bluuebunny/crossref_metadata_2025 huggingface dataset:
Water referencing for spectroscopic imaging
Authors: Spielman Daniel , Webb Peter , Macovski Albert
Published: March 2007

A water referencing algorithm for addressing the spectroscopic imaging problems of low SNR and main field inhomogeneities is proposed. Using the location of the water peak from each voxel and additional a priori information results in a parametric estimation problem. Optimum estimates of the desired metabolite concentrations can then be computed and displayed in an image format. The algorithm is shown to be very stable in the presence of noise and is insensitive to B0 inhomogeneity. A detailed error analysis as well as extensions to the basic data model are also discussed. Results from both 1H and 31P experiments are presented to verify the predicted good performance even with extremely low signal‐to‐noise ratio data. © 1989 Academic Press, Inc.
The application of spinors to pulse synthesis and analysis
Authors: Shinnar Meir , Leigh John S.
Published: March 2007

We show how spinors may be used to solve many problems in pulse synthesis and analysis. They provide an elegant simple notation for many problems. We show how one can specify the component of a spinor and then, by exactly solving the Bloch equations, synthesize a hard pulse sequence or a soft pulse which will yield the desired spinor. This is done by generalizing our previous approach to inverting the Bloch equations. This can be applied to synthesizing refocusing pulses. Finally, some simple consequences about symmetric pulses are derived. It is shown that given a symmetric inversion pulse, one can always synthesize an asymmetric inverting pulse of the same duration, which, as an inversion, is better. © 1989 Academic Press, Inc.
Study of acute renal ischemia in the rat using magnetic resonance imaging and spectroscopy
Authors: Terrier François , Lazeyras François , Posse Stephan , Aue Walter P. , Zimmermann Arthur , Frey Brigitte M. , Frey Felix J.
Published: March 2007

Magnetic resonance (MR) imaging and spectroscopy, chemical lactate measurements, and microscopic examinations were performed to investigate acute renal ischemia in rats. MR images (1H) and spectra (31P and 1H) were acquired on a 2.0‐T superconducting small‐bore magnet by using implanted coils. Occlusion of the renal artery induced a significant decrease in signal intensity of the renal parenchyma on T2‐weighted images, which was most obvious in the outer medulla (‐50 ± 15%, n = 8, P 0.001) and was the result of venous congestion, as verified histologically. 31P spectroscopy demonstrated a drop in pH from 7.3 ± 0.2 to 6.6 ± 0.2 (n = 18, P 0.001), characterized by a time constant (Tc) in the same range as that of the depletion of ATP (2.3 ± 1.3 min versus 1.9 ± 1.2 min, n = 10, P = ns). By means of 1H spectroscopy, a lactate peak was detected within 1.5 to 4 min of ischemia, still increasing in intensity after 1 h of ischemia. The Tc of the lactate buildup (15.9 ± 7.5 min, n = 8) was significantly longer than that of the drop in pH (P 0.005). The chemically measured intrarenal concentration of lactate was 1.3 ± 0.5 Mmol/g in control kidneys and 8.7 ± 3.2 μmol/g (P < 0.005) in kidneys made ischemic for 1 h. The present study demonstrated important features of acute renal ischemia: (a) acute ischemia induces venous congestion in the medulla; (b) accumulation of lactate is not the main cause of the intracellular acidification observed during ischemia. © 1989 Academic Press, Inc.
Improvement in 31P NMR signal‐to‐noise for ATP in vivo using homonuclear decoupling
Authors: Berkowitz Bruce A. , Balaban Robert S.
Published: March 2007

The efficiency of 31P homonuclear decoupling in vivo is demonstrated. In low‐field clinical situations, when Jpp is equal to or greater than Δv significant improvements in the precision of measuring the ATP resonance area can be expected upon decoupling due to the increase in signal‐to‐noise produced upon collapse of the J coupling. The sensitivity loss due to time sharing between the decoupler and receiver is discussed. © 1989 Academic Press, Inc.
A fast spectroscopic imaging method using a blipped phase encode gradient
Authors: Webb Peter , Spielman Daniel , Macovski Albert
Published: March 2007

Many methods of chemical shift imaging have been described recently. In most cases, these methods couple resolution and imaging time. The most flexible methods use time‐varying gradients to cover a large region of k space on each excitation. We present here a new time‐varying gradient method that offers a decrease in scan time (when SNR is sufficient), simplifies the reconstruction problem by retaining an essentially rectilinear sampling grid, and makes efficient use of scan time by minimizing gradient reversals. Implementation on a standard high‐field imaging system (GE Signa) is discussed, and experimental results are shown. An application of the method to the generation of water reference data sets is described. © 1989 Academic Press, Inc.
Cortical spectroscopy: localized spectroscopy of the cerebral cortex in rats
Authors: Houkin Kiyohiro , Nakada Tsutomu , Suzuki Nobuyuki , Kwee Ingrid L.
Published: March 2007

A method for obtaining nuclear magnetic resonance (NMR) spectroscopic signals confined to the cerebral cortex in rat using a cortical coil constructed based on the principles of the zig‐zag coil is described. We obtained 31P NMR spectra of normal cerebral cortex and cold‐induced injured cortex using this cortical coil. The cortical coil clearly demonstrated an increase in inorganic phosphate (Pi) confined to cerebral cortex which, by contrast, the conventional planar surface coil failed to detect. There are significant metabolic differences between cortex and subcortical tissues. The technique described here, capable of assessing cortical metabolism in vivo without contamination by the underlying tissue, has substantial application to studies of cerebral metabolism. © 1989 Academic Press, Inc.
13C spectroscopic imaging. A simple approach to in vivo 13C investigations
Authors: Müller S. , Beckmann N.
Published: March 2007

