bluuebunny/crossref_metadata_2025_split huggingface dataset:
Human brain proton localized NMR spectroscopy in multiple sclerosis
Authors: Van Hecke P. , Marchal G. , Johannik K. , Demaerel P. , Wilms G. , Carton H. , Baert A. L. 
Published: March 2007

AbstractLocalized proton spectroscopy of the brain was performed on MS patients (n = 18) and the results are compared with those of a control group (n = 17). The experiments were performed in a 1.5‐T Siemens Magnetom using the stimulated echo method and selective water suppression. Acquisition parameters were TR/TE/TM = 3000/270/30 ms, NA = 256, and Acq = 13 min. Localized volumes ranged from 8 to about 80 cc. The patients (ages 25 to 66) were at various stages of the disease. Three of the eighteen patients did not show any plaques on the MR images. VOIs were chosen to contain as much plaque volume as possible in the cerebrum white matter. In the controls and in the patients with no plaques, the VOI were localized in similar white matter regions. All spectra were characterized by the presence of Cho (3.2 ppm), PCr + Cr (3.0 ppm), and NAA (2.0 ppm). The ratios NAA/Cho and NAA/(PCr + Cr) were calculated for both the MS and the control group. The results for the three MS patients with no detectable plaques did not differ significantly from the results of the control group. The former group is, however, too limited to draw any conclusion for the moment. For the MRI positive patients, the following values were found (means ± 1 SD): NAA/Cho = 1.98 ± 0.33 and NAA/(PCr + Cr) = 2.16 ± 0.14. In the normals, these values were NAA/Cho = 2.54 ± 0.39 and NAA/(PCr + Cr) = 2.76 ± 0.25. The results quoted are TR and TE dependent. It is concluded that these ratios are significantly lower in the MS patients (p < 0.001). The decrease is attributed to a decrease in the NAA peak intensity. This is supported by the fact that the NAA/Cho and the NAA/Cr ratios are reduced by the same amount (0.78) in the MS patients. Also, this decrease in metabolite ratios is not significantly affected by the MS plaque density and the stage and duration of the disease. © 1991 Academic Press. Inc.
Multiple inversion recovery reduces static tissue signal in angiograms
Authors: Dixon W. Thomas , Sardashti Maziar , Castillo Mauricio , Stomp Guido P. 
Published: March 2007

AbstractSpin label angiography compares two images by subtraction. The first is obtained after blood in one region is labeled by inversion and flows into a region of interest. Labeling is not used for the second image, so only labeled blood remains in the final angiogram after subtraction. This subtraction is never perfect, but with starting images containing less static tissue signal, the remaining background can be reduced. This can be achieved by observing at the zero crossing following an inversion. Multiple inversions allow one to null the signal from tissues with differing T1 simultaneously. We present equations and sample calculations for inversion times and demonstrate the resistance to subject motions (peristalsis, breathing, speaking) resulting from two inversions. Adequate suppression of static tissue signal allows one to dispense with labeling and subtraction, halving the minimum time needed to acquire an image. © 1991 Academic Press. Inc.
Direct projective time‐of‐flight NMR angiography within 4 s
Authors: Matsuda Tetsuya , Doyle Mark , Pohost Gerald M. 
Published: March 2007

AbstractTo enhance contrast between flow and static tissue, NMR projective angiographic methods usually require data subtraction, or alternatively the application of special data processing routines such as the “maximum intensity projection” algorithm. We have successfully developed a direct projection method which yields sufficient flow/static contrast in a single acquisition, producing angiograms in under 4 s. Direct projection angiograms of the cervical and abdominal vessels were obtained. The cervical vessels were uniformly depicted in a number of different projection views. The abdominal vessels exhibit intensity variations due to the pulsatile flow pattern. A series of abdominal angiograms were acquired, each triggered at a different starting cardiac phase. When displayed as a movie sequence the pulsatile flow pattern was seen to advance along the arteries. To more uniformly represent the abdominal vessels a 24‐s average was adequate. This new technique should allow NMR angiograms to be obtained in a “fluoroscopic” mode. © 1991 Academic Press. Inc.
Analysis of the higher‐order echoes in SSFP
Authors: Kim D. J. , Cho Z. H. 
Published: March 2007

