bluuebunny/crossref_metadata_2025_split huggingface dataset:
Proton‐decoupled, overhauser‐enhanced, spatially localized carbon‐13 spectroscopy in humans
Authors: Bottomley Paul A. , Hardy Christopher J. , Roemer Peter B. , Mueller Otward M. 
Published: March 2007

AbstractSpatially localized, natural abundance, carbon (13C) NMR spectroscopy has been combined with proton (1H) decoupling and nuclear Overhauser enhancement to improve I3C sensitivity up to five‐fold in the human leg, liver, and heart. Broadband‐decoupled 13C spectra were acquired in 1 s to 17 min with a conventional 1.5‐T imaging/ spectroscopy system, an auxiliary 1H decoupler, an air‐cooled dual‐coil coplanar surface probe, and both depth‐resolved surface coil spectroscopy (DRESS) and one‐dimensional phase‐encoding gradient NMR pulse sequences. The surface coil probe comprised circular and figure‐eight‐shaped coils to eliminate problems with mutual coupling of coils at high decoupling power levels applied during I3C reception. Peak decoupler RF power deposition in tissue was computed numerically from electromagnetic theory assuming a semi‐infinite plane of uniform biological conductor. Peak values at the surface were calculated at 4 to 6 W/kg in any gram of tissue for each watt of decoupler power input excluding all coil and cable losses, warning of potential local RF heating problems in these and related experiments. The average power deposition was about 9 mW/kg per watt input, which should present no systemic hazard. At 3 W input, human 13C spectra were decoupled to a depth of about 5 cm while some Overhauser enhancement was sustained up to about 3 cm depth, without ill effect. The observation of glycogen in localized natural abundance 13C spectra of heart and muscle suggests that metabolites in the citric acid cycle should be observable noninvasively using 13C‐labeled substrates. © 1989 Academic Press, Inc.
Monitoring therapeutic response of human superficial tumors using phase‐encoded spectroscopy
Authors: Majors Anthony W. , Ng Thian C. , Xue Min , Meaney Thomas F. 
Published: March 2007

AbstractA one‐dimensional phase‐encoded spectroscopy sequence was implemented on a GE 1.5‐T Signa imager and the feasibility of its application to monitor the 31P metabolities of superficial tumors was demonstrated. Serial 31P spectra of I‐cm slices with adequate signal‐to‐noise ratio and insignificant T2 weighting can be obtained in 28 min. The degree of “bleeding” effect was reduced with increased phase‐encoding steps. © 1989 Academic Press, Inc.
Proton relaxation enhancement of albumin, immunoglobulin g, and fibrinogen labeled with gd‐dtpa
Authors: Paajanen Hannu , Reisto Timo , Hemmilä Ilkka , Komu Markku , Niemi Pekka , Kormano Martti 
Published: March 2007

AbstractBovine serum albumin, immunoglobulin G, and fibrinogen were labeled with Gd‐DTPA using a bifunctional chelating agent DTPA anhydride. The protein‐(Gd‐DTPA) conjugates had 1.4‐ to 2.0‐fold greater longitudinal relaxivities at 0.02 and 0.44 T than the relaxivity of plain Gd‐DTPA. The increase of longitudinal relaxivity was not directly related to the size of carrier protein. Up to 50 Gd‐DTPA chelates per protein, longitudinal relaxivity of the conjugates was proportional to the concentration of Gd and independent of the Gd/protein ratio.
Nmr and esr study of liposome delivery of mn2+ to murine liver
Authors: Bacic G. , Niesman M. R. , Magin R. L. , Swartz H. M. 
Published: March 2007

AbstractThe mechanism of tissue relaxation of liposome‐delivered Mn2+ as a contrast agent for magnetic resonance imaging (MRI) was examined using magnetic resonance and electron spin resonance (ESR) techniques. It is known that liposomes of the size and composition used in this study are taken up by fixed liver macrophages (Kupffer cells). It was determined that Mn2+ must be released from the liposomes in order to affect the water proton relaxation rate in the liver. As long as the Mn2+ was confined to the Kupffer cells, no substantial changes in the relaxation of the majority of the liver water were observed. Unlike other contrast agents delivered to the Kupffer cells (for example, Gd‐starch microspheres or magnetite), once the Mn2+ is delivered and released into the Kupffer cells, it can diffuse from the Kupffer cells and be rapidly taken up by the hepatocytes. This seems to be the mechanism for selective relaxation enhancement in the liver. A consequence of this behavior is that the time at which maximum contrast enhancement occurs for MRI can be varied by the choice of liposome phospholipid composition. ESR techniques were used to directly determine the state of Mn2+ and the integrity of liposomes in various stages of processing.
In vivo13c nuclear magnetic resonance investigations of choline metabolism in rabbit brain
Authors: Tunggal Budi , Hofmann Kay , Stoffel Wilhelm 
Published: March 2007