13C spectroscopic imaging (SI) is implemented and tested on a Siemens whole‐body MR instrument for in vivo localized 13C spectroscopy. The method provides spectroscopic maps of extended regions of interest. It is found that 13C SI is an ideal field of application for the spectroscopic imaging technique since most other localization methods suffer from chemical‐shift or offset artifacts for this nucleus. Applications of 13C SI with a single 13C rf channel as well as in combination with polarization transfer experiments and heteronuclear broadband decoupling are shown. © 1989 Academic Press, Inc.
Echo‐planar imaging with asymmetric gradient modulation and inner‐volume excitation
Authors: Feinberg David A. , Turner Robert , Jakab Peter D. , Kienlin Markus Von
Published: March 2007

Single‐shot echo‐planar imaging is notoriously vulnerable to image artifacts, arising from the necessity of alternate echo time reversal during image reconstruction and from static field inhomogeneity. A technique for overcoming these problems, which further permits imaging on systems with relatively poor gradient waveforms, when data are collected always with the same gradient polarity, is presented. Subsectional and 3D volume imaging are presented as well as a novel phase‐correction method for Hermitian symmetry in “half‐Fourier” echo‐planar imaging.
Epicardial and endocardia1 localized 31p magnetic resonance spectroscopy: evidence for metabolic heterogeneity during regional ischemia
Authors: Gober Joel R. , Schaefer Saul , Albert Camacho S. , Degroot Michael , Obregon Richard , Botvinick Elias H. , Weiner Michael , Massie Barry
Published: March 2007

Previous studies have noted that myocardial blood flow and high energy phosphates are heterogeneous across the myocardial wall during ischemia. In order to determine whether differences in metabolites between the subendocardium and subepicardium could be detected using 31P magnetic resonance spectroscopy, the Fourier series window (FSW) experiment was implemented on a porcine model of graded regional ischemia. FSW experiments using a planar phantom showed a 46% improvement in localization to the subendocardium compared to a one‐pulse experiment. Animal studies of graded ischemia demonstrated a gradient in the phosphocreatine to inorganic phosphate ratio in the myocardium that paralleled the gradient in blood flow. These studies demonstrate the ability of spatially localized 31P magnetic resonance spectroscopy to detect regional changes in myocardial high energy phosphates localized to the subepicardium and subendocardium.
Discriminant factor analysis of 31p nmr spectroscopic data in myopathies
Authors: Morvan D. , Jehenson P. , Duboc D. , Syrota A.
Published: March 2007

Discriminant factor analysis (DFA) enables one to distinguish among diagnostic groups using diagnostic variables. It provides discriminant functions that are linear combinations of the diagnostic variables and that optimally separate diagnostic groups. It was used to enhance the accuracy of 31P NMR data in the diagnosis of myopathies. DFA allowed a good separation of normal subjects, congenital neuromuscular disorders with type I fiber predominance, and McArdle's diseases. It elicited an unexpected homogeneity of idiopathic rhabdomyolyses, the metabolic origin of which is unknown, and suggested that the abnormality could involve the mitochondrial oxidative metabolism in some of them. In mitochondrial myopathies, an expected heterogeneity is shown by DFA. It may allow an automatic diagnosis of some myopathies from 31P NMR data or guide biochemists by comparing biochemical features of a new patient to those of previously established groups.
Mri quantitation of edema in focal cerebral ischemia in cats: correlation with cytochrome aa3 oxidation state
Authors: Kline R. A. , Negendank W. G. , Mccoy L. E. , Lester M. , Berguer R.
Published: March 2007

1H MRI permits detection of edema in the brain. In a middle cerebral artery stroke model in the cat, we found a significant correlation between an edema index based on MRI and a sensitive metabolic index of ischemia, the in vivo oxidation status of mito‐chondrial cytochrome aa3 determined by near‐infrared reflectance spectrophotometry (r= −0.70, α = 0.001). This result suggests that a simple, noninvasive study using MRI can provide an index of the extent of ischemic damage in an experimental acute stroke model.
In vivo19f spin relaxation in index finger bones
Authors: Code R. F. , Harrison J. E. , Mcneill K. G. , Szyjkowski M.
Published: March 2007

19F free induction decay (FID) signals have been observed from the index fingers of four male and two female adult volunteers using a 27‐MHz pulsed nuclear magnetic resonance spectrometer equipped with a split ring resonator probe. The value of the in vivo spin‐lattice relaxation time T1 of the fluoride ions naturally accumulated in bone mineral has been determined to be 2.0 ± 0.3 s. The shape of the observed FID signals in the inhomogeneous external magnetic field indicates that the F distribution is not uniform along the length of the finger. The fluoride ion content of the index finger (within a 65‐mm length from its distal end) was measured with a sensitivity of ±0.5 mg F within a 30‐min observation time
Assessment of a superparamagnetic iron oxide (ami‐25) as a brain contrast agent
Authors: Kent Thomas A. , Quast Michael J. , Kaplan Barry J. , Lifsey Robert S. , Eisenberg Howard M.
Published: March 2007

We have applied a superparamagnetic iron oxide formulation (AMI‐25, Advanced Magnetics, Inc., Cambridge, MA) to image the cerebral vasculature. Contrast‐enhanced images of normal anesthetized rats demonstrated excellent gray/white matter differentiation, consistent with known differences in blood perfusion, and cerebrospinal fluid spaces were clearly seen. Alterations in normal perfusion patterns due to barbiturate anesthesia and ischemia were clearly visible. We propose the use of this agent as an adjunct to MRI for the imaging of conditions with perfusion abnormalities. © 1990 Academic Press, Inc.
Nmr spectral analysis of kinetic data using natural lineshapes
Authors: Heineman F. W. , Eng J. , Berkowitz B. A. , Balaban R. S.
Published: March 2007

