bluuebunny/crossref_metadata_2025 huggingface dataset:
Shielded gradient coils and radio frequency probes for high‐resolution imaging of rat brains
Authors: Jasinski Andrzej , Jakubowski Tomasz , Rydzy Marek , Morris Paul , Smith Ian C. P. , Kozlowski Piotr , Saunders John K.
Published: March 2007

A shielded gradient system and radio frequency probes for a 4.7‐T/30‐cm horizontal bore magnet are described. The systems were designed principally to obtain images and localized spectra from rat brains. The gradients can operate in either a shielded or non shielded mode. The rf probe, which combines both highest sensitivity and highest resolution, consists of a large modified saddle type transmitter and a small surface reception coil, actively decoupled using diodes. The system performance is demonstrated on phantoms and on a rat brain, where an image with in plane resolution of 80μ m and a slice thickness of 150 μm is obtained. © 1992 Academic Press, Inc.
Magnetic resonance imaging of the uterine cervix using an intravaginal coil
Authors: Baudouin C. J. , Soutter W. P. , Gilderdale D. J. , Coutts G. A.
Published: March 2007

Cylindrical receiver coils designed for intravaginal use were utilized to image the uterine cervix. Good quality images of the cervix, vaginal wall, and parametrium were obtained and patient tolerance of the procedure was good. © 1992 Academic Press, Inc.
In vivo dynamic MR imaging of MBP‐induced acute experimental allergic encephalomyelitis in Lewis rat
Authors: Namaer I. J. , Steibel J. , Poulet P. , Armspach J. P. , Mauss Y. , Chambron J.
Published: March 2007

A dynamic in vivo study by MRI consisting of the measurement of relaxation times and in the visualization of the BBB permeability by Gd—DOTA was performed in an MBP‐induced acute EAE model of Lewis rat. Fourteen rats were immunized with an MBP/CFA mixture, eight by CFA alone, and three control rats were used to test the harmless effect of repeatedly performed MRI examinations. Beginning on the 8th or 9th days and in parallel with the emergence of clinical signs, rats immunized by the MBP/CFA mixture showed slight increases of relaxation times and of the BBB permeability. These abnormalities which always remain localized in the periventricular regions, become more pronounced toward the 10th and 11th days, just before (or at the same time) as paraplegia manifestations. After a plateau of a few days, they diminish with the clinical signs. This close correlation found in vivo establishes the essential role of BBB in the pathogenesis of clinical signs of this EAE model. © 1992 Academic Press, Inc.
31P MRS as an early prognostic indicator of patient response to chemotherapy
Authors: Redmond O. M. , Stack J. P. , O'Connor N. G. , Carney D. N. , Dervan P. A. , Hurson B. J. , Ennis J. T.
Published: March 2007

In this study 31P spectral changes were closely monitored following the initial administration of cytotoxic drugs and related to five parameters of patient response. Pre‐ and postchemotherapy 31P MRS examinations were performed on 16 patients with large, malignant tumors. These included four tumor types: (i) lymphoma (n = 7),(ii) breast carcinoma (n = 4), (iii) musculoskeletal tumors (n = 4), and (iv) adenocarcinoma (n = 1). A mean of 5 spectra/patient (range 2–10) was performed following the initial chemotherapy. The spectral trends exhibited by 14 of 16 patients reached “points of maximum change,” after which they began to revert toward prechemotherapy values. In 2 of 16 patients that did not respond to the initial chemotherapy regimen, no spectral trends were observed. The degree of change of certain spectral parameters, namely, decreases in PME, PME/ PDE, PME/PCr, PME/NTP, PDE/PCr, and tumor pH, as well as increases in the ratios Pi/PME and Pi/PDE, were associated with good patient response and separated responders from nonresponders. Pi/PME appears the most promising for discriminating partial from Complete responders.
Detection of significant features and statistical analysis of 2D and 3D images of 31p metabolites
Authors: Nelson Sarah J. , Vigneron Daniel B. , Brown Truman R.
Published: March 2007

The application of spectroscopy techniques to the study of normal and pathological tissue is currently limited by the difficulties of acquiring precisely localized spectraand analyzing the resulting, relatively low signal‐to‐noise data. Interpretation of multivoxel spectroscopy data is greatly facilitated by estimating peak parameters and representing their spatial distribution as metabolite images. We present herethe new algorithm MIM‐STATS, which performs an analysisof these images and determines whether the variations in the images are statistically significant. The algorithmhas been developed and tested by application to 31P CSI data from the human forearm and brain. Our results demonstrate that MIMSTATS can detect signal at a very low signal‐to‐noise ratio in a reliable and reproducible fashion and provides a sound basis for testinghypotheses concerning differences in distribution of metabolites.
Analysis of the temporal and spatial dependence of the Eddy current fields in a 40‐cm bore magnet
Authors: Robertson S. , Hughes D. G. , Liu Q. , Allen P. S.
Published: March 2007

Eddy current fields, generated in an animal‐size superconducting NMR magnet by a nominally rectangular pulsed transverse gradient applied in the vertical direction, have been studied by measuring the offset frequency of the proton NMR signal obtained from a small spherical sample. Measurements were made, after various time delays, at nine different locations in the sample space. Analysis of the data shows that the time‐dependent fields at all nine locations are quite well accounted for by the superposition of only four independent exponentially decaying components that have time constants in the range from 9 to 400 ms. Two of these were found to be caused by eddy currents generated in the magnet structure. They generate primarily linear gradients, though one of them also produces a B0 shift, indicating a significant asymmetry about the isocenter of the conducting structure in which the eddy current flows. The other two exponentially decaying components, which had very different time constants from the eddy currents and also initial amplitudes of the opposite sign, were generated by the preemphasis unit. This calls into question the procedure used to adjust the preemphasis unit and an alternative method is proposed.
Analysis of encoding efficiency in MR imaging of velocity magnitude and direction
Authors: Contur Thomas E. , Robinson Bruce H.
Published: March 2007

