bluuebunny/crossref_metadata_2025_split huggingface dataset:
The water resonance as an alternative pH reference: Relevance to in Vivo31P NMR localized spectroscopy studies
Authors: Madden Anthoula , Leach Martin O. , Collins David J. , Payne Geoffrey S. 
Published: March 2007

AbstractpH measurements require a suitable pH reference within the 31P NMR spectrum with respect to which the chemical shift of P1 and hence pH, may be calculated. In muscle spectra PCr is prominent and provides a reference frequency. However, recent localized tumor studies have reported the absence of PCr, for example, in breast tumors. The use of the α, β, and γ‐ATP peaks as suitable references has been suggested, but the position of the β‐ and γ‐ATP peaks is dependent upon the intracellular Mg2+ concentration. The α‐ATP is not affected by ionic concentrations; however, it contains UDPG and NAD+, the presence of which can lead to peak‐shape distortion. This paper considers the use of the H2O resonance from the proton spectrum used for shimming as a suitable pH reference, provided this is also localized to the same region of interest, using a sequence giving rise to eddy current effects comparable to those of the 31P NMR sequence. Localized in vivo measurements in the muscle and brain of volunteers indicate good agreement between the proton and phosphorus chemical shifts, allowing the PCr position to be predicted to within 0.01 ppm in all cases. © 1991 Academic Press, Inc.
On the use of a slice‐selective 270° self‐refocusing Gaussian pulse for magnetic resonance imaging
Authors: Doddrell David M. , Galloway Graham J. , Rose Stephen E. , Moulds Peter J. , Brereton Ian M. 
Published: March 2007

AbstractTheoretical and experimental results are presented demonstrating that the slice intensity resulting from a self‐refocusing 270° Gaussian pulse (L. Elmsley and G. Bodenhausen, Magn. Reson. in Med. 10, 273, 1989) is approximately 60% of that following an appropriately refocused 90° Gaussian pulse.
A magnetization transfer preparation scheme for snapshot FLASH imaging
Authors: Jones Richard A. , Southon Timothy E. 
Published: March 2007

AbstractA rapid method of generating images whose contrast is dependent on the exchange of magnetization between the free and restricted proton pools is presented. The contrast obtained is similar to that obtained from T2‐weighted spin‐echo images. The rapid nature of the sequence means that the RF power deposition problems encountered when using magnetization transfer in conjunction with conventional imaging sequences are avoided. © 1991 Academic Press, Inc.
In Vivo13C NMR spectroscopy of glucose metabolism of RIF‐1 tumors
Authors: Constantinidis Ioannis , Chatham John C. , Wehrle Janna P. , Glickson Jerry D. 
Published: March 2007

AbstractAn efficient method for measuring in vivo 13C NMR spectra of tumors has been developed and employed to monitor glucose metabolism in radiation‐induced fibrosarcomas (RIF‐1) subcutaneously implanted in C3H/HeN mice. [1‐13C]Glucose was injected directly into the tumors at a dose of 1 g/kg body wt. Spectra were obtained with a Bruker AM 360‐WB spectrometer (8.4 T/8.9 cm bore) employing a homebuilt probe equipped with a four‐turn solenoidal coil (1.5 cm outer diameter) for detection of 13C signals and a Helmholtz coil (two 3‐cm turns separated by a 3‐cm gap, oriented orthogonally to the 13C coil) for 1H decoupling. In addition to the natural abundance 13C resonances of the tumors, signals were detected from the α‐and β‐anomers of labeled glucose. Within 15 min following injection of labeled glucose [3‐13C]lactate and [3‐13C]alanine were detected. Lactate labeling approached steady state levels within about 50 min after glucose injection; in contrast, alanine labeling increased continuously over the duration of the experiment (70 min). Sixty minutes after glucose injection, the ratio of the intensity of [3‐ 13C]lactate to the principal lipid methylene resonance (30 ppm from external tetramethylsilane), which served as an internal intensity reference, was correlated with tumor size, whereas the corresponding ratio of the [3‐ 13C] alanine resonance was not. Labeling of glutamate was below the level of detection in the in vivo spectra; however, labeling of C4‐glutamate at a level approximately 50‐fold lower than the level of [3‐ 13C]lactate was detected in perchloric acid extracts. Incorporation of 13C label into C2‐and C3‐glutamate and C2‐lactate was also observed. © 1991 Academic Press, Inc.
Noise correlation
Authors: Jesmanowicz A. , Hyde James S. , Froncisz W. , Kneeland J. Bruce 
Published: March 2007