An automated rapid data analysis scheme for NMR spectroscopy time course studies is presented. This method uses a high signal‐to‐noise reference spectrum collected at the beginning of a time course as a lineshape model to analyze subsequent low signal‐to‐noise data collected with higher time resolution. The method is fast (approximately 1 s to evaluate two peaks in a 2K spectrum) and easily implemented on NMR spectrometer computers. An application of this method to spectroscopic studies on the heart is provided.
Assessment of intracellular magnesium depletion in rat striated muscle by in vivo31p nmr
Authors: Le Rumeur E. , Le Moyec L. , Yvin J. C. , Percehais S. , De Certaines J. D.
Published: March 2007

Previous in vivo studies have demonstrated that α, β. and γ ATP chemical shifts measured by 31P NMR spectroscopy can be used to determine intracellular magnesium in erythrocytes, but up to now such results have not been confirmed in striated muscle in vivo. We report BATP chemical‐shift in vivo measurements revealing the depletion of free intracellular magnesium in striated muscle of rats fed a magnesium deficient diet.
In vivo proton spectroscopy in presence of eddy currents
Authors: Klose Uwe
Published: March 2007

Spatially localized methods in spectroscopy often operate with magnetic field gradients for volume selection. The eddy currents induced by these gradients produce time‐dependent shifts of the resonance frequency in the selected volume, which results in a distortion of the spectrum after Fourier transformation. In whole‐body systems the complete compensation of eddy currents is a difficult procedure. To avoid this, a correction method is proposed for proton spectroscopy, which uses the signal of prominent water protons as a reference for the water‐suppressed signal. The correction is performed in the time domain, dividing the water‐suppressed signal by the phase factor of the water signal for each data point. The corrected spectra have a good resolution as shown by phantom measurements and brain and muscle spectra of volunteers. © 1990 Academic Press, Inc.
Interactions of nitroxides with plasma and blood: Effect on 1/T1 of water protons
Authors: Bennett Harold F. , Brown Rodney D. , Keana John F. W. , Koenig Seymour H. , Swartz Harold M.
Published: March 2007

Nitroxide stable free radicals (nitroxides) have potential utility as MRI contrast‐enhancing agents with the additional capability of reflecting redox metabolism. In order to gain a better understanding of their potential interactions in vivo, we have studied the longitudinal NMRD profiles (1 / T1 as a function of field strength) and ESR spectra for lipophilic and aqueous‐soluble nitroxides in blood, plasma, and plasma components. Typical water‐soluble nitroxides do not interact appreciably with blood, plasma, or plasma proteins. Fatty acid nitroxides do interact physically with blood, predominantly by intercalation within red blood cell membranes and binding to albumin. The latter interaction results in significantly enhanced relaxivity for the nitroxide/HSA complex. Relaxation of water protons in this case is dominated by inner sphere processes, ostensibly due to water molecules hydrogen bonded to nitroxide moieties. The rotational reorientation time for the complex, the electronic relaxation time, and the exchange time for the water molecule reversably bound to the nitroxide, all appear significantly to influence the correlation time (∼ 16 ns) for this inner sphere contribution. Inc. © 1990 Academic Press, Inc.
Regional phase correction of inversion‐recovery MR images
Authors: Borrello Joseph A. , Chenevert Thomas L. , Aisen Alex M.
Published: March 2007

Many MR imaging systems are limited in their ability to successfully display inversion‐recovery images. The reason is that part of the contrast is encoded as phase differences between pixels, whereas in the more commonly used spin‐echo pulse sequence all the information is contained in the pixel magnitude. Inversion‐recovery images are often displayed in magnitude form, resulting in loss of potentially useful phase information contained in the data. Before this phase information can be used, phase errors which result from scanner imperfections must be removed. While most of the necessary correction can be accomplished using data obtained by scanning a uniform phantom, this approach has several disadvantages. An alternative method by which phase errors can be readily removed without phantom data is described. This method has been applied to images of the head, knee, and liver with good results. It is concluded that this technique is useful for producing phase corrected inversion‐recovery MR images © 1990 Academic Press, Inc.
Mechanics and imaging of the macrocirculation
Authors: Caro C. G. , Parker K. H.
Published: March 2007

The mechanics of the macrocirculation are examined as a basis for imaging blood flow within the system. The macrocirculation is denned as that part of the circulation in which inertial forces are not negligible compared to viscous forces and as such in human subjects comprises the heart and large blood vessels. Because the flow in the system is so complicated, understanding is built up piecemeal by considering various relatively well‐characterized flows which can be seen as approximations to the actual flow. © 1990 Academic Press, Inc.
Time‐of‐flight effects in MR imaging of flow
Authors: Wehrli Felix W.
Published: March 2007

This article provides a brief overview of one of the two fundamental physical principles which lead to a modulation of the magnetic resonance signal of moving spins: the time‐of‐flight effect. It then discusses some of its characteristic manifestations in spin‐echo imaging and reviews strategies for exploiting the effect to quantitate vascular flow. © 1990 Academic Press, Inc.
Optimizing blood vessel contrast in fast three‐dimensional MRI
Authors: Haacke E. M. , Masaryk T. J. , Wielopolski P. A. , Zypman F. R. , Tkach J. A. , Amartur S. , Mitchell J. , Clampitt M. , Paschal C.
Published: March 2007

