bluuebunny/crossref_metadata_2025 huggingface dataset:
Postnatal NMR changes in guinea pig central nervous system: Potential relevance to experimental allergic encephalomyelitis
Authors: Noseworthy J. H. , Gilbert J. J. , Vandervoort M. K. , Karlik S. J.
Published: March 2007

The age of sensitization determines the clinical course of experimental allergic encephalomyelitis (EAE) in the guinea pig. Adult animals immunized with central nervous system (CNS) tissue develop acute, fulminant EAE, whereas a relapsing‐remitting illness resembling multiple sclerosis occurs if sensitization occurs in the first 2 weeks of life. This study characterized the changes in the proton nuclear magnetic resonance (NMR) relaxometry and imaging of the CNS during the immediate postnatal period. T1 and T2 relaxation times in cerebral hemispheres and spinal cords of strain 13 guinea pigs were consistently prolonged at birth, progressively shortened in the first few weeks of life, and achieved adult levels by age 6 to 11 weeks. There were no age‐dependent differences in T1 and T2 relaxation times and tissue specific gravity in either strain 13 or Hartley guinea pigs following immunization with complete Freund's adjuvant, an agent previously reported to disrupt the blood‐brain barrier to IgG and albumin in strain 13 guinea pigs. The CNS of neonatal guinea pigs appeared well myelinated by light microscopy and there was no apparent difference in the extent of myelination between newborn and adult animals. Although it was possible to distinguish gray from white matter in the cervical spinal cord of newborn guinea pigs by magnetic resonance imaging (MRI) techniques, gray/white contrast was less satisfactory in the cerebral hemispheres until approximately 6 weeks of life when it was possible to differentiate gray matter, white matter, and cerebrospinal fluid. This study indicates that NMR relaxation times change during early postnatal life, at a time corresponding to the unexplained differences in susceptibility to an immune challenge. These developmental changes appear to be independent of the degree of CNS myelination. © 1988 Academic Press, Inc.
Spin‐echo 1H NMR detected response of ergothioneine to oxidative stress in the intact human erythrocyte
Authors: Reglinski J. , Smith W. E. , Sturrock R. D.
Published: March 2007

Human erythrocytes were subjected to oxidative stress using arsenicals. The study is a model for thiol‐related redox processes observed in the etiology of diseases such as rheumatoid arthritis. Spin‐echo NMR spectroscopy of the living cell was used to monitor the cellular biochemistry. Oxidation of glutathione and the first demonstrated response of ergothioneine to a chemical stimulus in a cell were observed. The reversible nature of the ergothioneine response is interpreted as an environmental rather than a chemical change. © 1988 Academic Press, Inc.
Simultaneous image acquisition from the Head (or body) coil and a surface coil
Authors: Hyde James S. , Froncisz W. , Jesmanowicz A. , Kneeland J. B.
Published: March 2007

Any number of coils can in principle be used simultaneously and independently in magnetic resonance imaging if the mutual inductances are sufficiently small. Surface coils and head or body coils have equal sensitivity at some crossover depth of the order of 6 to 10 cm. Using a 7.5‐cm‐diameter surface coil that was intrinsically isolated from the head coil, images were acquired simultaneously from both coils and combined to improve the signal‐to‐noise ratio at 6 cm depth by 21/2. A similar experiment with the body coil showed 21/2 improvement at about 8 cm depth. © 1988 Academic Press, Inc.
Doubly tuned local coils for MRI and MRS at 1.5 T
Authors: Grist Thomas M. , Jesmanowicz A. , Kneeland J. Bruce , Froncisz W. , Hyde James S.
Published: March 2007

We describe a doubly tuned radiofrequency (RF) local coil probe designed specifically for performing in vivo image‐localized spectroscopy. The probe was designed using principles developed in connection with the counter‐rotating‐current (CRC) and planar‐pair loop gap resonators for magnetic resonance imaging (MRI). The probe design satisfies several criteria useful for in vivo 1H/31P experiments at 1.5 T. First, sensitivity on the low‐frequency mode is preserved relative to a singly tuned coil. This result was confirmed by bench‐test and in vitro MR experimental data. Second, through principles of intrinsic decoupling the probe is isolated from any externally applied uniform excitation field, which is desirable for in vivo 1H imaging and solvent suppression. Third, the regions of sensitivity of the high‐ and low‐frequency modes of the coil are similar, and therefore spectroscopic volumes of interest identified on an image will reflect the same volumes as those selected during spectroscopy. Finally, interface to the MR system is such that the high‐ or low‐frequency circuits may be selected entirely under software control, with no requirement for changing coils or cables or moving the subject. © 1988 Academic Press, Inc.
Parallel‐plate split‐conductor surface coil: Analysis and design
Authors: Gonord P. , Kan S. , Leroy‐Willig A.
Published: March 2007

A split‐conductor circular parallel‐plate resonator with one end shorted to ground can be used to one's advantage as a surface coil for NMR imaging experiments. It can be easily constructed by a printed‐circuit method and possesses a relatively high loaded Q with negligible frequency detuning. From the proposed equivalent circuit, an equation was derived that relates the self‐resonance frequency of the resonator to the split distance measured from a reference point. An example of a 101‐mm‐diameter surface coil operating at 26 MHz for 34P in vivo spectroscopy is given to illustrate the concordance between calculated and experimental results. Complementary equations and formulas are also included to assist researchers in designing their own antennas to meet specific requirements. © 1988 Academic Press, Inc.
Quantitation of phosphate metabolites in human leg in vivo
Authors: Venkatasubramanian P. N. , Mafee M. F. , Bárány M.
Published: March 2007

