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High Field (high + field)
Terms modified by High Field Selected AbstractsHigh-resolution 8 Tesla imaging of the formalin-fixed normal human hippocampusCLINICAL ANATOMY, Issue 2 2005Donald W. Chakeres Abstract The purpose of this study was to evaluate the capacity of high-resolution magnetic resonance imaging (MRI) to visualize the normal anatomic features of the human hippocampus in vitro, using high field imaging equipment, parameters, and acquisition times appropriate for imaging human subjects in vivo. This research compared high field, high-resolution MRI of formalin-fixed normal human hippocampus specimens to histologic sectioning of the same hippocampus samples. Four specimens were evaluated using an 8 Tesla (T), 80 cm bore whole-body MRI scanner equipped with a 12.7 cm single strut transverse electromagnetic resonator (TEM) coil. Hahn spin echo images were acquired with a repetition time (TR) of 800 msec, echo times (TE) of 20, 50, 90, and 134 msec, and an acquisition time (TA) of 3.25 min. The image quality was superb with demonstration of most of the features of the hippocampus. High field, high-resolution MRI can be used to depict multiple layers of the formalin-fixed human hippocampus in vitro using an 8 T whole-body scanner, a TEM coil, and short acquisition times compatible with human imaging in vivo. Clin. Anat. 18:88,91, 2005. © 2005 Wiley-Liss, Inc. [source] Variable-field relaxometry of iron-containing human tissues: a preliminary studyCONTRAST MEDIA & MOLECULAR IMAGING, Issue 4 2009Aline Hocq Abstract Excess iron is found in brain nuclei from neurodegenerative patients (with Parkinson's, Alzheimer's and Huntington's diseases) and also in the liver and spleen of cirrhosis, hemochromatosis and thalassaemia patients. Ferritin, the iron-storing protein of mammals, is known to darken T2 -weighted MR images. Understanding NMR tissue behavior may make it possible to detect those diseases, to follow their evolution and finally to establish a protocol for non-invasive measurement of an organ's iron content using MRI methods. In this preliminary work, the MR relaxation properties of embalmed iron-containing tissues were studied as well as their potential correlation with the iron content of these tissues. Relaxometric measurements (T1 and T2) of embalmed samples of brain nuclei (caudate nucleus, dentate nucleus, globus pallidus, putamen, red nucleus and substantia nigra), liver and spleen from six donors were made at different magnetic fields (0.00023,14 T). The influence of the inter-echo time on transverse relaxation was also studied. Moreover, iron content of tissues was determined by inductively coupled plasma atomic emission spectroscopy. In brain nuclei, 1/T2 increases quadratically with the field and depends on the inter-echo time in CPMG sequences at high fields, both features compatible with an outer sphere relaxation theory. In liver and spleen, 1/T2 increases linearly with the field and depends on the inter-echo time at all fields. In our study, a correlation between 1/T2 and iron concentration is observed. Explaining the relaxation mechanism for these tissues is likely to require a combination of several models. The value of 1/T2 at high field could be used to evaluate iron accumulation in vivo. In the future, confirmation of those features is expected to be achieved from measurements of fresh (not embalmed) human tissues. Copyright © 2009 John Wiley & Sons, Ltd. [source] Magnetic resonance microscopy of the equine hoof wall: a study of resolution and potentialEQUINE VETERINARY JOURNAL, Issue 5 2006M. D. KELLER Summary Reasons for performing study: Obtaining magnetic resonance images of the inner hoof wall tissue at the microscopic level would enable early accurate diagnosis of laminitis and therefore more effective therapy. Objectives: To optimise magnetic resonance imaging (MRI) parameters in order to obtain the highest possible resolution of the structures beneath the equine hoof wall. Methods: Magnetic resonance microscopy (MRM) was performed in front feet from 6 cadaver horses using T2 -weighted fast spin echo (FSE-T2), and T1 -weighted gradient echo (GRE-T1) sequences. Results: In T2 weighted FSE images most of the stratum medium showed no signal, however the coronary, terminal and sole papillae were visible. The stratum lamellatum was clearly visible and primary epidermal lamellae could be differentiated from dermal lamellae. Conclusion: Most structures beneath the hoof wall were differentiated. Conventional scanners for diagnostic MRI in horses are low or high field. However this study used ultra-high field scanners currently not available for clinical use. Signal-to-noise ratio (S/N) increases as a function of field strength. An increase of spatial resolution of the image results in a decreased S/N. S/N can also be improved with better coils and the resolution of high field MRI scanners will increase as technology develops and surface array coils become more readily available. Potential relevance: Although MR images with microscopic resolution were obtained ex vivo, this study demonstrates the potential for detection of lamellar pathology as it occurs. Early