AbstractCalculations and experiments that provide support for our previously stated theorem are presented: If two coils simultaneously receiving magnetic resonance signals from the same anatomic region exhibit zero mutual inductance, there can be no correlation of the noise. It is shown that correlation does not exist even in the presence of mutual inductance unless the two signal paths have amplifiers prior to signal combination. It is further found that in the presence of mutual inductance with ideal amplifiers (0 dB noise figure) in the two signal paths, there is no correlation of noise. In order to satisfy the condition of zero mutual inductance, it may be necessary to employ a decoupling circuit external to the body. A novel coil assembly, which was used in the experiments, places a single‐turn surface coil in the median plane between the two loops of a counter rotating current coil. The signal‐to‐noise ratio can be improved by combining signals. This is in analogy to quadrature receiving coils, where the mutual inductance is zero because vector reception fields are perpendicular. In the present geometry, vector reception fields are collinear, but are parallel and antiparallel on the two sides of the coil assembly, resulting in zero mutual inductance. © 1991 Academic Press, Inc.
NMR angiography of coronary vessels with 2‐D planar image scanning
Authors: Cho Z. H. , Mun C. W. , Friedenberg R. M. 
Published: March 2007

AbstractOn the basis of the principles of the time‐of‐flight method and the 3‐D angiogram obtained by the 2‐D planar image scanning technique using 90° RF pulses with short repetition time, we have obtained a coronary angiogram around the heart including the coronary arteries and veins. The cine NMR imaging technique is also incorporated in synchronizing ECG R waves to reduce the motion artifact and at the same time to induce the saturation effect on the static samples. Images of the large bulk blood flow corresponding to the heart chamber and descending aorta are further removed by postprocessing. The final 3‐D angiogram is then formed by stacking the 2‐D images and contrast is further enhanced by the maximum ray tracing algorithm. © 1991 Academic Press, Inc.
Delayed‐focus pulses for magnetic resonance imaging: An evolutionary approach
Authors: Wu Xi‐Li , Xu Ping , Freeman Ray 
Published: March 2007

AbstractAn evolutionary algorithm has been used to design a family of shaped radiofrequency pulses giving uniform absorption‐mode excitation across a predetermined frequency band. By allowing a free precession interval before signal acquisition, time is left for field gradients to be switched and for undesirable transients to decay. © 1991 Academic Press, Inc.
Cholesterol of myelin is the determinant of gray‐white contrast in MRI of brain
Authors: Koenig Seymour H. 
Published: March 2007

AbstractThe relative brightness of adult white matter in T1‐weighted MRI arises from myelin, but the mechanisms responsible remain to be clarified. Koenig et al. [Magn. Reson. Med. 14, 482 (1990)] conjectured that the cholesterol of myelin (∼ 30% of its lipid) was responsible. We present 1/T1 and magnetization transfer contrast imaging data [Wolff and Balaban, Magn. Reson. Med. 10, 135 (1989)] on a model system— 50% lipid—50% water by weight, with the lipid one‐half phosphatidyl cholinc (PC) and one‐half cholesterol—and a control in which the lipid is all PC. The differences between the model and control samples mimic the myelin contribution to white matter in both experiments. © 1991 Academic Press, Inc.
Proton spectroscopic imaging: A tool for studying intracerebral tumor models in rat
Authors: Bourgeois D. , Remy C. , Lefur Y. , Devoulon P. , Benabid A. L. , Decorps M. 
Published: March 2007