Slice‐selective 31P MR spectra were recorded from human legs with a pulse program which has only a 1.5‐ms delay between excitation and acquisition. The volume of the slice was calculated from its thickness and cross‐sectional area measured with the aid of a computer program. A phosphate reference standard spectrum was recorded from the Same interplanar location as that of the human leg slice. Since signal integral is proportional to the phosphate concentration and to the volume of the slice, metabolite concentrations in the selected slice could be quantitated. © 1988 Academic Press, Inc.
Comparison of intracellular pH measurements by 31P NMR and weak acid partitioning in Chinese hamster ovary fibroblasts
Authors: Gonzälez‐Méndez Ricardo , Hahn George M. , Wade‐Jardetzky Norma G. , Jardetzky Oleg
Published: March 2007

Intracellular pH measurements obtained by 31P NMR and DMO partitioning are compared. A continuous‐flow culture system was used to measure the intracellular pH of Chinese hamster ovary fibroblasts in response to changes in the extracellular pH. These measurements were repeated with the CHO cells in suspension and under similar experimental conditions using the weak acid partitioning technique employing 14C‐DMO. It is shown that the pHi values are identical, within experimental error, for both techniques in the 6.80–7.70 pH range, with the DMO technique giving slightly more acidic intracellular pH in the 6.00–6.80 range. It is concluded that both techniques give similar values for intracellular pH in the physiological range, with the DMO partitioning giving more acidic values at pH's less than 6.80. The range of validity for pHi measurements using 31P NMR lies between 6.70 and 7.50. © 1988 Academic Press, Inc.
An experimental approach to 31P spin–lattice relaxation time measurement in biological systems
Authors: Seo Yoshiteru , Murakami Masataka , Suzuki Eiji , Maeda Munehiko , Watari Hiroshi
Published: March 2007

The accuracy of measurement of the spin‐lattice relaxation time (T1) in biological systems using the variable nutation angle method is discussed using computer simulations. This method could reduce the time required for measurement to 10% of that using the inversion recovery method. In the perfused salivary gland of the rat (310 K), the T1 values of sugar phosphates, creatine phosphate, γ‐phosphate, and β‐phosphate of nucleotide triphosphates determined by this method were 5.2, 4.8, 0.9, and 0.8 s, respectively. During secretion of saliva, the T1 value of sugar phosphates decreased to 3.7 s, which could be due to an increased chemical exchange of phosphate in glycolysis. © 1988 Academic Press, Inc.
Projective Fourier angiography
Authors: Norris David G. , Jones Richard A. , Hutchison James M. S.
Published: March 2007

The Fourier imaging of flow is discussed, and the limitations of imaging time, spatial and velocity resolution, imposed on this technique when applied in conjunction with ECG synchronization are examined. It is argued that this method is best used in projective format, and in vivo examples are presented. The relative velocity spectrum obtained is largely system independent, and quantification of velocity is implicit in the Fourier technique. © 1988 Academic Press, Inc.
A simple method for processing NMR spectra in which acquisition is delayed: Applications to in vivo localized 31P NMR spectra acquired using the DRESS technique
Authors: Allman Tim , Holland G. A. , Lenkinski R. E. , Charles H. Cecil
Published: March 2007

It is a requirement of many localized NMR spectroscopy experiments, such as DRESS, that collection of the free induction decay be delayed a significant time after the middle of the last pulse. This leads to distortion of the spectra and seriously impedes the retrieval of quantitative information from these spectra. A technique is described in which a correction function is derived from the convoluted spectrum and is used to produce a spectrum with much reduced distortion from which quantitative information may easily be obtained by conventional techniques. © 1988 Academic Press, Inc.
Acute volume loading studied in cat myocardium with 31P Nuclear magnetic resonance
Authors: Osbakken Mary , Young Marie , Huddell Judy , Closter Jeffery , Prammer Manfred , Chance Britton
Published: March 2007

To study the effects of acute volume loading on myocardial metabolic and mechanical function, seven cats were volume loaded via anastomosis of the abdominal aorta to the vena cava (A V shunt). Metabolic effects were evaluated with31 P nuclear magnetic resonance (NMR). Mechanical function was evaluated with heart rate × systolic blood pressure product (HR × SBP). Shunts were opened for 1–2 h during which time phosphocreatine (PCr), adenosine triphosphate (ATP), inorganic phosphate (Pi), and HR × SBP were monitored. High‐energy phosphate energetics as determined by Pi/PCr and PCr/ATP ratios were correlated with HR × SBP. Opening of the AV shunts was associated with an increase (four cats) or a decrease (three cats) in HR × SBP. Pi/PCr ratios increased and PCr/ATP ratios decreased in cats with an increase in HR × SBP. In cats with a decrease in HR × SBP, Pi/PCr and PCr/ATP generally did not change significantly. In summary, acute volume loading could be associated with an increase or decrease in myocardial external work as evaluated by HR × SBP, accompanied by metabolic changes suggestive of appropriate induction of state 3 metabolism (active metabolic state: ADP + Pi → ATP) in those cats with increased mechanical work, and minimal change in bioenergetics in cats with no or minimal increase in mechanical work. These induced metabolic responses to myocardial mechanical loading can be evaluated with 31P NMR techniques and may provide insight into in vivo metabolic control mechanisms. © 1988 Academic Press, Inc.
Dependence of the solvent proton 1/T1 on the iron content in normal human serum
Authors: Yilmaz Ali , Chu Simon C. , Osmanoglu Semsettin
Published: March 2007