recognition of the development of laminitis to instigate effective therapy at an earlier stage and may improve the outcome for laminitic horses. Clinical MR is now readily available at 3 T, while 4 T, 7 T and 9 T systems are being used for human whole body applications. [source] Paramagnetic and ferromagnetic anisotropy of magnetic susceptibility in migmatites: measurements in high and low fields and kinematic implicationsGEOPHYSICAL JOURNAL INTERNATIONAL, Issue 3 2004Eric C. Ferré SUMMARY The separation of paramagnetic and ferromagnetic anisotropy of magnetic susceptibility (AMS) is achieved in this study by using a vibrating sample magnetometer and a torque magnetometer performing directional anisotropy measurements in sufficiently high fields to saturate the ferromagnetic phases. The studied material, a migmatite from Minnesota, has a magnetic mineralogy characterized by ferrimagnetic multidomain titanomagnetite, paramagnetic biotite and a diamagnetic quartzo-feldspathic matrix. The low-field AMS represents the sum of ferromagnetic and paramagnetic contributions because the quartz contribution can be neglected, its magnetic susceptibility being two orders of magnitude smaller than that of biotite. In contrast, measurements in a high field isolate the paramagnetic component of the magnetic fabric. The high-field AMS is consistent between specimens and correlates well with measurements done using the torque magnetometer. The magnetic fabrics of the ferromagnetic and of the paramagnetic minerals are not co-axial, i.e. the subfabrics of the biotite and the magnetite are distinct. We propose that this non-coaxiality is due to a vorticity component during regional deformation and that it reflects the general conditions of deep crustal orogenic deformation. [source] Comparing real-world advantages for the clinical neuroradiologist between a high field (3 T), a phased array (1.5 T) vs. a single-channel 1.5-T MR systemJOURNAL OF MAGNETIC RESONANCE IMAGING, Issue 1 2006Darren B. Orbach MD Abstract Purpose To evaluate signal-to-noise ratio (SNR) and neuroradiologists' subjective assessments of image quality in 3-Tesla (3-T) or phased-array MR systems that are now available for clinical neuroimaging. Materials and Methods Brain MR images of six normal volunteers were obtained on each of three scanners: a 1.5-T single-channel system, a 12-channel, phased-array system, and a 3-T single-channel system. Additionally, clinically optimized images acquired from 28 patients who underwent imaging in more than one of these systems were analyzed. SNRs were measured and image quality and artifact conspicuity were graded by two blinded readers. Results The phased-array system produced higher SNR than either the 1.5-T or the 3-T single-channel systems, and in no instance was it outperformed. Both blinded readers judged the phased-array images to be of higher quality than those produced by the single-channel systems, with significantly less artifact. The 3-T magnet produced images with high SNR, but with increased artifact conspicuity. The phased-array system markedly decreased acquisition times without introduction of artifacts. Conclusion Both quantitatively and qualitatively, the phased-array system provided image quality superior to that of the 1.5-T and 3-T single-channel systems. 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] Ex-vivo magnetic resonance image texture analysis can discriminate genotypic origin in bovine meatJOURNAL OF THE SCIENCE OF FOOD AND AGRICULTURE, Issue 4 2005Doaa Mahmoud-Ghoneim Abstract Texture analysis (TA) combined with dedicated gradient echo magnetic resonance imaging (MRI) at high field provides specific parametric maps of connective tissue and allows statistical analysis of the resulting texture. The present study clearly demonstrates that MRI-TA of bovine meat can discriminate between muscle types Gluteo biceps and Pectoralis profundus, and between genotype origins corresponding to the mutation on the myostatin gene: normal +/+, heterozygous mh/+ or homozygous double-muscled mh/mh Belgian White Blue bulls. Values of interclass separations reflect the significantly different collagen and fat contents in these genotypes. To our knowledge, no previous study has demonstrated such a correlation between MRI texture and genetics-related modifications. Copyright © 2004 Society of Chemical Industry [source] Preparation and Fluorescent and Magnetic Properties of Polyurethane/Eu(MA)3 FilmsMACROMOLECULAR CHEMISTRY AND PHYSICS, Issue 24 2007Shuxue Zhou Abstract Europium(III) (Eu3+)-doped polyurethane films were prepared by mixing Eu-methacrylic acid complex (Eu(MA)3) with aliphatic polyurethane oligomer and subsequently curing under UV irradiation. Transmission electron microscopy photos and the appearance of the resulting hybrid films showed that phase separation occurred only at an Eu(MA)3 content above 20 wt.-%. Fluorescence spectra indicated that the fluorescence of Eu3+ was barely influenced by the polyurethane matrix and its intensity increased with an Eu(MA)3 content in the range of approximately 0 to 10 wt.