bluuebunny/crossref_metadata_2025 huggingface dataset:
A method for in vivo MR imaging of the short T2 component of sodium‐23
Authors: Ra J. B. , Hilal S. K. , Cho Z. H.
Published: March 2007

A magnetic resonance imaging pulse sequence featuring a short echo time of 3.6 ms is described and used clinically for in vivo imaging of sodium‐23 in the human head. In living tissues, sodium exhibits at least two transverse relaxation constants, namely, (a) a short component T2s = 0.7–3.0 ms and (b) a long component T2l = 16–30 ms. Since our first in vivo imaging of sodium, an echo time of 10–15 ms has been used by us and by other investigators. This echo time is adequate for the observation of the long T2 component of sodium. However, a substantial fraction of the sodium, namely, the short T2 component, representing about 40%, has remained undetected by the imaging method with this echo time and is now observable by the new pulse sequence. The proposed method is a hybrid technique combining both projection reconstruction and Fourier encoding schemes. The projection reconstruction is used for the xy plane imaging while the Fourier encoding is used for slice separation. Sodium MR images of the human head produced with a short and a long TE are presented and analyzed. There is an increase in the MR signal and improved visibility of intraparenchymal sodium with the new scheme of short TE. © 1986 Academic Press, Inc.
Multiple field strength in vivo T1 and T2 for cerebrospinal fluid protons
Authors: Hopkins A. L. , Yeung H. N. , Bratton C. B.
Published: March 2007

To estimate the feasibility of measuring in vivo CSF protein, oxygen, or other solutes through their effect on proton relaxation times, the T1 and T2 of CSF protons has been measured within the human lateral ventricles, T1 was measured at 6.25, 25.4, and 60.1 MHz with a two‐point method. T2 was measured at 6.25 and 25.4 MHz using the CPMG sequence to acquire 8 echo images. The T1 was 4.3 s with no evidence of field dependence. The T2 was 2 s. Although these values approach those for water at the same temperature it is possible that the T1 is influenced by the normal oxygen concentration. Calculations based on the relaxivity of dissolved protein indicate that the use of these methods for the detection of elevated levels of CSF protein would be less sensitive than existing methods. © 1986 Academic Press, Inc.
31P NMR studies of adenosine‐stimulated ATP synthesis in perfused luteinized ovaries
Authors: Haseltine F. P. , Arias‐Mendoza F. , Kaye A. M. , Degani H.
Published: March 2007

31P NMR spectroscopy was utilized to study phosphate metabolism of perfused ovaries. In luteinized ovaries, a loss in ATP of ∼ 30% with a concomitant acidification was reversed by 50 μM adenosine. The results suggest that in the ovaries, adenosine can serve to regulate ATP concentration during periodic hypoxic challenges. © 1986 Academic Press, Inc.
Nuclear magnetic resonance study of high‐energy phosphate stores in models of adriamycin cardiotoxicity
Authors: Keller Andrew M. , Jackson Jay A. , Peshock Ron M. , Rehr Roger B. , Willerson James T. , Nunnally Ray L. , Buja L. Maximilian
Published: March 2007

Previous studies have suggested that one of the mechanisms of adriamycin (ADR) cardiomyopathy is depletion of high‐energy phosphate stores (HEP). To examine this hypothesis, we used 31P nuclear magnetic resonance to asses the adenosine triphosphate‐to phosphocreatine ratio (ATP‐to‐PCR ratio) in Langendorff‐Perfused rabbit hearts. Using either and acute (5 days of therapy at 5mg/kg /day) or chronic model (7 to 10 weeks of therapy at 1.2 or 1.5mg/kg twice a week) we compared isovolumetric LV systolic pressure, heart rate, ATP‐to‐PCR rations, and histologic lesions between the treated and control animals in each model. In the acute model, there was a significant incraease in the ATP‐to‐PCr ratio (P < 0.02), without significant change in myocardial function. Despite significant hemodynamic and histologic alterations in the chronic model, compared to controle, we were unable to identify significant differences in ATP‐to PCr ratios. We conclude that (a) there appear to be differences in energy metablism between the acute cardiotoxicity and the chronic cardiomyopathy of ADR in the rabbit model and (b) the mechanism of the chronic cardiomyopathy from ADR therpy does not appear to be related to progressive impariment of cellular high‐energy phosphate metabolims as measured by the ATP‐to‐PCr ratio. © 1986 Academic Press, Inc.
Quantitative proton chemical‐shift imaging
Authors: Buxton Richard B. , Wismer Gary L. , Brady Thomas J. , Rosen Bruce R.
Published: March 2007

Recently W. T. Dixon (Radiology 153, 189 (1984)) introduced a simple method of proton chemical‐shift imaging which requires only two images, a conventional (in‐phase) image and an image in which fat and water protons are 180° out of phase during signal acquisition, to separate the signals from fat and water protons. We have tested the application of this method to the quantitative determination of fat content and fat and water longitudinal relaxation times, and analyzed the effects of random and systematic errors. Ten phantoms were constructed with a range of fat contents (0–50% by weight) and water T1's (300–800 ms). Fat and water T1's were measured with a 0.6‐T clinical imaging system in two ways: (1) using the system as a spectrometer with all gradients off, and (2) from least‐squares fits to in‐phase and out‐of‐phase image data made with six values of TR. The image‐derived values of water T1 agreed well with spectrometer‐derived values (r = 0.97) and the image derived fat fraction correlated strongly with the fat fraction by weight (r = 0.995). The effects of random and systematic errors were analyzed for a minimum data set of four images: in‐phase and out‐of‐phase images at two values of TR. The pair of TR values which minimize the variance in water T1 were calculated, and for these pulse sequences the effects of two potential systematic errors were calculated: (1) inhomogeneities in the main field, which will reduce the intensity in out‐of‐phase images compared to in‐phase images even for pure water samples, and (2) an incorrect shift of the 180° pulse in the out‐of‐phase pulse sequence, corresponding to an inaccurate assumed chemical shift. With careful attention to such systematic effects the Dixon method is capable of producing reliable quantitative measurements. © 1986 Academic Press, Inc.
A simple fiber optic monitor of cardiac and respiratory activity for biomedical magnetic resonance applications
Authors: Legendre J. P. , Misner R. , Forester G. V. , Geoffrion Y.
Published: March 2007

