bluuebunny/crossref_metadata_2025 huggingface dataset:
Estimating radiofrequency power deposition in body NMR imaging
Authors: Bottomley Paul A. , Redington Rowland W. , Edelstein William A. , Schenck John F.
Published: March 2007

Simple theoretical estimates of the average, maximum, and spatial variation of the radiofrequency power deposition (specific absorption rate) during hydrogen nuclear magnetic resonance imaging are deduced for homogeneous spheres and for cylinders of biological tissue with a uniformly penetrating linear rf field directed axially and transverse to the cylindrical axis. These are all simple scalar multiples of the expression for the cylinder in an axial field published earlier (Med. Phys. 8, 510 (1981). Exact solutions for the power deposition in the cylinder with axial (Phys. Med. Biol. 23, 630 (1978) and transversely directed rf field are also presented, and the spatial variation of power deposition in head and body models is examined. In the exact models, the specific absorption rates decrease rapidly and monotonically with decreasing radius despite local increases in rf field amplitude. Conversion factors are provided for calculating the power deposited by Gaussian and sinc‐modulated rf pulses used for slice selection in NMR imaging, relative to rectangular profiled pulses. Theoretical estimates are compared with direct measurements of the total power deposited in the bodies of nine adult males by a 63‐MHz body‐imaging system with transversely directed field, taking account of cable and NMR coil losses. The results for the average power deposition agree within about 20% for the exact model of the cylinder with axial field, when applied to the exposed torso volume enclosed by the rf coil. The average values predicted by the simple spherical and cylindrical models with axial fields, the exact cylindrical model with transverse field, and the simple truncated cylinder model with transverse field were about two to three times that measured, while the simple model consisting of an infinitely long cylinder with transverse field gave results about six times that measured. The surface power deposition measured by observing the incremental power as a function of external torso radius was comparable to the average value. This is consistent with the presence of a variable thickness peripheral adipose layer which does not substantially increase surface power deposition with increasing torso radius. The absence of highly localized intensity artifacts in 63‐MHz body images does not suggest anomalously intense power deposition at localized internal sites, although peak power is difficult to measure.
A method for localizing high‐resolution NMR spectra from human subjects
Authors: Styles Peter , Scott Christopher A. , Radda George K.
Published: March 2007

Several methods are available for the localization of high‐resolution spectra. When the sample is a human subject, it may be difficult to realize a viable experimental protocol because the size and geometry of the subject often conflict with efficient probe design. In this paper a spectroscopic localization method is described which is based on the method of rotating frame imaging. A novel surface‐coil probe has been developed so that this experiment can be performed on a large sample. 31P spectra from the thorax of a human subject are presented in which signals from liver and intercostal muscle are resolved. These data demonstrate that spatially resolved spectra of metabolites in vivo may be obtained in a time that is acceptable for patient examination.
Neurometabolic effects of an inborn error of amino acid metabolism demonstrated in vivo by 1H NMR
Authors: Gadian David G. , Proctor Edward , Williams Stephen R. , Cady Ernest B. , Gardiner R. Mark
Published: March 2007

The elevated levels of brain histidine in histidinaemic mice are detected in vivo by 1H NMR at 8.5 and 1.9 T. The concentrations determined from the in vivo spectra correlate well with subsequent analytical determinations. This technique is discussed in relation to monitoring phenylalaninc in humans with phenylketonuria. © 1986 Academic Press, Inc.
Elimination of coupling between cylindrical transmit coils and surface‐receive coils for in vivo NMR
Authors: Bendall M. Robin , Connelly Alan , McKendry Jamie M.
Published: March 2007

Coupling between large transmit and surface‐receive coils is eliminated using a λ/4 cable, terminated with crossed diodes to ground, inserted between the receive coil and ground, and by using a cable of length a little less than λ/2 inserted between the transmit match capacitance and the normal crossed diodes in the transmit input line. © 1986 Academic Press, Inc.
31P and 23Na NMR studies of the structure and lability of the sodium shift reagent, bis(tripolyphosphate)dysprosium(iii) ([dy(p3O10)]7−) ion, and its decomposition in the presence of rat muscle
Authors: Matwiyoff N. A. , Gasparovic C. , Wenk R. , Wicks J. D. , Rath A.
Published: March 2007

The 31P NMR of aqueous [Dy(P3O10)2]7− demonstrates that it is in slow exchange with P3O on the NMR time scale. In the presence of tissue, [Dy(P3O10)2]7− decomposes to PO4 with an accompanying slow change of the tissue 23Na NMR of extracellular Na+ ion in several NMR distinguishable extracellular sites. © 1986 Academic Press, Inc.
Errors in the measurements of T2 using multiple‐echo MRI techniques. I. Effects of radiofrequency pulse imperfections
Authors: Majumdar S. , Orphanoudakis S. C. , Gmitro A. , O'Donnell M. , Gore J. C.
Published: March 2007

