bluuebunny/crossref_metadata_2025 huggingface dataset:
The center‐tapped slotted tube autotransformer resonator: A coil for use with a high‐resolution small animal imaging system
Authors: Martin M. , Lemaire C. , Tatton W. G. , Armstrong R. L. , Struk R.
Published: March 2007

A radiofrequency (rf) coil design based on a slotted tube resonator which allows highresolution imaging of the rodent brain with excellent anatomic definition on a standard G.E. CSI II 2.0‐T MR imaging unit with no modification of existing apparatus is described. The coil is easily constructed and permits very rapid tuning to different loading conditions, allowing a high sample throughput. © 1988 Academic Press, Inc.
Stability constants for Gd3+ binding to model DTPA‐conjugates and DTPA‐proteins: Implications for their use as magnetic resonance contrast agents
Authors: Sherry A. Dean , Cacheris William P. , Kuan Kah‐Tiong
Published: March 2007

Five DTPA‐amide and ester derivatives have been synthesized and their Gd3+ stability constants have been measured using a simple spectrophotometric method. These results are compared to stability constants measured for Gd3+ binding to two different DTPA‐conjugated proteins. Although the thermodynamic constants for Gd3+ binding to DTPA‐monopropylamide and DTPA‐monopropvlester relative to Gd( DTPA)2− decrease by log K = 2.6 and 3.4, respectively, the blood pH conditional constants differ from Gd( DTPA)2− only by log K = 1.2 and 1.9, respectively. The corresponding diprooylamide and ester conjugates of DTPA show considerably lower thermodynamic and conditional constants. This has important implications in the covalent attachment of chelates to macromolecules for use in magnetic resonance imaging. The measured binding constants for Gd(DTPA)‐IgG and Gd( DTPA)‐BSA suggest that many of the DTPA molecules in these systems, prepared under our experimental conditions, are diconjugated. The model compound results indicate that it is important to use methods in attaching DTPA to macromolecules which preclude diconjugation of the chelate. Otherwise, their affinity for Gd3+ and consequently their usefulness as MRI contrast agents may be severely compromised. © 1988 Academic Press, Inc.
Use of magnetic resonance imaging to identify changes in cerebral blood flow in epilepsia partialis continua
Authors: Fish D. R. , Brooks D. J. , Young I. R. , Bydder G. M.
Published: March 2007

The use of a phase mapping technique for detection of brain perfusion is described. The method was used in a patient with epilepsia partialis continua and displayed an area of abnormal perfusion in the frontal lobe during the ictal phase. Following improved treatment the perfusion pattern was near normal 12 weeks later. © 1988 Academic Press, Inc.
Spin probe reduction in cells and tissues
Authors: Kveder Marina , Sentjurc Marjeta , Schara Milan
Published: March 2007

The reduction rates of different nitroxides in rat lung tissue were measured by electron paramagnetic resonance. We confirmed that the reduction rate of nitroxide spin probe molecules is coupled with their structure and transport characteristics. Oxygen was found to slow down the reduction rate of nitroxides in rat lung tissues. On the basis of these findings it can be concluded that most nitroxide properties described for homogeneous systems—cells and tissue homogenates—are also valid for heterogeneous systems, which is important for the application of nitroxides as metabolically active NMR contrast agents. © 1988 Academic Press, Inc.
Simultaneous multislice acquisition of MR images
Authors: Weaver John B.
Published: March 2007

The simultaneous multislice technique is a method of imaging multiple parallel slices with the number of echoes normally used to image a single slice. Images of 16 slices have been obtained from a single 128‐echo acquisition. The distance between the slices can be decreased to approximately 15% of the field of view in the readout direction with the cost of significant image blurring. The image blurring is negligible when the distance between the slices approaches the field of view in the readout direction. The trade‐offs are de‐ scribed, and equations and images are presented. © 1988 Academic Press, Inc.
Gastrointestinal contrast agents: A diamagnetic approach
Authors: Listinsky Jay J. , Bryant Robert G.
Published: March 2007

The clay minerals kaolin and bentonite are demonstrated as gastrointestinal contrast agents for MRI. Weak field dependence of the relaxation efficiency assures effectiveness of these agents at all field strengths in clinical use. These agents eliminate signals from their immediate environment and are not toxic. © 1988 Academic Press, Inc.
SLIM: Spectral localization by imaging
Authors: Hu Xiaoping , Levin David N. , Lauterbur Paul C. , Spraggins Thomas
Published: March 2007

Nonspectroscopic magnetic resonance (MR) imaging often shows that a slice is composed of several compartments, each of which can be assumed to have a spatially homogeneous magnetic resonance spectrum, e.g., a limb composed of fat, muscle, bone marrow, and tumor. We show how to use structural information from such a nonspectroscopic image in order to increase the efficiency of subsequent localized spectroscopic measurements. Specifically, knowledge of the boundaries of N compartments makes it possible to reconstruct compartmental spectra from spectroscopic signals from an entire cross section with N or more different degrees of phase encoding. Experimental studies of a two‐compartment phantom show that this method (SLIM) can be used to derive regional hydrogen spectra of a single slice from signals with as few as 2 phase‐encoding steps, although Fourier transform chemical‐shift imaging requires 64 steps to achieve a result of comparable accuracy. SLIM required only 16 phase‐encoding steps to obtain accurate regional single slice spectra in a human limb with three compartments. Spectra of similar quality, obtained by Fourier transform chemical‐shift imaging, required 256 to 1024 Steps. © 1988 Academic Press, Inc.
Maximum Entropy and 2DFT NMR images
Authors: De Simone B. C. , De Luca F. , Maraviglia B.
Published: March 2007

