bluuebunny/crossref_metadata_2025 huggingface dataset:
Evaluation of ba1112 rhabdomyosarcoma oxygenation with microelectrodes, optical spectrophotometry, radiosensitivity, and magnetic resonance spectroscopy
Authors: Sostman H. Dirk , Rockwell Sara , Sylvia Avis L. , Madwed David , Cofer Gary , Charles H. Cecil , Negro‐Vilar Rosa , Moore Deborah
Published: March 2007

We studied tumor tissue oxygenation in the BA1112 rhabdomyosarcoma using microelectrode pO2 measurements, optical spectrophotometry, analyses of cell survival after irradiation, and 31 P magnetic resonance spectroscopy (MRS). Studies were carried out in WAG/Rij/Y rats breathing normoxic, hypoxic, and hyperoxic gas mixtures with and without iv administration of perfluorochemical. Significant changes in tissue oxygenation and metabolic status were found when pO2 values, optical measurements of hemoglobin saturation and cytochrome a, a3 reduction‐oxidation, radiation cell survival determinations, and MRS measurements of phosphometabolite ratios were obtained in rats breathing different gas mixtures. Inhalation of 100% O2 caused increases in tumor pO2, hemoglobin saturation, cytochrome a, a3 oxidation, tumor radiosensitivity, and PCr/Pi, NTP/Pi, and PDE/Pi ratios. Such changes were augmented by pretreatment with iv perfluorochemicals. Inhalation of hypoxic gas mixtures resulted in reductions in the above paramenters. These results indicate that tissue oxygenation can be manipulated reproducibly in the BA1112 rhabdomyosarcoma and suggest that 31 P MRS can be used to monitor changes in tumor oxygenation in this model system.
An NMR probe to study function and metabolism simultaneously in isolated human cardiac tissue
Authors: Lareau Sylvain , Moore Rayad , Mainwood Graham W. , Labow Rosalind S. , Keon Wilbert J. , Deslauriers Roxanne
Published: March 2007

Trabeculae isolated from human atrial appendages have been used to study preservation of donor hearts for cardiac transplantation. We have developed a perifusion system equipped with a fiber optic strain gauge to study mechanical performance of human atrial trabeculae (10‐20 mg) while simultaneously observing the energetic compounds by 31P NMR spectroscopy. The NMR probe consists of an eight‐turn solenoid coil (2.3 mm i. d. × 5 mm length, 24‐gauge wire) double tuned to allow observation of 1H and 31P nuclei. The probe and the perifusion system are temperature regulated and permit preservation studies using a variety of small muscles at low temperatures (down to 4°C) as well as at physiological temperature (37°C). 31P NMR spectra suitable for quantification can be obtained from ≈︁ 10 mg of human atrial trabeculae in 15 min. Spectra of 8‐to 12‐mg mouse extensor digitalis longus or soleus muscle can be obtained in less than 10 min. © 1991 Academic Press, Inc.
A complete solution to the model describing Carr‐Purcell and Carr‐Purcell‐Meiboom‐Gill experiments in a two‐site exchange system
Authors: Sobol W. T.
Published: March 2007

A general solution for the relaxation decay function observed in both CP and CPMG spin‐echo experiments, performed on systems governed by a two‐site chemical exchange mechanism, is presented. This solution not only provides the relaxation time constants, but also supplies complete information about relative component sizes. Solutions are analytical, but results are complex enough to warrant computer‐assisted calculations. Programming suggestions, based on the extensive tests performed, are provided. © 1991 Academic Press, Inc.
An analytical model for the design of RF resonators for MR body imaging
Authors: Foo Thomas K. F. , Hayes Cecil E. , Kang Yoon‐Won
Published: March 2007

A closed form, analytical solution describing the RF fields generated by an RF body coil resonator for MR imaging at 1.5 and 4.0 T is presented. This solution extends the results of earlier studies of RF penetration in the body by explicitly including the RF coil, the RF shield, and the field variation along the z axis for high‐pass birdcage coils. A salient feature of this treatment is the calculation of the axial propagation constant, kz, which determines the z dependence of the RF field. We have determined the relative power deposition in the body, the \documentclass{article}\pagestyle{empty}\begin{document}$ \vec B $\end{document}1, field homogeneity, and coil losses, which are functions of the coil‐to‐shield separation and body size. The relative power deposition in the body has been calculated to vary as the 1.58 power of the body radius. The calculations have also predicted that the field homogeneity in the z direction exhibits greater degradation at higher frequencies in a high‐pass coil than in a low‐pass coil. The model predicts an increase in coil losses by a factor of 2.8 as the coil‐to‐shield separation is reduced from 5 to 2 cm in a standard body resonator. Although the results for only a homogeneous cylindrical object or body are presented, the theory can be extended to a multilayered heterogeneous object of varying permittivity and conductivity. © 1991 Academic Press, Inc.
Evaluation of energy metabolism in brain using epimerization of 2‐deoxy‐2‐fluoro‐d‐glucose by 19F NMR: The effect of anesthesia
Authors: Shinohara Shunji , Kanazawa Yoko , Kojima Masaharu
Published: March 2007

The effect of anesthesia on the epimerization of 2‐deoxy‐2‐fluoro‐D‐glucose(‐6‐phosphate) to 2‐deoxy‐2‐fluoro‐D‐mannose(6‐phosphate) in mice was demonstrated with 19F NMR spectroscopy of excised tissue specimens from heart, muscle, and brain. Spectra from each of six excised organs confirmed that pretreatment with an anesthetic suppressed the conversion ratio, FDM/(FDG + FDM), in brain at 3 h from 52 ± 5 to 30 ± 6% under the dose of 100 mg/kg. We propose potential applications for NMR monitoring of FDG‐FDM conversion, including the assessment of regional brain metabolism and the evaluation of Various pharmacologic agents. © 1991 Academic Press, Inc.
A lineshape fitting model for 1H NMR spectra of human blood plasma
Authors: Hiltunen Y. , Ala‐Korpela M. , Jokisaari J. , Eskelinen S. , Kiviniitty K. , Savolainen M. , Kesäniemi Y. A.
Published: March 2007