AbstractWater‐suppressed 2D 1H spectroscopic imaging was used with surface coils to study in vivo the cerebral metabolism changes in rat brain induced by a glial tumor growing in situ. To achieve slice selection without a chemical‐shift artifact, we exploited the depth pulse properties of a spin‐echo sequence. In order to give a spectral response which is independent of the position, the water suppression was achieved by using a spin‐locking excitation and a binomial refocusing pulse. Spectroscopic images were obtained with an in‐plane resolution of 1.1 × 1.1 mm and a slice thickness of roughly 3 mm. The growing of the tumor induced dramatic modifications in the proton spectra, including a nearly complete loss of N‐acetyl aspartate, an increase of the 1.3‐ppm peak, an increase in choline, and a decrease in creatine. The results demonstrate the potential of spectroscopic imaging in the study of intracranial tumor models in rats. © 1991 Academic Press, Inc.
Elevation in relative levels of brain membrane unsaturated fatty acids in Alzheimer's disease: High resolution proton spectroscopic studies of membrane lipid extracts
Authors: Kwee Ingrid L. , Nakada Tsutomu , Ellis William G. 
Published: March 2007

AbstractUnsaturation indices of cerebral cortex membrane phospholipids in Alzheimer's disease were determined utilizing high resolution proton nuclear magnetic resonance (NMR) spectroscopy of lipid extracts. The unsaturation index of Alzheimer's brain was found to be significantly higher (P < 0.01) than that of age‐matched controls. The study provides further support for the hypothesis that alteration in phospholipid metabolism, especially an elevation in unsaturated fatty acids, may play a role in the pathogenesis of Alzheimer's disease. © 1991 Academic Press, Inc.
Real‐time magnetic resonance imaging of laser heat deposition in tissue
Authors: Bleier Alan R. , Jolesz Ferenc A. , Cohen Mark S. , Weisskoff Robert M. , Dalcanton Julianne J. , Higuchi Nobuya , Feinberg David A. , Rosen Bruce R. , McKinstry Robert C. , Hushek Stephen G. 
Published: March 2007

AbstractWe applied diffusion‐sensitive echo planar (Instascan) imaging to study thermal changes caused by a Nd:YAG laser. Images of phantom materials and normal rabbit brain tissue in vivo, acquired in 150 ms, every 2 s, clearly showed the dynamics of temperature‐related signal intensity changes in the regions irradiated by the laser. © 1991 Academic Press, Inc.
Hepatic D‐galactosamine toxicity studied with localized in Vivo31P magnetic resonance spectroscopy in intact rats
Authors: Weisdorf Sally , Hendrich Kristy , Buchthal Steven , Wike John , Bratt Gerald , Merkle Hellmut , Garwood Michael , Uǧurbil Kâmil 
Published: March 2007

AbstractSpatially resolved 13P magnetic resonance spectroscopy (MRS) at 4.7 T was applied to noninvasively assess liver phosphorus metabolites in a biochemically well‐characterized model of hepatotoxicity induced by injection of a sublethal dose of D‐galactosamine (galN). A newly developed hybrid method based on spectral localization with B0 and B1 gradients was employed to obtain multivoxel spectra in intact anesthesized rats. Spatially localized in vivo spectra were recorded 0 to 26 h after galN injection of female rats. In response to galN exposure, diphosphodiester peaks ascribed to UDP‐hexosamines became detectable by 4 h and persisted up to 26 h. A metabolite coresonating with inorganic phosphate increased rapidly in intensity by 2 h after galN and returned to baseline by 18 h; this resonance was shown not to be Pi and was assigned to galN‐1‐phosphate by subsequent high resolution MRS experiments on extracts prepared from these livers. These results confirmed in vivo the metabolic perturbations described previously for this model of hepatotoxicity following biochemical studies based on classical extraction methods. Unlike the in vitro studies, however, these noninvasive experiments provided additional information on the time course of metabolic alterations on the same animal. © 1991 Academic Press, Inc.
Hexagonal surface gradient coil for localized MRS of the heart
Authors: Jasinski Andrzej , Kozlowski Piotr , Urbanski Andrzej , Saunders John K. 
Published: March 2007