Magnetic resonance angiography has matured to the point where clinically useful images can be acquired in half an hour or less. In this paper, the role of 3D imaging techniques is primarily considered. Specifically, the optimal imaging parameters, sequences, and reconstruction techniques are evaluated for moving spins. A variant of FISP known as ROAST with low flip angles, short repeat times, and a thick slab has been found to yield the best 3D survey scan of the cranial vessels with roughly 1 × 1 × I‐mm3 resolution in each of the processed images (slices). For the faster flowing carotids, a sagittal scout with as short a TE as possible is required to avoid spin dephasing. Localization is accomplished in both cases by acquiring thin slab 3D, thin partition, larger flip angle, longer repeat time FLASH sequences. Different choices of dephaseirephase sequences and directions are also reviewed. These choices are discussed from a practical and theoretical perspective. In particular, improvements in contrast and resolution are evaluated using half‐Fourier, 512 acquisition, small fields of view and constrained reconstruction for both rephased gradient echo sequences and dephased thin slice long TR spin‐echo sequences. A resolution of 0.5‐0.75 mm is recommended to obtain sufficient image quality for consistent clinical interpretation of stenoses and vessel abnormalities. © 1990 Academic Press, Inc.
Early detection of regional cerebral ischemia in cats: Comparison of diffusion‐ and T2‐weighted MRI and spectroscopy
Authors: Moseley M. E. , Cohen Y. , Mintorovitch J. , Chileuitt L. , Shimizu H. , Kucharczyk J. , Wendland M. F. , Weinstein P. R.
Published: March 2007

Diffusion‐weighted MR images were compared with T2‐weighted MR images and correlated with 1H spin‐echo and 31P MR Spectroscopy for 6‐8 h following a unilateral middle cerebral and bilateral carotid artery occlusion in eight cats. Diffusion‐weighted images using strong gradient strengths (b values of 1413 s/mm2) displayed a significant relative hyperintensity in ischemic regions as early as 45 min after onset of ischemia whereas T2‐weighted spin‐echo images failed to clearly demonstrate brain injury up to 2‐3 h postocclusion. Signal intensity ratios (SIR) of ischemic to normal tissues were greater in the diffusion‐weighted images at all times than in either TE 80 or TE 160 ms T2‐weighted MR images. Diffusion‐ and T2‐weighted SIR did not correlate for the first 1‐2 h postocclusion. Good correlation was found between diffusion‐weighted SIR and ischemic disturbances of energy metabolism as detected by 31P and 1H MR Spectroscopy. Diffusion‐weighted hyperintensity in ischemic tissues may be temperature‐related, due to rapid accumulation of diffusion‐restricted water in the intracellular space (cytotoxic edema) resulting from the breakdown of the transmembrane pump and/or to microscopic brain pulsations. © 1990 Academic Press, Inc.
Differentiation of proliferating from resting cartilage in human fetal nasal septum by magnetic resonance imaging
Authors: Allegrini Peter R. , van Velzen Dick , van Loosen John , Bullock Gillian R.
Published: March 2007

Magnetic Resonance Imaging (MRI) has been used for the characterization of human fetal nasal septa. The images were made from fixed fetal heads from spontaneous abortions of different gestational age. The “in‐plane” resolution of the images (at a pixel size of 312 × 312 μm2) allowed a detailed anatomical analysis of the midfacial structures of the fetal heads. In T2 ‐weighted midsagittal sections a low signal intensity region of the septal cartilage could be seen. This part was shown to consist of immature proliferating cartilage by histochemical methods and contrasted to mature resting tissue at the rim of the septum. Direct comparison of the MR images with histological sections demonstrated the potential of MRI in pre‐ and postoperative evaluation of patients requiring surgical reconstruction of either traumatic or congenital defects of the face. © 1990 Academic Press, Inc.
Measurement of regional cerebral blood flow in cat brain using intracarotid 2H2O and 2H NMR imaging
Authors: Detre J. A. , Subramanian V. H. , Mitchell M. D. , Smith D. S. , Kobayashi A. , Zaman A. , Leigh J. S.
Published: March 2007

Cerebral blood flow (CBF) was measured in cat brain in vivo at 2.7 T using 2H NMR to monitor the washout of deuterated saline injected into both carotid arteries via the lingual arteries. In anesthetized cats, global CBF varied directly with PaCO2 over a range of 20‐50 mm Hg, and the corresponding global CBF values ranged from 25 to 125 ml‐100 g−1min−1. Regional CBF was measured in a 1‐cm axial section of cat brain using intracarotid deuterated saline and gradient‐echo 2H NMR imaging. Blood flow images with a maximum pixel resolution of 0.3 × 0.3 × 1.0 cm were generated from the deuterium signal washout at each pixel. Image derived values for CBF agreed well with other determinations, and decreased significantly with hypocapnia. © 1990 Academic Press, Inc.
Two‐volume acquisition in image‐guided proton spectroscopy
Authors: Hafner H.‐P. , Radü E. , Seelig J.
Published: March 2007

By combining two‐frequency excitation with 1H NMR STEAM spectroscopy, it is possible to measure two volumes of interest simultaneously without an increase in measuring time compared to single‐volume STEAM. Spatial selectivity and spectral resolution of this approach are demonstrated for test solutions and for human 1H NMR brain spectroscopy. First results with a tumor patient are also presented. © 1990 Academic Press, Inc.
A spoiling sequence for suppression of residual transverse magnetization
Authors: Wang Henry Z. , Riederer Stephen J.
Published: March 2007