A comparison between contrast and signal‐to‐noise ratio (SNR), as obtained by both maximum entropy (ME) and 2DFT reconstruction, is reported for NMR images. Our results show that in the ME elaboration the contrast and SNR are generally increased with respect to the 2DFT elaboration. The magnitude of such an increase depends on the ME statistical parameter and also, quite strongly, on the values of contrast and SNR of the 2DFT image. © 1988 Academic Press, Inc.
Fat suppression in the time domain in fast MR imaging
Authors: Szumowsiu J. , Plewes D. B.
Published: March 2007

Two gradient‐recalled lipid suppression sequences are proposed. A two‐excitation sequence cycles the TE interval between excitations to alter the lipid phase which is fol‐lowed by complex subtraction. A four‐excitation variant which improves the extent of lipid suppression by partially compensating for errors resulting from spin‐spin relaxation and Bo inhomogeneities is outlined. © 1988 Academic Press, Inc.
Calibrated uncoupling of tightly coupled concentric surface coils for in vivo NMR
Authors: Bendall M. Robin
Published: March 2007

Three known active methods of detuning rf coils have been tested by determining the efficiency of uncoupling two concentric transmit surface coils in a double‐coil probe. In a comparison at 80 MHz, the method based on the use of δ/4 cables was found to have advantages. These methods utilize the introduction of an additional resonance at the frequency of interest to completely detune a coil. By offsetting the detuning of the coil (by offsetting the additional resonance) a calibrated fraction of the rf field of the detuned coil can be added to or substracted from the rf field of the neighboring coil. © 1988 Academic Press, Inc.
Nuclear magnetic relaxation studies of the compartmentalized water in crosslinked polymer gels
Authors: Murase Norio , Watanabe Tokuko
Published: March 2007

Nuclear magnetic relaxation measurements of water in gels made of crosslinked dextran or polyacrylamide (water content, 30‐60 wt%) were carried out using broad‐line proton‐pulsed NMR. Both T1 and T2 values showed inflection against pore size, i.e., the size of the compartment made by crosslinks of the polymer gels. T2 (or T1) values obtained for gels with compartments smaller than the critical size remained low within the range of the water content used in this experiment. Those values of gels with larger compartments, on the other hand, became higher with increasing size. When the size of the compartment was larger than the critical size, T1 and T2 values also became higher with increasing water content. The inflection point can be considered to correspond to the critical compartment size below which the motion of compartmentalized water in gels is more or less restricted. When the compartment is small, however, not only the effect of the molecular motion of water but also that of the proton exchange between compartmentalized water and gel matrix or hydration water should be taken into consideration for the interpretation of the short relaxation times observed, especially by T2. The results obtained in this investigation might provide useful information in the explanation and evaluation of the relaxation values in tissue. © 1989 Academic Press, Inc.
Localized high‐resolution proton NMR spectroscopy using stimulated echoes: Initial applications to human brain in vivo
Authors: Frahm J. , Bruhn H. , Gyngell M. L. , Merboldt K. D. , Hänicke W. , Sauter R.
Published: March 2007

Water‐suppressed localized proton NMR spectroscopy using stimulated echoes has been successfully applied to detect metabolites in the human brain in vivo. The STEAM spectroscopy sequence allows single‐step localization by exciting three intersecting slices. Water suppression is achieved by preceding chemical‐shift‐selective (CHESS) rf pulses. High‐resolution (0.05 ppm) proton NMR spectra of healthy volunteers have been obtained on a conventional 1.5‐T whole‐body MRI system (Siemens Magnetom). Volumes‐of‐interest (VOI) of 64 ml(4 × 4 × 4 cm3) were localized in the occipital area of the brain and spectra were recorded within measuring times ranging from I s (single scan) to about 10 min. The experimental procedure is described in detail. Resonance assignments include acetate, N‐acetyl aspartate, γ‐amino butyrate, glutamine, glutamate, aspartate, creatine and phosphocreatine, choline‐containing compounds, taurine, and inositols. Cerebral lactate was found to be at a maximum concentration of 0.5 mM when assuming N‐acetyl aspartate in white matter to be 6 mM. © 1989 Academic Press, Inc.
Cerebral metabolism in man after acute stroke: New observations using localized proton NMR spectroscopy
Authors: Bruhn H. , Frahm J. , Gyngell M. L. , Merboldt K. D. , Hänicke W. , Sauter R.
Published: March 2007

Localized proton NMR spectroscopy at 1.5 T using stimulated echoes has been applied to study metabolic alterations in the postischemic phase of patients with acute cerebral infarction. A complete depletion of N‐acetyl aspartate in the area of infarction has been observed in a patient studied 4 days after stroke. This finding was paralleled by a dramatic increase in the concentration of lactic acid to about 16 mM within the lesion, indicating continued anaerobic glycolysis. The diluting effect of the edema has been estimated to reduce average metabolite concentrations by about a factor of 3. © 1989 Academic Press, Inc.
A model of the temperature rise in the head due to magnetic resonance imaging procedures
Authors: Athey T. Whit
Published: March 2007