-%. An obvious applied external-field-dependent magnetization (M) of polyurethane/Eu(MA)3 films, namely, an increasing M at low field and a decreasing M at high field, was observed at room temperature from the hysteresis loops, which was influenced by both the Eu(MA)3 content and the ultrasonication imposed on the coatings before curing. It seems that ultrasonication leads to a thermodynamically-unstable structure of Eu3+ in hybrid films, which can be fixed by UV curing but gradually rearranges to its original form during the thermal-curing process, and enhances the diamagnetic part of the hybrid film. Thus, the magnetic property of Eu3+ -doped polyurethane film at room temperature can be adjusted by simply changing the preparation method and the Eu(MA)3 content instead of the type of Eu3+ -organic complex. [source] STRAFI imaging of paramagnetic solids: 31P paramagnetic displacements,,MAGNETIC RESONANCE IN CHEMISTRY, Issue 1 2002Edward W. Randall Abstract One-dimensional stray field (STRAFI) profiles of 31P in phantoms containing, variously, calcium hydroxyapatite, calcium orthophosphate and cobaltous phosphate octahydrate were obtained in a STRAFI field of 11.7 T on a 19.6 T magnet at 206 MHz. The intrinsic spatial resolution with the apatite and orthophosphate samples was about 100 mum. The profile of the image from the paramagnetic cobaltous sample was displaced to high field by 1.2 MHz. The spatial resolution for the cobalt component was degraded because of the large linewidth of ,0.6 MHz. Copyright © 2001 John Wiley & Sons, Ltd. [source] Saturated double-angle method for rapid B1+ mappingMAGNETIC RESONANCE IN MEDICINE, Issue 6 2006Charles H. Cunningham Abstract For in vivo magnetic resonance imaging at high field (,3 T) it is essential to consider the homogeneity of the active B1 field (B1+), particularly if surface coils are used for RF transmission. A new method is presented for highly rapid B1+ magnitude mapping. It combines the double angle method with a B1 -insensitive magnetization-reset sequence such that the choice of repetition time (TR) is independent of T1 and with a multislice segmented (spiral) acquisition to achieve volumetric coverage with adequate spatial resolution in a few seconds. Phantom experiments confirmed the accuracy of this technique even when TR , T1, with the side effect being lowered SNR. The speed of this method enabled B1+ mapping in the chest and abdomen within a single breath-hold. In human cardiac imaging, the method enabled whole-heart coverage within a single 16-s breath-hold. Results from phantoms and healthy volunteers at 1.5 T and 3 T are presented. Magn Reson Med, 2006. © 2006 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] Radio frequency magnetic field mapping of a 3 Tesla birdcage coil: Experimental and theoretical dependence on sample properties ,MAGNETIC RESONANCE IN MEDICINE, Issue 2 2001Marcello Alecci Abstract The RF B1 distribution was studied, theoretically and experimentally, in phantoms and in the head of volunteers using a 3 T MRI system equipped with a birdcage coil. Agreement between numerical simulation and experiment demonstrates that B1 distortion at high field can be explained with 3D full-Maxwell calculations. It was found that the B1 distribution in the transverse plane is strongly dependent on the dielectric properties of the sample. We show that this is a consequence of RF penetration effects combined with RF standing wave effects. In contrast, along the birdcage coil z-axis the B1 distribution is determined mainly by the coil geometry. In the transverse plane, the region of B1 uniformity (within 10% of the maximum) was 15 cm with oil, 6 cm with distilled water, 11 cm with saline, and 10 cm in the head. Along z the B1 uniformity was 9 cm with phantoms and 7 cm in the head. Magn Reson Med 46:379,385, 2001. © 2001 Wiley-Liss, Inc. [source] Rat lung MRI using low-temperature prepolarized helium-3MAGNETIC RESONANCE IN MEDICINE, Issue 6 2001Frank Kober Abstract The purpose of this study was to evaluate the recently proposed technique of 3He prepolarization at low temperature and high field (Kober et al. Magn Reson Med 1999; 41:1084,1087) for fast imaging of the lung. Helium-3 was cooled to 2.4 K in a magnetic field of 8 Tesla to obtain a polarization of 0.26%. The polarized 3He was warmed up to room temperature and transferred to a rat, with a final polarization of about 0.1%, large enough for acquiring a 3D image of the rat lung in 30 s. Magn Reson Med 45:1130,1133, 2001. © 2001 Wiley-Liss, Inc. [source] In vivo31P MRS detection of an alkaline inorganic phosphate pool with short T1 in human resting skeletal muscleNMR IN BIOMEDICINE, Issue 8 2010H. E. Kan Abstract Non-invasive determination of mitochondrial content is an important objective in clinical and sports medicine. 