A lineshape fitting model was constructed for classifying the overlapping information in the 1H NMR spectrum of human blood plasma. A reliable assignment of the overlapping fatty acid (‐CH2‐)n and ‐CH3 resonances of the various lipoproteins (VLDL, very low density lipoprotein; LDL, low density lipoprotein; HDL high density lipoprotein) is introduced, and for the first time detailed characteristics (chemical shifts, half linewidths, and relative intensities) of the individual lipoprotein components were obtained directly from the whole plasma spectrum. This was achieved by combining the constructed lineshape fitting model and the proper 400 MHz proton NMR measurements from blood plasma of a healthy donor, from fractions of the different lipoproteins, and from plasma samples in which the lipoprotein fractions were separately added. The results suggest fair promise of future applications of the rapid and easy NMR analysis of lipoprotein distribution in various research and clinical situations. © 1991 Academic Press, Inc.
Quantitative measurement of blood flow using cylindrically localized fourier velocity encoding
Authors: Dumoulin Charles L. , Souza Steven P. , Hardy Christopher J. , Ash Stephen A.
Published: March 2007

A procedure for the quantitative measurement of blood velocity was developed and evaluated in the portal vein, aorta, and vena cava of healthy volunteers. This procedure utilizes Fourier velocity encoding and can be performed with or without cardiac gating. The accuracy of velocity measurements is determined by the accuracy of the gradient subsystem. How measurements derived from the velocity measurement are further limited in their accuracy by the luminal cross‐section measurement. Spatial localization is accomplished with an excitation pulse having a cylindrical rather than slab geometry. Data are acquired in the presence of a readout gradient to provide resolution along the cylindrical axis. © 1991 Academic Press, Inc.
Sensitivity enhancement and reduction of Gibbs artifact in T2‐ weighted imaging using variable tip angle excitation
Authors: Webb A. G. , Clarkson R. B.
Published: March 2007

Introduction of a Gaussian weighting function into the phase encoding of the spin‐echo imaging method via variable tip angle excitation, with concomitant optimization of the recycle delay, is shown to increase the sensitivity of T2‐weighted imaging by up to 40%. In addition, the Gibbs artifact associated with sharp boundaries is reduced considerably without the need for postprocessing of the data. © 1991 Academic Press, Inc.
Ferrioxamine B derivatives as hepatobiliary contrast agents for magnetic resonance imaging
Authors: Muetterties Kurt A. , Hoener Betty‐Ann , Engelstad Barry L. , Tongol Jose M. , Wikstrom Mats G. , Wang Shih‐Chang , Eason Robert G. , Moseley Michael E. , White David L.
Published: March 2007

Succinyl (SDF), phenylsuccinyl (PSDF), glutaryl (GDF), and phenylglutaryl (PGDF) derivatives of desferrioxamine B (DF) have been synthesized. In rats given the 59Fe(III) chelates of each these ligands at tracer levels, 82–94% of the 59Fe was eliminated within 1–2 days. 59Fe given as DF, SDF, and GDF chelates was excreted primarily in the urine, while nearly 50% of that given as PSDF and PGDF was excreted in the feces. Correspondingly, Fe‐DF, Fe‐SDF, and Fe‐GDF (0.2 mmol/kg) produced early, marked renal, but no gastrointestinal magnetic resonance imaging (MRI) enhancement. Fe‐PSDF and Fe‐PGDF (0.2 mmol/kg) produced marked and rapid MRI enhancement of the upper small intestine. In animals with cannulated bile ducts, 59Fe for 59Fe‐PGDF (carrier added, 0.1 mmol/kg) appeared rapidly in the collected bile, but not in the intestinal contents, proving that the contrast agent reaches the bowel via the bile. These changes in the excretion and MRI enhancement patterns brought about by the presence of a phenyl substituent apparently were not related to changes in lipophilicity or protein binding. © 1991 Academic Press, Inc.
pH‐lactate dissociation in neonatal anoxia: Proton and 31P NMR spectroscopic studies in rat pups
Authors: Hida Kazutoshi , Suzuki Nobuyuki , Kwee Ingrid L. , Nakada Tsutomu
Published: March 2007

The pH controlling capability of brain of 1‐day‐old rat pups was investigated using proton (1H) and phosphorus‐31 (31P) nuclear magnetic resonance (NMR) in vivo spectroscopy. Despite significantly high levels of lactate accumulation, brain of 1‐day‐old pups showed remarkable capability of maintaining brain pH virtually unchanged throughout 22 min of anoxia. The study supports the concepts that lactic acidosis is one of the important factors determining the outcome of cerebral anoxia and that the significantly higher pH controlling capability of immature brain plays a key role in the higher resistance toward anoxia. © 1991 Academic Press, Inc.
Proton NMR imaging of cerebral blood flow using H217O
Authors: Kwong K. K. , Hopkins A. L. , Belliveau J. W. , Chesler D. A. , Porkka L. M. , McKinstry R. C. , Finelli D. A. , Hunter G. J. , Moore J. B. , Barr R. G. , Rosen B. R.
Published: March 2007

Cerebral blood flow was quantitatively mapped by monitoring the cerebral washout of H2 17O using rapid, single‐shot proton NMR imaging. H2 17O acts as a freely diffusible contrast agent for proton imaging via its scalar‐coupled term, enhancing T2 relaxation. Measured values for CBF ranged from 29 to 106 ml/min/100 g over a range of arterial pCO2 between 23 and 81 Torr. © 1991 Academic Press, Inc.
Clinical hepatic imaging with paramagnetic positive enhancers
Authors: Bernardino Michael E.
Published: March 2007