A fiber optic reflectometer, capable of monitoring physiological parameters in a high magnetic field without significant disturbance of either rf or static fields, is described. Both cardiac and respiration rates were monitored with this optical device while31P NMR spectra of the liver of an anesthetized rat were acquired. © 1986 Academic Press, Inc.
Cardiac T1 calculations from MR spin‐echo images
Authors: Prato F. S. , Drost D. J. , King M. , Keys T. , Wisenberg G. , Galland C. , Pflugfelder P. W.
Published: March 2007

Normally, cardiac triggering in MR spin‐echo imaging restricts repetition times (TR) to integral values of the cardiac period (TC), and introduces irregularities in TR due to variations in TC. We have investigated how much these restrictions decrease the accuracy and precision of spin‐lattice relaxation (T1) values of the myocardium calculated from two cardiac‐triggered spin‐echo images. By introducing additional excitation pulses, TR can effectively be reduced to a fractional value of TC and considerable improvement in T1 precision is possible. For TC = 800 ms, the improvement in T1 precision is 30% when two spin‐echo images of TR = 1/2 TC and TR = 2 TC are used to calculate T1 instead of two images with TR = TC and TR = 2 TC. The irregularities in TR decrease both T1 precision and accuracy. Irregularities of the order of 15% in a mean TR of 800 ms produce a fourfold decrease in precision. Since irregularities in TC easily exceed 15%, MRI data should be acquired when individual TR values are approximately within ± 15% of the subject's mean TC. © 1987 Academic Press, Inc.
Determination of renal molar concentrations of phosphorus‐containing metabolites in vivo using 31P NMR
Authors: Shine Nancy R. , Xuan Jian Ai , Koretsky Alan P. , Weiner Michael W.
Published: March 2007

A technique to determine absolute metabolite concentrations of the kidney in vivo using 31P NMR is described. The technique is based on the use of methylphosphonic acid (MPA), which gives rise to a well‐resolved peak upfield from in vivo phosphorous metabolite resonances, as an “internal standard.” The method involves acquisition of a fully relaxed kidney spectrum with an implanted coil followed by intravenous infusion of MPA (4 ml of 150 mM) for a period of 30 min. The animal is then sacrificed to insure a steady state level of renal MPA and another spectrum is obtained. From these two spectra the ratio of intensities of MPA to β‐ATP was derived. In the method used here, no significant contribution from tissues outside the kidney was observed. In addition, a relatively homogenous distribution of MPA throughout the kidney was achieved. The amount of MPA per gram wet weight of kidney was also obtained through NMR methods by placing the excised organ in a phosphate‐calibrated solenoidal coil. The calibration spectra along with the ratio of intensities for MPA/β‐ATP were used to calculate the number of micromoles of ATP per gram wet weight of kidney. Infusion of a higher concentration of MPA (1.25 M) produced a visible MPA resonance in other organs besides the kidney. Thus, MPA could be useful in determining phosphate metabolite concentrations in other tissues. © 1987 Academic Press, Inc.
31P NMR spectroscopy of an experimentally induced intracerebral tumor in mice
Authors: Ross Brian D. , Higgins Robert J. , Conley Frances K. , True Nancy S.
Published: March 2007

31P surface coil NMR spectroscopy was used to evaluate in vivo high‐energy phosphorus metabolism in the brains of mice with experimentally induced primary intracranial and subcutaneous KHT sarcomas. 31P spectra of subcutaneous KHT tumors revealed a lack of detectable phosphocreatine (PCr) levels in the tumor as compared to the relatively high endogenous levels of PCr in normal mouse brain. As the intracerebral tumor size increased, there was a reduction in spectral PCr levels over a 23‐day postinoculation period in situ in the brain. No histologic or spectroscopic evidence of tumor‐associated necrosis or hypoxia was found. This study demonstrates that surface coil 31P NMR spectroscopy can be used to monitor changes in highenergy phosphate metabolism associated with progressive growth of an experimentally induced mouse brain tumor in situ. © 1987 Academic Press, Inc.
Gradient reversal technique and its applications to chemical‐shift‐related NMR imaging
Authors: Park H. W. , Kim D. J. , Cho Z. H.
Published: March 2007