AbstractThe metabolism of choline in rabbit brain was studied by the noninvasive approach of in vivo 13C NMR spectroscopy. 13C‐Enriched precursors were introduced into the brain. Surgery of the head skin was avoided through controlled localization of the surface coil. For long‐term accumulation studies in brain, repeated subcutaneous injections proved to be advantageous over other forms of application. The resorption kinetics was calculated to be zero order which suggests slow delivery from the subcutaneous depots. Choline metabolism was studied by two approaches: [N‐13CH3] choline and S‐[ 13CH3 ] methionine were administered separately to adult and myelinating rabbits (Days 5 to 32), respectively, over 4 weeks. [ N‐ 13CH3] Choline and the 13CH3 group of methionine were incorporated into lecithin and sphingomyelin of brain myelin. In vivo kinetic studies of the turnover of these labeled structures were carried out. Choline and methionine are readily transported through the blood‐brain barrier and utilized by the myelinating brain for the biosynthesis of its phospholipids.
Investigations concerning the potential for using 1h nmr relaxometry or high‐resolution spectroscopy of plasma as a screening test for malignant lung disease
Authors: Schuhmacher Jochen H. , Conrad Dorothea , Manke Hans G. , Clorius John H. , Matys Edmund R. , Hauser Harald , Zuna Ivan , Maier‐Borst Wolfgang , Hull William E. 
Published: March 2007

AbstractIn 158 plasma samples, obtained from patients with lung carcinoma, lung metastases, and infectious or inflammatory lung diseases and from healthy controls, the NMR relaxation times T1, and T2 of water protons were measured at a resonance frequency of 20 MHz by pulsed NMR techniques and adjusted to a standardized total plasma protein concentration. For one‐third of these samples water‐suppressed 500‐MHz 1H NMR spectroscopy at 37°C was used (a) to determine the widths of the composite lipid methyl and methylene signals, and (b) to quantitate individual lipid methylene signal components that could be detected in resolution‐enhanced spectra. In addition, hematological parameters and the plasma levels of several acute phase proteins and apolipoprotein‐A were monitored. No diagnostically significant differences between lung carcinoma patients and patients with nonmalignant lung disease could be found for any of the plasma NMR parameters, nor could T1, or lipid line width data distinguish between any patient group and healthy controls. However, the mean T2, was significantly shortened by about 15% for any kind of lung disease compared to healthy controls. Similar but less significant results were found for apolipoprotein‐A levels. A linear discriminant function, calculated from the apolipoprotein‐A and T2, data, did not improve the differentiation between malignant and nonmalignant lung disease but did improve the discrimination between tumor patients and healthy controls up to a sensitivity and specificity of 80 and 96.5%, respectively. T, correlates inversely with plasma fibrinogen levels and the blood sedimentation rate and, therefore, appears to monitor a general inflammatory status of a tumor patient rather than the presence or absence of cancer. For all groups except healthy pregnant women, the lipid methylene composite signal line width correlates inversely with the fraction of mobile triglyceride present (mainly as VLDL), as estimated from resolution‐enhanced spectra.
0.3‐second flash mri of the human heart
Authors: Frahm J. , Merboldt K. D. , Bruhn H. , Gyngell M. L. , Hänicke W. , Chien D. 
Published: March 2007

AbstractFlow‐suppressed FLASH MR images of the human heart have been recorded within a measuring time of 0.3 s using a 2.0‐T whole‐body research system (Siemens Magnetom) equipped with a conventional 10 mT m−1 gradient system. Subsecond imaging times have been achieved by reducing the repetition time to TR = 4.8 ms and by lowering the spatial resolution to 64 × 128 measured data points. The flip angle of the slice‐selective radiofrequency (rf) pulses was adjusted to 10o. Cardiac chambers, ventricular walls, and valves are well delineated in images from a single cardiac cycle using a field of view of 250 mm and a slice thickness of 8 mm. No motion artifacts were observed as a consequence of the short echo time of TE = 2.8 ms. Distinction between flowing blood and solid structures has been achieved by spatial presaturation of adjacent slices using two slice‐selective 90° rf pulses preceding the entire imaging sequence.
Optimization of survey protocols for mri
Authors: Mcveigh Elliot R. , Mark Henkelman R. , Bronskill Michael J. 
Published: March 2007