At the present time, there are two types of paramagnetic positive enhancers for hepatic imaging in the United States. One is gadolinium (DTPA) and nonionic forms, and the other is manganese DPDP. Gadolinium derivitives cause the liver to become hyperintense relative to tumors. However, the signal intensity may vary with time. Mn‐DPDP causes the liver to be positively enhanced while tumors are negative defects, thus contrasted against the hyperintense background. Both agents have advantages and drawback. During the past 4 years, we have had the opportunity to evaluate both agent. The following will be a clinical summation of our experience with these two compounds. © 1991 Academic Press, Inc.
Development of an in vivo19F magnetic resonance method for measuring oxygen deficency in tumors
Authors: Raleigh J. A. , Franko A. J. , Kelly D. A. , Trimble L. A. , Allen P. S.
Published: March 2007

A 19F magnetic resonance spectroscopy (MRS) approach to measuring hypoxia in experimental tumors in rats at a field strength of 2.35 T has been investigated in a combined study of in situ and excised tumors. The detection of tumor hypoxia is based on the hypoxia marker approach which depends on the selective, covalent binding of a fluorinated 2‐nitromidazole to hypoxic cells. The 19F MRS measurement of in vivo hypoxia marker binding was made at a fixed postinjection time when unbound, circulating marker molecule concentrations had dropped below detectable levels. A correlation between 19F MRS and scintillation counting measures of tumor‐bound, tritium‐labeled hypoxia marker was observed. There was no correlation between integrated 19F MRS hypoxia marker signals and the in vivo 31P MRS parameters of hypoxia which have been developed to measure normal tissue ischemia. Radiolabeling studies and previous immunohistochemical studies with the fluorinated hypoxia marker support the conclusion that the 19F MRS approach has promise as a physically noninvasive guide to the use of hypoxia‐dependent therapies at clinically usable MRS field strengths. © 1991 Academic Press, Inc.
In vivo phosphorus NMR spectroscopy of skin using a crossover surface coil
Authors: Chen Yuhchyau , Richards Todd L. , Izenberg Seth , Golden Robert N. , Williams David L. , Nelson James A. , Steen R. Grant
Published: March 2007

A modified crossover surface coil with minimal B1 field penetration was used for collection of skin phosphorus NMR spectra. Projection imaging experiments show that the coilsensitive volume is uniform at the phosphorus frequency, but strikingly nonuniform at s the proton frequency. Experiments with an in vitro phosphorus phantom, designed to simulate skin and underlying tissue, demonstrated that 45.1% (±1.2%) of total signal was derived from Sprague‐Dawley rat skin and 19.3% (±1.4%) of total signal was derived from Fischer‐344 rat skin. 31P MR spectra of rat skin in vivo permitted resolution of four phosphorus compounds: nucleoside triphosphates, phosphocreatine (PCr), inorganic phosphate (Pi), and phosphomonoester. Spectra collected after skin flap surgery in Fischer‐344 rats showed a 50.1% (±7.6%) reduction in the ratio of PCr/Pi within 30 min of surgery, compared to presurgical PCr/Pi levels (P < 0.01). Skin phosphorus spectra are potentially useful for assessment of skin flap and skin graft viability. © 1992 Academic Press, Inc.
Contrast‐to‐noise ratios in maximum intensity projection images
Authors: Brown Donna G. , Riederer Stephen J.
Published: March 2007

We present a statistical analysis of the maximum intensity projection (MIP) algorithm, which is commonly used for MR angiography (MRA). The analysis explains why MIP projection images display as much as a twofold increase in signal‐ and contrast‐to‐noise ratios over those of the source image set. This behavior is demonstrated with simulations and in phantom and MRA image sets. © 1992 Academic Press, Inc.
Reduction of susceptibility artifact in gradient‐echo imaging
Authors: Cho Z. H. , Ro Y. M.
Published: March 2007

A new technique with which susceptibility artifact in gradient‐echo imaging can be reduced substantially by use of a tailored RF pulse is described. The proposed technique can ideally be applied to the case where high local magnetic field inhomogeneity is dominated by the susceptibility. The signal loss and void phenomena due to susceptibility in a voxel are studied and a correction method is also proposed. The description of the tailored RF pulse and its proposed application are given and experimental results obtained using a human volunteer with a 2.0‐T KAIS NMR system are presented. © 1992 Academic Press, Inc.
The design of pulse sequences employing spatial presaturation for the suppression of flow artifacts
Authors: Mugler John P. , Brookeman James R.
Published: March 2007

The use of spatial presaturation to suppress the signal, and therefore also the artifacts, from flowing blood has become an important tool in the arsenal of techniques to suppress pulsatile flow artifacts in magnetic resonance images. However, a detailed theoretical analysis of the behavior of these flow artifact suppression pulses and of the important aspects of implementing suppression pulses in combination with particular imaging sequences has yet to be presented. In this paper we present a general theoretical framework to describe the flow artifact suppression technique. This analysis addresses the following four major issues: (1) the spin washout characteristics of the imaging sequence, (2) the interference between the flow signal suppression pulses and the imaging sequence, (3) the flow velocity range for a single application of the suppression pulse, and (4) the total flow velocity range for a suppression pulse repeated with a constant time interval between applications of the pulse. The predictions of our theoretical model are confirmed by experimental measurements made with stationary and flow phantoms. The results of this investigation provide guidelines for the design of flow artifact suppression pulse sequences and, in addition, should aid in the future development and refinement of the spatial presaturation technique as applied to flow Signal Suppression. © 1992 Academic Press, Inc.
The progression of spermatogenesis in the developing rat testis followed by 31P MR spectroscopy
Authors: van der Grond Jeroen , Laven Joop S. E. , van Echteld Cees J. A. , Dijkstra Grietje , Grootegoed J. Anton , de Rooij Dirk G. , Mali Willem P. Th. M.
Published: March 2007