AbstractIn the steady‐state free precession (SSFP) with an applied linear gradient, the transverse magnetizations are periodically distributed. Fourier analysis of this periodic distribution leads to the understanding of many interesting phenomena in SSFP. It is found that there are many other higher‐order echoes in SSFP in addition to the previously known echoes. By deriving general description of the transverse magnetization of SSFP and by expanding the echo time independent term with Fourier series, the higher‐order echoes including the two previously known FISP and CE‐FAST are understood and explained. These higher‐order echoes are studied in detail by both computer simulation and experiments and their results are reported. © 1991 Academic Press, Inc.
In vivo monitoring of changes in 5‐fluorouracil metabolism induced by methotrexate measured by 19F NMR spectroscopy
Authors: Koutcher Jason A. , Sawyer Robert C. , Kornblith Alice B. , Stolfi Robert L. , Martin Daniel S. , Devitt Mary L. , Cowburn David , Young Charles W. 
Published: March 2007

AbstractWe have used in vivo 19F NMR spectroscopy to study the metabolism of 5‐fluorouracil (FUra) in tumors with and without pretreatment with methotrexate (MTX). Using the CD8F1 murine mammary tumor as an in vivo model, we observed signals from FUra, α‐fluoro‐β‐alanine (FβALA), α‐fluoro‐β‐ureidopropionic acid (FUPA), and 5‐fluorouracil‐nucleotides (FUN) after intravenous or intraperitoneal injection of 150 mg/kg FUra. Formation of FUN was increased about 1.7‐fold in CD8F1 tumor with methotrexate pretreatment as determined by acid extraction and HPLC analysis. A comparison of in vivo NMR spectra from FUra and sequential MTX + FUra‐treated tumors showed a significantly higher ratio of the FUN signal to the initial total 19F signal in the MTX + FUra‐treated tumors (p < 0.001) for animals receiving FUra either intravenously or intraperi‐toneally. In addition, tumors treated with MTX + FUra had significantly longer time durations during which FUN was detected, independent of the mode of administration. These experiments indicate that in vivo 19F NMR spectroscopy can be used to noninvasively monitor alterations of 5‐fluorouracil metabolism that occur with administration of modulating agents such as methotrexate. Further studies, in both murine tumor models and patients, are indicated to determine if these results can be correlated with tumor response. © 1991 Academic Press, Inc.
NMR measurements of different tissue perfusion parameters
Authors: Dixon W. Thomas 
Published: March 2007

AbstractThe traditional perfusion rate is based on the amount of fluid flowing longitudinally down the capillaries, often given in ml/100 g tissue/min. In principle, fluid flowing radially out of or into the capillaries can be measured as well. Radial and longitudinal perfusion have the same units but independent values. If spins leave and reenter a capillary several times during a transit, radial perfusion can exceed longitudinal perfusion and it probably does. Radial perfusion measures capillary wall function. Progressively increasing the time between two gradient pulses in a proposed radial perfusion imaging sequence allows more magnetization to move into the vasculature to be dephased or removed. Progressive decreases in gradient strength keep diffusion effects constant allowing isolation of the desired perfusion effects. © 1991 Academic Press, Inc.
Intravoxel incoherent motion imaging using spin echoes
Authors: Le Bihan Denis , Turner Robert 
Published: March 2007

AbstractThe purpose of this paper is to review the basic principles of diffusion measurement with spin echoes. These principles can be combined with those of MR imaging to generate maps of diffusion coefficients. Diffusion imaging can be extended to imaging of other intravoxel incoherent motions (IVIM), such as blood microcirculation. Some of the technical problems encountered when implementing IVIM imaging are presented. © 1991 Academic Press, Inc.
Diffusion/perfusion MR imaging of acute cerebral ischemia
Authors: Kucharczyk John , Mintorovitch Jan , Asgari Haleh S. , Moseley Michael 
Published: March 2007