The chemical‐shift effect often degrades slice selectivity thereby degrading the contrast and spatial resolutions in a high‐field NMR imaging. We propose a new pulse sequence which can compensate for this chemical‐shift effect during slice selection. This technique provides correct slice definition as well as clear separation between water and lipid protons in high‐field proton NMR imaging. Particular applications of this technique are 2D imaging with a thin‐slice selection and chunk 3D imaging, where correction of the chemical‐shift effect in slice selection is important. Another interesting application of the technique is chemical‐shift‐selective (CHESS) imaging. This technique does not require spectral‐selective rf pulses and it takes advantage of the chemical‐shift effect during slice selection. The latter is found to be useful for human in vivo chemical‐shift imaging in high‐field NMR. In this paper, the theoretical derivation of the proposed gradient reversal technique, its applications, and related experimental results are presented. © 1987 Academic Press, Inc.
Magnetic resonance imaging of experimental mumps meningoencephalitis in suckling hamsters
Authors: Narayana P. A. , Wolinsky J. S. , Jensen D. J.
Published: March 2007

Mumps virus‐infected and normal newborn hamster brains were imaged with magnetic resonance (MR) within 24 h after birth and serially scanned. Hydrocephalus developed explosively on Day 6 postinfection and progressed until death occurred soon after Day 10. This study demonstrates the utility of MR in the investigation of experimental viral encephalitis in very small laboratory animals. © 1987 Academic press Inc.
The contrast‐to‐noise in relaxation time, synthetic, and weighted‐sum MR images
Authors: Lee James N. , Riederer Stephen J.
Published: March 2007

The contrast‐to‐noise ratio (CNR) in three types of computed MR images is compared in a computer simulation. The original data consist of two spin‐echo or two saturationrecovery images. Each pair of images is used to generate a relaxation time image, a synthetic image at arbitrary echo or repetition time, and an image which is a weighted sum of the original images. The CNR produced by these three methods is compared for signals spanning a wide range of relaxation times. In every comparison an optimally weighted sum produces the highest CNR that is statistically attainable. The CNR in the optimum synthetic image equals this bound only if contrast reversal does not occur in the original images. The CNR in relaxation time images is always less than the statistical bound and can be less than the CNR in the original images. © 1987 Academic Press, Inc.
Metabolic fate in the dog of the nitroxide moiety in a compound with potential utility as a contrast agent in MRI
Authors: Erikson Ulf G. , Ogan Marc D. , Peng Chin‐Tzu , Brasch Robert C. , Tozerc Thomas N.
Published: March 2007

Nitroxides, paramagnetic compounds with demonstrated effectiveness as contrast agents in proton magnetic resonance imaging, shorten the relaxation times of protons and therefore cause an increase in image intensity in tissues into which they distribute. In this study, the metabolic fate of the nitroxide moiety was examined in the dog using a pyrrolidine nitroxide derivative, 2,2,5,5‐tetramethylpyrrolidine‐l‐oxyl‐3‐carbxylic acid, for which contrast‐enhancing properties have been previously studied in animals. After radiolabeling by microwave discharge in the presence of tritium gas, the compound was administered intravenously to a dog. Ninety‐four percent of the radioactivity injected was recovered in urine within 3 days; the majority (90%) was excreted during the first 6 h. The radioactivity in the urine was identified as either the unchanged nitroxide or its corresponding hydroxylamine. Neither complete reduction of the nitroxide moiety to the amine nor any other metabolic transformation was observed. © 1987 Academic Press, Inc.
Random noise selective excitation pulses
Authors: Ordidge Roger J.
Published: March 2007

Several methods for the spatial localization of NMR signals from well‐defined regions of tissue within extended specimens have been proposed. Most of these techniques are prone to signal error which can arise from large volumes of sample that surround the region of interest. These errors can theoretically be reduced by several orders of magnitude by the application of a radiofrequency prepulse. The pulse acts to randomize the unwanted spin magnetization prior to the application of a spatial localization technique.
MR in renal disease: Importance of cortical–medullary distinction
Authors: Marotti Miljenko , Hricak Hedvig , Terrier Francois , McAninch Jack W. , Thuroff Joachim W.
Published: March 2007

The diagnostic value of MR contrast between renal cortex and medulla (CMC) as an indicator of renal disease was retrospectively studied in 51 patients (9 patients with obstructive disease, 7 with inflammatory disease, 12 with various noninfectious parenchymal medical disease, 5 with vascular disease, 2 with diffuse neoplastic disease, 7 with hemosiderosis, and 10 with renal trauma [blunt trauma and 9 postlithotripsy]). Additionally, normal kidneys from 20 control subjects were studied. On T1‐weighted spin‐echo images (SE 500/30), CMC was visible in all the normal kidneys (19% contrast ± 2% SD). A decrease in or an absence of CMC on T1‐weighted images (SE 500/28) was found to be a sensitive but nonspecific sign in most of the renal diseases studied. CMC was visibly preserved at normal levels in 7 of the 9 kidneys traumatized by lithotripsy and in all 4 kidneys with acute renal obstruction; CMC was above normal in kidneys with hemosiderosis. In conclusion, alteration in CMC is a sensitive but nonspecific indicator of renal disease. Furthermore, normal CMC can be seen in the presence of renal pathology. © 1987 Academic Press, Inc.
An MRI phantom material for quantitative relaxometry
Authors: Kraft K. A. , Fatouros P. P. , Clarke G. D. , Kishore P. R. S.
Published: March 2007

Most phantom media in current use exhibit T1 relaxation times that are significantly dependent on both temperature and operating frequency. This can introduce undesirable variability into relaxation measurements due to temperature fluctuations, and complicates direct comparison of imagers operating at different magnetic field strengths. Our investigations of a nickel‐doped agarose gel system have demonstrated near independence of the proton relaxation rates to a wide range of temperatures and frequencies. We therefore propose the adoption of Ni2+ as a relaxation modifier for phantom materials used as relaxometry standards. © Academic Press, Inc.
Functional evaluation of the heart with magnetic resonance imaging
Authors: Higgins Charles B. , Holt William , Pflugfelder Peter , Sechtem Udo
Published: March 2007

