They offer myelination changes and/or dendritic rearborization as a possible mechanism for the commonly observed white matter volume gain with prolonged abstinence. But the results also suggest a persistent abnormality in the nature and/or physical properties of white matter phospholipids in long-term abstinent alcoholics. [source] Sensitivity-encoded coronary MRA at 3TMAGNETIC RESONANCE IN MEDICINE, Issue 2 2004Michael E. Huber Abstract Long scan times are still a main limitation in free-breathing navigator-gated 3D coronary MR angiography (MRA). Unlike other MRI applications, high-resolution coronary MRA has not been amenable to acceleration by parallel imaging techniques due to signal-to-noise ratio (SNR) concerns. In the present work, mitigating SNR limitations by the transition to higher static magnetic field strength is proposed, thus enabling scan time reduction by the parallel sensitivity encoding (SENSE) technique. The study reports the implementation and evaluation of free-breathing navigator-gated 3D coronary MRA with SENSE at 3T. Results from 11 healthy subjects indicate that the approach permits significant scan time reduction in MRA of the left and right coronary systems. Quantitative image analysis and visual grading suggest that two-fold scan acceleration can be accomplished at nearly preserved image quality. The additional experiments appear to demonstrate that parallel MRA equally permits enhancing volume coverage and spatial resolution while maintaining scan time. Magn Reson Med 52:221,227, 2004. © 2004 Wiley-Liss, Inc. [source] Proton T2 relaxation study of water, N-acetylaspartate, and creatine in human brain using Hahn and Carr-Purcell spin echoes at 4T and 7TMAGNETIC RESONANCE IN MEDICINE, Issue 4 2002Shalom Michaeli Abstract Carr-Purcell and Hahn spin-echo (SE) measurements were used to estimate the apparent transverse relaxation time constant (T) of water and metabolites in human brain at 4T and 7T. A significant reduction in the T values of proton resonances (water, N-acetylaspartate, and creatine/phosphocreatine) was observed with increasing magnetic field strength and was attributed mainly to increased dynamic dephasing due to increased local susceptibility gradients. At high field, signal loss resulting from T decay can be substantially reduced using a Carr-Purcell-type SE sequence. Magn Reson Med 47:629,633, 2002. © 2002 Wiley-Liss, Inc. [source] New scaling relations in cluster radio haloes and the re-acceleration modelMONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 4 2007R. Cassano ABSTRACT In this paper we derive new expected scaling relations for clusters with giant radio haloes in the framework of the re-acceleration scenario in a simplified, but physically motivated, form, namely: radio power (PR) versus size of the radio emitting region (RH), and PR versus total cluster mass (MH) contained in the emitting region and cluster velocity dispersion (,H) in this region. We search for these correlations by analysing the most recent radio and X-ray data available in the literature for a well-known sample of clusters with giant radio haloes. In particular we find a good correlation between PR and RH and a very tight ,geometrical' scaling between MH and RH. From these correlations PR is also expected to scale with MH and ,H and this is confirmed by our analysis. We show that all the observed trends can be well reconciled with expectations in the case of a slight variation of the mean magnetic field strength in the radio halo volume with MH. A byproduct correlation between RH and ,H is also found, and can be further tested by optical studies. In addition, we find that observationally RH scales non-linearly with the virial radius of the host cluster, and this immediately means that the fraction of the cluster volume which is radio emitting increases with cluster mass and thus that the non-thermal component in clusters is not self-similar. [source] On the origin of the drifting subpulses in radio pulsarsMONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 2 2005G. Gogoberidze ABSTRACT We present a model for the main observational characteristics of the radio emission of pulsars with well-organized drifting subpulses. We propose that drifting subpulses result from the modulation of the radio emission mechanism due to long-wavelength drift waves in the magnetosphere. The drift waves are generated at shorter wavelengths, and their non-linear evolution favours accumulation in a specific azimuthal eigenmode with an integral number, m, of nodes encircling the magnetic pole. The electric field of the drift waves is along the magnetic field lines, and this modulates the distribution for particles and hence the radio emission mechanism. The ratio of the frequency of the eigenmode to the rotation frequency of the star is insensitive to the magnetic field strength and the period of rotation, and is of order unity. The period, P3, of the drifting subpulses is attributed to the mismatch between this frequency and the nearest harmonic of the