AbstractA method for evaluating the sensitivity of MRI protocols to changes in an arbitrary number of tissue parameters over a broad range of parameter values is presented. This analysis is useful for choosing an optimal basis set of images for either a “survey” protocol or tissue segmentation algorithms. A survey protocol is required when searching for a lesion of unknown type or location. Segmentation requires unique signal signatures for tissues that may cover a broad range of tissue parameter values. Data acquisition is modeled as a mapping of a domain of tissue parameter values into a signal manifold in a signal strength space defined by the MRI protocol. The efficacy of the protocol is evaluated by investigating the characteristics of the signal manifold. A figure of merit which maximizes the probability of discriminating each point in the domain of tissue parameters from all others is developed.
The use of laboratory microcomputers to hold nmr data bases
Authors: Moore T. A. , Morris P. G. 
Published: March 2007

AbstractComputer‐based data bases are essential tools for NMR spectroscopists working with complex mixtures such as tissue extracts. Algorithms are described which are easily implemented on a small laboratory microcomputer and which can be used to make, edit, and query personalized laboratory data files. The data are stored in a series of small files accessed by pointers to overcome inherent redundancy in the information. Performance times are tabulated for a BBC Model B microcomputer working in the BASIC language and using 5.25‐in. floppy discs as virtual memory.
1h nmr observation of tissue myoglobin: an indicator of cellular oxygenation in vivo
Authors: Jue T. , Anderson S. 
Published: March 2007

AbstractCellular oxygen status is a critical parameter. To measure the oxygen tension in vivo, however, demands extant techniques to surmount two experimental difficulties: invasive experimental protocols and imprecise tissue localization. NMR techniques have the potential to overcome these obstacles. Indeed we show in this study that cellular myoglobin is NMR visible and its proximal histidyl NH signal in the deoxy state can be used to monitor changes in cellular oxygenation. Coupled with recent advances in NMR signal localization, this 1H NMR strategy promises to lead directly to cellular oxygen measurement in specific tissue regions in vivo.
Why MEM does not work in MR image reconstruction
Authors: Constable R. T. , Henkelman R. M. 
Published: March 2007

AbstractThis paper discusses the theory and application of the Maximum Entropy Method (MEM) to the reconstruction of Magnetic Resonance (MR) images. It is shown that the MEM is inappropriate for MR image reconstruction and that the usual heuristic justification is invalid in this case. The application of the MEM in MR image reconstruction is characterized as merely one of many constrained regularization approaches. © 1990 Academic Press, Inc.
CNR enhancement in the presence of multiple interfering processes using linear filters
Authors: Brown D. G. , Lee J. N. , Blinder R. A. , Wang H. Z. , Riederer S. J. , Nolte L. W. 
Published: March 2007

AbstractGiven several images of the same slice, a linear filter can produce an image in which the contrast‐to‐noise ratio (CNR) between pathological and normal tissues is greater than in any of the initial images. To distinguish the pathology from more than one tissue, the filter should optimize the set of CNRs between the pathology and each of the interfering tissues. We define the optimal filter as the one which provides the largest value for the minimum CNR in the set and show how it is selected from a field of only four possibilities. The filter is demonstrated with both experimental phantom studies and clinical cases. Filter performance is compared with that of other techniques for distinguishing a desired feature from more than one interfering process. © 1990 Academic Press, Inc.
Analysis of T2 limitations and off‐resonance effects on spatial resolution and artifacts in echo‐planar imaging
Authors: Farzaneh Farhad , Riederer Stephen J. , Pelc Norbert J. 
Published: March 2007

AbstractSeveral aspects of blipped echo‐planar imaging (EPI) are treated mathematically. An expression relating the necessary readout gradient strength and sampling time to the spatial resolution and readout duration is derived. It is shown how the net spatial resolution may be limited by the object's T2 characteristics and Bo field homogeneity, irrespective of the number of sampled points. Additionally, off‐resonance effects result in a loss of spatial resolution and image distortion to a considerably greater degree than in conventional two‐dimensional Fourier transform imaging. The extent of these effects is directly related to the time required to acquire the data matrix, and is therefore amplified when EPI is implemented on a standard commercial whole‐body system which because of limited gradient performance uses necessarily longer sampling durations. Specific hardware modifications to a standard commercial imager are considered to allow successful EPI implementation. EPI image characteristics are compared quantitatively with those of conventional methods. © 1990 Academic Press, Inc.
A13C NMR study of the application of [U‐13C] succinate for metabolic investigations in rabbit renal proximal convoluted tubular cells
Authors: Jans Arnold W. H. , Willem Rudolph 
Published: March 2007