The iron content dependence of the spin‐lattice relaxation rates (I / T1) of solvent protons in healthy human serum has been studied by FT NMR at 60 MHz. A linear relationship has been established between 1/T1 and the iron content (with a correlation of 0.89). Our data suggest that Fe(III)–transferrin can contribute to the relaxation rate in healthy human Serum. © 1988 Academic Press, Inc.
Nodal inhomogeneity mapping by localized excitation—the “NIMBLE” shimming technique for high‐resolution in Vivo NMR spectroscopy
Authors: Doddrell David M. , Galloway Graham J. , Brewton Ian M. , Brooks William M.
Published: March 2007

A method (NIMBLE) for obtaining optimum Bo field homogeneity at voxels located away from the magnet isocenter for use in volume‐selected NMR spectroscopy is described. Voxels may be shimmed using only first‐order X, Y, and Z shims to produce three‐dimensional shim current maps, thus avoiding shim coupling problems. NIMBLE shimming prior to volume selection ensures optimum spectral resolution and improves the efficiency and accuracy of the volume‐selection experiment. The benefits of the technique are illustrated by a high‐resolution volume‐selected spectrum of human tibia marrow. © 1988 Academic Press, Inc.
Water proton NMR relaxation mechanisms in lung tissue
Authors: Kveder M. , Zupančič I. , Lahajnar G. , Blinc R. , Šuput D. , Ailion D. C. , Ganesan K. , Goodrich C.
Published: March 2007

The NMR relaxation times T2, T2, and T1 were measured in isolated rat lungs as functions of external magnetic field B0, temperature, and lung inflation. The observed linear dependence on B0 of the tissue‐induced free induction decay rate (T2)−1 provides independent confirmation of the air/water interface model of the lung. Furthermore, measurements of the Larmor frequency dependence of T1, are consistent with a spin‐lattice relaxation rate of the form 1/Tl = Aω−1/2+ B as expected for the case in which the relaxation arises from water‐biopolymer cross‐relaxation, which should be proportional to the surface area of the lung. This prediction was verified by observations of an approximately linear dependence of 1/T1, on transpulmonary pressure and thus on the lung surface area. © 1988 Academic Press, Inc.
Considerations of magnetic resonance angiography by selective inversion recovery
Authors: Nishimura Dwight G , Macovski Albert , Pauly John M.
Published: March 2007

In the selective inversion recovery method for projection angiography, upstream blood is tagged by an inversion excitation and then allowed to flow into the imaged region. The subtraction of this first image from a second image acquired without the tagging leaves a signal from only the selectively tagged blood. Pulse sequence design involves consideration of the duration of the blood transit interval, excitation timing and cardiac gating, static material suppression, inversion excitation pulses, and flow compensation. Each of these considerations must be viewed with respect to the particular application. The method has demonstrated potential application to areas such as the carotid arteries, aortic arch, and peripheral Vessels. © 1988 Academic Press, Inc.
Pulse sequence and parameter choice in NMR imaging as a problem of constrained multidimensional nonlinear optimization
Authors: Dreher Wolfgang , Börnert Peter
Published: March 2007

The advantage of the multiparametric nature of NMR imaging is connected with the problem of finding optimum pulse sequences and sequence parameters, which ensure a high contrast‐to‐noise ratio. For a given imaging task with m (m ≥ 2) regions characterized by sets of NMR parameters (e.g., p, T1, T2) two functions are proposed, which can be used to transform the search for an optimum pulse sequence into a problem of constrained multidimensional nonlinear optimization. The numerical algorithm is described and the results of two examples are presented and discussed. A short description of useful extensions of the proposed optimization approach, which are currently implemented, is given. © 1988 Academic Press, Inc.
Quantitative flow measurements on phantoms and on blood vessels with MR
Authors: Meier D. , Maier S. , Bösiger P.
Published: March 2007

A broad spectrum of MR methods has been published in the last few years for the visualization and the quantification of flow in human blood vessels. We describe the results of an extended study to measure the flow quantitatively using the MR phase modulation method. A gradient echo sequence which allows short repetition times was synchronized with the ECG. The instantaneous velocity profiles and the integrated flow rate can be determined throughout the cardiac cycle in up to 45 consecutive time intervals. The instantaneous velocity distributions can be displayed as 2D profiles over the lumen of the blood vessel. The technique has been successfully evaluated with a set of phantom experiments. Following this, quantifications of the blood flow rates in vivo were performed on the abdominal aortas of healthy volunteers. The MR flow results were compared to those obtained with conventional Doppler ultrasound examinations. The results of both methods are in good quantitative agreement. © 1988 Academic Press, Inc.
Deuterium NMR cerebral imaging in Situ
Authors: Ewy Coleen S. , Ackerman Joseph J. H. , Balaban Robert S.
Published: March 2007

Nuclear magnetic resonance imaging of deuterium is demonstrated in cat brain in vivo and in situ at 4.7 T magnetic field strength. Images were acquired at 4–5% deuterium enrichment, using D2O as a nuclear spin label, with as little as 10‐s time resolution. This suggests the potential application of D2O as an exogenous MRI label for quantitative flow imaging or contrast enhancement. The efficient quadrupolar relaxation mechanism of the deuterium nuclide results in a short ca. 250 ms spin–lattice relaxation time (T1). This allows for rapid signal averaging, thus increasing signal‐to‐noise in the deuterium image. Additionally, three widely dispersed deuterium spin–spin relaxation times (T2) are observed of ca. 10, 40, and 400 ms which provide high compartmental image contrast, thus yielding information of physiological as well as anatomical interest. T2‐weighted deuterium cerebral images are presented showing marked tissue relaxation discrimination. © 1988 Academic Press, Inc.
Snapshot head imaging at 0.5 T using the echo planar technique
Authors: Ordidge R. J. , Coxon R. , Howseman A. , Chapman B. , Turner R. , Stehling M. , Mansfield P.
Published: March 2007