This review examines the capability of cine MRI for evaluation of cardiovascular function and shows early results in valvular, ischemic, and congenital heart disease. MR assessment of left and right ventricular volumes is independent of geometrical models; dimensional values have been defined for normal individuals. Noninvasive measurement of peak and end systolic pressure along with cine MR imaging can be used to calculate left ventricular meridional wall stress which can be used for monitoring of myocardial diseases and evaluation of therapeutic intervention. Cine MR may be more accurate than angiography for identifying regional LV dysfunction since it can measure wall thickening as well as inward wall motion. Regurgitant jets due to valvular lesions are readily seen and their characteristics may be used to define the severity of aortic or mitral regurgitation. Calculation of the regurgitant volume separates patients with mild, moderate, or severe disease. Likewise, the shunt flow across ventricular and atrial septal defects has been visualized in cine MR images and shunt flow calculated. Cine MRI serves as a three‐dimensional imaging technique with high temporal resolution. It extends the capability of MRI in cardiac disease beyond the depiction of anatomy and renders a comprehensive cardiac imaging technique for quantitation of cardiac anatomy and function. © 1988 Academic Press, Inc.
Metabolic profiling of body fluids by proton NMR: Self‐poisoning episodes with paracetamol (acetaminophen)
Authors: Bales J. R. , Bell J. D. , Nicholson J. K. , Sadler P. J. , Timbrell J. A. , Hughes R. D. , Bennett P. N. , Williams R.
Published: March 2007

IH NMR spectra of urine and plasma from subjects who had taken paracetamol (acetaminophen) at a therapeutic dose or in self‐poisoning episodes (both fatal and nonfatal) are compared. They provide convenient metabolic profiles. For overdose cases, intense resonances corresponding to high levels of both drug and endogenous metabolites are observed. The ratios of glucuronide to sulfate conjugates are unusually high in urine from overdose cases. Elevated levels of the cysteinyl and N‐acetyl cysteinyl conjugates reflect increased glutathione conjugation in the liver. The observed excretion of high levels of amino acids by overdose subjects is suggestive of drug‐induced hepatic damage. No resonances for drug metabolites are detected in plasma samples. However, characteristic and abnormally intense resonances for the amino acids Phe, Tyr, His, Gin, Pro, Ala, Val, Lys, Met, Ser, and Thr are indicative of severe liver failure and disruption of normal deamination and transamination processes. © 1988 Academic Press, Inc.
31P NMR spectroscopy of the in vivo metabolism of an intracerebral glioma in the rat
Authors: Ross Brian D. , Higgins Robert J. , Boggan James E. , Knitteln Brian , Garwood Michael
Published: March 2007

The in vivo high‐energy phosphorus metabolic profile and pH of an experimental intracerebral C6 glioma in rats was examined using surface coil 31P NMR spectroscopy. Initially, phosphorus‐containing metabolites of the glioma were characterized by in vivo 31P surface coil spectroscopy of subcutaneously implanted tumors and by high‐resolution NMR studies of perchloric acid (PCA) extracts of both freeze‐clamped subcutaneous tumor tissue and cultured cells. These studies demonstrated that the C6 glioma has reduced levels of phosphocreatine (PCr) compared to the levels found in normal rat brain. Thus, reduced spectral PCr levels were useful as a metabolic indicator for monitoring the spatial selectivity of tumor metabolism distinct from that of adjacent normal brain tissue. To maximize 31P NMR signals from intracerebral tumors, tumor cells were stercotaxically placed superficially in the brain. Proton magnetic resonance imaging (1H MRI) was used to determine the size and location of the resultant brain tumors in order to preselect rats with large superficial tumors for spectroscopic study. 31P NMR spectra of the glioma tumors revealed a consistent reduction in the PCr/ATP ratio, an increase in the Pi/ATP ratio, and a slightly increased tissue pH. No correlation was found between levels of Pi/ATP and tumor pH in subcutaneous or intracerebral gliomas and the amount of necrosis as determined histologically. This study demonstrates that phosphorus metabolites of an experimental brain tumor in the rat can be monitored in vivo with minimal contributions from adjacent normal brain tissue metabolites using surface coil 31P NMR spectroscopy. © 1988 Academic Press, Inc.
31P NMR studies of the diabetic lens
Authors: Gonzalez R. Gilberto , Miglior Stefano , Von Saltza Ingrid , Buckley Lisa , Neuringer J. , Cheng Hong‐Ming
Published: March 2007

Phosphorus‐31 (31P) nuclear magnetic resonance (NMR) spectroscopic analyses of the crystalline lens from the experimental diabetic rat were performed. Qualitative and quantitative alterations in the phosphorus‐31 NMR metabolic profile were observed over the course of 3 weeks after the induction of diabetes mellitus. Most striking was the appearance of two new, as yet unidentified, metabolites. These metabolites which resonate at 6.6 and 5.8 ppm were not detected in the normal lens. Compared to the normal lens, glycerol‐3‐phosphate (G3P) underwent an eightfold increase in concentration and phosphorylcholine decreased to one‐third its initial level. The phosphodiesters, glycerophosphorylcholine (GPC) and glycerophosphorylethanolamine (GPE), decreased to barely detectable levels. Oral treatment of the diabetic animal with an aldose reductase inhibitor resulted in the preservation of an essentially normal lens 31P NMR spectrum. Except for the changes observed in glycerol‐3‐phosphate, these alterations have not been previously reported and raise new questions about the metabolic consequences of diabetes mellitus and the dependence of these alterations on the action of a single enzyme, aldose reductase. © 1988 Academic Press, Inc.
Direct FLASH MR imaging of magnetic field inhomogeneities by gradient compensation
Authors: Frahm Jens , Merboldt Klaus‐Dietmar , Hänicke Wolfgang
Published: March 2007