AbstractThe fate of the 13C label arising from [ U‐13C ] succinate in rabbit renal proximal convoluted tubular (PCT) cells, incubated with [U‐13C]succinate, was investigated by 13C NMR spectroscopy of the perchloric acid extracts of the cell pellets. The 13C label of [U‐13C] succinate was predominantly metabolized into glutamate, glutamine, and into glucose, lactate, and alanine, which is the consequence of a carbon efflux of the label from the Krebs cycle at the stage of α‐ketoglutarate and oxaloacetate, respectively. © 1990 Academic Press, Inc.
Flow artifact reduction in MRI: A review of the roles of gradient moment nulling and spatial presaturation
Authors: Ehman Richard L. , Felmlee Joel P. 
Published: March 2007

AbstractIn the past, flow artifacts and inconsistent depiction of vascular anatomy have represented significant problems in clinical MRI. These difficulties are now generally well addressed by the techniques of gradient moment nulling and spatial presaturation. Gradient moment nulling (GMN) is an effective method for eliminating flow artifacts in gradient echo images, while presaturation is more applicable to the same task in spin echo acquisitions. The GMN technique also has useful applications in spin echo imaging such as combating the effects of tissue and CSF motion in long TE sequences. In contrast to presaturation, however, GMN is not suitable for suppressing artifacts due to pulsatile blood flow in spin echo images. © 1990 Academic Press, Inc.
Moving average improves the signal‐to‐noise ratio of kinetic studies in magnetic resonance spectroscopy
Authors: Seguin F. , Berthiau F. , Le Pape A. , Grivet J. P. 
Published: March 2007

AbstractMoving average can be used to improve the signal‐to‐noise ratio of NMR kinetic studies. The method was tested on simulated spectra with time‐dependent intensities or peak positions. It was then applied to a series of in vivo spectra, showing the pharmacological effect of heptaminol on the intracellular pH of perfused hearts. © 1990 Academic Press, Inc.
31P NMR studies of ATP concentrations and Pi–ATP exchange in the rat kidney in Vivo: Effects of inhibiting and stimulating renal metabolism
Authors: Shine Nancy , Xuan Ai , Weiner Michael W. 
Published: March 2007

AbstractPrevious investigators found that cyanide (CN−) is a potent inhibitor of renal Na+ transport, while the uncoupling agent 2,4‐dinitrophenol (DNP) and fructose (both which lower ATP levels) are weak transport inhibitors. To examine the disparate effects of these substances measurements of ATP were performed, using 31P NMR, while simultaneously monitoring renal Na+ transport. Infusion of CN−, DNP, and fructose lowered whole kidney ATP levels by about the same extent (30%) while only CN− inhibited Na+ transport. This may be due to the fact that CN− has a potent action on the thick ascending limb of Henle, while fructose and DNP may have a more proximal action. Alternatively, ATP turnover may be a more important determinant of transport than ATP concentrations. Saturation transfer experiments were performed to measure Pi–ATP flux. Unilateral nephrectomy, high protein feeding, and methylprednisolone were used to stimulate metabolism and transport. The rate of Pi‐ATP flux was 20.1 μmol/min/g. However, because oxygen consumption was stimulated, the ATP/O ratio was 0.85, considerably less than the theoretical value of 3. Finally, atrial natriuretic factor, which increased Na+ transport, had no effect on Pi‐ATP flux. The results raise the possibility that the saturation transfer technique does not detect all Pi‐ATP flux, especially when renal metabolism is Stimulated. © 1990 Academic Press, Inc.
Real‐time interactive magnetic resonance imaging
Authors: Holsinger Anna E. , Wright Ronald C. , Riederer Stephen J. , Farzaneh Farhad , Grimm Roger C. , Maier Joseph K. 
Published: March 2007

AbstractWe describe a system for performing interactive MRI in real time. Using a TR/TE 7.1/ 3.5 ms sequence, the operator may alter a scan parameter and observe the effects of the alteration on the image within a few hundred milliseconds. With this system, we can interactively control the oblique scan slice orientation and, using inversion pulses, the image Contrast. © 1990 Academic Press, Inc.
3‐D MR angiography with scanning 2‐D images—simultaneous data acquisition of arteries and veins (SAAV)
Authors: Kim J. H. , Cho Z. H. 
Published: March 2007

AbstractA 3‐D MR angiography using a scanning 2‐D planar imaging technique with the 90° flip angle steady‐state free precession sequence is presented. This method, in essence, is the rapid scanning of 2‐D images to form a 3‐D volume image. The method is then extended to the simultaneous acquisition of the separated images of the arteries and veins. Using the proposed method a set of separate angiograms of 3‐D artery and vein of a volunteer's head of imaging volume of 220 × 220 × 120 mm was obtained with total imaging time of 16.5 min. © 1990 Academic Press, Inc.
In vivo MRS measurement of deoxymyoglobin in human forearms
Authors: Wang Zhiyue , Noyszewski Elizabeth A. , Leigh John S. 
Published: March 2007