The echo planar imaging (EPI) method and related variants of this technique can produce complete two‐dimensional images from the data collected in a single experiment lasting a fraction of a second. EPI methods are used at 0.5 T to produce snapshot images of the human head with a suatial resolution of less than 2 mm. © 1988 Academic Press, Inc.
In vivo localized proton spectroscopic studies of human gastrocnemius muscle
Authors: Narayana P. A. , Jackson E. F. , Hazle J. D. , Fotedar L. K. , Kulkarni M. V. , Flamigs D. P.
Published: March 2007

In vivo proton magnetic resonance spectroscopy studies of gastrocnemius muscle were performed in six normal volunteers. Both spatially resolved spectroscopy (SPARS) and stimulated echo acquisition mode (STEAM) sequences were used for volume localization. A number of water suppression sequences have been combined with these localization schemes. Among the various techniques investigated in these studies, STEAM with an inversion pulse (T1 ‐discriminated spectrum) seems to have the best potential for in vivo localized high‐resolution proton spectroscopy studies of human muscle. © 1988 Academic Press, Inc.
Quantitative NMR measurements of hippocampal atrophy in Alzheimer's disease
Authors: Seab J. P. , Jagust W. J. , Wong S. T. S. , Roos M. S. , Reed B. R. , Budinger T. F.
Published: March 2007

Nuclear magnetic resonance (NMR) imaging was employed to study 10 patients with Alzheimer's disease (AD) and seven healthy elderly control subjects. Coronal sections were used to make volumetric measurements of the hippocampus, ventricles, subarach‐noid space, and brain parenchyma. The hippocampal volume (normalized relative to the size of the lenticular nucleus) was reduced by 40% in the AD group compared to the controls, with no overlap between the two groups. Overall measures of brain atrophy and ventricular and sulcal enlargement also showed significantly different group means, although with overlap between the two groups. Hippocampal atrophy did not correlate with either overall brain atrophy or dementia severity, although the degree of brain atro‐phy was correlated with dementia severity. These results show that NMR is capable of providing in vivo quantification of diminished hippocampal size in AD which is not cor‐related with overall brain atrophy and which may differentiate AD from normal aging. © 1988 Academic Press, Inc.
Rapid31P NMR test of liver function
Authors: Thoma William J. , Uǧurbil Kâmil
Published: March 2007

The 31P NMR spectrum of perfused rat liver was found to be dependent on the exogenous carbon available to the tissue. When pyruvate was supplied to liver initially perfused with lactate, Pi decreased, phosphoenol pyruvate and phosphomonoesters increased, and nucieotide pools remained the same. It is proposed that these changes can be used to evaluate liver function. © 1988 Academic Press, Inc.
Noise reduction in magnetic resonance imaging
Authors: Brosnan Thomas , Wright Graham , Nishimura Dwight , Cao Qizhi , Macovski Albert , Sommer F. Graham
Published: March 2007

This paper describes a noise‐reduction technique applicable to multiple‐measurement systems. This method, known as measurement‐dependent filtering (or MDF), can be used to advantage in a number of MRI applications. We present the general theory for one of these applications, material‐canceled projection imaging. We discuss and show the results of MDF for material‐canceled images as well as for heavily T2‐weighted spinecho images and computed T2 images. Significant improvements in SNR are demonstrated while spatial resolution is preserved. © 1988 Academic Press, Inc.
Multicompartment analysis of blood flow and tissue perfusion employing D2O as a freely diffusible tracer: A novel deuterium NMR technique demonstrated via application with murine RIF‐1 tumors
Authors: Kim Seong‐Gi , Ackerman Joseph J. H.
Published: March 2007

Deuterium NMR is employed in concert with multicompartment kinetic analysis for measurement of tissue blood flow and perfusion through a bolus administration of D2O as a freely diffusible tracer. The traditional single‐compartment and two‐compartment in‐parallel flow models with no tracer recirculation are briefly discussed. The two‐compartment in‐series flow model with recirculation is developed to account for reflow of the stable (slowly excreted) deuterium tracer. With this model a monoexponential tracer washout curve is predicted. The rate ofblood flow and tissue perfusion is readily extracted by three‐parameter monoexponential analysis of the residue decay curve. A three‐compartment model with recirculation, incorporating one compartment in‐series with two compartments in‐parallel, is developed for analysis of biexponential tracer washout curves. With this model the flow rates through the two in‐parallel compartments (i.e., fast and slow) and the volume fractions of these two compartments are obtained by five‐parameter biexponential analysis of the residue decay curve. Application of these multicompartment tracer‐recirculation flow models is demonstrated with in situ determinations of murine RIF‐1 tumor blood flow and tissue perfusion. The blood flow rates determined by deuterium NMR and analyzed by the multicompartment flow models agree well with those determined by others using radiolabels. A companion article (S.‐G. Kim and J. J. H. Ackerman, Cancer Res. 48, 3449‐3453, 1988) discusses in more depth the practical aspects of applying these multicompartment models to tumor blood flow measurement. © 1988 Academic Press, Inc.
A 31P NMR study of the GI tract: Effect of fructose loading and measurement of transverse relaxation times
Authors: Karczmar G. S. , Tavares N. J. , Weiner M. W.
Published: March 2007