31P MRS approaches to obtain information on this parameter at low field strength typically require in-magnet exercise. Direct observation of the intra-mitochondrial inorganic phosphate (Pi) pool in resting muscle would constitute an alternative, simpler method. In this study, we exploited the higher spectral resolution and signal-to-noise at 7T to investigate the MR visibility of this metabolite pool. 31P in vivo MR spectra of the resting soleus (SOL) muscle were obtained with 1H MR image-guided surface coil localization (six volunteers) and of the SOL and tibialis anterior (TA) muscle using 2D CSI (five volunteers). A resonance at a frequency 0.38,ppm downfield from the cytosolic Pi resonance (Pi1; pH 7.0,±,0.04) was reproducibly detected in the SOL muscle in all subjects and conditionally attributed to the intra-mitochondrial Pi pool (Pi2; pH 7.3,±,0.07). In the SOL muscle, the Pi2/Pi1 ratio was 1.6 times higher compared to the TA muscle in the same individual. Localized 3D CSI results showed that the Pi2 peak was present in voxels well away from blood vessels. Determination of the T1 of the two Pi pools in a single individual using adiabatic excitation of the spectral region around 5,ppm yielded estimates of 4.3,±,0.4 s vs 1.4,±,0.5 s for Pi1 and Pi2, respectively. Together, these results suggest that the intra-mitochondrial Pi pool in resting human skeletal muscle may be visible with 31P MRS at high field. Copyright © 2010 John Wiley & Sons, Ltd. [source] Magnetic pinning-effect in Nd0.7Ca0.3MnO3/YBa2Cu3O7 bilayerPHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 12 2007Daniel Hsu Abstract The vortex lines of superconductor can be driven by electrical currents, which are often coupled with a reliable control of flux quanta movement by defects or magnetic domains. In this work, the magnetic pinning-effect in Nd0.7Ca0.3MnO3/YBa2Cu3O7 (NCMO/YBCO) bilayers is investigated. It is found that by increasing the field from 0 to 5 Tesla, the critical current Ic of pure YBCO film at 50 K is suppressed by three orders of magnitude. However, in the NCMO/YBCO bilayer Ic is less sensitive to the field and maintains at the level of 100 mA at high field. This result indicates that the magnetic pining effect of NCMO is much more efficient than the conventional routes, which maybe related to the fine domain structure of NCMO film. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Differential effects of cannabinoid receptor agonists on regional brain activity using pharmacological MRIBRITISH JOURNAL OF PHARMACOLOGY, Issue 2 2008C-L Chin Background and purpose: Activation of cannabinoid CB1 and/or CB2 receptors mediates analgesic effects across a broad spectrum of preclinical pain models. Selective activation of CB2 receptors may produce analgesia without the undesirable psychotropic side effects associated with modulation of CB1 receptors. To address selectivity in vivo, we describe non-invasive, non-ionizing, functional data that distinguish CB1 from CB2 receptor neural activity using pharmacological MRI (phMRI) in awake rats. Experimental approach: Using a high field (7 T) MRI scanner, we examined and quantified the effects of non-selective CB1/CB2 (A-834735) and selective CB2 (AM1241) agonists on neural activity in awake rats. Pharmacological specificity was determined using selective CB1 (rimonabant) or CB2 (AM630) antagonists. Behavioural studies, plasma and brain exposures were used as benchmarks for activity in vivo. Key results: The non-selective CB1/CB2 agonist produced a dose-related, region-specific activation of brain structures that agrees well with published autoradiographic CB1 receptor density binding maps. Pretreatment with a CB1 antagonist but not with a CB2 antagonist, abolished these activation patterns, suggesting an effect mediated by CB1 receptors alone. In contrast, no significant changes in brain activity were found with relevant doses of the CB2 selective agonist. Conclusion and implications: These results provide the first clear evidence for quantifying in vivo functional selectivity between CB1 and CB2 receptors using phMRI. Further, as the presence of CB2 receptors in the brain remains controversial, our data suggest that if CB2 receptors are expressed, they are not functional under normal physiological conditions. British Journal of Pharmacology (2008) 153, 367,379; doi:10.1038/sj.bjp.0707506; published online 29 October 2007 [source] The value of conventional high-field MRI in MS in the light of the McDonald criteria: a literature reviewACTA NEUROLOGICA SCANDINAVICA, Issue 3 2010L. S. Lunde Larsen Lunde Larsen LS, Larsson HBW, Frederiksen JL. The value of conventional high-field MRI in MS in the light of the McDonald criteria: a literature review. Acta Neurol Scand: 122: 149,158. © 2010 John Wiley & Sons A/S. The diagnosis of MS is based on the revised McDonald criteria and is multidisciplinary. Both clinical and paraclinical measures are included. High-field magnetic resonance imaging (MRI) is becoming increasingly available and it is therefore necessary to clarify possible advantages of high-field MRI in MS. The aim of this paper was to review MRI studies in MS where a direct comparison of MRI at high field with MRI at 1,1.5 tesla (T) had been performed. The studies evaluated were found by searching Pubmed with relevant terms including MeSH terms. The reviewed studies all found the conspicuity of lesions to be better at high field. Of the seven studies, six found more and bigger lesions at high-field MRI. In the present paper, the relevant MRI sequences are evaluated in detail. The detection of more lesions at high-field strength did not seem to lead to earlier diagnosis of clinically definite multiple sclerosis. Further larger