MR images based on gradient echoes are sensitive to artifacts caused by inhomogeneities of the static magnetic field. This paper describes the effects of local gradients in rapid FLASH MR images and presents a way of directly imaging affected areas. The idea is to compensate for signal losses due to mutual cancellation of dephased magnetizations by deliberate “misadjustments” of the refocusing part of the slice selection gradient. In contrast to conventional field imaging techniques no three‐dimensional data acquisition or subsequent Fourier analysis is required to obtain images at a particular gradient strength. Conventional as well as inhomogeneity compensated FLASH images have been obtained on phantoms and human heads using a 2.35‐T 40‐cm magnet and a 1.5‐T whole‐body system, respectively. © 1988 Academic Press, Inc.
Rapid line scan NMR angiography
Authors: Frahm J. , Merboldt K. D. , Hånicke W. , Gyngell M. L. , Bruhn H.
Published: March 2007

This paper describes a new technique for NMR angiography based on rapid line scan projection imaging and presaturation of stationary spins. The resulting line Scan angiograms are free from both misregistration artifacts common to subtraction methods and motion artifacts encountered in Fourier imaging. Moreover, line scan angiograms may be recorded within seconds and offer arbitrary fields of view as well as gradient zooming without problems due to aliasing. Three‐dimensional information is obtained by rotation of the read gradient axis generating multiple view angles. Experimental line scan angiograms of the forearms of healthy volunteers have been recorded using a Bruker 2.35‐T 40‐cm magnet. © 1988 Academic Press, Inc.
Detection of motion using B1 gradients
Authors: Karczmar G. S. , Tweig D. B. , Lawry T. J. , Matson G. B. , Weiner M. W.
Published: March 2007

An NMR method which makes use of a radiofrequency (RF) field gradient to detect diffusion, perfusion, or flow is demonstrated. The technique is analogous to the detection of motion using pulsed Bo gradients. The simplest form of the experiment is as follows: A spatially inhomogeneous RF field generated by a surface coil produces dispersal of magnetization in the YZ plane. After a delay, the RF field is applied with reversed phase to restore polarization along +Z, which is then sampled using an observe pulse or pulse sequence. If molecular motion occurs during the delay period the amplitude of Z magnetization will be. reduced. The lengths of the RF pulses and the delay period are varied so that the effects of relaxation, flow, and diffusion or perfusion can be distinguished. The present study demonstrates the use of this method to detect slow fluid flow. Advantages of this method include the availability of large RF gradients, and the avoidance of eddy currents. It is suggested that the method may have application to the study of perfusion and flow in vivo. © 1988 Academic Press, Inc.
Quantitative estimation of lactate in the brain by 1H NMR
Authors: Williams Stephen R. , Proctor Edward , Allen Kathryn , Gadian David G. , Crockard H. Alan
Published: March 2007

1H NMR was used to detect lactate accumulation in the intact gerbil brain postmortem. The lactate concentration was estimated from the spectra by comparison to signals from N‐acetylaspartate, creatine + phosphocreatine, and water. The effects of T2, phase modulation, and solvent suppression were taken into account. The estimated concentrations were compared to determinations performed on the same brains after extraction. The lactate concentration estimated from the intact brain spectra was between 70 and 90% of the values determined in vitro, on the extracts, depending on the concentration standard used. If N‐acetylaspartate was used as the standard then the proportion of detected lactate (92%) was not significantly different from 100%. © 1988 Academic Press, Inc.
A one‐shot lactate‐editing sequence for localized whole‐body spectroscopy
Authors: McKinnon G. C. , Boesiger P.
Published: March 2007

A pulse sequence is presented for performing localized lactate‐edited proton spectros‐copy in the whole‐body environment. The sequence is optimized for relatively low field strength (1.5‐T) clinical measurements. Characteristics of this method of lactate editing, which makes it more suitable for clinical applications than previous methods, include the following: The “one shot” nature of the method makes it relatively insensitive to patient motion; water suppression is high as all 90° pulses are binomial pulses; and very narrow band rf pulses, such as used in high‐field lactate‐editing sequences, but which are necessarily very long at low fields, are not required. Further, this lactate editing scheme can be very easily combined with localized spectroscopic measurements. © 1988 Academic Press, Inc.
31P NMR study of insulin effects on the isolated perfused rabbit urinary bladder
Authors: Fisher M. J. , Dillon P. F.
Published: March 2007

Insulin stimulates hexose transport, intermediary metabolism, and cell growth and development. These effects are well‐documented in skeletal but not smooth muscle. 31P NMR spectroscopy was performed on rabbit urinary bladders (n=4) to characterize insulin's actions on smooth muscle. The bladder and its vasculature were surgically isolated from the animal and perfused with a PSS/red blood cell perfusate. After a control steady state was achieved (approx 1−2 h), insulin (0.100 mU/ml) was added to the perfusate. Relative levels of intracellular phosphorylated compounds, pH, and free Mg2+ were measured and compared to control values. Also, extracellular pH and fractional volume were assessed using phenylphosphonate, a 31P NMR extracellular pH and volume indicator. Insulin induced significant increases in PCr (16 ± 9%) at the expense of Pi, intracellular pH ( Δ 0.24 + 0.07 ), and fractional extracellular volume (49 ± 1%). Intracellular free Mg2+ and extracellular pH did not change. These results indicate that in situ smooth muscle is sensitive to physiological levels of insulin. In fact, insulin improves the energy state of smooth muscle cells and the overall tissue perfusion. © 1989 Academic Press, Inc.
Flow‐induced phase effects and compensation technique for slice‐selective pulses
Authors: Yuan Chun , Gullberg Grant T. , Parker Dennis L.
Published: March 2007