A simple model of power deposition in the head is presented in which the temperature increase in the head in general and, in particular, in a small spherical region of unperfused tissue contained within the head is calculated. The result of the calculation provides a limit on the SAR needed to ensure that a 1°C temperature rise is not exceeded for unperfused spheres of different sizes, imaging sessions of different lengths of time, and different blood flow rates to the head. The model assumes that the rest of the body during a head imaging session can act as a perfect heat sink at 37°C. The model suggests that current practices in MRI imaging will not cause a temperature rise in the center of small unperfused regions such as the eye of more than 1°C. © 1989 Academic Press, Inc.
An analysis of magnetic cross‐relaxation between water and methylene protons in a model system
Authors: Gore J. C. , Brown M. S. , Armitage I. M.
Published: March 2007

Experiments have been performed to demonstrate and quantify cross‐relaxation between water and methylene resonances in a simple model system. Inversion recovery experiments on aqueous solutions of polyethylene glycol produce a transient nuclear Overhauser effect that alters the recovery of the methylene resonance. The relevant equations and parameters that describe this effect are identified and their values are explicitly quantified by analyzing the experimental results. It is shown that cross‐relaxation is measurable and significant in this system even though there are no strong hydrophilic interactions available to immobilize water. In studies of dog bile, the water and lipid resonances behave in a qualitatively similar fashion, lending support to the contention that cross‐relaxation cannot be neglected in solutions of biological macromolecules. © 1989 Academic Press, Inc.
Reversibility of chronic alcohol cardiac depression: 31P magnetic resonance spectroscopy in hamsters
Authors: Auffermann Wolfgang , Wu Shao , Parmley William W. , Higgins Charles B. , Wikman‐Coffelt Joan
Published: March 2007

In order to investigate the reversibility of chronic alcohol cardiac depression, hamsters were fed with 50% ethanol for 3 1/2 months, reaching serum alcohol levels of 0.13 ± 0.11 g/dl (mean ± SD). Alcohol was then withdrawn for 2 days. Isolated hearts were perfused according to a modified Langendorff method. Energy metabolites were studied using 31P magnetic resonance spectroscopy of isolated perfused hearts standardized by HPLC analysis of freeze‐clamped tissue. Total intracellular calcium [Ca2+]i, was measured with atomic absorption spectrophotometry, marking the extracellular space in vivo with K(CoEDTA). In alcohol‐treated hamster hearts developed pressure was significantly depressed compared to controls. End‐diastolic pressure was significantly increased. Coronary flow was not changed, whereas oxygen consumption and high‐energy phosphate levels were significantly depressed. Intracellular pH was significantly decreased. [Ca2+]i, was significantly increased. Heart weights were significantly lower. After alcohol withdrawal ventricular function, high‐energy phosphate levels, and [Ca2+]i were not significantly different from control. The results indicate that chronic alcohol consumption depresses ventricular function and energy levels and also leads to myocardial acidosis. The increase in intracellular calcium likely causes mitochondrial dysfunction. Withdrawal of alcohol is associated with reversibility of functional and energetic cardiac depression. © 1989 Academic Press, Inc.
MRI of “diffusion” in the human brain: New results using a modified CE‐FAST sequence
Authors: Merboldt Klaus‐Dietmar , Bruhn Harald , Frahm Jens , Gyngell Michael L. , Hänicke Wolfgang , Deimling Michael
Published: March 2007

“Diffusion‐weighted” MRI in the normal human brain and in a patient with a cerebral metastasis is demonstrated. The method employed was a modified CE‐FAST sequence with imaging times of only 6‐10 s using a conventional 1.5‐T whole‐body MRI system (Siemens Magnetom). As with previous phantom and animal studies, the use of strong gradients together with macroscopic motions in vivo causes unavoidable artifacts in diffusion‐weighted images of the human brain. While these artifacts are shown to be considerably reduced by averaging of 8‐16 images, the resulting diffusion contrast is compromised by unknown signal losses due to motion. © 1989 Academic press, Inc.
MRI Measurement of Hepatocyte Toxicity Using the New MRI Contrast Agent Manganese Dipyridoxal Diphosphate, a Manganese/Pyridoxal 5‐Phosphate Chelate
Authors: Young Stuart W. , Simpson Beverly B. , Ratner Adam V. , Matkin Chantal , Carter Edward A.
Published: March 2007

This study reports the first in vivo results using an MR contrast agent manganese dipyridoxal diphosphate (Mn‐DPDP) designed to estimate the functional status of the hepatocyte. Thirty New Zealand white rabbits were studied in groups of 5 as follows: No. 1, control, MRI scans only; No. 2 MRI before and up to 90 min following 50 μmol/kg of Mn‐DPDP iv; No. 3, rabbits received 9.3 g ethanol/kg and MRI; No. 4, as in No. 3 but following Mn‐DPDP; No. 5, MRI as in No. 2 but 18 h. following 1000 mg/kg Dgalactosamine used to induce hepatocyte necrosis; and No. 6, rabbits received D‐galactosamine and Mn‐DPDP. In this study significant ethanol‐and D‐galactosamine‐induced hepatocyte damage was indicated by the increased SGPT serum levels in the rabbit. The use of Mn‐DPDP allowed detection of early hepatocyte necrosis in these animals whereas conventional spin‐echo MRI did not. The fact that D‐galactosamine curves with and without Mn‐DPDP were not significantly different indicated virtually no membrane transport or metabolism of Mn‐DPDP in the liver. Ethanol curves were not normal, but there was still considerable residual Mn‐DPDP metabolism. Mn‐DPDP appears to be an attractive agent in assessing hepatocyte function. © 1989 Academic Press, Inc.
Improvements in MR Angiography Using Phase‐Corrected Data Sets
Authors: Chenevert Thomas L. , Fechner Klaus P. , Gelblum Daphna Y.
Published: March 2007