studies of patients with clinically isolated syndromes are needed to settle the question of a diagnostic consequence of high-field imaging in MS. We suggest that the next revision of the McDonald diagnostic criteria include a recommendation of field strength. [source] Regional energetic dysfunction in hippocampal epilepsyACTA NEUROLOGICA SCANDINAVICA, Issue 4 2005J. W. Pan Objectives , There is increasing evidence for a dysfunctional metabolic network in human mesial temporal lobe epilepsy (MTLE). To further describe this, we evaluated the bioenergetic status in unilateral MTLE inter-regionally and in relation to neuropathology. Materials and methods , We used whole brain high field (4 T) 31P MR spectroscopic imaging to determine in vivo PCr and ATP, studying n = 22 patients (all candidates for hippocampal resection) and n = 14 control volunteers. The degree of bioenergetic impairment was assessed by calculating the ratio of PCr to ATP. Results, Compared to controls, patients demonstrated significant decreases in PCr/ATP from the ipsilateral amygdala and pes (0.84 ± 0.14, 0.87 ± 0.10, respectively, patients vs 0.97 ± 0.15, 0.98 ± 0.16, controls). In patients, the ipsilateral thalamic energetics positively correlated with contralateral hippocampal energetics. In addition, the ipsilateral thalamic and striatal energetics negatively correlated with hippocampal total glial counts. Conclusions, These data are consistent with a view that in MTLE, the bilateral hippocampi, ipsilateral thalamus and striatum are linked in their energetic depression, possibly reflecting the propagation of seizures throughout the brain. [source] High-resolution 8 Tesla imaging of the formalin-fixed normal human hippocampusCLINICAL ANATOMY, Issue 2 2005Donald W. Chakeres Abstract The purpose of this study was to evaluate the capacity of high-resolution magnetic resonance imaging (MRI) to visualize the normal anatomic features of the human hippocampus in vitro, using high field imaging equipment, parameters, and acquisition times appropriate for imaging human subjects in vivo. This research compared high field, high-resolution MRI of formalin-fixed normal human hippocampus specimens to histologic sectioning of the same hippocampus samples. Four specimens were evaluated using an 8 Tesla (T), 80 cm bore whole-body MRI scanner equipped with a 12.7 cm single strut transverse electromagnetic resonator (TEM) coil. Hahn spin echo images were acquired with a repetition time (TR) of 800 msec, echo times (TE) of 20, 50, 90, and 134 msec, and an acquisition time (TA) of 3.25 min. The image quality was superb with demonstration of most of the features of the hippocampus. High field, high-resolution MRI can be used to depict multiple layers of the formalin-fixed human hippocampus in vitro using an 8 T whole-body scanner, a TEM coil, and short acquisition times compatible with human imaging in vivo. Clin. Anat. 18:88,91, 2005. © 2005 Wiley-Liss, Inc. [source] Variable-field relaxometry of iron-containing human tissues: a preliminary studyCONTRAST MEDIA & MOLECULAR IMAGING, Issue 4 2009Aline Hocq Abstract Excess iron is found in brain nuclei from neurodegenerative patients (with Parkinson's, Alzheimer's and Huntington's diseases) and also in the liver and spleen of cirrhosis, hemochromatosis and thalassaemia patients. Ferritin, the iron-storing protein of mammals, is known to darken T2 -weighted MR images. Understanding NMR tissue behavior may make it possible to detect those diseases, to follow their evolution and finally to establish a protocol for non-invasive measurement of an organ's iron content using MRI methods. In this preliminary work, the MR relaxation properties of embalmed iron-containing tissues were studied as well as their potential correlation with the iron content of these tissues. Relaxometric measurements (T1 and T2) of embalmed samples of brain nuclei (caudate nucleus, dentate nucleus, globus pallidus, putamen, red nucleus and substantia nigra), liver and spleen from six donors were made at different magnetic fields (0.00023,14 T). The influence of the inter-echo time on transverse relaxation was also studied. Moreover, iron content of tissues was determined by inductively coupled plasma atomic emission spectroscopy. In brain nuclei, 1/T2 increases quadratically with the field and depends on the inter-echo time in CPMG sequences at high fields, both features compatible with an outer sphere relaxation theory. In liver and spleen, 1/T2 increases linearly with the field and depends on the inter-echo time at all fields. In our study, a correlation between 1/T2 and iron concentration is observed. Explaining the relaxation mechanism for these tissues is likely to require a combination of several models. The value of 1/T2 at high field could be used to evaluate iron accumulation in vivo. In the future, confirmation of those features is expected to be achieved from measurements of fresh (not embalmed) human tissues. Copyright © 2009 John Wiley & Sons, Ltd. [source] A microfluidic study of mechanisms in the electrophoresis of supercoiled DNAELECTROPHORESIS, Issue 12 2008Dammika P. Manage Abstract In this work, microfluidic chips were used to study the electrophoresis of