Flowing spins experience a time‐varying frequency during the application of slice‐se‐lective radiofrequency (RF) pulses. As a result the flowing spins accumulate phase relative to stationary spins as the spins are rotated toward the transverse plane. Using finite difference techniques to solve the Bloch equations for flowing spins, the phase of the transverse magnetization after a slice‐selective pulse was evaluated for varying flow velocities and for tip angles which ranged between 0° and 180°. The following results were obtained for constant slice thickness: (1) For a fixed tip angle, the phase varies nonlinearly with velocity. (2) For a fixed velocity, the phase varies nonlinearly with tip angle. For small tip angles the nonlinearity in the variation as a function of velocity is very small but increases for tip angles greater than 90° and becomes especially severe near 180°. A method is proposed to desensitize the phase of flowing spins during the application of slice‐selective pulses. The compensation scheme depends upon tip angle but is virtually independent of flow velocity. The technique was tested and verified with clinical images. © 1989 Academic Prcrs. Inc.
Pathways for the synthesis of sorbitol from 13C‐labeled hexoses, pentose, and glycerol in renal papillary tissue
Authors: Jans A. W. H. , Grunewald R.‐W. , Kinne R. K. H.
Published: March 2007

Suspensions of rabbit renal papillary tissue were incubated with D‐[ 6‐13C]glucose, D‐[1‐13C]fructose, D‐[1‐13C] ribose, and [2‐13C]glycerol. The perchloric acid extracts of the above incubations were investigated with 13C NMR spectroscopy. All 13C‐labeled substrates give rise to 13C‐labeled D‐sorbitol. D‐[6‐13C]Glucose and D[1‐13C]fructose are converted directly into D‐sorbitol via the aldose reductase and sorbitol dehydrogenase pathway, respectively, whereas D‐[1‐13C] ribose and [2‐13C]glycerol give rise to labeling of the D‐glyceraldehyde pool which on its turn causes a labeling of D‐sorbitol. Label exchanges observed from incubations with glycerol and D‐ribose indicate that the pentose shunt plays a role in this synthesis of D‐sorbitol. © 1989 Academic Press, Inc.
Identification of a characteristic 31p NMR signal in acute experimental pancreatitis with the aid of 1H−31p correlated 2D measurements of intact pancreas
Authors: Kushnir T. , Kaplan O. , Askenasy N. , Navon G.
Published: March 2007

Two‐dimensional 1H–31P correlation spectroscopy and relaxation time measurements of intact diseased pancreas were performed in order to identify an unknown peak appearing at −0.18 ± 0.04 ppm in a31P NMR spectrum of taurocholate‐induced experimental acute pancreatitis in rats. The signal was identified as a solubilized lecithin taurocholate Complex. © 1989 Academic Press, Inc.
PEEP—A rapid chemical‐shift imaging method
Authors: Guilfoyle D. N. , Blamire A. , Chapman B. , Ordine R. J. , Mansfield P.
Published: March 2007

The phase‐encoded echo‐planar (PEEP) technique, a variant of echo‐planar imaging, is used to achieve simultaneous high‐speed spatial and chemical‐shift data acquisition. This technique is the 2DFT equivalent of the projection reconstruction echo‐planar method for chemical‐shift imaging. Examples of images and spectra obtained using the PEEP method are presented. © 1989 Academic Press, Inc.
Eigenimage filtering in MR imaging: An application in the abnormal chest wall
Authors: Haggar Allan M. , Windham Joe P. , Reimann David A. , Hearshen David O. , Froelich Jerry W.
Published: March 2007

A postprocessing linear filter was applied to spin‐echo images on 10 patients with known or suspected chest wall invasion due to bronchogenic carcinoma. This technique known as eigenimage filtering allows selective feature extraction of suspected abnormali‐ties from conventional MR images. The final result is an image with marked increased contrast range through enhancement of a desired process (tumor) with suppression of an interfering process (e.g., normal surrounding tissue). This preliminary work demon‐strates the ease with which the technique may be implemented, the contrast enhancement obtained between the desired and the interfering feature in the final eigenimage, and its ability to correct for partial volume averaging effects. Also demonstrated are artifacts that can interfere with the interpretation of the eigenimage and a method for minimizing these artifacts in the final eigenimage. © 1989 Academic Press, Inc.
Low‐frequency restoration
Authors: Jackson John , Macovski Albert , Nishimura Dwight
Published: March 2007

In magnetic resonance imaging, if the object of interest is known to be spatially bounded within the image field‐of‐view. then the high‐intensity, low spatial frequencies can be determined by postprocessing. This allows the system receiver gain to be increased, thereby decreasing the quantization noise from the analog‐to‐digital converters. No imaging sequence modifications are required. © 1989 Academic Press. Inc.
High‐Flux Signals and Spatial Localization in High‐Resolution 1H Spectroscopy with Surface Coils
Authors: Bourgeois D. , Decorps M. , Remy C. , Benabid A. L.
Published: March 2007