To evaluate the use of human testicular 31P MR spectroscopy as a diagnostic tool to differentiate between several stages of male infertility, we have studied the testicular levels of several phosphorus containing compounds in the rat in relation to the condition of spermatogenesis and the cell types present in the seminiferous tubules of the testis. During testicular maturation several characteristic changes occur in the 31P MR spectrum of the testis of male Wistar rats. The phosphomonoester/adenosine triphosphate (PM/ATP) ratio shows a decline from 1.61 to 1.02 between the age of 3 and 12 weeks, whereas the phosphodiester (PD)/ATP ratio increases from 0 to 0.72. The testicular pH increases in the same time from 7.06 to 7.32. Testicular MR data obtained after 12 weeks of age onward do not show significant change anymore. The high PM/ATP ratio is associated by a relative high amount of proliferating spermatogonia and spermatocytes during meiosis in the testis, whereas the PD peak seems to be correlated with the release and maintenance of spermatozoa. The MR spectra show a specific fingerprint in all developmental stages of the rat testis as a result of the different cell types in the testis. © 1992 Academic Press, Inc.
Effects of local irradiation on spin‐lattice relaxation time of phosphate metabolites in mouse tumors monitored by 31P magnetic resonance spectroscopy
Authors: Li Shi‐Jiang , Jin Guan‐Yuan , Moulder John E.
Published: March 2007

An inversion‐recovery pulse sequence and solenoidal surface coil were employed to determine the spin‐lattice relaxation time (T1) in murine tumors (RIF‐1 and SCCVII). Reduction in T1s of inorganic phosphate (Pi) and nucleotide triphosphates (NTP) has been observed in irradiated tumors compared with unirradiated tumors. The reduction is accompanied by tumor regression and improved tumor energetic status in both tumor lines. The results of the TI measurement of phosphate metabolites in tumors suggest that partial saturation effects may exist in spectra and could effect quantitative analysis when short repetition time is used. The reduction in T1s of Pi and NTP may be attributed to the active biochemical exchange and better tumor oxygenation in irradiated tumors. © 1992 Academic Press, Inc.
Tissue conductivity modifies the magnetic resonance intrinsic signal‐to‐noise ratio at high frequencies
Authors: Foster Thomas H.
Published: March 2007

Inclusion of a frequency‐dependent tissue conductivity in the calculation of the magnetic resonance imaging signal‐to‐noise ratio is considered. The linear dependence of field strength described previously by Edelstein is preserved for frequencies up to ≈60 MHz. At higher frequencies, tissue conductivity effects become significant. © 1992 Academic Press, Inc.
Proton nuclear magnetic resonance studies on water structure in peritumoral edematous brain tissue
Authors: Iwama T. , Yamada H. , Era S. , Sogami M. , Andoh T. , Sakai N. , Kato K. , Kuwata K. , Wataris H.
Published: March 2007

Spin–lattice relaxation times (T1) of water protons and cross‐relaxation times (TIS) between irradiated protein and water protons were measured to study the water structure in peritumoral edematous brain tissue of rats. Despite small changes in T1, water, and electrolyte contents, TIS values of water protons were significantly reduced in peritumoral edematous brain tissue when compared to those of the controls. Results indicate that the water structure in brain tissues may become altered at an early stage of edemic formation without causing any significant changes in cellular hydration. TIS, might serve as a sensitive parameter for studying the water structure in a variety of tissues, such as in edematous brain tissue. © 1992 Academic Press, Inc.
Noise correlation in multicoil receiver systems
Authors: Redpath T. W.
Published: March 2007

When two or more rf coils are used to receive NMR signals from the same part of the patient, the overall sensitivity of an image formed from some combination of these signals may be degraded if noise voltages in the coils are correlated. Whereas it is straightforward to calculate correlation caused by noise sources in the coils themselves, there is disagreement about noise correlation when that noise arises from thermally driven currents within the body itself. A general analysis based on the principles of reciprocity, superposition, and energy conservation yields an equation for sample‐induced noise correlation in terms of circuit impedances. Furthermore, the analysis yields a very simple expression for the total noise correlation (i.e., noise from patient and coil elements) between the coils. This latter expression is applicable to any two‐port receiver coil assembly, including single coils with two modes, such as a birdcage coil, and in general, to any two ports of an n‐port receiver system. © 1992 Academic Press, Inc.
T1ρ dispersion imaging and localized T1ρ dispersion relaxometry: Application in vivo to mouse adenocarcinoma
Authors: Rommel E. , Kimmich R. , Körperich H. , Kunze C. , Gersonde K.
Published: March 2007

The dispersion (frequency dependence) of the spin‐lattice relaxation time in the rotating frame, T1ρ, is considered for tissue characterization. Methods for the volume‐selective determination of the proper T1ρ, dispersion and for imaging of parameters characterizing this frequency dependence are described. On‐ and off‐resonance versions of the techniques are demonstrated. In vitro studies of excised rat tissues and in vivo applications to mice with implanted adenocarcinoma are reported. T1ρ, dispersion images show clear contrasts of the malignant tissue, whereas muscle tissue is completely suppressed. No contrast agent is required. The measuring time is only twice as long as that for conventional magnetic resonance images. The results suggest that the T1ρ, dispersion is less susceptible to the biological variability than the absolute values of the relaxation times. © 1992 Academic Press, Inc.
A hybrid bird cage resonator for sodium observation at 4.7 T
Authors: Pimmel P. , Briguet A.
Published: March 2007