We present a spoiler sequence which substantially eliminates residual transverse magnetization in rapid magnetic resonance imaging. Such magnetization is due to the repetition time TR being on the order of or shorter than the transverse relaxation time T2. This sequence was designed using computer simulation methods to model the slice profile and signal. The spoiler pulse is applied in the slice‐selecting direction and the magnitude of the gradient spoiler is incremented with each repetition as an arithmetic series. A finite number of different spoiler amplitudes is repeated with a cycle time several times greater than the anticipated T2. Each spoiler is shown to nullify the residual transverse magnetization from the just‐measured signal of the experiment as well as that from preceding repetitions. It is shown experimentally that the spoiler pulse can be as short as 2 ms. This is considerably shorter than existing methods using constant spoiling or phase‐tagged spoiling. This sequence was used to acquire. T1‐weighted images free of the central line artifact of FLASH imaging. Furthermore, images formed with the new spoiled technique are shown to have contrast‐to‐noise comparable if not superior to standard T 1‐weighted spin‐echo images while taking only a fifth of the scan time. © 1990 Academic Press, Inc.
Spin‐labeling angiography of the carotids by presaturation and simplified adiabatic inversion
Authors: Sardashti Maziar , Schwartzberg Daniel G. , Stomp Guido P. , Dixon W. Thomas
Published: March 2007

A new adiabatic inversion pulse is tested for a spin‐labeling subtraction angiography method. Adiabatic nature of the pulse is achieved by ramping the gradient during the RF pulse. In addition, with cardiac triggering, any irregularity of the heartbeat would decrease cancelation of the static tissue after subtraction. A 90° presaturation pulse applied to prevent this suppresses the background intensity from the static tissue by a factor greater than 2. Slice angiograms of carotid arteries are presented. © 1990 Academic Press, Inc.
Chronic carbon tetrachloride and phospholipase D hepatotoxicity in rat:In vivo1H magnetic resonance, total lipid analysis, and histology
Authors: Hazle John D. , Narayana Ponnada A. , Dunsford Harold A.
Published: March 2007

Magnetic resonance (MR) imaging, localizedin vivoproton spectroscopy, andT1relaxation measurements were obtained from the livers of rats treated chronically with carbon tetrachloride and phospholipase D. The MR data correlated well with lipid changes measured biochemically and histologically. MR images appeared generally hyperintense during fatty infiltration, changing to hypointense mottling during cirrhosis. WaterT1relaxation times showed no statistically significant change at any time during the experiments from the control value of 908 ms (SE = 42 ms). Minor changes in lipidT1values with time were noted. The average lipidT1curve demonstrated a linear relation with time (r= 0.81), increasing from the control value of 283 ms (±16 ms) to 365 ms (±53 ms) at the end of the third week and decreasing slightly through the end of the experiment. Water‐suppressedin vivospectra showed quantitative changes in liver lipids which correlated well with the biochemical and histologic analysis. From the MR images and spectroscopy results it was possible to distinguish early fatty liver from more advanced cirrhosis. © 1990 Academic Press, Inc.
Quantification of fluid changes in rat leg joints with adjuvant arthritis by a one‐dimensional magnetic resonance imaging experiment
Authors: Borah Babul , Szeverenyi Nikolaus M.
Published: March 2007

A simple and reliable method for quantifying the fluid content and characterizing the tissue T2 relaxation properties of animal extremities has been devised. This one‐dimensional magnetic resonance imaging experiment, applied to the adjuvant arthritis model in rats, provides a useful, noninvasive monitor of the course of the disease in vivo. Tissue is characterized through the analysis of the biexponential T2 decay of the NMR‐active hydrogen in the rat leg joint tissue. Long and short T2 components are identified, both of which are sensitive to the arthritic process. The long component is suggested to come from edema and increases by a factor of ca. 9 during the course of the disease, whereas the short T2 component may represent cellular influx into the joint and increases by a factor of ca. 3. These changes correlate with the severity of the disease and can be used to monitor therapeutic response. The main advantage of the technique over the more traditional two‐dimensional imaging approach is that only one spatial variable has to be resolved, resulting in shorter imaging time. © 1990 Academic Press, Inc.
Simultaneous spatial and spectral selective excitation
Authors: Meyer Craig H. , Pauly John M. , Macovskiand Albert , Nishimura Dwight G.
Published: March 2007

Using a k‐space interpretation of small‐tip excitation, a single excitation pulse has been designed that is simultaneously selective in space and resonant frequency. An analytic expression for the response of this pulse has been derived. The pulse has been implemented on a 1.5‐T imaging system. The pulse has been applied to a rapid gradient‐echo imaging sequence that forms both water and fat images within a breath‐holding interval. These rapid images are free of the chemical shift artifacts at organ boundaries that typically afflict conventional rapid images. The pulse can be applied to a variety of other sequences, such as multislice water/fat sequences and rapid k‐space scanning. © 1990 Academic Press, Inc.
Multislice snapshot FLASH using SIMUSIM
Authors: Müller S.
Published: March 2007

A combination of the SIMUSIM technique and snapshot ITASH which allows efficient multislice snapshot FLASH imaging is described. Simultaneously acquired images of deliberate slice position and thickness are obtained with an increased SNR compared to standard time sequential multislice experiments. Experimental results show four coronal cross sections through the human head measured in four acquisitions. © 1990 Academic Press, Inc.
Development of the “activated” high resolution 1H MR spectrum in murine T cells and B cells occurs in G1 phase of the cell cycle
Authors: Holmes K. T. , Lean C. L. , Hunt N. H. , King N. J. C.
Published: March 2007