The efficiency of balanced versus unbalanced techniques for phase‐angle‐based velocity magnitude and direction imaging is investigated. Methods having balanced flow‐encoding gradients (gradients in positive and negative directions with a zero center of gravity) are compared with unbalanced methods. For three‐dimensional imaging, a currently used balanced method is the six‐point technique having opposed gradients pairs for each orthogonal direction. A currently used unbalanced method is a four‐point null technique which has three orthogonal gradients and an additional acquisition having no specific flow encoding to correct the baseline (null) phase. In the gradient‐limited case of slow flow and perfusion. the balanced method is predicted to have higher velocity magnitude‐to‐noise ratio per time (SNRv) by a factor of 1.63, with similar results for velocity direction. In the wraparound‐limited case of faster flows and motions, similar results are found when a null acquisition is added to the balanced method. This results in a seven‐point balanced method having an SNRv, 1.51 times that of the four‐point unbalanced method. If null phases are within the [–π/2, π/2] interval, this additional null acquisition is unnecessary. Other four‐point methods are also considered. These results indicate that, in general, balanced methods have advantages over unbalanced methods for velocity imaging. © 1992 Academic Press, Inc.
The application of 13C NMR to the characterization of phospholipid metabolism in cells
Authors: Ronen Sabrina M. , Degani Hadassa
Published: March 2007

31P and 31C NMR spectroscopy of lipid extracts of T47D human breast cancer spheroids and the use of 13C‐labeled lipid precursors [3‐13C ] serine, [1,2‐13C] ethanolamine, and [1,2‐13C]choline enabled us to determine the rate of 13C incorporation into the major phos‐pholipids and to show that the synthesis of phosphatidylethanolarnine in T47D cells is via both the CDP‐ethanolamine pathway and serine decarboxylation, with the extent of each depending on the concentration of ethanolamine in the medium. In the presence of low ethanolamine (3.4 μ M), both pathways contribute in equal proportions, while in the presence of high ethanolamine, the CDP‐ethanolamine pathway predominates. © 1992 Academic Press, Inc.
Theory of contrast agents in magnetic resonance imaging: Coupling of spin relaxation and transport
Authors: Bauer W. R. , Schculten K.
Published: March 2007

The role of diffusive transport on the enhancement of nuclear spin relaxation through NMR contrast agents is described by means of diffusion‐Bloch equations. These equations are solved in the mean relaxation time approximation [W. Nadler and K. Schulten, J. Chem. Phys. 82, 151‐160 (1985)]. A model presented considers relaxation enhancement in tissue in which contrast agents confined to intravascular spaces affect nuclear spin in the extravascular volume. We show how the mean relaxation time depends on capillary density, on permeability, and on diffusion. A second model describes enhanced phase relaxation of liver tissue in the presence of magnetic particles in Kupffer cells. The relationship between relaxation rate and density of Kupffer cells is investigated. The diagnostic value of enhanced nuclear relaxation in the presence of contrast agents is discussed on the basis of the systematic mathematical results obtained.
31P NMR of electrically stimulated rectus femoris muscle: An in vivo graded exercise model
Authors: Matheson Gordon O. , Mckenzie Donald C. , Gheorghiu Daniel , Ellinger David C. , Quinney H. Arthur , Allen Peter S.
Published: March 2007

This study reports on the development of a model for studying skeletal muscle metabolism in humans using NMR spectroscopy. Graded exercise was simulated using electrical stimulation in 10 healthy, fit subjects (mean VO2max = 53 ± 4 ml. kg‐1 min‐1). The effects of varying the stimulation parameters, namely, the stimulation frequency, the stimulation intensity, and the duty cycle, as well as the spectral interrogation volume, were compared using data acquired from the rectus femoris muscle. With stimulation, the inorganic phosphate to phosphocreatine concentration ratio ([P1]/ [PCr]) and the intracellular pH both follow curvilinear relationships over the stimulation frequencies from 3 to 30 Hz, with the magnitude of the observed change related closely to stimulation intensity and duty cycle. Oxidative phosphorylation predominates at stimulation frequencies below 12 Hz, while anaerobic metabolism increases sharply above 12 Hz. Our findings show clearly the interdependence of the effects of the various stimulation parameters and emphasize the care that must be exercised in interpreting the physiological significance of the biochemical data obtained from electrical stimulation models used to study skeletal muscle metabolism.
Proton nuclear magnetic resonance lineshape studies on human blood plasma lipids from newborn infants, healthy adults, and adults with tumors
Authors: Hiltunen Y. , Ala‐Korpela M. , Jokisaari J. , Eskelinen S. , Kiviniitty K.
Published: March 2007