In principle, multiple‐echo magnetic resonance imaging (MRI) can be used to estimate the spin‐spin relaxation time, T2, which can then be used for quantitative tissue characterization. Although multiple echoes can be used to enhance the signal‐to‐noise ratio in an image, by echo addition, rf pulse imperfections modify the echo amplitudes resulting in significant errors in the estimate of T2. Imperfect 180° pulses do not completely invert the transverse magnetization so that the magnitude of the transverse component is reduced and a longitudinal component is generated. Successive application of such imperfect pulses generates many components that interact in a complex manner. The amplitudes of successive echoes are affected whenever the transverse components refocus, whereas the longitudinal components may be rotated into the transverse plane by subsequent pulses and may often add to the image signal or give rise to an image artifact. These effects have been analyzed theoretically and have been demonstrated for a wide range of rf pulse imperfections using both simple and composite pulses, through computer simulations based on the numerical solution of the Bloch equations. The theoretical and simulation results have been substantiated through experiments performed on a mineral oil phantom using a resistive prototype MR scanner operating at 6.35 MHz. In this paper we report the effects of improper pulse amplitude or duration for nonselective rf pulses on resonance. We separately describe the other types of imperfections caused by off‐resonance effects and the use of selective pulses. © 1986 Academic Press, Inc.
31P NMR spectroscopy of isolated perfused lungs
Authors: Pillai R. P. , Buescher P. C. , Pearse D. B. , Sylvester J. T. , Eichhorn G. L.
Published: March 2007

31P NMR spectra of isolated blood‐perfused pig lungs were obtained by degassing the lungs in vivo to remove field inhomogeneities caused by air‐tissue interfaces. The spectra show the presence of ATP, phosphodiester, inorganic phosphate, and phosphomonoester, but no phosphocreatine. All the metabolites remained stable for more than 4 h when the lungs were perfused with oxygenated blood. Blood gas tensions, glucose concentration, pH, and temperature were controlled throughout the experiment. During anoxia or isch‐emia, ATP and intracellular pH declined and Pi increased but returned to control levels during subsequent normoxia or reperfusion. These results demonstrate the applicability of NMR spectroscopy to isolated perfused lungs, enabling studies of metabolic processes in normal and pathologic lungs, as well as establishment of optimal conditions for lung preservation for transplantation. © 1986 Academic Press, Inc.
Double pulse echoes‐A novel approach for fat‐water separation in magnetic resonance imaging
Authors: Kunz Dietmar
Published: March 2007

A novel method to obtain separate fat and water images is presented. It is based on the replacement of the first echo generating π pulse by two π/2 pulses separated by a time delay corresponding to one‐half cycle of the resonance frequency difference between fat and water protons. © 1986 Academic Press, Inc.
Effect of a 1.5 T static magnetic field on body temperature of man
Authors: Shellock Frank G. , Schaefer Daniel J. , Gordon Christopher J.
Published: March 2007

Reports in the literature concerning the effect of static magnetic fields on the body temperature of mammals have been contradictory and confusing. A significant increase in body temperature in human subjects exposed to the static magnetic fields used in magnetic resonance imaging (MRI) would have important safety implications. Therefore, in two separate studies we determined body temperature in 20 subjects exposed to a 1.5 T static magnetic field. One group of subjects (Group I, N = 9) had sublingual pocket temperature measured immediately before and after a 60 min exposure, while another group of subjects (Group II, N = 11) had esophageal temperature determined at 2 min intervals during a 20 min exposure. No statistically significant changes in body temperatures were observed in either Group I or II subjects during exposure to the 1.5 T static Magnetic field. We conclude that a relatively intense static magnetic field has no effect on body temperature of normal human subjects. © 1986 Academic Press, Inc.
A perfusion technique for 13C NMR studies of the metabolism of 13C‐labeled substrates by mammalian cells
Authors: Lyon Robbe C. , Faustino Patrick J. , Cohen Jack S.
Published: March 2007

We describe an improved perfusion system designed for NMR studies with 13C‐labeled metabolites. Using this system we have monitored the uptake and metabolism of [13C]acetate and [13]Clglucose in pooled human lymphocytes cast in an agarose gel thread. © 1986 Academic Press, Inc.
Fourier imaging using rf phase encoding
Authors: Maudsley A. A.
Published: March 2007

Fourier imaging methods encode information in the amplitudes and phases of a NMR signal over multiple acquisitions. Several of the techniques that can be used for encoding this information are reviewed and a general theory of phase encoding presented. The discussion is then extended to include encoding as part of the rf excitation sequence. Radiofrequency phase encoding can be obtained using tailored excitation techniques or special‐purpose rf field gradient coils, and may be applied prior to excitation or incorporated within the excitation or refocusing pulses. This phase‐encoding method may be used for spatial and spectral discrimination, as well as being combined with other methods of image formation. An example of the proposed imaging method is described which enables Fourier imaging of short T2 signals. © 1986 Academic Press, Inc.
RARE imaging: A fast imaging method for clinical MR
Authors: Hennig J. , Nauerth A. , Friedburg H.
Published: March 2007

Based on the principles of echo imaging, we presnet a method to acquire sufficient data for a 256 × 256 image in from 2 to 40s. The image contrast is dominated by the transverse relaxation time T2 Sampling all projections for 2D FT image reconstruction in one (or a few) echo trains leads to image artifacts due to the different T2 weighting of the echo. These artifacts cannot be described by a simple smearing out of the image in the phase direction. Proper distribution of the phase‐encoding steps on the echoes can be used to minimize artifacts and even lead to resolution enhancement. In spite of the short data acquisition times, the signal amplitudes of structures with long T2 are nearly the same as those in a conventional 2D FT experiment. Our method, therefore, is an ideal screening technique for lesions with long T2. © 1986 Academic Press, Inc.
Detection of metabolites in rabbit brain by 13C NMR spectroscopy following administration of [1‐13C]glucose
Authors: Behar K. L. , Petroff O. A. C. , Prichard J. W. , Alger J. R. , Shulman R. G.
Published: March 2007