The effect of fructose loading on high‐energy phosphates in the jejunum, ileum, and large intestine of rats was studied using 31P NMR. Following fructose loading, an increase in the intensity of the PME resonance was observed in the jejunum, indicating an accumulation of fructose‐1‐phosphate. There were no significant changes in ATP or Pi. This demonstrates that the activity of fructokinase in the jejunum can be monitored by 31P NMR. Fructose loading had no detectable effect on metabolite levels in the ileum and large intestine. Resolution of intestinal spectra was poor due to unusually large linewidths and the presence of broad underlying signals. To study the mechanism of line broadening, the T2's of the phosphorus resonances were measured using a solenoidal coil. The T2's ofthe ATP or Pi, PME. and PCr resonances were much longer than the T2's, suggesting that the linewidths of these resonances are primarily due to susceptibility gradients and/or compartmentation of metabolites. Other signals, particularly in the PDE region, were homogeneously broadened and had very short T2's. Spin echoes obtained with evolution times of 1 to 4 ms suppressed these broad components, with little loss of intensity in the inhomogeneously broadened resonances; as a result, resolution was improved. © 1989 Academic Press, Inc.
Magnetic resonance imaging with adiabatic pulses using a single surface coil for RF transmission and signal detection
Authors: Garwood Michael , Uĉurbil Kǎmil , Rath Alan R. , Bendall M. Robin , Ross Brian D. , Mitchell Steven L. , Merkle Hellmut
Published: March 2007

In order to overcome the problems that arise from nonuniform B1, fields, there has been interest in developing pulses that are insensitive to large variations in RF power. Pulses derived from adiabatic passage principles that can execute spin inversion, excitation, and 90°and 180° plane rotations in the presence of B1, inhomogeneities have recently been described. When driven with optimized modulation functions, these pulses can execute uniform excitation, refocusing, and slice‐selective inversion over a 10‐fold or greater variation in B1 magnitude. This insensitivity to B1 strength enables the execution of T and/or T weighted spin‐echo imaging experiments using coils, such as the surface coil, with extremely inhomogeneous B1 profiles. We have successfully acquired images with these pulses at 200 MHz using a single surface coil as the transmitter and receiver. Images of the slice definition, the region over which the excitation and refocusing pulses operate with a surface coil, and brain images obtained with slice planes perpendicular to the plane of the surface coil are presented. Results demonstrate that these pulses can be transmitted with a surface coil to yield high‐quality T and/or T weighted images without B1, artifacts. © 1989 Academic Press, Inc.
In Vivo functioning of creatine phosphokinase in human forearm muscle, studied by 31P NMR saturation transfer
Authors: Rees Deborah , Smith Michael B. , Harley Judith , Radda George K.
Published: March 2007

31P nuclear magnetic resonance (NMR) saturation transfer has been used to measure enzymatic flux through the creatine phosphokinase reaction in the direction of ATP synthesis in the human forearm muscle flexor digitorum superficialis. Modification of the ratio method for measurement of spin‐lattice relaxation (R. Freeman, H. D. W. Hill, and R. Kaptein, J. Mags. Reson. 7, 82 (1972) was tested and used to appreciably shorten the duration of the measurement. Under conditions of steady state work intracellular pH decreased slightly by 0.06 units and the spin‐lattice relaxation time of phosphocreatine in muscle was unchanged, while flux from phosphocreatine to ATP was 64 ± 10% of the resting value. This is contrary to the increase in flux of 155% predicted from previous saturation transfer studies carried out in vitro on rabbit skeletal muscle creatine phosphokinase using metabolite concentrations to mimic those in vivo (E. A. Shoubridge, J. L. Bland, and G. K. Radda, Biochim. Biophys. Acta 805, 72 (1984). This discrepancy could be accounted for by an underestimation of the ADP concentrations to which the enzyme is exposed due to inaccurate assumptions about the total metabolite concentrations, or possibly by compartmentation of creatine phosphokinase and its reactants. © 1989 Academic Press, Inc.
Water suppression with B0 field gradient homospoil pulses in high‐resolution NMR spectroscopy
Authors: Brereton I. M. , Field J. , Moxon L. N. , Irving M. G. , Doddrell D. M.
Published: March 2007

The combination of a frequency nonselective excitation suppression method (1331 sequence) with selective excitation followed by gradient‐induced dephasing of water transverse magnetization yielded suppression ratios of greater than 10,000:1. The need for gradient preemphasis and correction of Bo field shifts is discussed. The suppression efficiency of this method compared favorably to results obtained using the CPMG spin‐ echo technique to observe metabolite resonances in a urine sample. © 1989 Academic Press, Inc.
Determination of halothane distribution in the rat head using 19F NMR technique
Authors: Wyrwicz A. M. , Conboy C. B.
Published: March 2007

The distribution of halothane in the rat head was examined with 19F NMR rotatingframe zuegmatography and 2DFT 19F NMR imaging. The rotating frame experiments were conducted at varying times following anesthesia to assess the time dependence of the halothane distribution. The results of these experiments demonstrate that halothane and halothane metabolite are unequally partitioned through the rat tissues examined. 19F spin‐echo imaging experiments were conducted immediately following anesthesia. The results of these experiments are compared with those of the spectroscopic technique. © 1989 Academic Press, Inc.
Single‐scan volume‐selective spectral editing by homonuclear polarization transfer
Authors: Knüttel A. , Kimmich R.
Published: March 2007