supercoiled DNA (SC DNA) in agarose. This system allowed us to study the electrophoretic and trapping behaviours of SC DNA of various lengths, at various fields and separation distances. Near a critical electric field the DNA is trapped such that the concentration falls exponentially with distance. The trapping of such circular DNA has been explained in terms of the ,lobster trap' or ,impalement' model where shorter fibres become trapping sites at higher fields, leading to an ongoing (and gradual) increase in trapping with increasing field. By contrast, the present study suggests that under some circumstances the traps have a barrier such that only when the DNA has sufficient energy (at high enough fields) can it become trapped, leading to a sudden transition in behaviours at the critical field. We propose an ,activated impalement' mechanism of trapping in which only at sufficiently high fields is the SC DNA impaled and trapped for long times. The critical electric field appears to be inversely proportional to the length of the DNA molecule, suggesting that the force required to impale the SC DNA is constant. [source] Paramagnetic and ferromagnetic anisotropy of magnetic susceptibility in migmatites: measurements in high and low fields and kinematic implicationsGEOPHYSICAL JOURNAL INTERNATIONAL, Issue 3 2004Eric C. Ferré SUMMARY The separation of paramagnetic and ferromagnetic anisotropy of magnetic susceptibility (AMS) is achieved in this study by using a vibrating sample magnetometer and a torque magnetometer performing directional anisotropy measurements in sufficiently high fields to saturate the ferromagnetic phases. The studied material, a migmatite from Minnesota, has a magnetic mineralogy characterized by ferrimagnetic multidomain titanomagnetite, paramagnetic biotite and a diamagnetic quartzo-feldspathic matrix. The low-field AMS represents the sum of ferromagnetic and paramagnetic contributions because the quartz contribution can be neglected, its magnetic susceptibility being two orders of magnitude smaller than that of biotite. In contrast, measurements in a high field isolate the paramagnetic component of the magnetic fabric. The high-field AMS is consistent between specimens and correlates well with measurements done using the torque magnetometer. The magnetic fabrics of the ferromagnetic and of the paramagnetic minerals are not co-axial, i.e. the subfabrics of the biotite and the magnetite are distinct. We propose that this non-coaxiality is due to a vorticity component during regional deformation and that it reflects the general conditions of deep crustal orogenic deformation. [source] Improved homogeneity of the transmit field by simultaneous transmission with phased array and volume coilJOURNAL OF MAGNETIC RESONANCE IMAGING, Issue 2 2010Nikolai I. Avdievich PhD Abstract Purpose: To improve the homogeneity of transmit volume coils at high magnetic fields (,4 T). Due to radiofrequency (RF) field/tissue interactions at high fields, 4 T to 8 T, the transmit profile from head-sized volume coils shows a distinctive pattern with relatively strong RF magnetic field B1 in the center of the brain. Materials and Methods: In contrast to conventional volume coils at high field strengths, surface coil phased arrays can provide increased RF field strength peripherally. In theory, simultaneous transmission from these two devices could produce a more homogeneous transmission field. To minimize interactions between the phased array and the volume coil, counter rotating current (CRC) surface coils consisting of two parallel rings carrying opposite currents were used for the phased array. Results: Numerical simulations and experimental data demonstrate that substantial improvements in transmit field homogeneity can be obtained. Conclusion: We have demonstrated the feasibility of using simultaneous transmission with human head-sized volume coils and CRC phased arrays to improve homogeneity of the transmit RF B1 field for high-field MRI systems. J. Magn. Reson. Imaging 2010;32:476,481. © 2010 Wiley-Liss, Inc. [source] Minimization of Nyquist ghosting for echo-planar imaging at ultra-high fields based on a "negative readout gradient" strategyJOURNAL OF MAGNETIC RESONANCE IMAGING, Issue 5 2009Wietske van der Zwaag PhD Abstract Purpose: To improve the traditional Nyquist ghost correction approach in echo planar imaging (EPI) at high fields, via schemes based on the reversal of the EPI readout gradient polarity for every other volume throughout a functional magnetic resonance imaging (fMRI) acquisition train. Materials and Methods: An EPI sequence in which the readout gradient was inverted every other volume was implemented on two ultrahigh-field systems. Phantom images and fMRI data were acquired to evaluate ghost intensities and the presence of false-positive blood oxygenation level-dependent (BOLD) signal with and without ghost correction. Three different algorithms for ghost correction of alternating readout EPI were compared. Results: Irrespective of the chosen processing approach, ghosting was significantly reduced (up to 70% lower intensity) in both rat brain images acquired on a 9.4T animal scanner and human brain images acquired at 7T, resulting