1H‐decoupled 13C NMR spectra (20.2 MHz) of the living rabbit brain were collected with a surface coil following the intravenous infusion of [1‐13C]glucose. Within 15 min of infusion, the α and β anomers of glucose were detected and, shortly thereafter, the carbon atoms at positions C4, C3, and C2 of glutamate and(or) glutamine. After reductions of inspired oxygen from 30 to 5%, lactate C3 was detected. The intensity of the lactate resonance rose progressively during hypoxia and later fell during recovery with oxygen. The 13C fractional isotopic enrichment of arterial blood glucose was measured by 1H NMR providing information on the rate and extent of blood glucose labeling. © 1986 Academic Press, Inc.
Correlative study of properties of water in biological systems using ultrasound and magnetic resonance
Authors: Sehgal Chandra M. , Greenleaf James F.
Published: March 2007

Ultrasonic and nuclear magnetic resonance properties of media rich in water are investigated. The chemical shift of the water proton in pure water, aqueous solutions of tertiary butanol, and sodium chloride is shown to be linearly correlated to the reciprocal of sound speed in these media. A new method of determining the self‐diffusion coefficient of water by using acoustic nonlinearity and sound speed is proposed. The method is tested on a on a variety of media that include pure water, aqueous solutions of glycerol, serum albumin, egg constituents, plant tissues, frog muscle and liver, and excised human tissues. In all the cases the results are found to compare closely to diffusion coefficients measured by magnetic resonance. The results presented here indicate that the acoustic and magnetic resonance modalities, though inherently different in their origin, can provide closely related information on the properties of water. © 1986 Academic Press, Inc.
Rapid Fourier imaging using steady‐state free precession
Authors: Hawkes R. C. , Patz S.
Published: March 2007

Reversal of the read gradient in a SSFP imaging experiment allows a full spin echo to be collected in the interval τ between successive rf pulses. Orthogonal gradient pulses are used to dephase and subsequently rephase the transverse magnetization each τ enabling 2D or 3D Fourier techniques. The minimum data collection time per slice in the 3D technique is 3.1 s (128 × 256). For a 2D data collection, an oscillating bipolar sawtooth gradient is used to select the slice. Each phase‐encode value must be averaged over an equivalent portion of the oscillating slice‐selection gradient and this condition gives a minimum of 25 s for 2D data collection. Excellent slice selection is achieved with less than 5% of the signal lying outside the slice profile central lobe. Images at 0.14 T show tissue contrast may be manipulated by changing the rf pulse angle, an example of which is the presence or absence of gray/white matter contrast at rf pulse angles of 30 and 90°, respectively. The pulse angle θ dependence of five samples with different values of T2/T1 was measured and numerically calculated with good agreement between theory and experiment for θ ⩽ 90°. © 1987 Academic Press, Inc.
31P magnetic resonance spectroscopy of mesenteric ischemia
Authors: Kass Deborah A. , Banville Debra L. , Gooding Charles A. , James Thomas L.
Published: March 2007

31P magnetic resonance spectroscopy (MRS) was performed in vivo on normal and ischemic rat intestine. Within 3 min after induction of ischemia, there is a dramatic fall in adenosine triphosphate (ATP) and rise in inorganic phosphate (Pi). Our results suggest that MRS may prove useful in the early detection of mesenteric ischemia. © 1987 Academic Press Inc.
Quadrature detection surface coil
Authors: Hyde James S. , Jesmanowicz A. , Grist Thomas M. , Froncisz W. , Kneeland J. Bruce
Published: March 2007

A surface coil assembly consisting of two interleaved coplanar resonators that are intrinsically decoupled from each other is described for imaging at 1.5 T. Vector reception fields on‐axis at 3 cm depth are orthogonal and of equal magnitude. Both components of magnetization were received and combined resulting in a 2 1/2 improvement in signal‐to‐noise for temporomandibular joint images. © 1987 Academic Press, Inc.
Biological tissue simulation and standard testing material for MRI
Authors: De Luca F. , Maraviglia B. , Mercurio A.
Published: March 2007

The polyacrylamide gel is proposed here as a phantom material for NMR imaging. This substance has electrical and NMR relaxation characteristics very similar to those of biological tissues. The thermal and time stabilities also make this material a convenient standard for MRI. © 1987 Academic Press, Inc.
MR angiography by selective inversion recovery
Authors: Nishimura Dwight G. , Macovski Albert , Pauly John M. , Conolly Steven M.
Published: March 2007

A modified inversion‐recovery sequence is introduced which performs subtraction angiography by varying time‐of‐flight effects of blood flowing into an imaged slab. The selective 180° excitation inverts different regions between measurements to isolate arterial and/or venous blood. On normal human subjects, high‐resolution carotid artery angiograms have been obtained. © 1987 Academic Press, Inc.
1H NMR relaxation measurements of human tissues in situ by spatially resolved spectroscopy
Authors: Luyten Peter R. , Anderson Charles M. , den Hollander Jan A.
Published: March 2007