An RF and field gradient pulse sequence is presented permitting the single‐scan volume‐selective spectral editing of the signals of coupled spins. The attribute “single scan” means that the editing of resonance lines is performed in each accumulation or phase cycling scan rather than by subtraction of independently acquired signals. As an example the methyl line of lactate has been investigated. The method is considered to be a useful tool in biomedical research using lactate as an ischemic parameter. The basic principles applied are the VOSY pulse scheme for volume selection and the INEPT sequence for homonuclear polarization transfer from the CH to the CH3 groups. As an intrinsically single‐scan editing method (“homonuclear single‐scan VOSING procedure”), the pulse train is expected to provide results that are more reliable than the two‐scan subtraction methods previously reported. © 1989 Academic Press, Inc.
23Na NMR measurement of the maximal rate of active sodium efflux from human red blood cells
Authors: Knubovets T. L. , Revazov A. V. , Sibeldina L. A. , Eichhoff U.
Published: March 2007

The method for 23Na NMR measurement of the maximal rate of active Na+ efflux from human red blood cells (RBC) is proposed. The nonpenetrating paramagnetic shift reagent (SR) bis(tripolyphosphate)dysprosium(III) complex is used to distinguish extracellular Na+ ions from intracellular. RBC are proved to retain their physiological activity in the presence of SR. Intracellular Na+ is shown to be 100% NMR visible. The levels of intracellular and extracellular Na+ and K+ ions are changed to decrease their concentration gradients across the erythrocyte membrane to make active Na+ efflux the only 23Na NMR measurable process; so the integrated areas of intra‐and extracellular Na+ peaks remain invariant throughout the incubation period in the presence of 0.25 mM ouabain, a specific inhibitor of Na+, K+‐ATPase. The accuracy of the proposed technique is evaluated to be 10%. The maximal Na+ efflux is determined to be 10.1 ± 1.0 mM/h/liter of Cells. © 1989 Academic Press, Inc.
Determination of triacylglycerol lipase activity using carbon‐13‐labeled triacylglycerols and nuclear magnetic resonance spectroscopy: Evidence that hepatic lipase hydrolyzes medium‐chain triacylglycerols
Authors: Dimand R. J. , Bradbury E. M. , Cox K. L.
Published: March 2007

Triacylglycerol lipse activity was studied using glycerol [1‐13C] trioctanoate mixed with postheparin rat plasma. 13C NMR spectroscopy demonstrated triacylglycerol hydrolysis into free fatty acids with no difference at the 1,3 or 2 glycerol positions. There was no inhibition by high sodium concentration, consistent with lipase of hepatic origin. © 1989 Academic Press, Inc.
Addendum to “Rapid Local Rectangular Views and Magnifications: Reduced Phase Encoding of Orthogonally Excited Spin Echoes”
Authors: Conturo Thomas E. , Price Ronald R. , Beth Albert H.
Published: March 2007

Attention is called to a previous work of Feinberg et al. on inner volume MRI, a work which was not known to the present authors when preparing a recent similar manuscript on imaging local fields of view. The rationale is discussed for tandemly offsetting the reconstruction window and excited volume. © 1989 Academic Press, Inc.
In vivo pharmacokinetics by electron magnetic resonance spectroscopy
Authors: Berliner Lawrence J. , Wan Xiaoming
Published: March 2007

Low‐field in vivo electron spin resonance (ESR) has been used to follow the course of metabolism and distribution of a paramagnetic spin probe, 3‐carboxamido‐2,2,5,5‐tetramethylpyrrolidine‐1‐oxyl. Sprague‐Dawley rats (250‐300 g) were catheterized in the jugular vein and given serial doses ofthe nitroxide spin probe above. The decrease in the tail blood nitroxide ESR spectrum with the time was followed. This reflects both normal distribution/excretion and a significant metabolic step–reversible reduction of the nitroxide group to its hydroxylamine. The studies serve as important and useful comparisons to the nitroxide reduction kinetics in vitro while offering the important advantage of avoiding those non‐steady‐state artifacts frequently expected in ex vivo procedures. This study represents the first report of systematic in vivo phannacokinetics of a paramagnetic probe. © 1989 Academic Press, Inc.
The uncommon longitudinal relaxation dispersion of human brain white matter
Authors: Fischer Helmut W. , Van Haverbeke Yves , Schmitz‐Feuerhake Inge , Muller Robert N.
Published: March 2007

Human brain white matter exhibits an uncommonly strong dispersion of 1/T1 at high fields. An additional relaxation pathway via the myelin lipids, which are not directly visible to medical NMR due to their fast T2 decay, is proposed. Relaxation dispersion data are successfully analyzed on the basis of this model. © 1989 Academic Press, Inc.
Fluid shear and spin‐echo images
Authors: Kuethe Dean O. , Herfkens Robert J.
Published: March 2007

Because clinical studies have indicated that shear in fluids may be one of the major causes of magnetic resonance image artifacts, we imaged an apparatus that would separate the effects of shear from the plethora of other motion artifacts. The apparatus contained fluid between two concentric cylinders. To produce shear, we turned the outer cylinder. To produce motion without shear, we turned both cylinders as one. Shear rates near 200 s−1 (similar to those in large arteries) can cause pixel intensities either to increase 40% or decrease to background levels. Increases can occur when the velocities are nearly parallel to the phase‐encoding gradient. Decreases can occur when velocities are in the direction of the frequency gradient. The decreases are similar to those predicted from phase dispersion within a “voxel” so long as the voxel's phase warp does not exceed 2π. © 1989 Academic Press. Inc.
A model of acute regional myocardial ischemia and reperfusion in the rat
Authors: Sievers R. E. , Schmiedl U. , Wolfe C. L. , Moseley M. E. , Parmley W. W. , Brasch R. C. , Lipton M. J.
Published: March 2007