rotation frequency of the star. [source] Implications of magnetar non-precessionMONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY: LETTERS (ELECTRONIC), Issue 1 2010K. Glampedakis ABSTRACT The objects known as anomalous X-ray pulsars and soft gamma repeaters are commonly identified with magnetars, neutron stars with ultrastrong magnetic fields. The rotational history of these objects has, so far, revealed no evidence of free precession. At the same time, these objects do not generally appear to have magnetic axes nearly parallel or orthogonal to their spin axes. In this Letter we show that the combination of these two observations, together with simple rigid-body dynamics, leads to non-trivial predictions about the interior properties of magnetars: either (i) elastic stresses in magnetar crusts are close to the theoretical upper limit above which the crustal matter yields or (ii) there is a ,pinned' superfluid component in the magnetar interior. As a potentially observable consequence of these ideas we point out that in the case of no pinned superfluidity, magnetars of stronger magnetic field strength than those currently observed would have to be nearly aligned/orthogonal rotators. [source] Putaminal magnetic resonance imaging features at various magnetic field strengths in multiple system atrophy,MOVEMENT DISORDERS, Issue 12 2010Hirohisa Watanabe MD Abstract We delineated the effects of magnetic field strength on signal intensities to facilitate the specific findings of multiple system atrophy (MSA). Fifteen patients with probable MSA were imaged by 0.35T fast spin-echo (FSE), 1.5T FSE, and 3.0T FSE using a consistent protocol, testing all field strengths on the same day. Sixty patients with probable Parkinson's disease (PD) also underwent imaging. Moderate or marked hyperintensity at the dorsolateral outer putaminal margin, hyperintensity of the putaminal body, hypointensity relative to the globus pallidus at the dorsolateral putaminal margin, and infratentorial signal changes were evaluated as specific findings for MSA. As the field strength increased, the occurrence of hyperintensity both at the dorsolateral outer putaminal margin and of the putaminal body decreased, while the occurrence of hypointensity at the dorsolateral putaminal margin increased in MSA. The occurrence of uniform mild hyperintensity of the outer putaminal margin was evident in 7% at 0.35T, 40% at 1.5T, and 47% at 3.0T in MSA and in 5% at 0.35T, 60% at 1.5T, and 75% at 3.0T in PD. However, no PD patients showed hyperintensity at the dorsolateral outer putaminal margin and that of the putaminal body. Putaminal magnetic resonance imaging (MRI) findings in MSA were altered considerably by magnetic field strength. The severity and distribution of signal changes are important for assessing putaminal MRI findings in MSA. © 2010 Movement Disorders Society [source] Advances in MR imaging of the skin,NMR IN BIOMEDICINE, Issue 7 2006Jacques Bittoun Abstract MR imaging of the skin is challenging because of the small size of the structures to be visualized. By increasing the gradient amplitude and/or duration, skin layers can be visualized with a voxel size of the order of 20,µm, clearly the smallest obtained for in vivo images in a whole-body imager. Currently, the gradient strength of most commercial systems enables acquisition of such a small voxel size, and the main difficulty has thus become to achieve sufficient detection sensitivity. The signal-to-noise ratio (SNR) can be increased either by increasing the magnetic field strength or by minimizing noise with small coils; cooling copper coils or superconducting coils can enhance the SNR by a factor of 3 or more. MR imaging, because of the large number of parameters it is able to measure, can provide more than the microscopic architecture of the skin: physical parameters such as relaxation times, magnetization transfer or diffusion, and chemical parameters such as the water and fat contents or phosphorus metabolism. In spite of the amount of information they have provided to date, MR imaging and spectroscopy have had limited clinical applications, mainly because cutaneous pathologies are easily accessible to the naked eye and surgery. However, MR technologies indeed represent powerful research tools to study normal and diseased skin. Copyright © 2006 John Wiley & Sons, Ltd. [source] The apparent dependence of the diffusion coefficient of N-acetylaspartate upon magnetic field strength: evidence of an interaction with NMR methodologyNMR IN BIOMEDICINE, Issue 8 2003David N. Guilfoyle Abstract An inverse relationship between applied magnetic field strength and the apparent diffusion coefficient (ADC) of several important brain metabolites including N -acetyl- l -aspartate (NAA), choline and creatine, measured in vivo using proton magnetic resonance spectroscopy (MRS), has been reported. In this investigation, using phantom studies of NAA at magnetic field strengths of 3 and 7,T, these observations have been verified under controlled MRS conditions