The objective of this work is refinement of an MR angiography technique via postprocessing removal of phase errors which inhibit static signal subtraction. Projective views of the object are obtained using interleaved flow‐compensated and noncompensated gradient waveforms. Complex subtraction of data sets is required since a projection dephase pulse is used for static signal suppression. This renders the difference image susceptible to systematic phase errors which are modeled asa smoothly varying multiplicative phase function. The error function is estimated by comparison of heavily spatial filtered renditions of the object acquired without projection dephasing in order to minimize influence of flow. The phase correction is then applied to high‐resolution data sets collected with projection dephasing to enhance flow sensitivity. The technique is demonstrated by improvement of MR angiograms of rats acquired on a 2‐T, 31‐cm‐bore system. © 1989 Academic Press. Inc.
Simultaneous Multislice imaging (SIMUSIM) for improved cardiac imaging
Authors: Müller S.
Published: March 2007

In conventional ECG gated multislice imaging of the heart, slice position and phase in the heart cycle are not independent parameters. This drawback is removed by simultaneous imaging of multiple slices. This paper describes a technique which is based on simultaneous excitation of several slices by multifrequency selective rf pulses. In comparison to conventional cardiac multislice imaging an improved quality of heart images is obtained, because more acquisitions are attributed to the MR signal of the slices. The gain in signal‐to‐noise ratio per measurement time increases with the square root of the number of slices investigated simultaneously. This is demonstrated using phantom experiments and cardiac images. © 1989 Academic Press, Inc.
Preliminary results of nuclear magnetic resonance studies of healthy human saliva
Authors: Coudert J. L. , Lissac M. , Teyssier R. , Bejat C. , Magnin P. , Peyrin J. O. , Bene G. J.
Published: March 2007

Relaxation times T1 and T2 of water protons for stimulated and unstimulated parotid and submandibular saliva from healthy patients were measured in the conventional way using the Bruker PC 20 Minispec. Some measurements of dispersion were also carried out. An interpretation of the average values for T1 and T2, observed in the 20 MHz range is proposed for these types of saliva in relation to biochemical composition (total proteins, amylase activity, sialic acids and hexosamins) and viscosity. For parotid saliva T−12−T−11 correlates significantly with amylase activity. In the submandibular saliva T−12−T−11 correlates significantly with both mucins and α‐amylase activity. © 1989 Academic Press, Inc.
1H and 31P NMR measurement of cerebral lactate, high‐energy phosphate levels, and pH in humans during voluntary hyperventilation: associated EEG, capnographic, and doppler findings
Authors: van Rijen P. C. , Luyten P. R. , Van der Sprenkel J. W. Berkelbach , Kraaier V. , van Huffelen A. C. , Tulleken C. A. F. , den Hollander J. A.
Published: March 2007

In order to explore the sensitivity of spatially resolved 1H and 31P NMR spectroscopy on a whole‐body NMR instrument, cerebral metabolic changes in human volunteers were measured during hyperventilation provocation. During hyperventilation the flow velocity in the middle cerebral artery decreased significantly and the EEG showed a marked increase in slow activity. 1H NMR spectra revealed an increase in cerebral lactate concentration. 31P NMR spectra showed no changes in ATP or PCr peak heights, but a shift toward tissue alkalosis was derived from changes in Pi chemical shift. During subsequent recovery, lactate concentration decreased and a slight intracellular acidosis was detected. In three experiments broadening of the lactate resonance peak resulted in separation into two components at 1.32 and 1.48 ppm, in which the latter signal possibly arose from alanine. © 1989 Academic press. Inc.
Missing pulse steady‐state free precession
Authors: Patz S. , Wong S. T. S. , Roos M. S.
Published: March 2007

A fast imaging technique, missing pulse steady‐state free precession (MP‐SSFP), is described. MP‐SSFP is one of a class of steady‐state free precession techniques in which every nth RF pulse is missing. MP‐SSFP has been implemented for the case where every third RF pulse is omitted: {‐θ1,‐τ‐θ2‐echo‐τ‐}. A RF‐refocused echo forms at the time of the missing pulse. This echo is less sensitive to field inhomogeneities than the gradient‐recalled echoes used in most fast imaging methods. An analytical expression is obtained for the signal strength as a function of the flip angles θ1 and θ2, the interpulse interval τ, and the amount of interpulse dephase. The expression shows that θ1 and θ2 provide two degrees of freedom to optimize the signal‐to‐noise ratio and improve tissue contrast. Two different cases, θ1=θ2 and θ1 = ‐θ2, are described to demonstrate the difference in contrast. The first case gives a strong signal from spins with short T1 and short T2 while the second case has contrast very similar to a conventional SSFP technique. The theoretical expression predicts that the signal consists of multiple components which may be observed experimentally by adjusting the gradient pulses.
Implanted coil MR microscopy of renal pathology
Authors: Farmer T. H. R. , Johnson G. A. , Cofer G. P. , Maronpot R. R. , Dixon D. , Hedlund L. W.
Published: March 2007