Studies were conducted in 76 rats to describe and validate a new closed‐chest in vivo model for acute ischemia and reperfusion of the left coronary artery. Radiolabeled microsphere distribution in six rat hearts confirmed a significant reduction in arteriolar flow at the center of the ischemic zone (93% reduction of total myocardial counts compared to nonischemic region, P < 0.01) after 7 min of occlusion. Arteriolar flow returned to control values upon reperfusion. While hemodynamic parameters in 10 ratsduring 7 min of occlusion and 7 min of reperfusion were monitored, end diastolic pressures increased significantly (P < 0.01) during occlusion. Finally, the utility of this rat model was demonstrated in a study of contrast enhanced magnetic resonance imaging (N=4). Normal myocardium could not be differentiated from acutely ischemic myocardium on noncontrast‐enhanced MR images. After 5 min of myocardial ischemia and following contrast administration (albumin‐Gd‐DTPA), the ischemic zone appeared less enhanced than normal myocardium. Upon release ofthe occluder the left ventricular free wall once again yielded a homogeneous signal similar to that of the normal myocardium. © 1989 Academic Press, Inc.
Snapshot imaging at 0.5 t using echo‐planar techniques
Authors: Ordidge R. J. , Howseman A. , Coxon R. , Turner R. , Chapman B. , Glover P. , Stehling M. , Mansfield P.
Published: March 2007

Echo‐planar imaging using a magnetic field strength of 0.5 T has resulted in an improvement in image quality compared with recent images published at 0.1 T. The sensitivity of the technique to main magnetic field inhomogeneity and transient eddy currents has necessitated innovations in gradient and radiofrequency coil design. These improvements are described, and new variations in the echo‐planar pulse sequence which provide better contrast and allow separate imaging of water and fat distributions are presented. © 1989 Academic Press, Inc.
Magnetic field modulation of receptor binding
Authors: Chiles Catherine , Hawrot Edward , Gore John , Byck Robert
Published: March 2007

Although it is widely held that the magnetic fields encountered during magnetic resonance imaging (MRI) and other procedures have no discernible effect on biological systems, we find that at early times of incubation, the amount of binding of the neurotoxin, α‐bungarotoxin, to nicotinic acetylcholine receptor is significantly reduced in a constant 2.0‐T magnetic field. This finding suggests that steady magnetic fields can directly affect the functional activity of biologically important macromolecules, in this particular case a neurotransmitter receptor. © 1989 Academic press, Inc.
High field localized proton spectroscopy in small volumes: greatly improved localization and shimming using shielded strong gradients
Authors: van Zijl Peter C. M. , Moonen Chrit T. W. , Alger Jeffry R. , Cohen Jack S. , Chesnick Scott A.
Published: March 2007

The availability of shielded gradients facilitates accurate single‐voxel localized spectroscopy. Exact localization (90−99%) of volumes as small as 2 × 2 × 2 mm is demonstrated using a modified stimulated echo sequence. Strong gradient pulses (up to 200 mT/m) are employed to clear the stimulated echo of unwanted magnetization, enabling superior (single‐scan) shimming of the selected volume. In vivo and in vitro proton NMR results at 4.7 T are presented. © 1989 Academic Press, Inc.
In vivo localized ESR spectroscopy reflecting metabolism
Authors: Bacic G. , Nilges M. J. , Magin R. L. , Walczak T. , Swartz H. M.
Published: March 2007

Localized electron spin resonance spectroscopy in Live mice was performed using a surface coil operating at 1.1 GHz with sufficient sensitivity and stability to measure quantitatively the time course of the distribution, uptake, and reduction of nitroxides in selected organsfregions (liver, bladder, head) of mice. The ability to measure regional concentrations of nitroxides in vivo could be used for pharmacokinetic analysis of drugs labeled with nitroxides and for measurement of oxygen concentrations and redox metabolism. © 1989 Academic Press, Inc.
Self‐refocusing 270° gaussian pulses for slice selection without gradient reversal in magnetic resonance imaging
Authors: Emsley Lyndon , Bodenhausen Geoffrey
Published: March 2007

It is demonstrated, on the grounds of simulations, how 270° Gaussian pulses can be used for slice selection in nuclear magnetic resonance imaging experiments. It is shown that the usual gradient reversal procedure can be omitted if the selective 90° pulse normally used is replaced by a self‐refocusing 270° pulse with a Gaussian timedomain amplitude profile, and some of the properties which are specific to this type of pulse are explored. © 1989 Academic Press, Inc.
An automated iterative algorithm for the quantitative analysis of in vivo spectra based on the simplex optimization method
Authors: Lenkinski Robert E. , Allman Tim , Scheiner Jacob D. , Deming Stanley N.
Published: March 2007