Spatially resolved spectroscopy (SPARS) is a method for obtaining high‐resolution NMR spectra of well‐defined volumes of human tissues in situ. This method was combined with the Carr‐Purcell‐Meiboom‐Gill multiple‐echo sequence for T2, and with inversion recovery for T1 relaxation measurements. Relaxation times obtained by SPARS were compared with standard CPMG and IR relaxation measurements and with imaging methods, using a number of relaxation phantoms. Spectroscopically resolved relaxation data of human bone marrow, muscle, and adipose tissue in situ were obtained. T2 measurements of human adipose tissue gave different results when using single‐echo measurements rather than the CPMG method. This difference was interpreted as a J modulation effect, which shows up in fatty acid proton resonances. This J modulation effect influences the intensity of adipose tissue in routine 1H NMR images. © 1987 Academic Press, Inc.
31P magnetization transfer studies of creatine kinase kinetics in living rabbit brain
Authors: Degani Hadessa , Alger Jeffery R. , Shulman Robert G. , Petroff Ognen A. C. , Prichard James W.
Published: March 2007

The kinetics of the CK reaction in the living rabbit brain was studied by three 31P magnetization transfer methods: inversion recovery (IR), inversion transfer (IT), and steadystate saturation transfer (SSST). Longitudinal relaxation rates (T−1) were determined from IR and IT experiments. The values were 0.88 ± 0.08 s−1 for PCr and 2.45 ± 0.39 s−1 for γ‐ATP. Analysis of the results of SSST experiments in which γ‐ATP was saturated yielded a forward rate constant kF of 0.53 ± 0.07 s−1. Upon saturation of PCr no change in the γ‐ATP signal could be detected in SSST. An average reverse rate constant (kR ± S.D.) of 0.52 ± 0.04 s−1 was estimated by analyzing IT data from three experiments with selective inversion of γ‐ATP. The standard error of kR was 50%. The average [PCr]/[ATP] of 1.21 ± 0.16 together with the values of kF and kR yielded a forward‐to‐reverse flux ratio of 1.23. Within our limits of accuracy this ratio was not significantly different from 1.0, thus suggesting that in the brain the forward and reverse CK fluxes are equal. © 1987 Academic Press, Inc.
Multiecho magnetic resonance angiography
Authors: Dumoulin C. L. , Souza S. P. , Feng H.
Published: March 2007

Several pulse sequences which generate projected MR angiograms are presented. These pulse sequences exploit multiple‐gradient refocused echoes to obtain several independent angiograms, which can be combined or separately analyzed to provide more information than an individual angiogram. For example, a series of angiograms, each with a different projection axis, can be obtained in the time required to obtain a single angiogram using a single‐echo method. If the view angle of each echo is the same, then the acquired angiograms can be added to enhance the signal‐to‐noise ratio. Another pulse sequence simultaneously obtains two or more angiograms, sensitive to orthogonal flow components of the overall blood flow. These angiograms are then added to give an angiogram which is sensitive to flow in all directions. © 1987 Academic Press, Inc.
Proton transverse relaxation rate of 17O‐enriched water
Authors: Yeung Hong N. , Lent Arnold H.
Published: March 2007

Proton transverse relaxation rates of 17O‐enriched water at pH in the neutral range were determined with isotopic compositions of 17O varying from natural abundance to 5%. Meiboom's account of the proton T caused by the scalar interaction between the proton and 17O is generalized to accommodate new data. The generalized formulation covers 17O enrichment above the limit to which Meiboom and his co‐worker constrained all their work.
Effects of slice selection and diffusion on T2 measurement
Authors: Wong S. T. S. , Roos M. S.
Published: March 2007

This study examines slice selection and diffusion as sources of systematic error in T2 estimates obtained from imaging experiments. The selective refocusing pulses in a multislice, two‐echo, spin‐warp experiment cause slice profiles of sequential echoes to change in shape. This results in bias in T2 images calculated from the two‐echo data set. A method to correct the bias is presented. The effect of diffusion on T2 images obtained with typical two‐echo imaging sequences was found to be negligible. © 1987 Academic Press, Inc.
Optimizing the precision in T1 relaxation estimation using limited flip angles
Authors: Wang Henry Z. , Riederer Stephen J. , Lee James N.
Published: March 2007

In this article we describe the precision in the estimation of the spin–lattice relaxation time TI from MRI signals acquired for various flip angles with the repetition time TR held constant. We review the estimation procedure itself and present a model for the propagation of noise in the signal into the calculated TI. This model is verified by both Monte Carlo simulations and experimental data taken on image phantoms. Based on this model, we find that for a given TR/TI there exist two optimal flip angles that will minimize the uncertainty in the estimated TI. We also show how two optimal angles can be selected for a given range of TR/TI values. In addition, T1 estimation using the two optimal angles can be comparable to or better than using multiple evenly spaced angles. Finally, in an initial comparison with the two‐point saturation recovery method of calculating T1, results for equal total scanning time TRTot suggest that for T1 > 0.5 TRTot, the limited flip angle approach gives better TI precision whereas for TI < 0.5 TRTot, the saturation recovery approach is better. © Academic Press, Inc.
Visibility of mammalian hepatic glycogen to the NMR experiment, in vivo
Authors: Shalwitz Robert A. , Reo Nicholas V. , Becker Nancy N. , Ackerman Joseph J. H.
Published: March 2007