T and B lymphocytes stimulated with mitogens develop 'HMR spectra characteristic of triglycerides in an isotropic environment. These distinctive signals, which are also observed in malignant cells, cannot be suppressed by compounds which inhibit progression through the cell cycle. Cellular proliferation is thus not essential for the development and maintenance of high resolution lipid spectra in activated cells. © 1990 Academic Press, Inc.
An in vivo NMR imaging determination of multiexponential Hahn T2 of normal lung
Authors: Shioya Sumie , Christman Rebecca , Ailion David C.
Published: March 2007

We describe the first in vivo imaging determination of normal lung tissue's multiexponential transverse magnetization decay. Normal spontaneously breathing rats were used for the measurements. To obtain motion‐insensitive images, we used a modified line scan imaging technique which we call the interleaved line scan (ILS). The ILS overcomes the following difficulties associated with imaging lungs: low signal‐to‐noise ratio (S/N) due to lung's low proton density and short T2 decay, artifacts associated with cardiac and respiratory motion, and excessively long imaging times with conventional line scan techniques. Using the ILS, a 16‐line 32‐average image with an 8‐s repetition time requires 4.3 min. From a series of 16 Hahn spin‐echo images with echo times ranging from 16 to 90 ms, we obtained a two‐component T2 decay for normal peripheml lung tissue. The measured fast and slow T2 components were 9.5 ± 1.0 and 34 ± 5.0 ms for the right lung and 9.0 ± 1.5 and 32 ± 4.5 for the left lung. The relative magnetization for the slow T2 component was 7.0 ± 4.5% for the right lung and 10 ± 3.0% for the left lung. © 1990 Academic Press, Inc.
Magnetohydrodynamics of blood flow
Authors: Keltner John R. , Roos Mark S. , Brakeman Paul R. , Budinger Thomas F.
Published: March 2007

The changes in hydrostatic pressure and electrical potentials across vessels in the human vasculature in the presence of a large static magnetic field are estimated to determine the feasibility of in vivo NMR spectroscopy at fields as high as 10 T. A 10‐T magnetic field changes the vascular pressure in a model of the human vasculature by less than 0.2%. An exact solution to the magnetohydrodynamic equations describing a conducting fluid flowing transverse to a static magnetic field in a nonconducting, straight, circular tube is used. This solution is compared to an approximate solution that assumes that no magnetic fields are induced in the fluid and that has led previous investigators to predict significant biological effects from static magnetic fields. Experimental results show that the exact solution accurately predicts the magnetohydrodynamic slowing of 15% NaCl flowing transverse to 2.3‐ and 4.7‐T magnetic fields for fluxes below 0.5 liter/min while the approximate solution predicts a much more retarded flow. © 1990 Academic Press, Inc.
Nuclear relaxation of human brain gray and white matter: Analysis of field dependence and implications for MRI
Authors: Fischer Helmut W. , Rinck Peter A. , van Haverbeke Yves , Muller Robert N.
Published: March 2007

The dependence of 1 / T1 on the magnetic field strength (the relaxation dispersion) has been measured at 37°C on autopsy samples of human brain gray and white matter at field strengths corresponding to proton Larmor frequencies between 10 kHz and 50 MHz (0.0002‐1.2 T). Additional measurements of 1 / T1 and 1 / T2 have been performed at 200 MHz (4.7 T) and 20 MHz (0.47 T), respectively. Absolute signal amplitudes are found to be proportional to the sample water content, not to the “proton density,” and it is concluded that the myelin lipids do not contribute to the signal. Transverse magnetization decay data can be fitted with a triple exponential function, giving characteristic results for each tissue type, and are insensitive to variations of the pulse spacing interval. The longitudinal relaxation dispersion curves show characteristic shapes for each tissue type. The most striking difference is a large dispersion for white matter at very high fields. As a consequence, the relative difference in 1 / T1 between gray and white matter shows a marked maximum around 10 MHz. Possible implications for MRI are discussed. A weighted least‐squares fit of the dispersions has been performed using a four‐parameter function of the form

The quality of the fit is superior to that of other functions proposed previously. The results of these fits are used to predict image contrast between gray and white matter at different field strengths. © 1990 Academic Press, Inc.
In vivo flow 31P FT‐NMR spectroscopy of a nematode parasite
Authors: Thompson S. N. , Platzer E. G. , Lee R. W.‐K.
Published: March 2007

31P NMR spectroscopy of a parasitic nematode, Steinernema carpocapsae, is described. In vivo spectra were generated from nematode suspensions continuously circulating through the spectrometer. By flowing the organism, saturation effects were avoided and short in‐terpulse delays significantly reduced spectral generation time. To maximize sensitivity, 90° pulses were employed. Changes in energetic status in response to oxygen availability were easily and rapidly monitored in circulating nematodes. © 1990 Academic Press, Inc.
Does IVIM measure classical perfusion?
Authors: Henkelman R. Mark
Published: March 2007

MR measurements based on motion encoding gradients provide interesting information about diffusion in tissues and have also been advanced as a way to measure tissue perfusion. This communication shows why IVIM cannot measure perfusion in the classical sense. Attempts to do so result from an unclear understanding of classical perfusion measurements and from confusion between terminal deposition (or uptake) and blood volume flow. © 1990 Academic Press, Inc.
Quantitative spectroscopy using multiple surface coil probes
Authors: Styles Peter
Published: March 2007

The performance of the rotating frame localization method is discussed, with emphasis on performing the experiment and processing the data in the optimum manner. Studies on phantom samples are presented to illustrate various imperfections which affect the confidence that can be placed on acquired data. © 1991 Academic Press, Inc.
Gradient coil design using active magnetic screening
Authors: Bowtell R. , Mansfield P.
Published: March 2007