The success in utilizing in vivo NMR to identify and/or monitor metabolic abnormalities will be determined in large part on the reliability with which the spectral parameters of the metabolites present can be measured. For these reasons it is clear that there is a need for the development of algorithms with which to obtain quantitatively reliable estimates ofthe spectral parameters ofthe peaks present. In this report we describe an adaptation of the simplex algorithm which we have found useful in fitting in vivo spectral data in the frequency domain. This simplex algorithm was implemented on an IBM‐PC AT compatible computer. We evaluated the simplex algorithm on three representative kinds of spectral data: a simulated spectrum, 31P spectrum of normal calf muscle, and the 31P spectrum of a pediatric patient with a brain tumor. In each case we generated a set of spectra by adding varying amounts of noise. On the basis of our simulations and the two examples discussed, we conclude that the simplex method generates parameters which are reliable estimates of the areas of the peaks present when the signal‐to‐noise is above 8:1 for phosphocreatine. We found that the speed of convergence of the algorithm was improved by overestimating the linewidths of the peaks present. We also found that the method converged more rapidly in the presence of a moderate amount of noise. We conclude that the algorithm described here can provide a robust method with which to analyze in vivo spectra in a quantitative manner. Because the method requires little user intervention, it lends itself to implementation in a semi‐, or fully, automated fashion. © 1989 Academic Press, Inc.
Use of ultralong echo time imaging to assist in measuring the velocity of perfused flow in vivo
Authors: Young I. R. , Coutts G. A. , Bryant D. J. , Bydders G. M.
Published: March 2007

The measurement of the velocity of perfused flow in tissue in vivo is complicated by the presence ofstationary as well as moving spins and by a variety ofdephasing phenomena which affect signal amplitudes. This paper describes a technique by which, using flow‐sensitized spin‐echo sequences with a set of very long TE times, the velocity of the moving component can be assessed. © 1989 Academic Press, Inc.
Myocardial creatine kinase exchange rates and 31P NMR relaxation rates in intact pigs
Authors: Martin Joel F. , Guth Brian D. , Griffey Richard H. , Hoekenga David E.
Published: March 2007

In this study, we used 31P NMR to investigate the relationship between cardiac work load and creatine kinase flux in intact pigs. NMR measurements were performed on anesthetized miniature swine in which a surface coil was surgically implanted on the surface of the left ventricle. Cardiac workload was varied by infusion of norepinephrine. Phosphate exchange between creatine phosphate and ATP was measured by a combined saturation transfer, saturation recovery pulse sequence. Exchange measurements showed that creatine kinase flux and concentrations of PCr and ATP were independent of workload for a 2.5‐fold range of cardiac rate‐pressure products. It appears that, if creatine kinase flux is coupled to work load, the pig heart operates in a regime where small changes in metabolite concentrations or creatine kinase flux are sufficient to maintain elevated workloads. Exchange and relaxation measurements, at 2.0 and 4.7 T, yielded T1 relaxation times for creatine phosphate and ATP which are longer than most reported values. Analysis of the T1 data indicates that chemical‐shift anisotropy is a plausible mechanism for a portion of the spin‐lattice relaxation rate at high field strengths. © 1989 Academic Press. Inc.
Motional phase artifacts in fourier transform MRI
Authors: Wedeen Van J. , Wendt Richard E. , Jerosch‐Herold Michael
Published: March 2007

Most magnetic resonance imaging (MRI) techniques are subject to a “motional blurring” arising from the acquisition of data in the presence of a frequency‐encoding gradient. The Fourier transform of the signal from a spin moving along a magnetic field gradient obeys an equation analogous to the free space Schrijdinger equation. Computer simulations of the Bloch equations illustrate the implications of this motional blurring in MRI. © 1989 Academic Press, Inc.
Problems with achieving saturation using methods based on bursts of rf pulses with spoilers in magnetic resonance imaging
Authors: Young I. R. , Bydder G. M. , Bryant D. J.
Published: March 2007

Attempts at saturation by nonselective rf pulses, followed by gradient spoiler pulses, are sometimes used as the basis of a method of measuring T1 in magnetic resonance imaging, because a method of this type is perceived as being less affected by slice shape artifact than partial saturation methods. This note suggests that, unless care is taken, this assumption can be quite erroneous.
In vivo31P nuclear magnetic resonance spectroscopy of rat 9l gliosarcoma treated with BCNU: Dose response of spectral changes
Authors: Grant Steen R. , Tamargo Rafael J. , Brem Henry , Glickson Jerry D. , Wehrle Janna P.
Published: March 2007

The 9L gliosarcoma, grown subcutaneously in juvenile Fischer 344 rats, was studied by in vivo 31P NMR spectroscopy following treatment with 1,3‐bis(2‐chloroethyl)‐ 1‐nitrosourea. Dose‐dependent increases in the proportion of high‐energy phosphates were observed for doses between 10 and 36 mg/kg (from 80% of the LD10 to greater than the LD50). These doses reduced clonogenic cell survival in a dose‐dependent fashion by as much as 3 log orders and resulted in up to 16 days of growth delay (to pretreatment tumor volume). Increases in high‐energy phosphates (relative to Pi) in the tumor were greater at higher doses despite the higher levels of clonogenic cell killing and the substantial host Systemic toxicity.
Conformal NMR spectroscopy: Accurate localization to noncuboidal volumes with optimum SNR
Authors: Sharp Jonathan C. , Leach Martin O.
Published: March 2007

“Conformal Spectroscopy” is a general method for the acquisition of accurately localized NMR spectra from noncuboidal regions with optimum signal‐to‐noise ratio (SNR). The method is based upon the localization of volumes defined by a number of intersecting oblique slices and may be implemented using standard imager hardware. Conformal techniques can enhance many existing localization sequences such as ISIS (31P) and STEAM (1H) resulting in typical SNR improvements of around 1.8, equivalent to a more than threefold reduction in acquisition time. Applications include in vivo tumor Spectroscopy.
A computer simulation of T2 decay effects in echo planar imaging
Authors: Oshio Koichi , Singh Manbir
Published: March 2007

The effect of spatially variant T2 decay in echo planar images has been investigated. A simple, direct method to remove T2 effects, requiring no knowledge of actual T2 values, is also reported. The method is based on taking the geometric mean of two Hermitian symmetric data points before Fourier transformation.