An in vivo 13C NMR study was performed to investigate whether the relaxation properties of the C‐1 carbon of the glucopyranose residues of glycogen changed as the molecule increased in size. There was no change in resonance intensity or linewidth. Therefore, no significant change in T1, or T2 was observed. © Academic Press, Inc.
19F NMR imaging of blood oxygenation in the brain
Authors: Eidelberg D. , Johnson G. , Barnes D. , Tofts P. S. , Delpy D. , Plummer D. , McDonald W. I.
Published: March 2007

Perfluorcarbon (PFC) emulsions have been developed as oxygen carrying blood substitutes. High fluorine concentrations allow them to be used in 19F NMR imaging of blood vessels. Furthermore, 19F relaxation times in PFCs are dependent on oxygen tension (pO2) so that NMR imaging may provide a noninvasive method of measuring spatially localized pO2 values in vivo. Using these principles, we have formed 19F images and calculated pO2 maps of the cat brain. © 1988 Academic Press, Inc.
Renal imaging studies at 1.5 and 9.4 T: Effects of diuretics
Authors: Sarkar Susanta K. , Holland George A. , Lenkinski Robert E. , Mattingly Mark A. , Kinter Lewis B.
Published: March 2007

We have studied the effects of two diuretics, selective for renal cortical (furosemide) and inner medullary (vasopressin antagonist) water handling, in rat kidney at 1.5 T and find that furosmide completely dissipates the cortical‐inner medullary T2 gradient whereas the vasopressin antagonist has little effect. This phenomenon appears to be related to changes in luminal water content. We also demonstrate the feasibility of obtaining live mouse kidney images with a resolution of 100 × 100 × 700 μm at 9.4 T. © 1988 Academic Press, Inc.
Patient anesthesia and monitoring at a 1.5‐T MRI installation
Authors: Karlik S. J. , Heatherley T. , Pavan F. , Stein J. , Lebron F. , Rutt B. , Carey L. , Wexler R. , Gelb A.
Published: March 2007

This paper describes the facilities successfully used to provide patient monitoring and anesthesia support in a 1.5‐T imaging installation. The requirements for the MRI site for anesthetic gases, shielded power, and radiofrequency ports are outlined. Specific modifications in anesthesia machines, anesthesia art, laryngoscope, mercury sphygmomanometer, oximeter, and remote blood pressure devices are described. Additional aspects of patient monitoring and support, e.g., electrocardiogram and pressure infusion, are also discussed. © 1988 Academic Press, Inc.
Investigation of a whole‐body receiver coil operating at liquid nitrogen temperatures
Authors: Hall A. S. , Barnard B. , McArthur P. , Gilderdale D. J. , Young I. R. , Bydder G. M.
Published: March 2007

This communication describes the design and application of a receiver coil operating at liquid nitrogen temperature and intended as a surface coil in a whole‐body imager. Its particular application is seen as the external receiver for parasitic internal or implanted detectors. © 1988 Academic Press, Inc.
Heating effects of metallic implants by MRI examinations
Authors: Buchli R. , Boesiger P. , Meier D.
Published: March 2007

Magnetic radiofrequency fields applied in magnetic resonance imaging examinations induce electrical currents in metallic implants. These eddy currents may heat up the implants and thus may be capable of causing localized tissue heating. The rf power deposition and the joule heating of the implant can be calculated by solving Maxwell's equations for the specific problem. First, extreme in vitro worst‐case experiments were performed with a large and very thin aluminum sheet, which was placed in a 1.5‐T MRI device in a position parallel to the magnetic rf field. In agreement with the theoretical results the temperature rise of a thermally insulated sheet amounted to only 0.08oC after a 15‐min MRI examination at 64 MHz. No temperature rise in the aluminum sheet could be measured for a sheet immersed in a saline solution. Second, in vitro experiments with a hip joint prosthesis and an osteosynthetic plate were performed to confirm the theoretical results, which predict nearly no temperature rise in the metallic implants. No temperature rise in the implants could be measured. © 1988 Academic Press, Inc.
Human in vivo phosphate metabolite imaging with 31P NMR
Authors: Bottomley P. A. , Charles H. C. , Roemer P. B. , Flamig D. , Engeseth H. , Edelstein W. A. , Mueller O. M.
Published: March 2007

Phosphorus (31P) spectroscopic images showing the distribution of high‐energy phosphate metabolites in the human brain have been obtained at 1.5 T in scan times of 8.5 to 34 min at 27 and 64 cm3 spatial resolution using pulsed phase‐encoding gradient magnetic fields and three‐dimensional Fourier transform (3DFT) techniques. Data were acquired as free induction decays with a quadrature volume NMR detection coil of a truncated geometry designed to optimize the signal‐to‐noise ratio on the coil axis on the assumption that the sample noise represents the dominant noise source, and self‐shielded magnetic field gradient coils to minimize eddy‐current effects. The images permit comparison of metabolic data acquired simultaneously from different locations in the brain, as well as metabolite quantification by inclusion of a vial containing a standard of known 31P concentration in the image array. Values for the NMR visible adenosine triphosphate in three individuals were about 3 mM of tissue. The ratio of NMR detectable phosphocreatine to ATP in brain was 1.15 ± 0.17 SD in these experiments. Potential sources of random and systematic error in these and other 31P measurements are identified. © 1988 Academic Press, Inc.
Reactive hyperemia monitored on rat muscle using perfluorocarbons and 19F NMR
Authors: Authier Bertrand
Published: March 2007