Inductively coupled implanted coils have been shown to provide up to a 10‐fold increase in signal‐to‐noise ratio when compared to whole‐body imaging of small animals. The current study was designed to extend the implanted coil imaging technique to a rodent model of renal pathology. Resonant radiofrequency (RF) coils were implanted around the left kidney of four rats and inductively coupled from within a birdcage body coil. All images were acquired at 2 T using a T1‐weighted spin‐echo sequence with TR = 500 ms and TE = 20 ms. In vivo MR microscopy with voxels of 117 × 117 × 2000 μm demonstrated cortex, inner and outer medulla, and major vascular structures on baseline images. Mercuric chloride‐induced nephrotoxic acute tubular necrosis (ATN) diminished cortico‐medullary contrast at 24 h after dosing with pathologic evaluation demonstrating nephrotoxic changes in the inner cortex. The kidney regained a baseline MR appearance 360 h after dosing and resolution of the damage was confirmed with histology. T1 data were gathered on excised kidneys as an adjunct to the images to help correlate the loss and return ofcortico‐medullary contrast with the pathology and pathophysiology of nephrotoxic ATN. With implanted RF coils we were able to demonstrate renal pathology and follow its subsequent resolution. Specifically, loss and return of cortico‐medullary contrast as a result of nephrotoxic ATN were serially documented in four rats. Such serial in vivo studies performed on single animals should further the use of MR microscopy by minimizing the number of animals required for adequate biostatistics. © 1989 Academic Press, Inc.
Effects of intravoxel incoherent motions (IVIM) in steady‐state free precession (SSFP) imaging: application to molecular diffusion imaging
Authors: Bihan D. Le , Turner R. , Macfall J. R.
Published: March 2007

A theoretical analysis of the effects of diffusion and perfusion in steady‐state free precession (SSFP) imaging sequences sensitized to intravoxel incoherent motions by magnetic field gradients is presented and supported by phantom studies. The capability of such sequences to image diffusion and perfusion quickly was recently demonstrated. The possible residual effects of T1 and T2 in diffusion measurements are evaluated, as are the effects of the sequence design and the acquisition parameters (repetition time, flip angle, gradient pulses). It is shown theoretically and confirmed by experiments on phantoms that diffusion coefficients can be directly measured from SSFP images when large enough diffusion gradient pulses are used. © 1989 Academic Press, Inc.
Power deposition and noise correlation in NMR samples
Authors: Carlson J. W.
Published: March 2007

A general solution for the power deposited in an NMR sample by an rf coil is presented. The result is simplified in the long wavelength, long skin depth approximation. This formalism is used to derive an expression for noise correlation in two independent receiver coils. © 1989 Academic press, Inc. © 1989 Academic Press, Inc.
Double‐quantum filtered volume‐selective NMR spectroscopy
Authors: üttel A. Kn , Kimmich R.
Published: March 2007

An RF and field‐gradient pulse sequence is presented, permitting the recording of localized double‐quantum filtered proton spectra. In this way distinction between overlapping resonances of coupled and uncoupled spins is possible. The editing of the lactate methyl line is demonstrated in a test experiment. © 1989 Academic Press, Inc.
Localized proton NMR spectroscopy in different regions of the human brain in vivo. Relaxation times and concentrations of cerebral metabolites
Authors: Frahm J. , Bruhn H. , Gyngell M. L. , Merboldt K. D. , Hänicke W. , Sauter R.
Published: March 2007

High‐resolution proton NMR spectra of normal human brain in vivo have been obtained from selected 27‐ and 64‐ml volumes‐of‐interest (VOI) localized in the insular area, the occipital area, the thalamus, and the cerebellum of normal volunteers. Localization was achieved by stimulated echo (STEAM) sequences using a conventional 1.5‐T whole‐body MRI system (Siemens Magnetom). The proton NMR spectra show resonances from lipids, lactate, acetate, Nacetylaspartate (NAA), γ‐aminobutyrate, glutamine, glutamate, aspartate, creatine and phosphocreatine, choline‐containing compounds, taurine, and inositols. While T1 relaxation times of most of these metabolites were about 1100–1700 ms without significant regional differences, their T2 relaxation times varied between 100 and 500 ms. The longest T2 values of about (500 ± 50) ms were observed for the methyl protons of NAA in the white matter of the occipital lobe compared to (320 ± 30) ms in the other parts of the brain. No significant regional T2 differences were found for choline and creatine methyl resonances. The relative concentrations of NAA in gray and white matter were found to be 35% higher than those in the thalamus and cerebellum. Assuming a concentration of 10 mM for total creatine the resulting NAA concentrations of 13–18 mMare by a factor of 2–3 higher than previously reported using analytical techniques. Cerebral lactate reached a maximum concentration of about 1.0 mM. © 1989 Academic Press, Inc.
31P NMR studies of the thermodynamics and kinetics of the creatine kinase reaction
Authors: Eldar H. , Degani H.
Published: March 2007