AbstractA surface gradient coil designed to obtain localized magnetic resonance spectroscopy of the heart in vivo is described. Images and 31P spectra from phantoms and both pig and dog hearts in vivo are shown. The coil was used in conjunction with a rf surface coil to obtain 31P spectra from transmural sections of the left ventricular wall of a dog heart in vivo to demonstrate differences between normal and ischemic tissue. © 1991 Academic Press, Inc.
Localized proton NMR observation of [3‐13C] lactate in stroke after [1‐13C] glucose infusion
Authors: Rothman D. L. , Howseman A. M. , Graham G. D. , Petroff O. A. C. , Lantos G. , Fayad P. B. , Brass L. M. , Shulman G. I. , Shulman R. G. , Prichard J. W. 
Published: March 2007

AbstractTo assess whether elevated lactate in stable stroke is being actively produced from blood glucose localized 1H NMR stimulated echo spectra were obtained from a patient in the region of a 32‐day‐old cortical infarct before and 60–100 min after infusion of [1‐13C]glucose. Prior to the infusion the spectrum from the region of the infarct contained an elevated resonance from C3 lactate and a greatly reduced resonance from N‐acetyl groups relative to an unaffected contralateral region. After the infusion two additional resonances were observed at 62 and −64 Hz relative to the unlabeled resonance of C3 lactate which were assigned on the basis of chemical shift and relative intensity to[3‐13C]lactate. The [3‐13C]lactate fractional enrichment in the infarct region was measured to be 32% which is within error one‐half the average [1‐13C]plasma glucose enrichment during the postinfusion NMR measurement. The result suggests that the stroke lactate pool was completely derived from infused glucose. © 1991 Academic Press, Inc.
In Vivo measurement of cerebral oxygen consumption and blood flow using 17O magnetic resonance imaging
Authors: Pekar J. , Ligeti L. , Ruttner Z. , Lyon R. C. , Sinnwell T. M. , van Gerderen P. , Fiat D. , Moonen C. T. W. , McLaughlin A. C. 
Published: March 2007

AbstractWe used 17O NMR imaging techniques to measure the H217O concentration in a 0.8‐ml voxel in the cat brain following injection of an arterial bolus of enriched H217O and during inhalation of enriched 17O2. We also measured the H217O concentration in arterial blood during 17O2 inhalation. The data from the first measurement were used to calculate the blood flow in the voxel. The data from all three measurements were combined to calculate the oxygen consumption in the voxel. The values of cerebral blood flow and oxygen consumption calculated with 17O NMR techniques agree reasonably well with values calculated for a similar region of the cat brain using autoradiographic techniques. © 1991 Academic Press, Inc.
A clinically viable technique of fat suppression for abdomen and pelvis
Authors: Mao Jintong , Bidgood W. Dean , Ang Peter G. P. , Mancuso A. , Yan Hong 
Published: March 2007

AbstractChemical‐shift selective imaging with an improved selective presaturation pulse can be used to suppress the fat signal uniformly across the entire abdominal cavity. The required magnetic field homogeneity is no higher than for a routine diagnostic scan. Therefore, no extra setup time for shimming is needed. The technique has been implemented on our clinical system for routine fat suppression scans. © 1991 Academic Press, Inc. © 1991 Academic Press, Inc.
Fatty‐acyl iminopolycarboxylates: Lipophilic bifunctional contrast agents for NMR imaging
Authors: Kim Sung K. , Pohost Gerald M. , Elgavish Gabriel A. 
Published: March 2007