Perfluorinated blood substitutes can be detected by 19F NMR in vivo in small concen‐ trations. Reactive hyperemia was induced in rat leg by the transient application of a tourniquet, causing a 50% increase in 19F NMR signal. These results show that this method can be used to monitor the kinetics of tissue perfusion. © 1988 Academic Press, Inc.
Electron spin resonance imaging of tissues with lipid‐rich areas
Authors: Bačič G. , Walczak T. , Demsar F. , Swartz H. M.
Published: March 2007

Electron spin resonance imaging and spectroscopy of lipid‐rich samples were studied at 9 GHz. Using both lipid‐ and aqueous‐soluble nitroxides good delincation of fat‐ and muscle‐rich regions of tissue was obtained. Several different principles can be used to differentiate between these types of tissues and potentially between different types of lip‐ids. These principles include lipophilicity of nitroxides, viscosity (which is higher in lipids), oxygen solubility (oxygen is four times more soluble in lipids), and the distribution of paramagnetic metal ions. These techniques have potential applicability for directly studying metabolism and oxygen concentration in tissues by ESR techniques and for investigating potential contrast agents for in vivo NMR techniques. © 1988 Academic Press, Inc.
Boron‐11 MRI and MRS of intact animals infused with a boron neutron capture agent
Authors: Kabalka George W. , Davis Mark , Bendel Peter
Published: March 2007

Boron neutron capture therapy (BNCT) depends on the delivery of boron‐containing drugs to a targeted lesion. Currently, the verification and quantification of in vivo boron content is a difficult problem. Boron‐11 spectroscopy was utilized to confirm the presence of a dimeric sulfhydryl dodecaborane BNCT agent contained in an intact animal. Spectroscopy experiments revealed that the decay time of transverse magnetization of the boron‐11 spins was less than 1 ms which precluded the use of a 2DFT imaging protocol. A back‐projection protocol was developed and utilized to generate the first boron‐11 image of a BNCT agent in the liver of an intact Fisher 344 rat. © 1988 Academic Press, Inc.
A method for correctly setting the rf flip angle
Authors: Perman William H. , Bernstein Matt A. , Sandstrom John C.
Published: March 2007

Currently the accepted method for setting the correct rf power levels to achieve 90° and 180° rf pulses for MR imaging is to peak the echo amplitude of a rf spin‐echo sequence. The echo amplitude of this α‐2α pulse sequence is proportional to sin3(α) and has a relatively broad maximum. Recently another method for setting the rf flip angle by maximizing the ratio of the stimulated echo to the primary echo amplitudes (in a 3α sequence) demonstrated accuracy similar to that of the spin‐echo method using a shorter repetition time. We present a new, more sensitive, and more accurate method for setting the correct rf power levels for 90° and 180° rf pulses. In this method, based upon the stimulated echo pulse sequence, we are able to accurately set the rf power to within ±0.1 dB by minimizing the signal amplitude of the third spin echo. This null method works for both selective and nonselective rf pulses of flip angle 90° or 180°, allowing the user to accurately adjust the relative amplitudes of the four rf pulse types within a single pulse sequence. © 1989 Academic Press, Inc.
NMR relaxation of water in hydrogel polymers: A model for tissue
Authors: Gore John C. , Brown Mark S. , Zhong Jianhui , Mueller K. Fritz , Good William
Published: March 2007

The NMR relaxation rates ofa class of hydrated polymers (hydrogels) have been investigated over a wide range of frequencies (0.01 to 60 MHz) and compositions. The gels comprise long chains of polytetramethylene oxide diol crosslinked by copolymers of dimethylacrylamide and methylmethacrylate. The longitudinal relaxation rate dispersion curves of these materials are very similar to those shown by human tissues and they can be altered in flexible fashion by changing the polymer content. By substitution of the water by deuterium oxide, the contribution of intermolecular cross‐relaxation effects has been shown to account for two‐thirds the total water relaxation rate. With their close similarity to tissue relaxation behavior, hydrogels of differing compositions are particularly well‐suited to MRI phantoms and test objects. © 1989 Academic press, Inc.
MRI detection of myocardial perfusion changes by gadolinium‐DTPA infusion during dipyridamole hyperemia
Authors: Miller D. Douglas , Holmvang Godtfred , Gill John B. , Dragotakes Donna , Kantor Howard L. , Okada Robert D. , Brady Thomas J.
Published: March 2007

To detect abnormal regional myocardial coronary flow reserve, serial spin‐echo MR tomograms of four control dogs and six with a partial balloon occlusion of the left anterior descending (LAD) coronary artery were acquired before and after dipyridamole infusion and during the paramagnetic effect of a bolus plus infusion of gadolinium‐DTPA. Microsphere myocardial blood flow was measured for correlation with serial regional changes in MR signal intensity. Significant difference in gadolinium‐enhanced MR signal intensity existed between the hypoperfused LAD and the hyperemic left circumflex perfusion beds (46 ± 22% vs 78 ± 29% above baseline, respectively; P < 0.05). The percentage changes in gadolinium‐enhanced MR signal and microsphere myocardial blood flow were significantly correlated (r2 = 0.93). © 1989 Academic Press, Inc.
Characterization of normal brain tissue using seven calculated MRI parameters and a statistical analysis system
Authors: Hyman Timothy J. , Levy George C. , Kurland Robert J. , Shoop Jon D.
Published: March 2007