The usefulness of proton NMR spectroscopy of human blood plasma for cancer research has been extensively studied in recent years. Two main starting points have been offered by Fossel et al. (N. Engl. J. Med. 315, 1369 (1986)) and Mountford et al. (FEBS Lett. 203, 164 (1986)). In this work the experimental proton NMR spectra of blood plasma were analyzed with the aid of the multivariate lineshape fitting method. An appropriate model structure, in terms of the various lipoprotein (VLDL, LDL. and HDL) signals, for the methylene region was used. Neonates, healthy adults, and adults with nonmalignant and malignant tumors were studied. The linewidth of the methylene region was found to be linearly dependent on the relative concentrations of the lipoproteins. The correlation coefficient was ‐0.89 (P < 0.001) for VLDL and 0.88 (P < 0.00 1) for HDL. A correlation between VLDL concentration and age, 0.76 (P < 0.001), was also established. VLDL was modeled using two components. The half‐linewidth of the lower field component was slightly elevated for the adults with large metastases. This might be in association with the fucose‐containing proteolipid complex detected earlier in cancer cells or in sera of cancer patients. Some signals of this complex may fall in the same region of the spectra. The spectra for the neonates were indicated to be totally different from the adults. This and other related questions were explained by means of the model parameters and the relative concentrations of the lipoproteins VLDL, LDL, and HDL. The presented technique can be used as a rapid research tool for figuring out the relative concentrations of the lipoproteins in blood plasma and explaining the reasons behind the changes in the spectra.
Rapid T1 estimation using tagged magnetization‐prepared gradient‐echo MR imaging
Authors: Niitsu Mamoru , Campeau Norbert G. , Riederer Stephen J. , Anno Izumi , Itai Yuji
Published: March 2007

A technique for estimation of the longitudinal relaxation time of a large homogeneous object with an acquisition time of 4s or less was developed by combining spatially selective rf tagging pulses with a T1‐weighted magnetization‐prepared gradient‐echo sequence. Multiple 5‐mm‐wide tagged areas are laid orthogonal to the imaging section of interest. The contrast between each tag and the untagged regions differs because each tag is produced at a different time. The T1 value is determined from the nulling time at which tagged and untagged areas have no contrast.
Effect of lithium on the double‐quantum behavior of 23na in normal human erythrocytes
Authors: Gullapalli Rao P. , Hawk Roger M. , Komorosk Richard A.
Published: March 2007

The doublé‐quantum behavior of 23Na in the presence of different concentrations of Li in human erythrocytes was investigated. The 23Na double‐quantum signal was quenched in both the extracellular and the intracellular compartments with increasing concentration of Li in each compartment, along with an increase in the 23Na T1 both intra‐ and extracellularly. Some extracellular quenching could be observed at the near therapeutic concentration of 2 mM Li. The ratio of slow to fast spin‐spin (T2) relaxation times, obtained from the dependence of the double‐quantum signal on creation time, approached unity at an overall Li concentration of 40 mM. These results provide evidence that Li and Na compete for both intra‐ and extracellular binding sites in erythrocytes.
A nuclear magnetic resonance investigation of the upper airways in ferrets. ii. contrast‐enhanced imaging to distinguish vascular from other nasal fluids
Authors: Reo Nicholas V. , Alexander Marise E. , Goel Rashmi
Published: March 2007

Proton magnetic resonance imaging (MRI), used in conjunction with the intravascular contrast agent albumin‐(Gd‐DTPA), provides a means to distinguish vascular fluids from other nasal fluids in the upper airways. Ferrets were given an intravenous dose of albumin‐(Gd‐DTPA) followed by an intranasal challenge with either histamine (HS) or methacholine (MC). An observed increase in image intensity indicates that HS and MC both cause an accumulation of fluids in the nasal turbinate region. The MRI data are also influenced by the presence of blood, which contains the contrast agent, and a clear distinction can be made between vascular fluids and other nasal fluids (i.e., cellular and glandular secretions). The results show that HS causes an increase in vascular fluids in the nasal turbinates while MC does not. This methodology represents a new means to investigate airway pharmacology and the pathophysiology associated with various pharmacological agents, allergens, or viral infections.
The design of liposomal paramagnetic mr agents: effect of vesicle size upon the relaxivity of surface‐incorporated lipophilic chelates
Authors: Tilcock Colin , Ahkong Quet Fah , Koenig Seymour H. , Brown Rodney D. , Davis Mark , Kabalka George
Published: March 2007

The 1/T1 NMRD profiles of lipid vesicles with the paramagnetic ion Gd attached via a chelate covalently linked to the membrane surface show a peak at approximately 20 MHz indicating that fluctuations of ∼10−8 contribute to the form of the dispersion profile. If the correlation time for fluctuations of the paramagnetic chelate on the membrane surface is much less than the correlation time for rotation of the lipid vesicle, it would be expected that the measured 1/T1 relaxation rate for solvent protons should be invariant with vesicle size above a certain minimum vesicle diameter. We show that this is indeed the case for vesicles in the size range 50 to 400 nm average diameter and discuss general design considerations for the preparation of vesicle‐associated MR contrast agents based upon paramagnetic chelates either trapped within the vesicle interior or attached to the membrane surface.
Characteristics of extracellular sodium relaxation in perfused hearts with pathologic interventions
Authors: Foy Brent D. , Burstein Deborah
Published: March 2007