in vitro, and the ADC of NAA has been found to vary inversely with magnetic field strength, decreasing at a rate of 2.5%/T at 20°C. We have also assessed whether the effect is a function of a systemic bias in methodology, or if the effect is actually on the rate of molecular diffusion. This was done using an MRS-independent method for measurement of molecular diffusion in NAA phantoms at 0, 0.025 and 7,T applied magnetic field strengths. As a result, it has been demonstrated that the observed apparent magnetic field dependence of the ADC of NAA is a consequence of the NMR measurement and is apparently not a real effect on molecular diffusion. Copyright © 2003 John Wiley & Sons, Ltd. [source] Magnetoabsorption coefficient of donor impurities in CdS quantum dotPHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 8 2006A. Didi Seddik Abstract A theoretical study of the donor-related absorption coefficient in spherical CdS quantum dots (QD) in the presence of a uniform magnetic field is performed. The wave functions and the eigenvalues of the initial and final states are obtained in the effective-mass approximation by using a variational method and a perturbation method, respectively. The results obtained show that the absorption coefficient presents essentially two peaks; one associated with on-center donors and another related to transitions involving donors at the QD edge. The dependences of the absorption coefficient on sample dimensions, the magnetic field strength and the light polarization are discussed. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Synthesis and magnetic properties of novel polymeric complexes containing bithiazole ringsPOLYMERS FOR ADVANCED TECHNOLOGIES, Issue 12 2007Weihong Lin Abstract A novel linear polymer (PFABT) containing bithiazole rings was synthesized by polycondensation of 2,2,-diamino-4,4,-bithiazole (DABT) and formaldehyde. The complexes of PFABT with two transition metal ions (Fe2+, Cu2+) were prepared for the first time. The polymer was determined through FT-IR, 1H-NMR and elemental analysis (EA), and the complexes were characterized by FT-IR. The magnetic behaviors of these complexes were measured as a function of magnetic field strength (0,50,kOe) at 4,K and as a function of temperature (4,300,K) under an applied magnetic field of 30,kOe. The results show that PFABT-Cu2+ is a ferromagnet while PFABT-Fe2+ is an anti-ferromagnet. Copyright © 2007 John Wiley & Sons, Ltd. [source] Spectropolarimetric analysis of 3D MHD sunspot simulationsASTRONOMISCHE NACHRICHTEN, Issue 6 2010J.M. Borrero Abstract We have employed 3D non-grey MHD simulations of sunspots to compute theoretical Stokes profiles and compare the levels of circular and linear polarization in the simulations with those observed in a real sunspot. We find that the spatial distribution and average values of these quantities agree very well with the observations, although the polarization levels in the simulations are slightly larger. This can be explained by a slightly larger magnetic field strength or a larger temperature gradient in the simulated penumbra as compared to the observations (© 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] A chromospheric dark-cored fibril in Ca II IR spectraASTRONOMISCHE NACHRICHTEN, Issue 6 2010C. Beck Abstract We investigate the thermodynamical and magnetic properties of a "dark-cored" fibril seen in the chromospheric Ca II IR line at 854.2 nm to determine the physical process behind its appearance. We analyse a time series of spectropolarimetric observations obtained in the Ca II IR line at 854.2 nm and the photospheric Fe I line at 630.25 nm. We simultaneously invert the spectra in both wavelength ranges with the SIR code to obtain the temperature and velocity stratification with height in the solar atmosphere and the magnetic field properties in the photosphere. The structure can be clearly traced in the line-of-sight (LOS) velocity and the temperature maps. It connects from a small pore with kG fields to a region with lower field strength. The flow velocity and the temperature indicate that the height of the structure increases with increasing distance from the inner footpoint. The Stokes V signal of 854.2 nm shows a Doppler-shifted polarization signal with the same displacement as in the intensity profile, indicating that the supersonic flow seen in the LOS velocity is located within magnetized plasma. We conclude that the chromospheric dark-cored fibril traces a siphon flow along magnetic field lines, driven by the gas pressure difference caused by the higher magnetic field strength at the inner footpoint. We suggest that fast flows guided by the magnetic field lead to the appearance of "dark-cored" fibrils in intensity images. Although the observations included the determination of the polarization signal in the chromospheric Ca II IR line, the signal could not be analysed quantitatively due to the low S/N. Chromospheric polarimetry will thus require telescopes of larger aperture able to collect a sufficient number