A statistical analysis system for classifying normal brain tissue has been applied to the analysis of MRI scans on 45 volunteers. The Bayes Maximum Likelihood method was used to achieve a discrimination accuracy of 84% for 13 tissue types among three age group sets, with classification accuracies for individual regions ranging from 50 to 100%. In order to attain this level of discrimination a set of seven derived relaxation‐type parameters was used to categorize the tissue types. Values for these experimentally estimated parameters were derived from the MRI intensities of eight images in the following pulse sequences: (1) a Carr‐Purcell‐Meiboom‐Gill (CPMG) four‐echo train, (2)a single‐echo inversion recovery, and (3) three single‐echo sequences with varying repetition times, TR, and echo delays, TE. The T2 values derived from ratios of single‐echo intensities showed better discrimination power than those from the four‐echo CPMG train. The general precision of the seven estimated parameters was excellent, with percentage stan‐ dard deviations ranging from 4 to 18% for the various regions studied. The tissue discrimination achieved by use of just three relaxation parameters, T1, T2, and proton density, calculated from intensities of images from a four‐echo sequence, an inversion recovery sequence, and a short TR single‐echo sequence, was not as good, being only 55%. © 1989 Academic Press. Inc.
Magnetic resonance imaging of estrogen‐induced pituitary hypertrophy in rats
Authors: Van Nesselrooij Joop H. J. , Szeverenyi Nikolaus M. , Ruocco Martin J.
Published: March 2007

Estrogen‐induced pituitary hypertrophy has been studied using magnetic resonance imaging in a group of 15 control and 30 experimental rats. Following the subcutaneous implantation of an estrogen pellet, differences in the anatomical appearance of the pituitary gland of the implanted rats can be detected in as little as 16 days, when compared to the control animals. The gland in the experimental animals appears diffusely enlarged with rounded margins, when viewed in sagittal T 1‐weighted magnetic resonance images. Additionally, a uniform signal intensity is not detected in the hypertrophic pituitary glands of estrogen‐implanted rats, while in the control rats this is a common finding. A satellite study of 300 animals (treated in a manner identical to that in the imaging study) demonstrates that the weights of excised pituitaries in estrogen‐treated rats increases to a statistically significant level in the interval 18 to 35 days. Changes in the appearance and volume of the pituitary gland observed with magnetic resonance imaging seem to have promise for the early detection of pituitary lesions in rats. © 1989 Academic Ress. Inc.
A liposomal MRI contrast agent: Phosphatid ylethanolamine‐DTPA
Authors: Grant Chris W. M. , Karlik Stephen , Florio Eugene
Published: March 2007

The chelating agent, diethylenetriaminepentaacetic acid (DTPA), was attached via one‐COOH group to the amino headgroup of phosphatidylethanolamine to produce a phospholipid which is also a powerful chelating agent. It readily assembles into the walls of lipid bilayer structures as a liposome‐associated camer of cations for MR contrast or radioisotope studies. Freeze‐etch electron microscopy showed that phosphatidylethanolamine‐DTPA formed satisfactory sonicated vesicles when mixed with natural phospholipids at up to 50 wt%. The resultant structures with bound gadolinium effectively shortened T1 and T2 of surrounding water protons. When sonicated liposomes bearing chelating agent with bound 111In3+ were injected intravenously into rats, uptake was primarily by liver and spleen. By 24 h postinjection there was biliary excretion of this material. Phosphatidylethanolamine‐DTPA may have some general utility as an amphiphilic liposomal chelating agent for polyvalent cations.
Diagnosis and assessment of mitral and aortic valve disease by cine‐flow magnetic resonance imaging
Authors: Mitchell Leslie , Jenkins Jeremy P. R. , Watson Yvonne , Rowlands Derek J. , Isherwood Ian
Published: March 2007

Seventy‐six aortic and mitral valves, in 44 patients and 5 normal volunteers, were studied by Cine‐Flow MRI (on a 0.26‐T superconducting magnet system), utilizing compound oblique imaging planes and a Field Echo Even Rephasing sequence. All patients had had cardiac catheterization and echocardiography. All patients with valvular stenosis and aortic sclerosis (n = 45) showed complete signal loss distal to the respective valve. Length of signal loss distal to the aortic valve in those in whom it was measured (n = 15) allowed differentiation of aortic stenosis (n = 9) from sclerosis (n = 6). This also permitted grading of stenosis with highly significant correlation ( T = 0.86; P < 0.002) with pressure gradient measurement. In mitral stenosis (n = 12) calculation of the area of signal loss distal to the mitral valve as a percentage of left ventricular cross‐sectional area showed a highly significant correlation (T = 0.77; P = 0.001) with pressure gradient measurement. Clinically significant valvular regurgitation was graded by size and duration of signal loss proximal to the valve with concordance with angiocardiography. It is concluded that Cine‐Flow MRI has a clinical role in the diagnosis and assessment of valvular heart disease. © 1989 Academic Press, Inc.
Volume‐selective determination of the spin‐lattice relaxation time in the rotating frame, T1ρ, and T1ρ, imaging
Authors: Rommel E. , Kimmich R.
Published: March 2007