Active magnetic screening allows the production of gradient coils which are magnetically decoupled from their surroundings. Using such coils the eddy current problems associated with the generation of large, rapidly switched gradients within the confines of a superconductive magnet can be eliminated. In this paper the principles of active screening are outlined and some of the methods of designing screened gradient coils are described. Problems relating to the construction of screened gradient coils are also addressed. © 1991 Academic Press, Inc.
New magnet designs for MR
Authors: Hawksworth D.
Published: March 2007

The evolution of MRI magnets is reviewed. New magnet developments are discussed with reference to improved performance, novel system features, and lower cost. © 1991 Academic Press, Inc.
Simultaneous cardiac mechanics and phosphorus‐31 NMR spectroscopy during myocardial ischemia and reperfusion in the intact dog
Authors: Miller D. Douglas , Salinas Felix , Walsh Richard A.
Published: March 2007

To investigate the high‐energy phosphate metabolic correlates of left ventricular (LV) dysfunction during the onset and recovery from severe, global myocardial ischemia in vivo, seven preinstrumented closed‐chest dogs had ECG‐gated phosphorus‐31 (31P) NMR‐spectroscopy (NMR‐S) studies performed and LV micromanometer and sonomicrometer data measured before, during, and every 5 min following severe occlusive global myocardial ischemia. Ischemic LV + dP/dtmax fell from 2396 ± 576 mm Hg/s at baseline to 2185 ± 478 mm Hg/s (p < 0.05) and did not normalize until after 30 min of reperfusion. LV ejection fraction (EF) decreased significantly (0.32 ± 0.07 EF units to 0.12 ± 0.13 EF units; P < 0.05) and did not recover by 30 min of reperfusion (0.27 ±0.09 units; P < 0.05 vs baseline). Simultaneous 31P NMR‐S studies demonstrated excellent β ‐ATP signal‐to‐noise (10 ± 4:1). Myocardial acidosis occurred during global ischemia (ApH = −0.22 ± 0.23 units; p < 0.05), with recovery at 30 min of reperfusion. Inorganic phosphate/ phosphocreatine ratio (Pi/PCr) increased significantly during ischemia (0.46 ± 0.07 to 0.61 ± 0.07; P < 0.05), with delayed normalization of this ratio at 30 min of reperfusion. β‐ATP peak area did not change during ischemia. Pi/PCr and LV contractility ( + dP/ dtmax ) were significantly correlated at baseline (r = −0.70) and during global ischemia (r = −0.78; p < 0.01), but not during recovery (r = 0.006; p = NS). Therefore, the simultaneous evaluation of high‐fidelity hemodynamic data and topical 31P NMR‐S can be performed in the intact State. © 1991 Academic Press, Inc.
The use of gradient flow compensation to separate diffusion and microcirculatory flow in MRI
Authors: Maki Jeffrey H. , Macfall James R. , Johnson G. Allan
Published: March 2007

This paper describes a new MR imaging technique termed Modified Stejskal Tanner versus Flow Compensation (MST/FC) for the separation of diffusion and microcirculatory flow. The theory behind the sequence is explained, along with a five‐component model of microcirculation applicable to any “perfusion” imaging technique. Phantom data is presented showing that (1) diffusion effects can be matched between MST and FC (suggesting the possibility of flow‐compensated diffusion imaging), and (2) the technique is a quantitative method of separating diffusion and slow (<0.25 mm/s) tortuous flow through a Sephadex column. Furthermore, animal images show the technique to be feasible and quantitative in measuring rat brain microcirculation under normal, vasodilated (hypercarbia), and no‐flow (post mortem) conditions. © 1991 Academic Press, Inc.
Phosphonate‐modified GdDTPA complexes. I. NMRD study of the solution behavior of new tissue‐specific contrast agents
Authors: Adzamli I. Kofi , Blau Monte
Published: March 2007

NMRD profiles, the magnetic field dependence of the water proton longitudinal relaxation rates, have been acquired for two new diphosphonate‐modified GdDTPA complexes currently under evaluation as relaxation agents for the MRI detection of soft‐tissue calcifications. Fresh dilute solutions show profiles identical to that of unmodified GdDTPA, which remain unchanged for up to 9 weeks. Solutions containing Gd species at MRI significant concentrations, 100 to 500 mM, show the presence of oligomers (n = 5 or more) upon aging, with much higher high‐field relaxivities. Aggregation is attributed to the interactions between a gadolinium center and the phosphonate terminus of a neighboring molecule, and is prevented by esterification of the phosphonate terminus. Oligomers are also easily disrupted by dilution with phosphate‐buffered saline, where the exogenous phosphate ions compete with the phosphonate. Other nucleophiles such as are present in protein side chains of bovine serum albumin also compete with the phosphonate in these associations, the result being species with even higher relaxivities. © 1991 Academic Press, Inc.
Effect of homonuclear J modulation on 19F spin‐echo images
Authors: Babcock Evelyn E. , Mason Ralph P. , Antich Peter P.
Published: March 2007

The effect of homonuclear J modulation on 19F spin‐echo images is evidenced by a substantial reduction in signal when the echo time, TE, approaches 1 /2J, with a subsequent increase in signal at longer TEs. Suppression of the J‐modulation effect is demonstrated using chemical Shift‐Selective 180° refocusing pulses. © 1991 Academic Press, Inc.
Effect of aging and diet on proton NMR spectra of rat urine
Authors: Bell J. D. , Sadler P. J. , Morris V. C. , Levander O. A.
Published: March 2007