To perform in vivo localized proton spectroscopy with water suppression, spin‐echo sequences, made of binomial pulses, are commonly used with surface coils. The frequency selective response to such a sequence is also spatially dependent, that is dependent on the sample shape and on the pulse angle adjustment. It is consequently pointed out in this paper that quantitative analysis for relative peak intensities may be strongly affected by the contribution of the high‐flux regions. In vivo proton spectroscopy of rat brain exemplifies this difficulty. It is shown that the use of selective prepulses to suppress high‐flux signals may be of poor efficiency depending on chemical shift, while the use of hard nonselective prepulses works for any chemical shift.
Relative contributions of chemical exchange and other relaxation mechanisms in protein solutions and tissues
Authors: Zhong Jianhui , Gore John C. , Armitage Ian M.
Published: March 2007

Transverse relaxation times T2 of water protons were measured in 5% protein solutions and soaked rat liver in different static magnetic fields (0.15 to 11 T). Protein molecular weight varied between 1.4 and 480 kDa in solutions of yarying degrees of deuteration. The data obtained are analyzed in terms of a model system consisting of three phases of different relaxation characteristics: protein protons, hydration layer water protons, and bulk water protons. The contributions to relaxation due to hydrodynamic effects on water protons, cross relaxation between the hydration layer water protons and the protein protons, and chemical exchange between the hydration layer water protons and the bulk water protons are separately estimated. The experimental results indicate that the “hydrodynamic interactions” are about the same magnitude in rat liver and all the proteins studied, but the contribution of the cross relaxation differs by several orders in different protein systems. Fast chemical exchange between the hydration layer water and the bulk water causes considerable shortening of T2 at high magnetic fields for all the protein solutions and rat tissue studied. Selected samples were studied at different temperatures (2 13‐3 18 K) and with different intervals in the CPMG sequence. The rates of chemical exchange and fractional populations of different phases are determined, and the results obtained provide support for the model in which fast exchange among the different water phases is an important feature of the overall relaxation behavior.
On the use of double‐quantum coherence from an AX3 system (protons in lactate) for spectral editing
Authors: Nosel W. , Trimble L. A. , Shen J. F. , Allen P. S.
Published: March 2007

The suppression of water signals in in vivo proton spectra by means of multiple‐quanturn filtering can be brought about in several ways. This communication exposes the shortcomings of using purely subtractive filtering techniques to observe signals from metabolites that contain proton couplings of the form AX3.
Intrauterine fetal brain NMR spectroscopy: 1H and 31P studies in rats
Authors: Nakada Tsutomu , Kwee Ingrid L. , Suzuki Nobuyuki , Houkin Kiyohiro
Published: March 2007

Fetal brain metabolism was investigated in utero noninvasively using multinuclear nuclear magnetic resonance spectroscopy in rats at two representative prenatal stages: early (17‐18 days) and late (20‐21 days) stages. Phosphorus‐31 (31P) spectroscopy revealed that phosphocreatine is significantly lower in the early stage and increases to the level of early neonates by the late prenatal stage. Intracellular pH at the early stage was found to be strikingly high (7.52 ± 0.21) and decreased to a level similar to that of neonates by the late stage (7.29 ± 0.07). Phosphomonoester levels at both stages were similar to the values reported for early neonates. Water‐suppressed proton (1H) spectroscopy demonstrated a distinctive in vivo fetal brain spectral pattern characterized by low levels of N‐acetyl aspartate and high levels of taurine. High‐resolution proton spectroscopy and homonuclear chemical‐shift correlate spectroscopy of brain perchloric acid extracts confirmed these in vivo findings. In vitro 31P spectroscopy of acidified chloroform methanol extracts showed the characteristic membrane phospholipid profiles of fetal brain. The phosphatidylethanolamine (PE)‐to‐phosphatidylcholine (PC) ratio (PE/PC) did not show significant changes between the two stages at 0.40 ± 0.11, a value similar to that of early neonates. © 1989 Academic Press, Inc.
On the origin of paramagnetic inhomogeneity effects in blood
Authors: Brooks Rodney A. , Brunetti Arturo , Alger Jeffry R. , Chiro Giovanni Di
Published: March 2007

Hydrogen, sodium, and fluorine (added F‐) NMR spectra of venous and oxygenated blood were measured. The fluorine resonance was seen as a single peak in both samples, and all three resonances exhibited the same deoxy‐oxy shift. Because F‐ exchanges slowly across the red cell membrane, and because sodium is 95% extracellular, these results suggest that the intra‐extracellular field difference ΔB is less than 0.1 ppm. A small value of ΔB tends to rule out transmembrane exchange as an important contributor to relaxation in MRI of blood and hematomas. However, the broadening of the resonances with deoxygenation, by 0.3‐0.4 ppm, indicates that both intra‐ and extracellular gradients are of comparable and sufficient magnitude to produce the T2‐weighted hypointensity seen in clinical magnetic resonance images of hematomas at high fields. © 1989 Academic Press, Inc.
Phospholipid bilayer contribution to 31P NMR spectra in vivo
Authors: Murphy Elizabeth J. , Rajagopalan Bheeshma , Brindle Kevin M. , Radda George K.
Published: March 2007