Sodium spectroscopy and imaging sequences designed to emphasize fast T2 decay or the multiple quantum signal have previously demonstrated a high contrast between normal and pathologic tissue which may be due to changes in intracellular versus extracellular sodium distribution. Since alterations in the amount of signal with fast T2 decay have previously been shown to occur with changes in intracellular sodium content, this study investigated the fast T2 relaxation characteristics of extracellular sodium during pathologic interventions on nonsubmerged perfused rat hearts. T2 data on total sodium content were obtained while global ischemia (stopping all perfusate flow) and extracellular edema (due to long perfusion times) were induced in the heart. The data were fit to a biexponential, with Mf (T2f) the magnitude (time constant) of the fast component of decay. Mf increased significantly in both pathologies (to 319 ± 26%, n = 3, of baseline for ischemia and to 527 ± 284%, n = 3, of baseline for edema); the increase with edema was demonstrated to be due to extracellular sodium by intermittently perfusing the heart for a short period with shift reagent. When shift reagent was not used until the conclusion of the edema experiment, Mr increased to 169 ± 35% of baseline, also due mainly to extracellular sodium. T2f did not exhibit any trends with these experiments, with values ranging from 1.7 to 5.5 ms. We believe that these results indicate that compartmental sodium content will most likely not be quantifiable in pathologic states in the heart with relaxation‐based techniques. However, correlations between the pathologic state of the tissue and the sodium NMR signal obtained with pulse sequences or images that emphasize a particular aspect of relaxation may prove to be Useful.
Nuclear magnetic relaxation dispersion profiles of aqueous solutions of a series of gd(nota) analogs
Authors: Geraldes Carlos F. G. C. , Brown Rodney D. , Brucher Erno , Koenig Seymour H. , Sherry A. Dean , Spiller Marga
Published: March 2007

Nuclear magnetic relaxation dispersion (NMRD) profiles and ESR linewidths have been measured for a series of neutral Gd3+ ‐triazamacrocyclic complexes and compared with previous data for the simplest member of the macrocyclic triaza series, Gd(NOTA), and for the widely studied linear triaza complex, Gd(DTPA)2‐. Water proton relaxivities and their temperature dependence were found to vary widely with the size of the triaza macrocycle and the identity of the side‐chain chelating groups. The number of rapidly exchanging water molecules directly coordinated to the Gd3+ ion (q) was found to vary from 2 to 4 for eight of the ten complexes examined and a linear relationship between the 50‐MHz relaxivity value and integral values of q is presented for this series of complexes. τs values derived from ESR linewidths for some of the complexes are in reasonable agreement with those derived from their NMRD profiles; however, those complexes which either tended to form aggregates in solution or gave evidence for multiple averaged solution structures showed broad, near Lorentzian linewidths which were clearly not dominated by the electron spin relaxation time (τs).
Changes in probe sensitivity during nmr spectroscopic studies of the perfused rat heart: a warning
Authors: Nédélec Jean‐François , Saunders John K. , Morris Paul , Clarke Kieran
Published: March 2007

During NMR experiments on isolated, perfused rat heart, we observed a 57% change in probe sensitivity when the perfusion buffer surrounding the heart was replaced by either a low‐ionic‐strength mannitol solution or air and the heart was made ischemic. Such changes in sensitivity, should they go unrecognized, would result in substantial quantification errors.
A simple procedure for obtaining high‐quality nmr spectra of semiquantitative value from small tissue specimens: cervical biopsies.
Authors: Kuesel Annette C. , Kroft Thérèse , Saunders John K. , Préfontaine Michel , Mikhael Nadia , Smith Ian C. P.
Published: March 2007

The handling of small tissue biopsy samples (<100 μl) for NMR investigations poses special problems. Optimal and stable positioning of the samples within the sensitive volume of the radiopfrequency coil can be achieved by inserting the sample in a capillary. Methods for quantitation of the spectral information from samples requiring histological evaluation after the NMR experiment are discussed, in particular with respect to cervical biopsies.
NMR Venography Using the Susceptibility Effect Produced by Deoxyhemoglobin
Authors: Cho Z. H. , Ro Y. M. , Lim T. H.
Published: March 2007

A new angiography technique using the susceptibility effect is proposed. Blood containing deoxyhemoglobin is more paramagnetic than surrounding tissue and thereby produces a susceptibility effect at blood‐tissue interfaces. By use of a specially tailored RF pulse, signals from normal tissues are suppressed while the signals from blood interfaces, where strong susceptibility‐induced fields are created, are enhanced. The design and characteristic behavior of the tailored RF pulse are discussed and experimental results obtained using both a phantom and a human volunteer with a 2.0‐T whole‐body NMR system are also presented.© 1992 Academic Press,Inc.
Phasing Spin‐Echo‐Acquired 31P Spectroscopic Images Using Complex Conjugate Data Reversal
Authors: Bourgeois Dominique , Deslauriers Roxanne
Published: March 2007

A simple method has been developed for phasing 31P spectroscopic images acquired with short echo‐time (1–2 ms) spin‐echo sequences. The technique is based on reconstructing complete echoes in the time domain by the reversal of the complex conjugate of the data. After Fourier analysis, a magnitude reconstruction is used, which no longer broadens the lines. Advantages of the method compared to other phasing procedures are discussed.© 1992 Academic Press,Inc.
Feasibility of 19F Imaging of Perfluorochemical Emulsions to Measure Myocardial Vascular Volume
Authors: Judd Robert M. , Rottman Gerald A. , Forder John R. , Yin Frank C. P. , Blackband Stephen J.
Published: March 2007