The thermodynamic and kinetic parameters of the reaction catalyzed by creatine kinase (CK) were measured in vitro in the temperature range 13 to 35°C, using 31P NMR spectroscopy, including magnetization transfer methods. The apparent equilibrium constant of the reaction and the associated enthalpy for the formation of ATP at 35°C, pH 8.2, and excess [Mg2+] were 3.5 × 109 M−1 and −2.4 ± 0.5 kcal/mol, respectively. The rates at equilibrium at 35°C catalyzed by 1 unit/ml CK were 12.4 and 10.7 μM /s at pH 7 and 8, respectively. The rate constants per 1 unit CK/ 1 ml at 35°C, pH 7, were 1.3 × 108 s−1M−2 and 9.9 × s−1 M−1 in the direction of ATP and PCr formation, respectively. The activation energies in both directions were similar and corresponded to 15 ± 2 kcal/mol at pH 7 and 17.5 ± 1.5 kcal/mol at pH 8. Comparison of in vivo results with the above in vitro data may provide information regarding the activity and kinetics of the CK reaction.
Relaxation measurements at 300 MHz using MR microscopy
Authors: Dockery S. E. , Suddarth S. A. , Johnson G. A.
Published: March 2007

Previous data on changes in tissue TI with field have suggested the convergence of tissue TI values toward a common value at high (>4.0 T) fields. Measures of T2 dependence have suggested reduction of T2 with field. The purpose of this study was to observe the T1 and T2 at 85.5 and 300 MHz of microstructures in excised rat kidneys by employing MR microscopy. This study represents the first attempt of MR microscopy at 7.0 T with regard to the subject of magnetic field dependence of TI and T2 As expected, TI did increase with increasing field strength but not as dramatically as might be expected. Subtle differences in the microstructures of the kidney and the binding of water in those structures were discernible on the basis of T1 differences at 300 MHz. T2 values decreased, raising speculation concerning the mechanism for this dependence. The improved SNR permits smaller samples to be examined at much higher resolutions (< 30 ± 30 ± 200 μm), further extending the potentials for MR microscopy.
High‐Resolution NMR imaging of an antigen‐induced arthritis in the Rabbit Knee
Authors: Checkley David , Johnstone Donna , Taylor Kay , Waterton John C.
Published: March 2007

High‐resolution, serial, spin‐echo images were obtained for an antigen‐induced knee arthritis in six rabbits. The animals were imaged prior to intra‐articular challenge and at various time points up to 14 weeks after challenge. Extensive high‐signal inflammatory changes were seen at Day 1 in the lymph node, capsule, and surrounding muscle. The muscle and lymph node response decreased rapidly after the first week. The capsule high‐signal area reached a maximum at Day 10, but was still extensive at Day 39. The infrapatellar fat pad was replaced more slowly by high signal and the appearance of high signal in both the tibia and femur was a late change. Terminal histological examination showed that the capsule and fat pad high‐signal areas corresponded to fibrous and synovial proliferation. The bone changes were a result of edema and cyst formation. The separation of the various time courses of the inflammatory changes may be of value in understanding the model and evaluating potential anti‐arthritic drugs. © 1989 Academic Press, Inc.
Precise relaxation time measurements of normal‐appearing white matter in inflammatory central nervous system disease
Authors: Miller D. H. , Johnson G. , Tofts P. S. , Macmanus D. , McDonald W. I.
Published: March 2007

Precise relaxation time (RT) measurements have been made, with a standard deviation of 3% for T1 and T2 in white matter in normal volunteers. This sets an upper limit to the instrumental random errors (imprecision). Achieving this precision requires careful adjustment and use of the imager. The wide variation in RTs seen by other workers may be in part due to larger instrumental errors. We have measured RTs (both T1 and T2) in normal‐appearing white matter in 16 normal controls and patients with multiple sclerosis (MS, 18), systemic lupus erythematosis (SLE, 16) and cerebral sarcoidosis (8). Both RTs were significantly higher in MS than in other patient groups and controls (P < .05), possibly caused by microscopic lesions. T2 was elevated in SLE, patients relative to controls and sarcoidosis patients (P < .05), possibly because of microhemorrhages. Lesion RTs were abnormal but more variable and no significant differences between diseases were found.
Exposure to a 1.5‐T static magnetic field does not alter body and skin temperatures in man
Authors: Shellock Frank G. , Schaefer Daniel J. , Crues John V.
Published: March 2007

The literature has conflicting reports concerning the effect of static magnetic fields on body and skin temperatures in mammals. Since temperature changes induced by static magnetic fields would have important safety implications for clinical magnetic resonance imaging, body (sublingual pocket) and skin (abdomen, forehead, chest, upper arm, forearm, thigh, and calf) temperatures were determined in six normal subjects using a fluoroptic thermometry system during a 20‐min exposure to a 1.5‐T static magnetic field. Ambient conditions were controlled and held constant. An analysis of variance for re‐ peated measures revealed that there were no statistically significant changes in body or any of the skin temperatures recorded. We conclude that exposure for 20 min to a 1.5‐T static magnetic field does not alter body and skin temperatures in man.
Flow‐compensated limited flip angle MR angiography
Authors: Lee James N. , Riederer Stephen J. , Pelc Norbert J.
Published: March 2007

A method of subtraction angiography that has an acquisition time of 8 s per slice is described. Flow‐compensated and uncompensated measurements are acquired in an interleaved fashion using limited flip angles and gradient refocusing. Magnitude images are reconstructed and subtracted to generate the angiogram. Results were generated in vivo in the imaging of the carotid bifurcation of several human volunteers. Susceptibility and inhomogeneity induced artifacts are prominent in thick slices, but can be greatly reduced by imaging several thin slices and adding them together. Thin slices do not require de‐phasing gradients to reduce the dynamic range, and there is no signal cancellation in overlapping vessels. The method is ideal for acquiring scout angiograms, and with averaging may produce images of diagnostic quality. © 1989 Academic Press, Inc.
The use of finite impulse response filters in pulse design
Authors: Shinnar Meir , Bolinger Lizann , Leigh John S.
Published: March 2007