AbstractNew fatty‐acyl contrast agents, N3−2′‐myristoyloxyethyl‐ N6−2′‐hydroxyethyl‐1, 8‐dioxotriethylenetetraamine‐N, N, N′, N′ ‐tetraacetic acid (MHE‐DTTA) and N3, N6‐bis (2′‐myristoyloxyethyl)‐1, 8‐dioxo‐triethylenetetraamine‐N, N, N′, N′‐tetraacetic acid (BME‐DTTA) were prepared by sequential alkylation, acylation, and catalytic hydrogenation from bis(hydroxyethyl)‐ethylenediamine with satisfactory yields (overall 36–46%). The 1:1 gadolinium complexes of the ligands MHE‐DTTA and BME‐DTTA were incorporated into liposomes and their relaxivities in vitro were determined. The relaxivities of both agents were similar and were greater than those of Gd3+ aquoion, Gd(EDTA), and Gd(DTPA) at both 0.23 T and 0.47 T. The relaxivities of these two agents increased from the lower to the higher magnetic field, indicating a positive field dependence. This is advantageous because of the widespread use of high‐field (B0 > 0.5 T) NMR imaging instruments. Stability constants (log K) of Gd(MHE‐DTTA) and Gd(BME‐DTTA) were found to be 15.27 ± 2.21 and 16.78 ± 0.36, respectively. LD50 of both compounds was >0.2 mmol/kg. These stabilities and lower limits of LD50 indicate the possible in vivo application of these agents. © 1991 Academic Press, Inc.
High‐speed STEAM MRI of the human heart
Authors: Frahm J. , Hänicke W. , Bruhn H. , Gyngell M. L. , Merboldt K. D. 
Published: March 2007

AbstractHigh‐speed STEAM MR images of the normal human heart were obtained from single cardiac cycles using a 2.0‐T whole‐body system equipped with conventional 10 mT m−1 gradients. The single‐shot 90°‐TE/2–90°‐TM‐(α‐TE/2‐Acq)n pulse sequence acquires n differently phase‐encoded stimulated echoes. Measuring times of 127–254 ms were achieved using a “repetition time” of 3.96 ms in conjunction with data matrices of 32–64 × 128 pixels covering a field‐of‐view of 250–350 mm. The sequence provides easy access to anatomical short‐axis and long‐axis views of the heart by single and double oblique rotation of the image orientation. STEAM images resemble the features of spinecho images with respect to chemical shifts, susceptibilities, and flow. Thus, no additional techniques are required for the suppression of blood signals. EKG‐triggered acquisitions demonstrate that slice‐selective STEAM sequences using short TM intervals allow an unambiguous delineation of those parts of the myocardium that remain stationary within the selected plane throughout the entire imaging process. Neither spins leaving nor entering the slice defined by the initial 90° RF pulses give rise to a stimulated echo and therefore do not contribute to the resulting image. © 1991 Academic Press, Inc.
Echo‐planar time course MRI of cat brain oxygenation changes
Authors: Turner Robert , Bihan Denis Le , Moonen Chrit T. W. , Despres Daryl , Frank Joseph 
Published: March 2007

AbstractWhen deoxygenated, blood behaves as an effective susceptibility contrast agent. Changes in brain oxygenation can be monitored using gradient‐echo echo‐planar imaging. With this technique, difference images also demonstrate that blood oxygenation is increased during periods of recovery from respiratory challenge. © 1991 Academic Press, Inc.
High‐dose applications of gadolinium chelates in magnetic resonance imaging
Authors: Runge Val M. , Kirsch John E. , Thomas Greg S. 
Published: March 2007