19F magnetic resonance images were obtained of the ventricular walls of isolated rabbit hearts perfused with a perfluorochemical (PFC) emulsion. Since the PFC is known to stay within the vascular space in normal myocardial tissue, the 19F signal should reflect myocardial vascular volume. 19F MRI of PFC emulsions represents a new investigational tool for the study of coronary vascular volume.© 1992 Academic Press,Inc.
Sodium Ion Transport in Rat Hearts during Cold Ischemic Storage: 23Na and 31P NMR Study
Authors: Askenasy Nadir , Vivi Antonio , Tassini Maria , Navon Gil
Published: March 2007

The success of heart transplantation is limited by the negative correlation between the length of the cold ischemic storage period and the quality of functional recovery. We use 23Na, 31P NMR spectroscopy, and hemodynamic parameters to describe temperature‐dependent changes in sodium influx and the concentration of phosphorus high‐energy compounds during different storage periods. Perfusion with Krebs—Henseleit solutions containing Dy(TTHA)3‐ permitted discrimination of intra‐ and extracellular sodium during cold ischemic storage. The 23Na NMR visibilities under the acquisition and processing parameters used in our experiments were 40 ± 4% for the intracellular compartment and 97 ± 11% for the extracellular compartment. At 4°C, the intracellular Na+ accumulation exceeded that observed at 15 and 22°C. The ATP and PCr depletion rates were much lower at 4°C and the left ventricular contractility was higher after longer periods of storage, as the storage temperature decreased. The intracellular Na+ concentration cannot serve as a marker for the postischemic recovery probability. The relative activity of the Na/K ATPase pumps is not correlated with the preservation success. However, intracellular sodium ion accumulation is a major factor in the time lag of the reperfusion recovery.© 1992 Academic Press,Inc.
Simultaneous Imaging of Proton and Fluorine at Moderate Field
Authors: Lou Th. , Briguet A. , Deguin A. , Desgoutte P. , Lapray C.
Published: March 2007

Simultaneous imaging of proton and fluorine nuclei distributed in a unique sample has been performed by multiplexing the receiver coil's frequency for nmr signal acquisition. Implementation of the technique and modifications of a conventional spectrometer are described for operating at 0.13 T.© 1992 Academic Press,Inc.
Simultaneous measurement of intracellular and extracellular oxygen concentrations using a nitroxide‐liposome system
Authors: Glockner James F. , Norby Shong‐Wan , Swartz Harold M.
Published: March 2007

The concentration of oxygen within cells is important in many physiological and pathological processes, but such oxygendependent phenomena are generally studied as a function of the concentration of extracellular oxygen, due to a lack of suitable methods. Electron parmamagnetic resonance (EPR) oximetric techniques offer an attractive alternative to make such measurements. Previous EPR oximetric studies of extracellular‐intracellular oxygen gradients have been hindered, however, by the fact that separate samples, prepared in slightly different ways, were required for individual measurements of extracellular and intracellular oxygen concentrations. In this study we demonstrate a technique that allows simultaneous measurement of intracellular and extracellular oxygen concentrations in a single sample: extracellular measurement is achieved using positively charged nitroxides encapsulated in liposomes, while intracellular oxygen is determined using a membrane‐permeable nitroxide along with an extracellular broadening agent. Application of this system to the measurement of oxygen concentrations in suspensions of rat myoblast cells gave results which are consistent with nonsimultaneous measurements and which show substantial extracellular‐intracellular oxygen gradients in these rapidly respiring cells.
In vivo31P NMR studies of paraplegics' muscles activated by functional electrical stimulation
Authors: Levy M. , Kushnir T. , Mizrahi J. , Itzchak Y.
Published: March 2007

The bioenergetics of paralyzed muscles of spastic paraplegic patients under functional electrical stimulation (FES) was studied in vivo using 31P NMR. The protocol included rest, 3 min of induced tetanic isometric contraction through surface electrodes and 40 min of recovery. The continuous stimulation, the force recording and the 31P NMR measurements were sampled simultaneously inside the whole body imager. Normal values were found for the phosphorous metabolite ratios at rest. During contraction, prominent changes were detected including: a) accumulation of inorganic phosphate (P) accompanied by an unusually strong signal in the phosphomonoester (PME) region, b) phosphocreatine (PCr) decline, and c) a decrease in the intracellular pH. In the following recovery period the physiological state of the muscle was monitored and quantitated by 31P NMR. No metabolic and mechanical irreversible damage was detected in the paraplegics' muscles activated by FES under our experimental conditions.
A unified view of relaxation in protein solutions and tissue, including hydration and magnetization transfer
Authors: Koenig Seymour H. , Brown Rodney D. , Ugolini Raphael
Published: March 2007

Protein in water solution increases magnetic relaxation rates of solvent nuclei to an extent that depends on magnetic field strength and molecular weight. Koenig and Schillinger (J. Biol. Chem. 244, 3283 (1969)) showed that a small fraction of the water molecules in the first hydration shell, bound irrotationally with a residence lifetime in the range 01.1 to 10 us, would account for the phenomena. No experiments, as yet, have proven the existence of such long‐lived waters, nor yielded a value for their lifetime. Analogous measurements on solutions of both denatured and cross‐linked protein give data different from that of native protein, but much like results for tissue. By comparing proton and deuteron relaxation rates in solutions of native and cross‐linked protein, it is possible to demonstrate the existence of these relatively long‐lived waters; the data indicate that 1% of a monolayer of the waters of hydration of protein have lifetimes that cluster near 1 us and, it is argued, are held in place by multiple hydrogen bonds. Assigning shorter lifetimes for waters held by fewer bonds, it is possible to develop a unified view of relaxation of water nuclei in protein solutions and in tissue, and to relate it to recent crystallographic data on hydrated protein.
On the extracellular contribution to multiple quantum filtered 23Na NMR of perfused rat heart
Authors: Jelicks Linda A. , Gupta Raj K.
Published: March 2007