We develop a new way of synthesizing pulse sequences with desirable frequency characteristics. By combining our previous results with techniques from the theory of finite impulse response filters, we can specify (1) the total duration of the pulse sequence, (2) the frequency ranges it is desired to perturb, (3) the desired perturbation, and (4) the frequency range it is desired not to perturb. We can then synthesize a hard pulse sequence which will yield that desired perturbation with the minimal possible error. The minimum error is global, in the sense that no pulse sequence can do better at achieving the specifications, and is not just a local minimum, around the pulse sequences close to the derived pulse. © 1989 Academic Press, Inc.
Compensation for effects of linear motion in MR imaging
Authors: Korin Hope W. , Farzaneh Farhad , Wright Ronald C. , Riederer Stephen J.
Published: March 2007

Various compensation methods for different types of motion during MR image acquisition have been proposed. Presented here is a postprocessing scheme for eliminating artifacts due to linear, intra‐slice motion of known velocity. The data for each phase encoding or “view” acquired from a moving object are shown to differ from those which would be measured from the stationary object by a phase factor which depends on the object's displacement from a reference point. This derivation is then used to propose a correction scheme for linear motion in which all phase encodings measured at different positions of the moving object are collapsed onto the same reference position. After subsequent reconstruction, the object appears perfectly “focused.” By selection of different reference positions, the method permits positioning of the compensated object as desired within the field of view of the image. This property allows the method to be extended to create sequences of corrected images with smooth object motion between frames of the sequence. The basic correction scheme and its variations were tested experimentally in phantom studies with velocities as large as 8 cm/s. © 1989 Academic Press, Inc.
Regional effects of repetition time on NMR quantitation of water in normal and edematous lungs
Authors: Cutillo Antonio G. , Morris Alan H. , Ganesan Krishnamurthy , Ailion David C. , Case Thomas A. , Durney Carl H. , Watanabe Fumi
Published: March 2007

It is well known that pulmonary edema is, in general, spatially nonuniform. Since the NMR spin‐lattice relaxation time (T1) is increased by lung edema, the spatial distribution of T1 will be nonuniform. When the repetition time (TR) is short relative to the T1 of edematous lung, lung water content will be underestimated and this underestimation will be spatially nonuniform as well. Therefore, technical artifacts which are a complex function of lung edema and its spatial distribution are expected. We compared overall and regional (topographic) lung water density measurements obtained from living rats (with normal or edematous lungs) using repetition times of 2.0 and 6.2 s (at a magnetic field of 1 T), to quantify this uneven T1 effect for normal and edematous lungs. NMR measurements at TR = 2.0 s underestimated whole lung water density (ρ―H2O) (at TR = 6.2 s) by an average of 7.2% in normal rats and 22.5% in rats with pulmonary edema. Regional ρ―H2O underestimation (%Δρ―H2O) varied from 2.2 to 8.8% (group means) in normal lungs and from 7.3 to 30.8% in edematous lungs. As a result, the interquartile range (of the voxel distribution as a function of pH2O) underestimated the spatial nonuniformity of lung water density by 28.0% in edematous lungs, likely because of greater loss of NMR signal from high‐water‐density, long‐T1 lung regions. Both %ΔpH2O and T1, were significantly correlated with ρ―H2O at TR = 6.2 s. Artifactual distortion of the spatial distribution of NMR signal intensity cannot be predicted from average T1 values characterizing the whole lung, but rather requires a knowledge of the spatial distribution of T1. © 1989 Academic Press, Inc.
Correction of distortions due to the pulsed magnetic field gradient‐induced shift in B0 field by postprocessing
Authors: Jehenson P. , Syrota A.
Published: March 2007

Gradient pulses used in most localization techniques induce time‐dependent shifts in B0 that strongly distort NMR signals. A postprocessing correction method requiring no additional hardware is proposed. The phase shift produced by the B0 shift is calculated from a reference free induction decay (FID) and used to correct any FID acquired with the Same sequence. © 1989 Academic Press, Inc.
9.4‐T NMR microimaging studies of hepatic metastases of human colorectal tumors in nude mice
Authors: Sarkar Susanta K. , Clark Robert K. , Rycyna Robert E. , Mattingly Mark A. , Greig Russell
Published: March 2007

We have applied NMR microimaging at 9.4 T to detect metastatic deposits in the liver of nude mice noninvasively, using an animal model for metastatic colon cancer that mimics several aspects of the human disease. Images were obtained with a resolution of 100 X 100 X 900 μm and the tumor deposits were clearly distinguished from the normal liver tissue with excellent contrast. Comparison of NMR images with corresponding histologic sections indicates that lesions as small as 900 μm were detected. © 1989 Academic Press, Inc.
Phase‐distortion‐free in vivo surface coil proton spectroscopy
Authors: Alger J. R. , Brunetti A.
Published: March 2007

A 1‐17 water suppression pulse sequence for phase‐distortion‐free surface coil NMR spectroscopy was constructed and tested in vivo on cat brain. The sequence produces brain spectra free of phase distortions, but some degradation of water suppression quality compared to closely related sequences which produce phase distortions was observed. © 1989 Academic Press, Inc.
Snapshot flash mri. applications to t1, t2, and chemical‐shift imaging
Authors: Haase A.
Published: March 2007