in a reduction of sources of false-positive activation in fMRI data. Conclusion: It is concluded that at high B0 fields, substantial gains in Nyquist ghost correction of echo planar time series are possible by alternating the readout gradient every other volume. J. Magn. Reson. Imaging 2009;30:1171,1178. © 2009 Wiley-Liss, Inc. [source] Super-resolved spatially encoded single-scan 2D MRIMAGNETIC RESONANCE IN MEDICINE, Issue 6 2010Noam Ben-Eliezer Abstract Single-scan MRI underlies a wide variety of clinical and research activities, including functional and diffusion studies. Most common among these "ultrafast" MRI approaches is echo-planar imaging. Notwithstanding its proven success, echo-planar imaging still faces a number of limitations, particularly as a result of susceptibility heterogeneities and of chemical shift effects that can become acute at high fields. The present study explores a new approach for acquiring multidimensional MR images in a single scan, which possesses a higher built-in immunity to this kind of heterogeneity while retaining echo-planar imaging's temporal and spatial performances. This new protocol combines a novel approach to multidimensional spectroscopy, based on the spatial encoding of the spin interactions, with image reconstruction algorithms based on super-resolution principles. Single-scan two-dimensional MRI examples of the performance improvements provided by the resulting imaging protocol are illustrated using phantom-based and in vivo experiments. Magn Reson Med, 2010. © 2010 Wiley-Liss, Inc. [source] Enhanced T2 contrast for MR histology of the mouse brainMAGNETIC RESONANCE IN MEDICINE, Issue 4 2006Anjum Ali Sharief Abstract A 3D Carr-Purcell-Meiboom-Gill (CPMG) sequence was implemented to obtain enhanced T2 contrast in actively stained (perfusion with fixative and contrast agent) mouse brains at 9.4 T. Short interecho spacing was used to minimize diffusion and susceptibility losses. The sequence produced 16 3D volumes with an interecho spacing of 7 ms for isotropic 43-,-resolution images of the mouse brains in a scan time of 4 hr. To enhance the signal-to-noise ratio (SNR) and contrast, the multiecho frequency domain image contrast (MEFIC) method was applied, resulting in a composite image with T2 -weighted contrast. The high SNR and contrast thus achieved revealed aspects of mouse brain morphology, such as multiple cortical layers, groups of thalamic nuclei, layers of the inferior and superior colliculus, and molecular and granular layers of the cerebellum, with a high degree of definition and contrast that was not previously achieved in T2 -weighted acquisitions at high fields. Magn Reson Med, 2006. © 2006 Wiley-Liss, Inc. [source] Optimized detection of lactate at high fields using inner volume saturationMAGNETIC RESONANCE IN MEDICINE, Issue 4 2006Richard A.E. Edden Abstract In localized proton MR spectroscopy (1H-MRS) in vivo, the detection of lactate (Lac) is affected by modulation of its resonances due to homonuclear scalar couplings (J). A simple and convenient way to distinguish Lac from lipids is to set the TE to 1/J so that the Lac signal is inverted while other resonances (such as lipid) remain in-phase. However, at high field strengths, such as 3 Tesla or above, the modulation of the Lac signal is complicated by chemical shift effects that cause modulation patterns to vary within different subregions of the localized volume. Under some conditions the Lac signal may even disappear completely. In this note we introduce the concept of inner volume saturation (IVS), which makes use of high bandwidth spatial pulses to remove the signal corresponding to the regions of the localized volume that contribute unwanted modulation patterns. The method is described theoretically and demonstrated experimentally at 3 Tesla in a phantom and a patient with acute stroke. The phantom measurements indicate that virtually 100% of the Lac signal can be recovered using this method. The method should be feasible at magnetic fields above 3 Tesla, and may also be applied to other coupled spin systems in which modulation effects are important. Magn Reson Med, 2006. © 2006 Wiley-Liss, Inc. [source] Magnetic-field-driven quantum criticality and thermodynamics in trimerized spin-1/2 isotropic XY chain with three-spin interactionsPHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 9 2010L. J. Ding Abstract The quantum criticality and thermodynamics for the trimerized spin-1/2 isotropic XY chain with three-spin interactions in an external magnetic field are investigated by means of the Green's function theory combined with Jordan,Wigner transformation. The ground-state phase diagrams are explored, in which various phases are identified and described by typical M,h curves. Therein, two cusps emerge for strong three-spin interactions in two gapless phases at low and high fields, respectively. Moreover, the spin correlations and two-site entanglement entropy are calculated for a further understanding of quantum phase transition (QPT). It is also found that the magnetic-field-driven quantum criticality is closely related to the energy spectrum, in which an energy gap responsible for the appearance of 1/3 magnetization