We investigated the contribution of extracellular Na+ to the multiple‐quantum filtered 23Na NMR signal of perfused rat hearts to determine if the presence of shift reagent Dy(PPPi)2 and inorganic phosphate were somehow responsible for the generation of extracellular multiple quantum coherence. Neither phosphate nor shift reagent caused an increase in the total multiple‐quantum filtered signal intensity or in the percent contribution from extracellular ions. On the contrary, addition of Dy(PPPi)2 actually decreased the total signal intensity from intra‐ and extracellular ions. Further addition of 1.5 mM Gd(PPPi)2 eliminated the extracellular contribution. These data indicate that the previously reported extracellular contribution in perfused hearts is a true contribution of extracellular ions, and not an artifact originating from their interaction with the shift reagent.
Carbon‐13 “magic‐angle” sample‐spinning nuclear magnetic resonance studies of human myelin, and model membrane systems
Authors: Husted Cynthia , Montez Bernard , Le Carl , Moscarello Mario A. , Oldfield Eric
Published: March 2007

We have obtained high‐field (11.7 Tesla), high‐resolution carbon‐13 solid‐state “magic‐angle” sample‐spinning nuclear magnetic resonance (NMR) spectra of a variety of phospholipids, sphingolipids, myelin and white matter samples, resolving and assigning over 40 resonances in the spectra of human and bovine myelin. The NMR results indicated no large spectral changes due to sample preparation, sample freezing, or brain location, and also no changes in myelin structure detectable via light microscopy, electron microscopy, thin layer chromatography, or sodium dodecyl sulfate‐polyacrylamide gel electrophoresis, attributable to the sometimes lengthy NMR data acquisition process. Human myelin and white matter chemical shift assignments were made based on 13C “magic angle” sample spinning (MAS) NMR spectra of individual model lipids, as well as on spectra of lipid mixtures. In all myelin samples there were essentially no features attributable to membrane proteins, with the exception of one small feature due to Cξ of Arg residues, primarily in the myelin basic proteins. The general similarity between the model lipid and intact myelin spectra suggested no major effects of protein on lipid mobility. We have also investigated human myelin samples as a function of developmental age (4,15, 48 months and adult), and our results showed only small changes in overall lipid composition, although there were significant decreases in lipid hydrocarbon chain unsaturation with age, as determined by computer line‐shape simulations of myelin and model compounds. The spectrum of an infant leukoencephalopathy myelin showed marked decreases in galactocerebrosides. Overall, the ability to resolve and assign over 40 resonances in the 13C MAS NMR spectra of myelin, and to detect changes as a function of development and disease, should provide a useful starting point for further more detailed studies of myelin membrane molecular motions, and function.
pH mapping in living tissues: An application of in vivo31P NMR chemical shift imaging
Authors: Morikawa Shigehiro , Inubushi Toshiro , Kito Kohichi , Kido Chie
Published: March 2007

Chemical shifts were extracted from in vivo3‐dimensional31P NMR CIS data and pH images were constructed. The images could spatilly resolve tissue pH ranging from 5.8 to 7.2 (with uncertainty of 0.11‐0.17 pH unit)in an ischemia‐reperfusion model of diabetic rat calf muscles.
Dissecting and implementing steam spectroscopy
Authors: Riddle William R. , Gibbs S. Julian , Willcott M. Robert
Published: March 2007

A rapid, simple method for constructing a site‐specific STEAM sequence from a basic Hahn three‐pulse sequence is presented. The method assures maximum signal available from the hardware.
In situ changes in purine nucleotide and n‐acetyl concentrations upon inducing global ischemia in cat brain
Authors: van Zijl Peter C. M. , Moonen Chrit T. W.
Published: March 2007

Spectral changes upon death (global ischemia) were recorded in situ in cat cerebral cortex. A rapid signal loss of 10 ± 4% in the N‐acetyl resonance was observed (five cases), after which it remained constant for 1 h. For the first time signal changes are reported for low‐field resonances, which are assigned to adenosine/inosine and hypoxanthine.
RF pulse design using the inverse scattering transform
Authors: Buonocore Michael H.
Published: March 2007

The inverse scattering transform (IST) is a mathematical transformation that can be used to derive RF pulses from functions called continuous spectra describing the final state of the spin system. This paper reviews three seemingly unrelated numerical algorithms that have appeared in the literature, and shows that they are all derivable from the IST. When the continuous spectra are rational, the finite rank kernel method is used to convert the IST to a matrix equation that is easily solved. Another algorithm, equivalent to the so‐called “layer stripping” algorithm used in seismology, is derived by assuming that the spectra are Fourier series. Finally, the Shinnar‐Le Roux (SLR) algorithm is derived by assuming that the spectra are ratios of Fourier series. With proper interconversion between the rational, series, and ratio of series forms of the continuous spectra, these algorithms generate RF pulses with identical or nearly identical shapes and performance properties, and can be regarded as equivalent.
Some contrast agents in oilwell logging and in medical MRI
Authors: Brown Robert J. S.
Published: March 2007

Magnetite particles and paramagnetic ion chelates are used as contrast agents in both nuclear magnetism logging of oilwells and in medical MRI. An analytic expression for reduction of T2 for free precession signal decay (or gradient echoes) by magnetite particles does not depend on diffusion and agrees with published Monte Carlo computations.
A knowledge‐based approach to minimize baseline roll in chemical shift imaging
Authors: Saeed Nadeem , Menon David K.
Published: March 2007