A bird cage resonator operating at 52.9 MHz is described. The particularity of the presented design is due to fixed capacitors between conductors. Tuning is performed by adjusting a self‐capacitance system without breaking the coil symmetry. This structure denoted as “hybrid” is suitable for biological lossy samples. © 1992 Academic Press, Inc.
Measurement of blood‐brain barrier permeability using dynamic Gd‐DTPA scanning—a comparison of methods
Authors: Larsson H. B. W. , Tofts P. S.
Published: March 2007

Two recently published methods of blood‐brain barrier permeability measurement using Gd‐DTPA scanning are compared by authors representing each group. The physiological models are reconciled. Results from both groups agree. These show that the transfer constant (the permeability surface area product per unit volume of tissue) of the defective blood‐brain barrier in multiple sclerosis is in the range 1‐12·10−4s−1 © 1992 Academic Press, Inc.
ECG‐optimized phase contrast line‐scanned MR angiography
Authors: Korosec F. R. , Mistretta C. A. , Turski P. A.
Published: March 2007

We describe a rapid phase contrast line scan MR angiographic imaging technique. A projection angiogram is obtained by sequentially imaging a series of thin slices oriented perpendicular to the primary flow direction. Bipolar gradient subtraction is employed to suppress signal from static tissues, which in turn allows elimination of phase encoding in the depth dimension. The sequence is cardiac gated to improve image quality and to allow observation of hemodynamics. To further improve image quality, the amplitude of the bipolar gradient is altered throughout the cardiac cycle to provide maximum vessel signal at all cardiac phases. The ECG‐gated phase contrast line scan sequence has been used to image regions where cardiac pulsatility and respiratory motion compromise the quality of images obtained using standard spin warp angiographic methods. © 1992 Academic Press, Inc.
Selective intracellular lactate invisibility in Enterococcus faecalis
Authors: Hockings P. D. , Bendall M. R. , Rogers P. J.
Published: March 2007

In this article we will demonstrate that differences in Hahn T2, relaxation of the 1H NMR signal from cytosolic and extracellular lactate can be exploited to monitor lactate concentration gradients in bacterial cells and provide information on lactate transport mechanisms. As a by‐product of this study we have determined that there are at least three pools of lactate in bacterial cells with differing visibility in the NMR experiment. This has serious implications for the spectral editing techniques that are so vital for in vivo spectrocopy. © 1992 Academic Press, Inc. © 1992 Academic Press, Inc.
Water‐suppressed one‐dimensional 1H NMR spectroscopic imaging of myocardial metabolites in vivo
Authors: Balschi James A. , Hetherington Hoby P. , Pohost Gerald M.
Published: March 2007

Excitation by conventional B1 pulses in surface coil chemical‐shift imaging experiments yields resonance intensities that vary greatly with position. B1 compensated semi‐selective pulses overcome much of this problem. These pulses are employed for excitation and refocusing in 1H NMR spectroscopic localization in the intact heart.
Correlations between in vivo31P MRS measurements, tumor size, cell survival, and hypoxic fraction in the murine EMT6 tumor
Authors: Wendland Michael F. , Iyer Sujata B. , Fu Karen K. , Lam Kitty N. , James Thomas L.
Published: March 2007

Phosphorus metabolite ratios were measured using 31P magnetic resonance spectroscopy shortly before measurement of cell survival and radiobologic hypoxic fraction (HF) in EMT6/SF tumors, transplanted into a hindlimb of Balb/c mice. A total of 58 tumors with a volume range of 180 to 1250 mm3 were examined in experiments entailing no anesthesia. Postirradiation tumor cell viability was measured using an in vitro clonogenic assay. Correlations between tumor volume, surviving fraction (SF), HF, phosphorus metabolite ratios, and intracellular pH were computed. Both SF and HF increased significantly with tumor volume as did the metabolite ratios of inorganic phosphorus and phosphomonoesters to nucleoside triphosphates (Pi/NTP and PME/NTP, respectively), as well as Pi to phosphocreatine (Pi/PCr). In comparison to HF, the ratios of PiNTP, Pi,/PCr, and PME/NTP each yielded significant positive correlations (Kendall correlation coefficients (τ) = 0.25 to 0.33). However, these were not significantly stronger than the correlation between HF and volume (τ = 0.21). Apparent values of tumor pH did not correlate with any other measured parameter. While these results indicate a statistical relationship between HF and the measured metabolite ratios, the widely scattered data, as reflected by |τ| < 0.35, made metabolite ratios poor predictors of HF in individual tumors. © 1992 Academic Press, Inc.
Metabolic response of the human heart to inotropic stimulation: In vivo phosphorus‐31 studies of normal and cardiomyopathic myocardium
Authors: Schaefer Saul , Schwartz Gregory G. , Steinman Sean K. , Meyerhoff Dieter J. , Massie Barry M. , Weiner Michael W.
Published: March 2007

In order to determine if an increase in myocardial oxygen consumption is accompanied by changes in high energy phosphates in normal subjects and patients with dilated cardio‐myopathy, phosphorus‐31 spectra were acquired under resting conditions and during do‐butamine infusion. In seven normal subjects, dobutamine raised the rate‐pressure product to 226% of control. The ratio of PCr/ATP was 1.86 ± 0.17 (mean ± SE) under resting conditions and 1.90 ± 0.22 (P = 0.44) with dobutamine infusion. In eight patients with dilated cardiomyopathy, dobutamine raised the rate‐pressure product to 161% of control. As in the normal subjects, the ratio of PCr/ATP under resting conditions (1.63 ± 0.24) was unchanged during dobutamine infusion (1.57 ± 0.24, P = 0.38). These data indicate that increases in cardiac work do not have a major effect on high energy phosphate concentrations in normal subjects or in patients with clinically compensated dilated cardiomyopathy. © 1992 Academic Press, Inc.
Elimination of oblique flow artifacts in magnetic resonance imaging
Authors: Frank Lawrence R. , Crawley Adrian P. , Buxton Richard B.
Published: March 2007