AbstractIn vivo echo‐planar MR imaging was used to measure apparent diffusion coefficients (ADC) of cerebral tissues in a comprehensive noninvasive evaluation of early ischemic brain damage induced by occlusion of the middle cerebral artery (MCA) in a cat model of acute regional stroke. Within 10 min after arterial occlusion, ADC was significantly lower in tissues within the vascular territory of the occluded MCA than in normally perfused tissues in the contralateral hemisphere. Sequential echo‐planar imaging was then used in conjunction with bolus injections of the magnetic susceptibility contrast agent, dysprosium DTPA‐BMA, to characterize the underlying cerebrovascular perfusion deficits. Normally perfused regions of brain were identified by a dose‐dependent 35–70% loss of signal intensity within 6–8 s of contrast administration, whereas ischemic regions appeared relatively hyperintense. These data indicate that sequential diffusion/perfusion imaging may be diagnostically useful in differentiating permanently damaged from reversibly ischemic brain tissue. © 1991 Academic Press, Inc.
In Vitro proton spectroscopy of normal and abnormal prostate
Authors: Yacoe Marshall E. , Sommer Graham , Peehl Donna 
Published: March 2007

AbstractPrevious biochemical and 13C NMR spectroscopic data have suggested that the metabolism of citrate, a secretory product of normal prostate, may be interrupted in prostate cancer. In the present study in vitro 1H NMR spectroscopy was used to see if cell strains derived from prostate cancers could be reliably distinguished from those of normal prostate epithelium. High‐resolution one‐dimensional and two‐dimensional J‐resolved 1H NMR spectra as well as gas chromatography coupled with mass spectroscopy were used to study extracts of highly defined cell strains from normal peripheral zone, normal central zone, adenocarcinoma, and benign prostatic hyperplasia. Resonances assigned to citric acid and related metabolites were identified. Cell strains derived from prostate cancers tended to have smaller amounts of citrate than those from normal prostate epithelium. However, the differences were small and not statistically significant. The lack of statistically significant differences may reflect the variability present in both normal and abnormal cell strains and thus underscore the well‐known difficulty in differentiating normal and cancerous tissues. © 1991 Academic Press, Inc.
Localized 1H NMR spectroscopy in Canavan's Disease: A report of two cases
Authors: Austin S. J. , Connelly A. , Gadian D. G. , Benton J. S. , Brett E. M. 
Published: March 2007

AbstractTwo children with Canavan's Disease, an autosomal recessive leukodystrophy, were studied by localized 1H spectroscopy. The N‐acetylaspartate (NAA) signal intensity was high relative to other metabolite signals, and the signal intensity from choline‐containing compounds was low. These findings are discussed in relation to a possible role for NAA in normal myelination. © 1991 Academic Press, Inc.
Dextran magnetite as a liver contrast agent
Authors: Magin R. L. , Bacic G. , Niesman M. R. , Alameda J. C. , Wright S. M. , Swartz H. M. 
Published: March 2007

AbstractThe superparamagnetic particle dextran magnetite was studied as a liver tumor contrast agent for magnetic resonance imaging (MRI). The effects of dextran magnetite on the longitudinal (T1) and transverse (T2) relaxation times in liver, spleen, and an implanted rat liver tumor were measured at 0.47 T (IBM/Bruker PC‐20 relaxometer) over the dose range of 23 to 69 μmol Fe/kg. Dextran magnetite substantially reduced the T2 of the liver and spleen, but not of the tumor, thereby providing a basis for improved tumor imaging. The T1 of the tumor was not affected following injection of dextran magnetite in the dose range studied, while the spleen T1 was reduced substantially more than the T1 of the liver. Histological studies using the iron reaction for Prussian blue clearly showed dextran magnetite in the liver and spleen, but not in the tumor. While dextran magnetite was sequestered in macrophages in both liver and spleen, the distribution in the liver was more diffuse (70 μm average particle separation) than that in the spleen (25 μm separation). The lack of a T1 effect in the liver is consistent with the fact that a majority of the water in the tissue cannot diffuse to the relaxational centers on the time scale of the liver's intrinsic T1 (280 ms). In the spleen, however, the dextran magnetite is more densely packed in the red pulp allowing a significant fraction of the water to be relaxed by a T1 mechanism. Spin‐echo images of the implanted tumor (mammary adenocarcinoma, R3230AC) in the livers of Fischer 344 rats were obtained at 0.50 T (Siemens Magnetom). The tumor‐to‐liver contrast was improved for both T1 and T2‐weighted spin‐echo images after intravenous injection of the dextran magnetite contrast agent. The contrast determined from these images agreed with that predicted by the measured T1 and the T2 (Hahn spin‐echo) values. In addition, gradient‐echo T2‐weighted images with good contrast were obtained in a much shorter imaging time than was needed for T2‐weighted spin‐echo images. These results demonstrate that the MRI contrast enhancement observed with dextran magnetite is based on its selective uptake and distribution in the macrophages in the liver and spleen and that this agent has substantial potential as a superparamagnetic MR contrast agent. © 1991 Academic Press, Inc.
Pre‐ and postmortem diffusion coefficients in rat neural and muscle tissues
Authors: Macfall J. R. , Maki J. H. , Johnson G. A. , Hedlund L. W. , Cofer G. P. 
Published: March 2007