500 MHz 1H NMR studies of rat urine are used to assess metabolic changes resulting from aging (0.5‐20 months) and changes in diet (casein versus chow). Aging rats fed chow diets decrease their excretion of citrate and 2‐oxoglutarate, while the output of taurine and creatinine increases. Only young rats (1 month or less postweaning) excrete significant amounts of betaine and trimethylamine‐N‐oxide. Rats fed casein diets for 1 month postweaning do not excrete 2‐oxoglutarate and excrete lower levels of hippurate, succinate, and citrate compared to rats fed chow diets. They also excrete N‐methylnicotinamide. These high resolution proton NMR studies provide metabolic profiles which are not readily available by other techniques. © 1991 Academic Press, Inc.
An evaluation of new processing protocols for in vivo NMR spectroscopy
Authors: Mazzeo A. R. , Levy G. C.
Published: March 2007

In vivo NMR spectroscopy is often complicated with problems of low signal‐to‐noise, poor resolution, undefined peak shapes, and nonlinear baselines despite the efforts of investigators to optimize their experiments. Several data processing options are available to spectroscopists to enhance resolution and signal‐to‐noise and /or to flatten baselines. There is some question about how these processing protocols affect quantitative information. This paper evaluates five different processing protocols for their ability to extract quantitative information from a set of nonideal spectra. Three of the protocols involve recently developed statistical signal processing methods, maximum entropy Fourier spectral deconvolution, linear prediction singular value decomposition, and baseline deconvolution. These protocols are compared with the conventional processing methods of convolution difference and zeroing initial data points of the FID. The methods are evaluated by use of a quantitative 31P model sample and also are demonstrated on surface coil 31P data. © 1991 Academic Press, Inc.
Use of Paramagnetic Chelated Metal Derivatives of Polysaccharides and Spin‐Labeled Polysaccharides as Contrast Agents in Magnetic Resonance Imaging
Authors: Bligh S. W. A. , Harding C. T. , Sadler P. J. , Bulman R. A. , Bydder G. M. , Pennock J. M. , Kelly J. D. , Clatham I. A. , Marriott J. A.
Published: March 2007

Soluble and insoluble polysaccharides were derivatized with diethylenetriaminepentaacetic acid (DTPA) and/or spin‐labeled with 2,2,6,6‐tetramethylpiperidine‐1‐oxyl (TEMPO). Polysaccharides derivatized with DTPA were prepared via cyanogen bromide activation, coupling to a diamine linker, and to DTPA anhydride. Spin‐labeled polysaccharides were also prepared via cyanogen bromide activation. The extent of derivatization for dextran (18 kDa) was about 120 glucose units per DTPA, and for cellulose and starch about 15–30 units per DTPA. For spin‐labeled polysaccharides, the average loading ranged from 1 nitroxide per 16 glucose units for starch to 181 for dextran (82 kDa). These derivatized paramagnetic polysaccharides were shown to be more effective relaxants than the small paramagnetic molecules alone. Both soluble and insoluble polysaccharide‐linker‐DTPA‐Gd(III) complexes were effectively cleared from the body (rats) after oral administration. After intravenous administration, the biodistribution of dextran‐linker‐DTPA‐Gd(III) complexes differed significantly from that of GdDTPA. Reduction of the nitroxide by ascorbic acid was retarded in the polysaccharide derivatives, particularly in starch enrivatized with both nitroxide and linker‐DTPA‐Cu(II). These agents showed contrast enhancement in the gastrointestinal tract of rabbits. © 1991 Academic Press, Inc.
A pitfall associated with lactate detection using stimulated‐echo proton spectroscopy
Authors: Sotak Christopher H. , Alger Jeffry R.
Published: March 2007

At TE values of 136 ms, it has recently been shown that the lactate methyl signal, when obtained with a stimulated‐echo (STE) sequence, is modulated at the zero‐quantum (ZQ) frequency when TM is varied. Here we describe an additional modulation of the ZQ lactate signal, due to spin‐spin coupling, that results in a 10‐fold reduction in the lactate signal for TM intervals ranging between 48 and 84 ms (and at multiples of 136 ms thereof). Because of this J‐modulation, improper choice of TE and TM intervals may give false negative results for lactate detection by STE spectroscopy. © 1991 Academic Press, Inc.
Ultrafast Low‐Angle RARE: U‐FLARE
Authors: Norris David G.
Published: March 2007

The subsecond application of the RARE technique is described. Two possible methods of implementation are discussed, one in which T2 contrast is manipulated by temporal reordering of the phase‐encoding gradient, and the other in which the phase‐encoding order is held constant and the contrast is manipulated by means of a spin‐echo preparation experiment. In vivo images obtained with the latter method are presented and applications of the sequence discussed. © 1991 Academic Press, Inc.
Rebound alkalosis and persistent lactate: Multinuclear (1H, 13C, 31P) NMR spectroscopic studies in rats
Authors: Nakada Tsutomu , Houkin Kiyohiro , Hida Kazutoshi , Kwee Ingrid L.
Published: March 2007

Intracellular pH levels of infarcted brain determined by phosphorus‐31 nuclear magnetic resonance (NMR) spectroscopy disclosed a notable phenomenon. The acidotic brain pH seen in the acute stage of infarction was observed to rebound into the alkalotic range in the subacute phase before returning to the normal range in the chronic phase. This “rebound alkalosis” which was usually observed between the 24th and the 48th hour after experimental induction of infarction in rats was accompanied by significant lactate levels as detected by proton NMR spectroscopy. Analysis of the satellite methyl resonance of 13C‐lactate using high‐resolution proton NMR spectroscopy after 13C‐glucose infusion indicated that no lactate was produced in the subacute phase of infarction and that the lactate detected during this phase must have been generated prior to this phase of infarction. © 1991 Academic Press. Inc.