A method has been developed to minimize baseline roll in chemical shift imaging (CSI). The technique is fully automated and employs knowledge based data processing in the frequency domain. The key feature of the algorithm is the computation of the “trough” and “ripple” components in the CSI data. The baseline roll can be regarded as an artifact that appears as a result of the summation of several sinc functions. Using prior knowledge, a mirror component corresponding to the artifact is created and added to the delayed spectrum. The method compensates for noise and zero‐order phase error when computing the roll artifact. The results obtained on implementing the baseline roll minimization procedure on simulated time‐delayed spectra indicated that the peak heights and areas were between 91% and 97% in magnitude when compared with the same peaks in the nondelayed spectra. The correction procedure was also assessed on clinical in vivo spectra. Nonlocalized 31P MR spectra of the liver were obtained with and without an acquisition delay of 2.1 ms, and the time delayed spectra subjected to the baseline minimization routine. Metabolite peak heights and areas in the corrected spectra were approximately 94% in magnitude when compared with the same peaks in the original nondelayed whole volume spectra. Implementation of the baseline minimization procedure on in vivo localized spectra with varying signal to noise ratios produced good results. It takes approximately 13 s to implement the baseline roll minimization procedure. In this paper, the technique will be referred to as BaseLine Artifact Suppression Technique (BLAST) routine.
Imaging time reduction through multiple receiver coil data acquisition and image reconstruction
Authors: Carlson J. W. , Minemura T.
Published: March 2007

A technique is described for the simultaneous acquisition of MRI data using two independent receiver coils surrounding the same region of tissue, which enables the collection of data necessary for image reconstruction in a reduced number of phase‐encoded acquisitions. This results in a 50% reduction in minimum scan time and may be useful in time‐critical procedures. The algorithm and imaging procedures are described, and example images are shown that illustrate the reconstruction. Signal to noise is decreased by the square root of the time savings, making this technique applicable to cases in which the need to decrease minimum scan time outweighs the signal to noise penalty.
Limits to neural stimulation in echo‐planar imaging
Authors: Mansfield P. , Harvey P. R.
Published: March 2007

Simple electrical circuits are used to model neural stimulation. The Stimulation current is evaluated for a variety of magnetically induced waveforms and for sinusoidal stimulation as a function of frequency. Experimental results obtained using a small scale magnetic stimulator show that the transient response rather than the steady‐state behavior determines the stimulation characteristics thus suggesting a nonlinear model. We show that a nonlinear circuit changes a steady‐state current solution into a repeated transient solution and thereby better explains our experimental results. Our model also shows that for very short times and high frequencies, contrary to the current widely held view, neural stimulation is independent of the magnetic field switching rate dBldt, but depends on the final magnetic field value, Bm. At lower frequencies and rise‐times, there may be a small advantage in using square wave over sine wave gradient modulation for whole body echo‐planar imaging (EPI). It is found that the peak stimulation fields, Bm, for both sinusoidal and trapezoidal waveforms are equal for equal risetimes. This means that for a given image array size and imaging time, trapezoidal modulation EPI ultimately can be made to operate below the neural triggering threshold while the equivalent sine modulation EPI version transcends the threshold.
Automatic, localized in Vivo adjustment of all first‐and second‐order shim coils
Authors: Gruetter Rolf
Published: March 2007

The implementation of a “fast, automatic shimming technique by mapping along projections” (FASTMAP) on a 2.1‐Tesla whole‐body system is described. The method provides a localized adjustment of all first‐ (X, Y, Z) and second‐order (Z2, ZX, ZY, X2‐Y2, 2XY) coils in 2 min. The time savings are achieved by mapping the magnetic field along six projections rather than from whole‐imaging data sets. An analysis of noise error propagation suggests that in 64‐ml volumes the residual linewidths obtained with the method are negligible when the signal‐to‐rms‐noise ratio is above 30. The initial application of the method to localized 13C, 31P, and 1H spectroscopy of the human brain resulted in linewidths of ∼2 Hz for 13C (144‐ml volume), ∼2.5 Hz for 31P (36‐ml volume) and ∼4 Hz for 1H (36‐ml volume) with symmetric and reproducible lineshapes.
Shift reagent enhanced concurrent 23Na and 1H magnetic resonance spectroscopic studies of transcellular sodium distribution in the dog brain in vivo
Authors: Eleff Scott M. , McLennan Ian J. , Hart Graeme K. , Maruki Yuichi , Traystman Richard J”︁ , Koehler Raymond C”︁
Published: March 2007

The intracellular to extracellular sodium distribution is one of the primary determinants of action potentials necessary for the electrical function of organs such as brain, heart and skeletal muscle. The ability of shift reagent enhanced 23Na MRS to directly measure the intracellular and extracellular sodium distribution in brain is controversial and centers on the relative contributions of bulk magnetic susceptibility and hyper‐fine interactions to the observed chemical shifts. In this study, infusion of dysprosium (111) triethylenetetraminehexacetate (Dy(TTHA)−3), resulted in a 23Na MRS spectrum of dog brain with two well resolved peaks at 9 and 0.4 ppm. The 9 ppm peak corresponded to the resonance seen in aspirated blood. After disruption of the blood brain barrier, the single peak at 0.4 ppm split into two peaks at 3 and 0 ppm. The ability of Dy‐(lTHIA)−3 enhanced 23Na MRS to follow global changes in brain sodium distribution was tested during cardiac arrest. The expected rapid Na influx into the intracellular space produced a marked decrease in the 3 ppm signal and a parallel increase in the 0 ppm peak. This is consistent with the assignment of the 3 ppm peak as interstitial sodium and the 0 ppm peak as intracellular sodium.
Magnetic resonance‐guided thermal surgery
Authors: Cline H. E. , Schenck J. F. , Watkins R. D. , Hynynen K. , Jolesz F. A.
Published: March 2007