We present an analysis of how flow oblique to the frequency‐encoding direction generates displacement artifacts in MR imaging and show that for flow which has constant velocity between the start of the phase encoding and the center of the echo it is possible to eliminate these artifacts by gradient moment nulling in the phase‐encoding direction. However, unlike the standard moment nulling calculations for flow compensating the frequency‐encode and slice‐selection gradients, the phase‐encoding first moment must be nulled specifically with respect to the echo center. Limitations of this method imposed by finite gradient strengths are analyzed. In 3D volume acquisitions with two axes phase encoded it is possible to correct for oblique flow in all directions, and this is demonstrated in images of a human volunteer. Correction for oblique flow displacement artifacts may be particularly useful in quantitative flow and angiographic applications. © 1992 Academic Press, Inc.
Modification of the carr‐purcell sequence for single‐shot echo‐planar imaging
Authors: Hennel Franciszek
Published: March 2007

An artifact caused by the RF field inhomogeneity in echo‐planar imaging (EPI) with the CPMG sequence is analyzed. A modified sequence is presented, using 90° phase alternation of the π pulses, which suppresses the spurious components of the signal. Thus the phase cycling procedure can be avoided and the π‐pulsed EPI experiment can be reduced to a single shot.
The magnetic properties and water dynamics of the red blood cell: A study by proton‐NMR lineshape analysis
Authors: Gasparovic Charles , Matwiyoff Nicholas A.
Published: March 2007

The magnetic properties and water dynamics of human red blood cells were examined by analysis of the water proton spectra of suspensions of oxygenated, deoxygenated, carbon monoxide‐treated, and methemoglobin‐containing cells at a magnetic field strength of 7.05 T. Total lineshape analysis of spectra from deoxygenated red blood cell suspensions was performed to determine the transmembrane water exchange rate, the contribution of diffusion in local magnetic field gradients to the transverse relaxation rate, and the difference between the intra‐and extracellular chemical shifts of water protons. Mathematical models are proposed to account for the dependence of the chemical shifts and linewidths of these spectra on the magnetic susceptibility or density of the cells.
Spatial heterogeneity of the metabolic response of RIF‐1 tumors to a vasoactive agent evaluated in vivo by one‐dimensional 31P chemical‐shift imaging
Authors: Bhujwalla Z. M. , Blackband S. J. , Wehrle J. P. , Glickson J. D.
Published: March 2007

Localized 31P NMR spectroscopy was used to evaluate the spatial heterogeneity of the metabolic response of RIF‐1 tumors to hydralazine. Volume localized 31P spectra were obtained from subcutaneous RIF‐1 tumors using one‐dimensional chemical‐shift imaging, before and 20 min after treatment with 5 mg/kg hydralazine, administered intravenously. Following treatment all of the tumors showed an overall decrease in the ratio of nucleoside triphosphate (NTP) to inorganic phosphate (Pi) and a decrease in pH. However, spatial localization revealed that the reduction in NTP/Pi was not uniform within some tumors. This was partly due to regional differences in the levels of metabolites existing before treatment. Normal tissue adjacent to the tumor did not show a significant decrease in high‐energy metabolites or pH.
Proton magnetic resonance spectroscopy of human brain: Applications to normal white matter, chronic infarction, and MRI white matter signal hyperintensities
Authors: Sappey‐Marinier Dominique , Calabrese Giovanna , Hetherington Hoby P. , Fisher Sarah N. G. , Deicken Raymond , Dyke Craig Van , Fein George , Weiner Michael W.
Published: March 2007

A modified ISIS method, for image‐selected localized proton magnetic resonance spectroscopy (1H MRS), was used to determine the ratios and T2 relaxation times of proton metabolites in normal subjects and in patients with chronic infarction and MRI white matter signal hyperintensities (WMSH). First, in patients with cerebral infarctions, increased concentrations of lactate were found in the majority of patients, and N‐acetyl aspartate (NAA) was reduced to a significantly greater extent than choline (Cho) or creatine (Cre). For TE = 270 ms, the raw ratios of Cho/NAA, Cre/NAA, and Lac/NAA were significantly (P < 0.05) increased from 0.23 ± 0.02 (mean ± SE), 0.20 ± 0.01, and 0.05 ± 0.01, respectively in the normal group to 0.39 ± 0.08, 0.37 ± 0.05, and 0.48 ± 0.15 in the stroke group. Also, the T2 relaxation time of creatine was significantly (P = 0.007) increased from 136 ms in normal white matter to 171 ms in cerebral infarcts. Second, in patients with WMSH, no significant change of the proton metabolite concentrations could be detected with the exception of the choline which was significantly (P = 0.003) altered. The Cho/NAA ratio, after T2 and excitation profile correction, increased from 0.47 ± 0.02 in the normal group to 0.64 ± 0.05 in the WMSH group. Third, in normal white matter, the concentration of N‐acetyl aspartate, choline, and lactate was estimated to 11.5, 2.0, and 0.6 mM, respectively, by assuming a total creatine concentration of 10 mM.
31P NMR spectroscopy of the human heart at 4 T: Detection of substantially uncontaminated cardiac spectra and differentiation of subepicardium and subendocardium
Authors: Menon Ravi S. , Hendrich Kristy , Hu Xiaoping , Uǧurbil Kǎmil
Published: March 2007