The magnetic field‐dependent phosphodiester(PDE) signal found in 31PNMR spectra of liver and brain has been studied using saturation transfer and proton decoupling techniques. This PDE component, which accounts for as much as 45% of the signal in vivo, has been identified as primarily phospholipid bilayer with a small contribution from a motionally averaged macromolecule(S). © 1989 Academic Press, Inc.
Phosphorus‐31 magnetic resonance spectroscopy in humans by spectroscopic imaging: Localized spectroscopy and metabolite imaging
Authors: Twieg D. B. , Meyerhoff D. J. , Hubesch B. , Roth K. , Sappey‐Marinier D. , Boska M. D. , Gober J. R. , Schaefer S. , Weiner M. W.
Published: March 2007

In in vivo phosphorus magnetic resonance spectroscopy (MRS), spectroscopic imaging (SI) can be used as a flexible localization technique, producing spectra from multiple volumes in a single examination. Presented here are phosphorus SI studies of human organs in which a selective‐volume SI reconstruction was used rather than the usual array‐format SI reconstruction. A linear predictor technique was used to estimate the initial points of the free induction decay missing because of the delay needed for phase‐encoding gradients, significantly reducing the baseline artifacts which commonly complicate interpretation of SI spectra. In studies of heart, brain, liver, and kidney, the performance of SI was found to compare favorably with that of ISIS. SI phosphorus metabolite intensity images from a brain tumor patient were obtained at 2 X 2‐cm in‐plane resolution (with “slice” thickness of roughly 16 cm, determined by coil sensitivity) in 34 min, demonstrating the feasibility of obtaining clinically useful metabolite images in clinically reasonable examination times. © 1989 Academic Press, Inc.
T1ρ, dispersion imaging and volume‐selective Tlρ dispersion weighted NMR spectroscopy
Authors: Rommel E. , Kimmich R.
Published: March 2007

Pulse sequences which permit imaging and volume‐selective determination of parameters characterizing the frequency dependence of the spin‐lattice relaxation time in the rotating frame, T1ρ are presented. The contrasts are due to slowly moving macromolecules or paramagnetic contrast agents. In vivo test experiments were carried out with tumorous mice treated with a contrast agent. It is shown that the contrast effect is dramatically enhanced in T1ρ dispersion images compared with images weighted by any of the relaxation times. © 1989 Academic Press, Inc.
Real‐time MR fluoroscopic data acquisition and image reconstruction
Authors: Wright Ronald C. , Riederer Stephen J. , Farzaneh Farhad , Rossman Phillip J. , Liu Yu
Published: March 2007

We describe an experimental system for performing high‐speed reconstruction of MR image data acquired with a GRASS sequence. System characteristics are an image acquisition time of 627 ms, continuous image reconstruction at a rate of 6 images/s, and an image reconstruction time of 120 ms. The result is a system for performing MR imaging in real time. © 1989 Academic Press, Inc.
Bulk magnetic susceptibility shifts in nmr studies of compartmentalized samples: use of paramagnetic reagents
Authors: Chu Ksimon ‐.C. , Xu Yan , Balschi James A. , Springer Charles S.
Published: March 2007

The bulk magnetic susceptibility (BMS) shift of a nuclear resonance frequency caused by a paramagnetic compound is of importance in in vivo NMR, both magnetic resonance spectroscopy and magnetic resonance imaging. However, since it is a rather complicated phenomenon, it has been the source of many misinterpretations in the literature. We have reworked and organized the theory of the BMS shift. This includes accounting for the important effects of local susceptibility. We have conducted experiments on phantom samples in order to illustrate the principles involved. Our phantoms consist of capillaries and coaxial cylinders. They simulate the situations of blood vessels oriented parallel and perpendicular to the magnetic field and the interstitial spaces surrounding them. In most of our experiments, the paramagnetic compound was one of several different hyperfine shift reagents for cation resonances. These were chosen to cover a range of potencies, in both magnitude and sign, of the shifts they produce. However, we also used a reagent which was incapable of inducing a hyperfine shift and thus could cause only a BMS shift. Although we report only 23Na spectra in this paper, the latter samples simulate the cases where one observes the water 1H resonance in experiments employing hyperfine shift reagents for cations. There have been a number of such investigations recently reported in the literature. The principles considered in this paper allow us to offer new interpretations for the results of several experiments published in the last few years.
Spin‐lattice relaxation time measurements using hybrid csi–phantom study
Authors: Hornak Joseph P. , Smith Aric C. , Szumowski Jerzy
Published: March 2007

The spin‐lattice relaxation time T1 of multicomponent tissues is often determined by fitting relaxation data to monoexponential functions. This process can lead to large errors in the relaxation time. We describe a procedure using chemical‐shift imaging (CSI) which separates the NMR signal into water and lipid components thus allowing the two signals to be individually analyzed for relaxation times. This procedure yields more representative relaxation times than those obtained by both monoexponential and biexponential fitting schemes.
Heterotopic transplanted rat heart: a model for in vivo determination of phosphorus metabolites during ischemia and reperfusion
Authors: Rozenman Yoseph , Kantor Howard L.
Published: March 2007

A model of heterotopic isogenic rat heart transplantation was developed in order to noninvasively observe the acute and chronic metabolic changes of ischemia. This study presents the results of 31P spectroscopy during acute global ischemia and reperfusion. The advantages of this model over other surface coil in vivo ischemia experiments are: (1) Thoracotomy for surface coil positioning is not required, thus the results are not influenced by the effect of recent major surgery. (2) Survival is not influenced by the degree of ischemic damage to the transplant, and the model enables repeated long‐term studies of the metabolic effect of reversible ischemia, and myocardial infarction. (3) The pathologic process created is homogeneous and thus the results are not complicated by variation in the severity of myocardial ischemia.