AbstractPulsed gradient diffusion‐weighted spin‐echo images (7 to 11 gradient strengths) were obtained in a coronal slice through the midbrain for five normal adult white rats before and after sacrifice in a 2‐T CSI system with air temperature control. The pulse sequence was cardiac gated and respiratory synchronized in order to minimize motion artifacts (Tr > 2 s, Te ‐ 30 ms). Diffusion coefficients reflecting several tissue compartments (D*) in brain and muscle were calculated and referenced to simultaneously imaged tubes of water. In the living animals, brain cortical matter had a value of D* = (0.82 ± 0.02) × 103 mm2/s, deeper brain regions had a value of D* = (0.73 ± 0.02) × 10‐3 mm2/s, and the muscle had a value of D* = (1.4 ± 0.1) × 103 mm2/s. Postmortem the values in brain dropped by approximately 30%, while remaining constant in muscle. Signal intensity in the spin‐echo images for muscle tissue rose by 50% over a 1‐ to 2‐h interval after sacrifice while that of brain tissue remained relatively stable. © 1991 Academic Press, Inc.
The effects of chronic ethanol consumption on the intact rat liver studied by in vivo31P NMR spectroscopy
Authors: Brauer Manfred , Ling Mingfu 
Published: March 2007

AbstractIn vivo 31P nuclear magnetic resonance (NMR) spectroscopy provides unique opportunities to study the biochemistry of an organ within the intact animal in a totally noninvasive way. We have used in vivo and in vitro 31P NMR spectroscopy to study steady state changes in the major phosphorus‐containing metabolites of the rat liver in control and chronically ethanol‐treated rats. Chronic (4 month) ethanol treatment caused a statistically significant increase in the inorganic phosphate and phosphodiester resonances of rat liver in in vivo 31P NMR spectra relative to pair‐fed control rats. Phosphomonoester and adenosine 5'‐triphosphate resonances, as well as intracellular pH, were not appreciably altered. The effects of chronic ethanol treatment were particularly apparent in the response of the liver to a metabolic challenge of glycerol. Glycerol is phosphorylated almost exclusively in the liver and metabolized predominately via glycolysis and gluconeogenesis. Our in vivo 31P NMR results after administration of glycerol showed a significant increase in the phosphomonoester resonance in the liver of chromic ethanol‐treated rats but not for their pair fed controls. In vitro 31P NMR studies of perchloric acid extracts of liver showed that the increase was due to an accumulation of sn‐glycerol 3‐phosphate. This effect is due to the NAD+ ‐dependent glycerol 3‐phosphate dehydrogenase step being inhibited in the chronic ethanol‐treated rats. This glycerol test may be useful in assessing the ability of the liver to rapidly regenerate NAD+ in situ and may be a more sensitive indicator of redox imbalance than steady state ratios of redox pairs (e. g., lactate /pyruvate). © 1991 Academic Press, Inc.
Temporal and spatial analysis of fields generated by eddy currents in superconducting magnets: Optimization of corrections and quantitative characterization of magnet/gradient systems
Authors: Boesch Ch. , Gruetter R. , Martin E. 
Published: March 2007

AbstractWe propose methods for the spatial and temporal characterization of time‐dependent magnetic fields generated by eddy currents after switching gradients. For an on‐line determination of the temporal variations of the fields, we extract two terms from the unresolved signal of an extended sample, describing the time evolution of a frequency shift γΔBz (t) and of a decay constant k(t). This procedure allows us to optimize interactively the multiexponential pre‐emphasis as well as any spectral volume selection method with respect to eddy currents, Additionally, we suggest an imaging sequence which allows us to determine the spatial distribution of eddy current fields at a chosen time‐point after any gradient sequence to be tested. Expansion of these eddy currents fields into spherical harmonic functions proves the existence of a higher order terms, which cannot be corrected by a standard pre‐emphasis device, where time constants and amplitudes are adjusted on the X, Y, Z and Z0 coils. The proposed numerical analysis gives a tool to characterize any magnet/ gradient system quantitatively with respect to eddy current performance. © 1991 Academic Press, Inc.
Fucose in 1H COSY spectra of plasma membrane fragments shed from human malignant colorectal cells
Authors: Lean Cynthia L. , Mackinnon Wanda B. , Mountford Carolyn E. 
Published: March 2007