of photons for a reliable determination of polarization in deep and only weakly polarized spectral lines (© 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Parsec-scale jet in the distant gigahertz-peaked spectrum quasar PKS 0858,279ASTRONOMISCHE NACHRICHTEN, Issue 2-3 2009Y. Y. KovalevArticle first published online: 13 FEB 200 Abstract The high redshift GPS quasar PKS 0858,279 exhibits the following properties which make the source unusual. Our RATAN-600 monitoring of 1,22 GHz spectrum has detected broad-band radio variability with high amplitude and relatively short time scale. In the same time, the milliarcsecond scale structure observed in a snapshot VLBA survey turned out to be very resolved which is not expected from the fast flux density variations. We performed 1.4,22 GHz VLBA observations of this quasar in 2005,2007. It has revealed a core-jet morphology. A high Doppler factor , is suggested for the jet, its nature is discussed in this report on the basis of the multi-frequency VLBA and RATAN data collected. Synchrotron self-absorption was confirmed to be dominating at low frequencies, the magnetic field strength of the dominating jet feature is estimated of an order of 0.1, mG (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Electromagnetic field exposure and health among RF plastic sealer operatorsBIOELECTROMAGNETICS, Issue 1 2004Jonna Wilén Abstract Operators of RF plastic sealers (RF operators) are an occupational category highly exposed to radiofrequency electromagnetic fields. The aim of the present study was to make an appropriate exposure assessment of RF welding and examine the health status of the operators. In total, 35 RF operators and 37 controls were included. The leakage fields (electric and magnetic field strength) were measured, as well as induced and contact current. Information about welding time and productivity was used to calculate time integrated exposure. A neurophysiological examination and 24 h ECG were also carried out. The participants also had to answer a questionnaire about subjective symptoms. The measurements showed that RF operators were exposed to rather intense electric and magnetic fields. The mean values of the calculated 6 min, spatially averaged E and H field strengths, in line with ICNIRP reference levels, are 107 V/m and 0.24 A/m, respectively. The maximum measured field strengths were 2 kV/m and 1.5 A/m, respectively. The induced current in ankles and wrists varied, depending on the work situation, with a mean value of 101 mA and a maximum measured value of 1 A. In total, 11 out of 46 measured RF plastic sealers exceeded the ICNIRP reference levels. RF operators, especially the ready made clothing workers had a slightly disturbed two-point discrimination ability compared to a control group. A nonsignificant difference between RF operators and controls was found in the prevalence of subjective symptoms, but the time integrated exposure parameters seem to be of importance to the prevalence of some subjective symptoms: fatigue, headaches, and warmth sensations in the hands. Further, RF operators had a significantly lower heart rate (24 h registration) and more episodes of bradycardia compared to controls. Bioelectromagnetics 25:5,15, 2004. © 2003 Wiley-Liss, Inc. [source] In vivo magnetic resonance spectroscopy of gynaecological tumours at 3.0 TeslaBJOG : AN INTERNATIONAL JOURNAL OF OBSTETRICS & GYNAECOLOGY, Issue 2 2009SJ Booth Background, Magnetic resonance spectroscopy (MRS) uses the same hardware as MR imaging and allows us to analyse the biochemistry of tissues in vivo. Published data for gynaecological lesions are limited and are largely based on MRS carried out at the lower magnetic field strength of 1.5 Tesla (T). Objective, The purpose of this study was to determine whether in vivo proton MRS could be performed at the higher magnetic field strength of 3 T to characterise the spectra of a variety of benign and malignant gynaecological lesions. Design, Prospective, non-randomised study. Setting, MRI department within a tertiary referral centre for gynaecological cancers. Sample, All women with a pelvic mass under going 3T MRI. Methods, We carried out MRS on nonrandomised women undergoing routine 3 T MRI within our MRI department during investigation for gynaecological lesions from February 2006 to April 2008. Only those women for whom histopathological data were available were included. Main outcome measures, The presence of choline detected by in vivo 3T MRS. Results, Eighty-seven women underwent MRS, 57 of whom had newly diagnosed neoplasms. MRS data for 39 of these new women (18 were excluded because of technical errors or missing data) were used to detect the presence of choline, an indicator of basement membrane turnover. Overall, choline was present in 13 of the 14 ovarian cancers, 8 of the 11 cervical tumours and all 4 of the uterine cancers. There was no statistical significant difference between choline levels in various lesion types (P= 0.735) or between benign and malignant disease (P= 