plateau can be opened up by three-spin interactions. The critical behavior disappears when the temperature becomes nonzero, yielding only a crossover behavior. In addition, the gapped low-lying excitations are responsible for the observed thermodynamic behaviors, wherein a structure with three peaks in the temperature dependence of specific heat is unveiled. [source] 3rd Workshop on Semiconductor Nanodevices and Nanostructured Materials (NanoSemiMat-3)PHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue S2 2004E. F. da Silva Jr. The 3rd Workshop on Semiconductor Nanodevices and Nanostructured Materials (NanoSemiMat-3) took place in Salvador, Bahia, Brazil, 24,27 March 2004. The NanoSemiMat network is part of the Brazilian Initiative on Nanoscience and Nanotechnology (N&N). The papers include the following topics: Photodetectors, Lasers and LEDs, Porous Materials, New Materials, New Technologies, Molecular Technology and Interfaces, Nanostructured Materials and Nanobiotechnology. The presentations reflect theoretical and experimental research on nanostructured semiconductor materials such as III,V and II,VI, Si and SiC based nanodevices, wide gap materials, ceramics, polymers, porous materials, optical and transport properties of low-dimensional structures, magnetic nanostructures and structures under the influence of high fields, spintronics and sensor applications. This issue is devoted to Prof. J. R. Leite, Sao Paulo, former Regional Editor of physica status solidi and Guest Editor in memoriam of the present Proceedings. [source] Preface: phys. stat. sol. (c) 1/S2PHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue S2 2004E. F. da Silva Jr. The papers in this special issue of physica status solidi (c) are selected manuscripts including diverse research lines presently in development in the ambit of the NanoSemiMat network in Brazil. The 3rd Workshop on Semiconductor Nanodevices and Nanostructured Materials (NanoSemiMat-3) took place in Salvador, Bahia, Brazil, at the Catussaba Resort Hotel, during the period of 24,27 March 2004. The NanoSemiMat network is part of the Brazilian Initiative on Nanoscience and Nanotechnology (N&N), with strategic cooperative research support in this area. The initiative started in 2001, through the formation of four research networks nationwide in different scientific fields associated to NanoScience and Nanotechnology (N&N). The 3rd Workshop on Nanodevices and Nanostructured Materials (NanoSemiMat-3) is an evolution of the two previous meetings which were held in Recife, PE, Brazil and Natal, RN, Brazil in 2002 and 2003, respectively. The meeting comprised 16 invited plenary talks, each 30 minutes long, given by eminent researchers from Brazil, Canada, France, Germany and the United States of America. These invited talks extend through different topics of N&N associated to Nanodevices and Nanostructured Materials: Photodetectors, Lasers and LEDs, Porous Materials, New Materials, and New Technologies, among others. There were short talks presented by representatives of the other N&N networks in Brazil dealing with Molecular Technology and Interfaces, Nanostructured Materials and Nanobiotechnology. Also a poster session, with about 60 presentations, highlighted the main research activities presently being developed by the network members at the different sites which constitute the NanoSemiMat network. The presentations reflected theoretical and experimental research lines which lead to the development of basic and applied research in nanostructured semiconductor materials such as III,V and II,VI, Si and SiC based nanodevices, wide gap materials, ceramics, polymers, porous materials, optical and transport properties of low dimensional structures, magnetic nanostructures and structures under the influence of high fields, spintronics and sensor applications. The participants of the workshop came from 20 research institutions within Brazil and from 7 research laboratories and universities in Europe and North America. In total about 120 researchers, members of the network, invited researchers, representatives of supporting and funding agencies in Brazil, undergraduate and graduate students, technical staff and supporting personal as well as researchers from complementary fields were present. The realization of the NanoSemiMat-3 was possible due to the financial support of the Brazilian Ministry of Science and Technology (MCT) and the Brazilian National Research Council (CNPq) and the logistic support of Federal University of Bahia. All activities during the NanoSemiMat-3 were open to the general public with interest in nanoscience and nanotechnology. In this third workshop of the series, we highlight the expansion of its format, with plenary and invited talks, poster sessions, as well as the presence of seven invited speakers from abroad. We expect that the continuation of the NanoSemiMat series will be a forum for discussions of state-of-the-art research developed in Brazil on N&N and the multidisciplinary field of semiconductor nanodevices and nanostructured materials as well as its superposition to other branches of science. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] | ||||||||||||||||||||||