31 P NMR spectroscopy of the human heart was undertaken at 4 T to investigate whether spectra localized exclusively to the myocardium can be obtained. Utilizing a Fourier series window approach to spectroscopic imaging, we find that at least two layers across the anterior left ventricle wall can be detected, with voxel sizes of about 8 cm3.
A nuclear magnetic resonance investigation of the upper airways in ferrets. i. effects of histamine and methacholine
Authors: Reo Nicholas V. , Barnett Jeanne K. C. , Neubecker Thomas A. , Alexander Marise E. , Goecke Carol M.
Published: March 2007

Alterations induced in the upper airways of ferrets by intranasal provocation with methacholine (MC) and histamine (HS) were monitored using proton magnetic resonance imaging (MRI) and spin‐spin relaxation rate (R2) measurements. Both MC and HS cause a significant increase in the MRI signal intensity and a decrease in R2 in the nasal turbinates. A dose‐dependent response is observed for 20 to 315 nmol of HS, with a maximum increase in intensity of ca. 50% occurring above 80 nmol. A single unilateral challenge with MC yields a 62 ± 3% increase in intensity. Control animals (saline‐treated) show little change in image intensity. MC and HS cause decreases in the proton R2 by −27.0 ± 5.5% and −17.2 ± 4.3%, respectively. These data are indicative of an accumulation of fluid in the nasal airways. MRI provides an effective means to monitor changes in the nasal airways which occur as a result of pharmacological treatment.
Magnetic resonance imaging of myocardial kinematics. technique to detect, localize, and quantify the strain rates of the active human myocardium
Authors: Wedeen Van J.
Published: March 2007

A magnetic resonance imaging (MRI) method is presented to detect, localize, and quantify myocardial kinematics by measuring the material rate‐of‐strain tensor at each pixel in gated NMR images of the heart. The immediate, local effect of muscular activity is self‐deformation, and the strain tensor is the basic mathematical device by which such deformation may be quantified. The present method, called “strain‐phase” MRI (SP‐MRI), entails four steps: (1) the velocity of the myocardium is encoded by means of a set of motion‐sensitive NMR image acquisitions, one image per velocity component; (2) the spatial derivatives of the velocity are computed at each pixel; (3) the velocity‐derivative data are combined to compute an approximation of the strain‐rate tensor of the myocardium at each pixel; and (4) the strain‐rate tensor data are simplified to produce a color‐coded functional image which represents strain‐rate components which are of particular biomedical interest in the myocardium. We present a quantitative SP‐MRI methodology suited to conventional MRI, and in addition present an “echo‐planar” methodology, able to produce qualitative functional images of myocardial kinematics at almost real‐time speeds. Two‐dimensional strain‐phase MRI data acquired in normal human subjects are presented. These data demonstrate the practicability of SP‐MRI in vivo, that SP‐MRI resolves myocardial kinematics at the single‐pixel scale, having resolution comparable to that of conventional MRI, and that SP‐MRI data may have a signal‐to‐noise ratio up to 50% as great as that of the conventional MRI data from which they are produced. SP‐MRI measurements of the local instantaneous strain rates in the human left ventricular myocardium are quantitatively consistent with known transmural average values of myocardial strain.
Determination of concentrations by time domain fitting of proton nmr echo signals using prior knowledge
Authors: Van Dijk J. E. , Mehlkopf A. F. , Van Ormondt D. , Bovée W. M. M. J.
Published: March 2007

A fast and flexible time domain iterative fitting procedure that can be used to fit free induction decays as well as echo‐like signals is described. Damping constants of the first and second part of the echo do not have to be identical. Prior knowledge can be used to diminish the number of parameters to be fitted, which results in an improved accuracy. It is shown how prior knowledge is mathematically incorporated in the Gauss‐Newton method. From proton NMR measurements of model solutions actual prior knowledge is extracted. With this knowledge relative concentrations are determined from a mixture of metabolites. The fitted results agree with the true values within the margins of the noise. After some minor changes the same prior knowledge was successfully used to analyze a series of in vivo rat brain measurements.
A novel method for fat suppression in rare sequences
Authors: Higuchi N. , Hiramatsu K. , Mulkern R. V.
Published: March 2007

Rapid acquisition relaxation‐enhanced (RARE) sequences (Hennig et al., Magn. Reson. Med. 3, 823 (1986)) utilize one or several Cam‐Purcell–Meiboom–Gill (CPMG) echo trains to sample a number of k‐space lines each repetition time TR. The technique can rapidly generate multislice T2‐weighted images which, as a rule, are strikingly similar in contrast to conventional T2‐weighted spin‐echo (SE) images. An exception to this rule is the appearance of very bright signal from fat in T2‐weighted RARE images as compared to conventional T2‐weighted SE images. To reduce this fat signal, we introduce a time delay, τc, between the 90ox and first 180oy pulse of each echo train such that a phase angle of π/2 develops between fat and the reference (water) line at echo maxima. The technique leads to single‐acquisition fat suppression without the use of frequency‐selective saturation pulses and concomitant loss of slices per TR. A Bloch equation analysis is used to identify two major mechanisms contributing to suppression of off‐resonance spins such that Wτc = π/2. Namely, the CPMG sequence becomes a CP sequence with no self‐correction properties for imperfect 180° pulses leading to enhanced signal decay, and the raw k‐space data matrix become segemented into blocks alternately multiplied by ±i, leading to signal dispersion following Fourier transformation.
Multiexponential proton relaxation processes of compartmentalized water in gels
Authors: Watanabe Tokuko , Murase Norio , Staemmler Martin , Gersonde Klaus
Published: March 2007