Snapshot FLASH magnetic resonance imaging techniques have been developed to enable real‐time imaging of MR parameters. The first realization of the method is based on a 64 × 128 FLASH tomogram acquired within 200 ms, using improved MR system hardware conditions. The soft tissue contrast obtained in FLASH MRI almost disappears by using flip angles of less than 5° and repetition times of 3 ms. This work describes extensions of FLASH MRI placing conventional MR experiments before the whole imaging sequence. This creates images of any desired contrast without changing the measuring time. Examples of inversion‐recovery T1, spin‐echo T2, chemical‐shift‐selective, and spectroscopic FLASH MRI are presented. Further extensions to real‐time MRI of blood vessels, diffusion coefficients, combination with two‐dimensional MR spectroscopy experiments, and other nuclei are discussed.
Detection of metabolites in body fluids and biological tissue by a 1d soft cosy technique
Authors: Stryjewski Detlef , Oschkinat Hartmut , Leibfritz Dieter
Published: March 2007

With a semiselective ID COSY, related to the soft COSY sequence, metabolites with concentrations of a few millimolar can be detected, while highly abundant molecules as water or lipids are efficiently suppressed.
The crossover surface coil: an efficient in vivo nmr detector
Authors: Nagel Timothy L. , Stolk Jacob A. , Alderman Donald W. , Schoenborn Robin , Schweizer Martin P.
Published: March 2007

The crossover surface coil is constructed with two turns of copper foil using a unique transposition construction which incorporates an explicit center tap ground of the widened bottom layer. The coil reduces dielectric and inductive losses by effective shielding of electric fields and uniform distribution of magnetic fields for minimum Q losses upon loading of the coil. Flexible, copper foil construction permits easy conformation to tissues of interest, enhancing coil performance. Construction details of the crossover coil and Q data for coils of various sizes operating at a number of frequencies are given.
A study of optimization of the complex hyperbolic secant inversion pulses
Authors: Mao Jintong , Virapongse C. , Fitzsimmons J. R.
Published: March 2007

The conjugate gradient method is used to optimize the inversion slice profile produced by complex hyperbolic secant selective pulses. An improved quality is obtained for the inversion slice profile at a price, however, of a lower immunity to the amplitude variation of radiofrequency pulses.
In vitro magnetic resonance microimaging of the spinal cord
Authors: Lemaire C. , Duncan E. G. , Solsberg M. D. , Armstrong R. L.
Published: March 2007

A 2.0‐T small animal imager equipped with 3 G/cm imaging gradient coils was used to obtain images of en bloc segments of the vertebral column containing the rat spinal cord and of a cadaveric human spinal cord. These images demonstrate the applicability of MR micro‐imaging techniques to the study of interesting problems in medicine and biology. Images of transverse sections of the spinal cord with in‐plane resolution of better than 0.1 mm were obtained from slices 1 mm thick. The images of normal and injured rat spinal cord vividly show that spinal cord injury in the rat can be visualized using MRI techniques. The MR image of the cadaveric human spinal cord shows subanachroid gray and white matter structures. A comparison with a photomicrograph indicates that it is the superior contrast of the MR image that leads to increased conspicuity. © 1990 Academic Press, Inc.
In vivo detection of injected free radicals by overhauser effect imaging
Authors: Grucker D.
Published: March 2007

Proton dynamical polarization is a method which unites the advantages of continuous wave ESR sensitivity and pulsed NMR imaging in order to localize free radicals. Injected nitroxide has been imaged for the first time in living rats. The high sensitivity of this method to oxygen is demonstrated. © 1990 Academic Press, Inc.
Microcirculatory considerations in NMR flow imaging
Authors: Bassingthwaighte James B.
Published: March 2007

Regional flow estimation can be accomplished either by measuring the concentration of a deposited tracer whose extraction during transit through the organ is 100%, or by observing the time course of concentration of a tracer whose transport passage through the organ is flow‐limited. The deposition method is simpler and applies not only to micro‐spheres or other large particles that lodge in the microcirculation, but also to molecular markers which are trapped. It has the advantage of having substantial time in which to observe the local concentrations by external detection. In contrast, flow‐limited markers must traverse the tissue without barrier limitation or other diffusional influence on the exchange. When the marker is limited strictly to the intravascular space, the transit time through the organ is short and observations must be made rapidly with a high resolution technique. An indicator which distributes throughout a large volume of distribution within the tissue has a slower washout, providing more time in which to make observations; tracer water is a suitable marker, except perhaps in the brain. For flow measurement by NMR, markers which fulfill these criteria without causing side effects are needed. © 1990 Academic Press, Inc.
The application of phase shifts in NMR for flow measurement
Authors: Firmin D. N. , Nayler G. L. , Kilner P. J. , Longmore D. B.
Published: March 2007

A brief overview of the history of the application of phase shifts in NMR, and in particular NMR imaging, is presented. The imaging methods include direct phase mapping, Fourier flow imaging (where the flow data are Fourier transformed into one dimension of an image), and alternative methods, where flow‐related phase shifts are utilized for flow measurement from the magnitude of the signal. A discussion then follows of the principal errors that can affect the accuracy of the various flow imaging techniques, with particular reference to the phase mapping methods that have been used extensively in our institution. The results from a number of experiments are included to illustrate the extent of the errors and methods of removing or minimizing these effects are Suggested. © 1990 Academic Press, Inc.