0.550). Conclusions,In vivo MRS can be performed at 3 T to provide biochemical information on pelvic lesions. The way in which this information can be utilised is less clear but may be incorporated into monitoring tissue response in cancer treatments. [source] Multicontrast black-blood MRI of carotid arteries: Comparison between 1.5 and 3 tesla magnetic field strengthsJOURNAL OF MAGNETIC RESONANCE IMAGING, Issue 5 2006Vasily L. Yarnykh PhD Abstract Purpose To compare black-blood multicontrast carotid imaging at 3T and 1.5T and assess compatibility between morphological measurements of carotid arteries at 1.5T and 3T. Materials and Methods Five healthy subjects and two atherosclerosis patients were scanned in 1.5T and 3T scanners with a similar protocol providing transverse T1 -, T2 -, and proton density (PD)-weighted black-blood images using a fast spin-echo sequence with single- (T1 -weighted) or multislice (PD-/T2 -weighted) double inversion recovery (DIR) preparation. Wall and lumen signal-to-noise ratio (SNR) and wall/lumen contrast-to-noise ratio (CNR) were compared in 44 artery cross-sections by paired t -test. Interscanner variability of the lumen area (LA), wall area (WA), and mean wall thickness (MWT) was assessed using Bland-Altman analysis. Results Wall SNR and lumen/wall CNR significantly increased (P < 0.0001) at 3T with a 1.5-fold gain for T1 -weighted images and a 1.7/1.8-fold gain for PD-/T2 -weighted images. Lumen SNR did not differ for single-slice DIR T1 -weighted images (P = 0.2), but was larger at 3T for multislice DIR PD-/T2 -weighted images (P = 0.01/0.03). The LA, WA, and MWT demonstrated good agreement with no significant bias (P 0.5), a coefficient of variation (CV) of <10%, and intraclass correlation coefficient (ICC) of >0.95. Conclusion This study demonstrated significant improvement in SNR, CNR, and image quality for high- resolution black-blood imaging of carotid arteries at 3T. Morphologic measurements are compatible between 1.5T and 3T. J. Magn. Reson. Imaging 2006. © 2006 Wiley-Liss, Inc. [source] Magnetic resonance microscopy at 17.6-Tesla on chicken embryos in vitroJOURNAL OF MAGNETIC RESONANCE IMAGING, Issue 1 2001Bianca Hogers PhD Abstract The non-destructive nature and the rapid acquisition of a three-dimensional image makes magnetic resonance microscopy (MRM) very attractive and suitable for functional imaging investigations. We explored the use of an ultra high magnetic field for MRM to increase image quality per image acquisition time. Improved image quality was characterized by a better signal-to-noise ratio (SNR), better image contrast, and higher resolution compared to images obtained at lower magnetic field strengths. Fixed chicken embryos at several stages of development were imaged at 7.0-T (300 MHz) and at 17.6-T (750 MHz). Maximum intensity projection resulted in three-dimensional vascular images with ample detail of the embryonic vasculature. We showed that at 750 MHz frequency, an image with approximately three times better SNR can be obtained by T1 -weighting using a standard gadolinium contrast agent, compared to the same measurement at 300 MHz. The image contrast improved by around 20 percent and the contrast-to-noise ratio improved by almost a factor of 3.5. Smaller blood vessels of the vascular system were identified at the high field, which indicates a better image resolution. Thus, ultra high field is beneficial for MRM and opens new areas for functional imaging research, in particular when SNR, resolution, and contrast are limited by acquisition time. J. Magn. Reson. Imaging 2001;14:83,86. © 2001 Wiley-Liss, Inc. [source] 51V magic angle spinning NMR in VOPO4 phasesMAGNETIC RESONANCE IN CHEMISTRY, Issue 12 2004Renée Siegel Abstract 51V magic angle spinning NMR was applied to the ,II, , and , phases of VOPO4 at three magnetic field strengths (4.7, 7.1, and 11.7 T). The 51V quadrupole and chemical shift tensors were determined by iterative fitting of the NMR lineshapes at the three magnetic field strengths. The applicability of the method is illustrated by comparison with literature data. Although determined chemical shift tensors are completely axially symmetric and of the same magnitude, all studied phases can clearly be distinguished by their quadrupole coupling tensor. Relationships between the 51V NMR data and structural characteristics such as crystal symmetries are discussed. Copyright © 2004 John Wiley & Sons, Ltd. [source] A simple low-SAR technique for chemical-shift selection with high-field spin-echo imagingMAGNETIC RESONANCE IN MEDICINE, Issue 2 2010Dimo Ivanov Abstract We have discovered a simple and highly robust method for removal of chemical shift artifact in spin-echo MR images, which simultaneously decreases the radiofrequency power deposition (specific absorption rate). The method is demonstrated in spin-echo echo-planar imaging brain images acquired at 7 T, with complete suppression of scalp fat signal. When excitation and refocusing pulses are sufficiently different in duration, and thus also