AbstractIn vivo MRS measurement of deoxymyoglobin (deoxy‐Mb) in human forearms was performed by observing the N‐δ proton of F8 proximal histidine. The concentration of deoxy‐Mb reflects the oxygen level in the muscle. In resting muscles, the deoxy‐Mb level was below the detection sensitivity. When ischemia was introduced by arterial occlusion, the time‐resolved NMR spectra (with 1 min resolution) was recorded to follow the change in the deoxy‐Mb signal. The result shows that deoxy‐Mb signal builds up and levels off within 6 min. This technique may be used to study bioenergetics of muscle during exercise and under pathological conditions. © 1990 Academic Press, Inc.
Measurement of ATP synthesis rates by 31P‐NMR spectroscopy in the intact myocardium in vivo
Authors: Robitaille Pierre‐Marie , Merkle Hellmut , Sako Edward , Lang Gregory , Clack Rose Marie , Bianco Richard , From Arthur H. L. , Foker John , Uǧurbil Kǎmil 
Published: March 2007

AbstractThe ability to measure ATP synthesis rates using 31P‐NMR spectroscopy is demonstrated in the normal, ischemic, and postischemic myocardium in vivo. Cardiopulmonary bypass (CBP) was employed to induce 20 min of global myocardial ischemia, and to conduct magnetization transfer measurements during the ischemic episode and following reperfusion and return to normal circulation. For the first few minutes of ischemia, transfer of magnetization from ATPγ to P1 was extensive and the resultant fractional reduction (ΔM/Mo) in the Pi resonance intensity reached approximately 100%. Subsequent to reperfusion and stabilization off CPB and on normal circulation, both the fractional reduction and the spin‐lattice relaxation time, T, of the Pi resonance were determined when ATP, spins were saturated. Under these conditions, the unidirectional ATP synthesis rate was 0.41 ± 0.09 (SEM, N = 4) μmol/s/g wet wt. The data suggest that in the canine myocardium in vivo, glycolytic enzymes mediate a very rapid exchange between Pi and ATP γ‐phosphates during early phases of ischemia; in the postischemic reperfused myocardium, however, the glycolytic contribution to the unidirectional Pi → ATP rate measured by NMR in vivo is relatively small compared to that observed in glucose‐perfused, postischemic rat hearts. © 1990 Academic Press, Inc.
Effect of repetitive brief episodes of cardiac ischemia on 31P magnetic resonance spectroscopy in the cat
Authors: Holt William W. , Wendland Michael F. , Derugin Nikita , Finkbeiner Walter E. , Higgins Charles B. 
Published: March 2007

AbstractAngina is characterized by brief periods of ischemia followed by reperfusion; the cumulative effect of these episodes on energetics of the myocardium has not been fully elucidated. This study used an in vivo feline model for the assessment of high‐energy phosphate compounds during brief sequential periods of ischemia and reperfusion. Nine adult, open‐chest, anesthetized cats were prepared with a reversible occluder around the proximal left anterior descending artery and a 1.2‐cm‐inside diameter coil sutured on the myocardial surface in the distribution of the left anterior descending coronary artery. Levels of PCr, Pi and ATP (β‐phosphate signal) were measured by 31P MRS in a GE CSI 2‐T NMR spectrometer/imager. Measurements were obtained during a control period and during three successive occlusion‐deocclusion periods of roughly 12 and 20 min' duration, respectively. The last deocclusion period was observed for 60 min. Electron microscopy was performed in two animals. PCr declined (P < 0.01) rapidly following each occlusion to 51 ± 5.2% (occlusion 1), 53 ± 5.8% (occlusion 2), and 48 ± 5.7% (occlusion 3) of the control value by 6 min. Pi rose (P < 0.01) with the three sequential occlusions to 253 ± 46, 288 ± 57, and 277 ± 46%, respectively. PCr and Pi returned to baseline promptly with reperfusion, while ATP showed a gradual decline throughout the experiment, decreasing to 77 ± 7.2% of control at the end of the last reperfusion (P < 0.05). Although PCr returned to baseline during reperfusion, ATP did not, suggesting a reduction in the nucleotide pool. These findings indicate that the repeated episodes of ischemia, which are insufficient to produce necrosis, can have an effect on myocardial high‐energy phosphate metabolism as evidenced by mild depletion of ATP. © 1990 Academic Press, Inc.