The proton relaxation times, T1 and T2, of water in Sephadex gels, exhibiting pores of varying size (i.e., with exclusion limits of molecular weight between l03 and 105) and water contents in the range 30 to 70% (w/w, weight of water to total weight), were measured at 20 MHz in the temperature range 5 to 50°C. Multiexponential analysis of the relaxation curves revealed the existence of two relaxation components in all gel systems. A component with long T1 and T2 (T1,1 and T2,1) is associated with a large water fraction α1,1 and α2,1 and a component with short T1 and T2 (T1,2 and T2,2 with a small water fraction α1,2 and α2,2 An analysis of the temperature behavior of the relaxation components gives insight into the relaxation mechanisms. The relaxation process in water, compartmentalized in the gel matrix, is mainly controlled by dipole‐dipole interactions. In addition, proton exchange processes between hydration water and hydroxyl groups of the matrix chain contribute under specific conditions and lead to a dramatic enhancement of the relaxation rate. In particular, for gels with small pores and with low water content proton exchange is observed. Compartments of water in gels could be models for compartments of water in biological tissues.
Tissue characterization and assessment of preoperative chemotherapeutic response in musculoskeletal tumors by in vivo31p magnetic resonance spectroscopy
Authors: Redmond O. M. , Bell E. , Stack J. P. , Deran P. A. , Carney D. N. , Hurson B. , Ennis J. T.
Published: March 2007

This study investigates the potential of in vivo 31P magnetic resonance spectroscopy (MRS) to characterize musculoskeletal tumors and to determine preoperative levels of histological necrosis, which is an important clinical indicator of patient response. Pretherapy MRS was performed on 28 patients with large musculoskeletal tumors: 13 with osteosarcoma, 3 with chondrosarcoma, 5 with malignant fibrous histiocytoma, 1 with desmoid tumor, 1 with Ewing's, 2 with hemangioendothelioma, 1 with myxoid liposarcoma, 1 with synovial cell sarcoma, and 1 with rhabdomyosarcoma. Fifteen patients had follow‐up MRS examinations after commencement of chemotherapy (mean of five/patient), eight of whom have now had surgery. Elevated levels of PMEs (P < 0.01), Pi (P < 0.01), and PDEs (P < 0.02) as well as elevated tumor pH (P < 0.05) were. observed in all patients. The synovial cell sarcoma was characterized by high levels of PMEs (>20%) and low pH(pH 6.76). This contrasted with the spectra obtained from the malignant fibrous histiocytomas which had high levels of PDEs (17±5%). Reductions in PDE levels postchemotherapy were associated with a high degree of necrosis (>90%) at surgery, while an increase in PDE levels was associated with a low level of histological necrosis. Likewise, reductions in the ratios PDE/NTP and PDE/PCr and an increase in Pi/PDE were also associated with a high level of necrosis.
in vivo identification and monitoring of changes in rat brain glucose by two‐dimensional shift‐correlated 1h nmr spectroscopy
Authors: Peres M. , Fedeli O. , Barrere B. , Gillet B. , Berenger G. , Seylaz J. , Beloeil J‐C.
Published: March 2007

Intracerebral glucose resonance was directly detected and resolved in vivo by two‐dimensional shift‐correlated (COSY) 1H NMR spectroscopy in anesthetized rats (n = 4). The relative changes in brain glucose concentration were measured by volume integration of the α‐D‐glucose cross peak in the 2D COSY spectra. This report demonstrates the possibility of monitoring the variations in cerebral glucose following iv injection of glucose.
Real‐time observation of transient focal ischemia and hyperemia in cat brain
Authors: Crespigny A. J. De , Wendland M. F. , Derugin N. , Kozniewska E. , Moseley M. E.
Published: March 2007

Gradient‐recalled echo‐planar (T2‐weighted) imaging was used to noninvasively monitor regional blood oxygenation state changes in real time during transient episodes of focal ischemia in cat brain. Varying ischemic intervals (12 s to 30 min) were caused by middle cerebral artery occlusion. A rapid signal drop was noted upon occlusion, due to deoxygenation of static blood in the ischemic tissues. Upon successful reperfusion, the signal intensity recovered immediately and increased above (overshot) the baseline level before slowly returning to normal. The “overshoot” response was strongly dependent on the duration of the ischemic interval and is thought to reflect reactive hyperemia.
Determination of Absolute Phosphate Metabolite Concentrations in RIF‐1 Tumors in Vivo by 31P‐1H‐2H NMR Spectroscopy Using Water as an Internal Intensity Reference
Authors: Shungu Dikoma C. , Bhujwalla Zaver M. , Li Shi‐Jiang , Rose Lucy M. , Wehrle Janna P. , Glickson Jerry D.
Published: March 2007

The absolute metabolite quantification method of Thulborn and Ackerman [J. Magn. Reson 55, 357 (1983)] in which the tissue water proton signal is used as an internal intensity standard and its more recent variation in which NMR peak intensities are referenced to that of the natural abundance deuterium signal of water [Li et al., SMRM Abstr. 2, 825 (1988); Song et al, Magn. Reson. Med. 25, 45 (1992) have been implemented to obtain absolute phosphate metabolite concentrations in subcutaneous RIF‐1 tumors during untreated growth and following treatment with 5‐fluorouracil. The equivalence of these two hydrogen isotopes as intensity standards and the validity of their use in the determination of absolute metabolite concentrations in vivo by NMR has been demonstrated. On matched in vivo and extract tumor samples (n = 5), excellent agreement has been obtained between nucleoside triphosphate concentrations determined by NMR and those derived by HPLC analysis for the control tumors. Following 3 days of untreated growth, absolute concentrations of phosphate metabolites in RIF‐1 tumors (n = 10) decreased significantly, except for the Pi concentration which did not vary. For the treated tumors (n = 10) there were no changes in metabolite concentrations except for a decrease in the PCr and, possibly, Pi concentrations. The PCr/Pi ratio in the latter tumors did not change. These observations suggest that changes in absolute metabolite concentrations may be more sensitive indices of response to therapy than changes in metabolite peak amplitude ratios, a parameter commonly used to express in vivo NMR data.© 1992 Academic Press,Inc.