A demonstration of MR guided thermal surgery involved experiments with imaging of focused ultrasound in an MRI system, measurements of the thermal transients and a thermal analysis of the resulting images. Both the heat distribution and the creation of focused ultrasound lesions in gel phantoms, in vitro bovine muscle and in vivo rabbit muscle were monitored with magnetic resonance imaging. Thermal surgical procedures were modeled by an elongated gaussian heat source where heat flow is controlled by tissue thermal properties and tissue perfusion. Temperature profiles were measured with thermocouples or calculated from magnetic resonance imaging in agreement with the model. A 2‐s T1‐weighted gradient‐refocused acquisition provided thermal profiles needed to localize the heat distribution produced by a 4‐s focused ultrasound pulse. Thermal analysis of the images give an effective thermal diffusion coefficient of 0.0015 cm2/s in (gel and 0.0033 cm2/s in muscle. The lesions were detected using a T2‐weighted spin‐echo or fast spin‐echo pulse sequence in agreement with muscle tissue sections. Potential thermal surgery applications are in the prostate, liver, kidney, bladder, breast, eye and brain.
Study of ischemic myocardial buffering capacity in perfused rat heart through rapidly interleaved 1H and 31P MRS measurements
Authors: Schussheim Adam E. , Radda George K.
Published: March 2007

We present a method for the direct correlation of quantitative changes in lactate concentration and intracellular pH during global ischemia in the perfused rat heart using rapidly interleaved 31P MRS and water‐suppressed 1H MRS acquisitions. The ischemic myocardial buffering capacity was determined and found to be consistent with previous experimentation.
In Vivo31P NMR measurement of glucose‐6‐phosphate in the rat muscle after exercise
Authors: Bloch G. , Chase J. R. , Avison M. J. , Shulman R. G.
Published: March 2007

Comparison of 31P NMR spectra of the rat gastrocnemius, obtained in vivo and from PCA extracts, after electrically induced contractions, demonstrates that glucose‐6‐phosphate (G6P) is the major metabolite in the low‐field part of the PME spectral region. In vivo 31P NMR can thus be used to measure the muscle G6P concentration after exercise.
Magnetic resonance imaging of perfusion in the isolated rat heart using spin inversion of arterial water
Authors: Williams Donald S. , Grandis Donald J. , Zhang Weiguo , Koretsky Alan P.
Published: March 2007

Measurement of regional myocardial perfusion is important for the diagnosis and treatment of coronary artery disease. Currently used methods for the measurement of myocardial tissue perfusion are either invasive or not quantitative. Here, we demonstrate a technique for the measurement of myocardial perfusion using magnetic resonance imaging (MRI) with spin tagging of arterial water. In addition, it is shown that changes in perfusion can be quantitated by measuring changes in tissue T1. Perfusion images are obtained in Lan‐gondorff‐perfused, isolated rat hearts for perfusion rates ranging from 5 to 22 ml/g/min. The MRI‐determined perfusion rates are in excellent agreement with perfusion rates determined from measurement of bulk perfusate flow (r = 0.98). The predicted linear dependence of the measured T1 (T1app) on per‐fusion is also demonstrated. The ability of perfusion imaging to measure regional variations in flow is demonstrated with hearts in which perfusion defects were created by ligation of a (coronary artery. These results indicate that MRI of perfusion using spin inversion of arterial water gives quantitative maps of cardiac perfusion.
Quantitative proton spectroscopy and histology of a canine brain tumor model
Authors: Barker P. B. , Blackband S. J. , Chatham J. C. , Soher B. J. , Samphilipo M. A. , Magee C. A. , Hilton J. D. , Strandberg J. D. , Anderson J. H.
Published: March 2007

Quaintitative, single voxel proton nuclear magnetic resonance (NMR) spectroscopy and histological analysis was performed in eight dogs implanted with the transplantable canine glioma model of Wodinsky (Proc. Am. Assoc. Cancer Res. 10, 99 (1969). Signals from choline, creatine, N‐Acetyl Aspartate (NAA) and lactate were converted to molar concentration units and correlated with the quantitative analysis of histologically determined tissue types within the localized volume selected for NMR spectroscopy. In general, compared with normal brain, the lesions were associated with reductions in all metabolite concentrations, with the exception of lactate, which was increased. NAA and creatine decreases were most significantly correlated with the total lesion volume (P < 0.01), suggesting that these compounds are present in normal brain only. Changes in choline levels did not correlate strongly with any particular tissue type. Lactate was found to increase with increasing total lesion volume (P < 0.01), but not with increasing percent tumor, suggesting that it accumulates in abnormal tissue other than the tumor. The spectra reported were similar to those observed in human glioblastomas, with the exception that elevations of choline were not observed. The transplant‐able canine gliosarcoma system appears to be a suitable tumor model for evaluation by clinical radiological techniques such as magnetic resonance imaging (MRI) and proton NMR spectroscopy.