AbstractThe methyl‐methine cross peak of bound fucose has been assigned in the COSY spectrum of plasma membrane shed from human malignant colorectal cells. This cross peak (1.33‐4.27 ppm), which is superimposed on the methyl‐methine cross peak of threonine, was assigned following hydrolysis of the sample. Acid hydrolysis led to a 28 ± 5% reduction in the intensity of the cross peak and the apperance of the α and ß forms of fucose. Chemical analysis confirmed the release of free fucose. Lactate anion. which was not perturbed by the hydrolysis, was used as an internal standard. © 1991 Academic Press, Inc.
13 C NMR visibility of rabbit muscle glycogen in vivo
Authors: Gruetter Rolf , Prolla Tomas A. , Shulman Robert G. 
Published: March 2007

AbstractThe integrated 13C NMR intensity of the glycogen Cl resonance was measured in skeletal muscle (biceps femoris region) of nine rabbits under in vivo conditions. Concurrent chemical determinations of glycogen content showed that the in vivo signal was 1.02 ± 0.06 the intensity of analytical samples, where glycogen is known to be ∼ 100% visible. © 1991 Academic Press, Inc.
Coil optimization for MRI by conjugate gradient descent
Authors: Wong Eric C. , Jesmanowicz A. , Hyde James S. 
Published: March 2007

AbstractA flexible iterative algorithm is presented for optimizing gradient and radio frequency coils for MRI. It is based on a model using discrete current elements and direct Biot‐Savart calculation of the fields. An error function is defined over a region of interest (ROI) and is minimized by conjugate gradient descent. The choice of error function allows optimization of the field uniformity, the inductance, and the efficiency of the coil in any combination. Neither the coil nor the ROI is restricted to any particular geometry. A 40‐ turn cylindrical z‐gradient coil of radius a and length 4a, designed for a ROI of radius 0.7a and length 2a has an average error in the gradient fields generated of 0.85%, an inductance of 0.014a mH/cm, and an efficiency of 6.65a−2 Gem/A. A 16‐turn birdcage‐like RF coil of radius 5 cm, designed for a ROI of radius 4 cm has an average error of 0.79%. © 1991 Academic Press, Inc.
Coupling effects in volume selective 1H spectroscopy of major brain metabolites
Authors: Ernst Th. , Hennig J. 
Published: March 2007

AbstractThe effect of PRESS and STEAM sequences on the spectra of coupled substances are discussed using the examples of weakly coupled AX and A2X systems. Maximum differences compared to uncoupled spins occur if the RF pulses are applied to antiphase magnetization. In this case, the spin echo of the PRESS experiment shows a modified dependence on the refocusing flip angle, which may lead to an attenuation of the acquired signal. In STEAM spectroscopy the evolution within the middle interval tm is dominated by zero quantum coherences and longitudinal polarization, whose maximum efficiencies are 25 and 12.5%, respectively. Zero quantum coherences may lead to strong modulations when the tm value is varied. The effects on the spectra of important coupled metabolites of the human brain such as glutamate, GABA, inositol, and particularly lactate, are demonstrated. The observed modulations seem to make the quantification of the spectra rather difficult at echo times above 50 ms. © 1991 Academic Press, Inc.
A simple method for obtaining cross‐term‐free images for diffusion anisotropy studies in NMR microimaging
Authors: Neeman Michal , Freyer James P. , Sillerud Laurel O. 
Published: March 2007

AbstractThe geometric average of two spin‐echo images obtained with opposite polarity diffusion gradients yields cross‐term‐free images that can be directly compared for diffusion anisotropy. This approach is demonstrated here for free water isotropic diffusion and anisotropic diffusion of water in the phloem system of celery (Apium graveolens). © 1991 Academic Press, Inc.