AbstractAdministration of gadolinium chclates at doses greater than 0.1 mmol/kg IV can potentially improve both lesion detection and the assessment of tissue perfusion. Preliminary results are presented in clinical patients and two animal models. In human intracranial metastatic disease, administration of 0.3 (cumulative dose) mmol/kg gadoteridol (Gd HP‐DO3A) has permitted detection of additional lesions not visualized at 0.1 mmol/kg. In a rabbit model of focal liver disease, 0.5 mmol/kg IV provided superior enhancement of both normal parenchyma and lesion rim compared to doses of 0.25 and 0.1. Dynamic imaging (T1‐weighted turbo‐FLASH) immediately following bolus injection of 0.5 mmol/kg permitted direct visualization (on unsubtracted images) of an acute perfusion defect in the cat brain not visible on conventional T1‐ and T2‐weighted scans. © 1991 Academic Press, Inc.
Electromagnetic fields of surface coil in vivo NMR at high frequencies
Authors: Keltner J. R. , Carlson J. W. , Roos M. S. , Wong S. T. S. , Wong T. L. , Budinger T. F. 
Published: March 2007

AbstractA high frequency solution of the electromagnetic field produced by a circular surface coil adjacend to a homogenous conducting, dielectric sphere is used to predict the attainable signal to noise ratio (S/N) and specific absorption rate (SAR) for in vivo 1H NMR spec troscopy experiments from 200 to 430 MHz (4.7–10T). Above 200 MHz the S/N increases more rapidly with frequency and the SAR increases less rapidly compared with the respective S/N and SAR frequency dependence below 200 MHz. The difference in frequency dependence is due to dielectric resonances of the magnetic field inside the sphere at frequencies above 200 MHz. It is predicted that surface coil 1H NMR experiments may be performed on a head‐sized sphere, having conductivity and relative dielectric constant of brain, at frequencies up to 430 MHz without exceeding 8 W/kg local SAR and 3.2 W/kg SAR. The calculations of the S/N and SAR are used to determine optimum surface coil geometries for NMR experments. The power radited by the surface coil in the absence of shielding and asymmetries in the received signal with respect to the plane defined by the surface coil axix and the direction of the static magnetic field are significant at high frequency. Experimental measurements of the magnetic field inside a head‐sized sphere verfy the presence of dielectric resonances at frequencies above 200 MHz. © 1991 Academic Press, Inc.
A localized in vivo detection method for lactate using zero quantum coherence techniques
Authors: Van Dijk J. E. , Bosman D. K. , Chamuleau R. A. F. M. , Bovee W. M. M. J. 
Published: March 2007

AbstractA method is described to selectively measure lactate in vivo using proton zero quantum coherence techniques. The signal from lipids is eliminated. A surface coil and additionally slice selective localization are used. The resulting spectra demonstrate the good performance of the method. © 1991 Academic Press, Inc.
Spin‐lattice relaxation in murine tumors after in vivo treatment with interferon α/β or tumor necrosis factor α
Authors: Macrì M. A. , Casieri C. , de Luca F. , Maraviglia B. , Belardelli F. , Proietti E. , Carpinelli G. , Podo F. 
Published: March 2007

Abstract1H NMR spin–lattice relaxation times (T1) were measured in vitro and in vivo in Friend leukemia cell tumors during subcutaneous tumor growth in syngeneic mice and after in vivo administration of either purified murine interferon α/β (IFN) or recombinant tumor necrosis factor α (TNF). Untreated tumors exhibited monoexponential T1 relaxation independently of tumor age at least until Day 16 after implantation. Histological examinations showed that under these conditions tumors were highly homogeneous and substantially free of necrotic areas. Peritumoral administrations of either IFN or TNF did not significantly alter the tumor relaxation properties at early stages of inhibition of tumor growth. The longitudinal relaxation decay became instead clearly biexponential at later stages (more than 7 days of IFN treatment or 2 days after TNF administration). While the T1 relaxation behavior could be unequivocally correlated with the presence of necrotic areas in these tumors, it could not be considered as an early marker of the altered growth capability, induced by administration of either IFN or TNF. © 1992 Academic Press, Inc.