different in the amplitude of their slice-select gradients, a spatial mismatch is produced between the fat slices excited and refocused, with no overlap. Because no additional radiofrequency pulse is used to suppress fat, the specific absorption rate is significantly reduced compared with conventional approaches. This enables greater volume coverage per unit time, well suited for functional and diffusion studies using spin-echo echo-planar imaging. Moreover, the method can be generally applied to any sequence involving slice-selective excitation and at least one slice-selective refocusing pulse at high magnetic field strengths. The method is more efficient than gradient reversal methods and more robust against inhomogeneities of the static (polarizing) field (B0). Magn Reson Med, 2010. © 2010 Wiley-Liss, Inc. [source] Dynamics of the solar tachocline , I. An incompressible studyMONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 1 2002P. Garaud Gough & McIntyre have suggested that the dynamics of the solar tachocline are dominated by the advection,diffusion balance between the differential rotation, a large-scale primordial field and baroclinicly driven meridional motions. This paper presents the first part of a study of the tachocline, in which a model of the rotation profile below the convection zone is constructed along the lines suggested by Gough & McIntyre and solved numerically. In this first part, a reduced model of the tachocline is derived in which the effects of compressibility and energy transport on the system are neglected; the meridional motions are driven instead by Ekman,Hartmann pumping. Through this simplification, the interaction of the fluid flow and the magnetic field can be isolated and is studied through non-linear numerical analysis for various field strengths and diffusivities. It is shown that there exists only a narrow range of magnetic field strengths for which the system can achieve a nearly uniform rotation. The results are discussed with respect to observations and to the limitations of this initial approach. A following paper combines the effects of realistic baroclinic driving and stratification with a model that closely follows the lines of work of Gough & McIntyre. [source] A turbulent MHD model for molecular clouds and a new method of accretion on to star-forming coresMONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 3 2001D. Balsara We describe the results of a sequence of simulations of gravitational collapse in a turbulent magnetized region. The parameters are chosen to be representative of molecular cloud material. We find that several protostellar cores and filamentary structures of higher than average density form. The filaments inter connect the high-density cores. Furthermore, the magnetic field strengths are found to correlate positively with the density, in agreement with recent observations. We make synthetic channel maps of the simulations, and show that material accreting on to the cores is channelled along the magnetized filamentary structures. This is compared with recent observations of S106, and shown to be consistent with these data. We postulate that this mechanism of accretion along filaments may provide a means for molecular cloud cores to grow to the point where they become gravitationally unstable and collapse to form stars. [source] Putaminal magnetic resonance imaging features at various magnetic field strengths in multiple system atrophy,MOVEMENT DISORDERS, Issue 12 2010Hirohisa Watanabe MD Abstract We delineated the effects of magnetic field strength on signal intensities to facilitate the specific findings of multiple system atrophy (MSA). Fifteen patients with probable MSA were imaged by 0.35T fast spin-echo (FSE), 1.5T FSE, and 3.0T FSE using a consistent protocol, testing all field strengths on the same day. Sixty patients with probable Parkinson's disease (PD) also underwent imaging. Moderate or marked hyperintensity at the dorsolateral outer putaminal margin, hyperintensity of the putaminal body, hypointensity relative to the globus pallidus at the dorsolateral putaminal margin, and infratentorial signal changes were evaluated as specific findings for MSA. As the field strength increased, the occurrence of hyperintensity both at the dorsolateral outer putaminal margin and of the putaminal body decreased, while the occurrence of hypointensity at the dorsolateral putaminal margin increased in MSA. The occurrence of uniform mild hyperintensity of the outer putaminal margin was evident in 7% at 0.35T, 40% at 1.5T, and 47% at 3.0T in MSA and in 5% at 0.35T, 60% at 1.5T, and 75% at 3.0T in PD. However, no PD patients showed hyperintensity at the dorsolateral outer putaminal margin and that of the putaminal body. Putaminal magnetic resonance imaging (MRI) findings in MSA were altered considerably by magnetic field strength. The severity and distribution of signal changes are important for assessing putaminal MRI findings in MSA. © 2010 Movement Disorders Society [source] | ||||||||||||||||||||||