A method for the volume‐and resonance line‐selective determination of the longitudinal relaxation time in the rotating frame, T1ρ, is described. The spin‐lock pulse intrinsic to the T1ρ sequence simultaneously replaces the first slice‐selective pulse of the VOSY method for localized spectroscopy. This is a further parameter suitable for the local characterization of tissue. On the same basis, T1ρ, can be used as a new contrast parameter for biomedical imaging purposes. An appropriate pulse sequence for T1ρ imaging is presented. Test experiments which promise some striking advantages compared with conventional magnetic resonance imaging are reported. © 1989 Academic Press, Inc.
Echo‐planar high‐resolution flow velocity mapping
Authors: Firmin D. N. , Klipstein R. H. , Hounsfield G. L. , Paley M. P. , Longmore D. B.
Published: March 2007

A technique for the very rapid measurement of blood flow with high spatial resolution is described. The method combines the previously validated technique of phase velocity mapping and echo‐planar principles. The relatively small diameter of blood vessels enables a high‐resolution echo‐planar flow measurement to be made with as few as 16 echoes such that the method can be incorporated into a near standard NMR scanner. Two sequence variations are tested and validatedin vitroand one is used to demonstratein vivoblood flow measurement. The results are shown to compare well with a previously validated less rapid method. The technique should enhance the potential of NMR flow imaging by enabling sudden changes in flow to be studied. It should also simplify the measurement of blood flow in small mobile vessels such as the coronary arteries. © 1989 Academic Press, Inc.
Cerebral metabolite dynamics during temporary complete ischemia in rats monitored by time‐shared 1h and 31p nmr spectroscopy
Authors: Chang L.‐H. , Shirane R. , Weinstein P. R. , James T. L.
Published: March 2007

The changes in cerebral phosphorus metabolites, intracellular pH, and lactate during 30 min of complete global ischemia and 2 h of reperfusion were monitored by time‐shared 1H and 31P in vivo NMR spectroscopy in rats. After the induction of ischemia, intracellular pH decreased from 7.14 ± 0.01 to 6.32 ± 0.10, and lactate concentration increased from 1.6 ± 0.4 to 15.8 ± 2.5 μmol/g; ATP and phosphocreatine were totally depleted, while inorganic phosphate increased 715 ± 47%. Within 1 h after blood flow was restored, high‐energy phosphates and lactate levels had recovered close to baseline levels. The changes in intracellular pH and lactate levels during ischemia and reperfusion correlated Well.
Magnetic relaxation in blood and blood clots
Authors: Bryant Robert G. , Marill Keith , Blackmore Craig , Francis C.
Published: March 2007

Nuclear magnetic relaxation rates are measured for whole blood, blood plasma, whole blood clots, and plasma clots in vitro. Relaxation rates are linear in the hematocrit and transverse relaxation rates are significantly greater than longitudinal relaxation rates. Longitudinal relaxation rates measured from 0.01 to 42 MHz for proton Larmor frequencies are found to decline monotonically with increasing magnetic field strength; however, the dispersion curves do not follow a simple Lorentzian behavior, which is anticipated in a suspension of particles in a solution of proteins having a distribution of molecular weights. The transverse relaxation rate is a function of the acquisition parameters, in particular, the choice of TE in either Hahn echo experiments or in echo‐train experiments. The origin of this dependence of T2 on TE or the interpulse spacing in an echo train is identified with the exchange of water from inside the red blood cell to the outside and is only an important relaxation mechanism in the case where the blood cell membrane is intact and the cell contains deoxygenated hemoglobin. The dependence of the apparent transverse relaxation rate on the interpulse spacing in a Meiboom‐Gill‐Carr‐Purcell pulse sequence provides the estimate that the mean residence time of water inside the blood cell is about 10 ms. These data provide a sound basis for understanding the dependence of magnetic images on magnetic field strength and the choices of the image acquisition parameters, TE and TR.
Spectral baseline correction using clean
Authors: Mckinnon G. C. , Burger C. , Boesiger P.
Published: March 2007

Baseline distortion in NMR spectroscopy, caused by the “dead time” between signal excitation and detection, makes quantitative interpretation difficult and is aesthetically displeasing. Here the use of the CLEAN algorithm for deconvolving the effect of signal dead time to produce a distortionless baseline is discussed. Unlike other nonlinear spectral estimation techniques, CLEAN is easy to program, easy to use, quite robust, and fast.
Quantitative studies of hydrodynamic effects and cross‐relaxation in protein solutions and tissues with proton and deuteron longitudinal relaxation times
Authors: Zhong Jianhui , Gore John C. , Armitage Ian M.
Published: March 2007

Longitudinal relaxation times T1 of water protons were measured in 5% protein solutions at different static magnetic fields (0.47, 2, and 7 T), for proteins with molecular weight ranging between 1.4 and 480 kDa and in solvents of varying degrees of deuteration. T1, values were also obtained for rat liver soaked with Krebs‐Ringer solutions of varying degrees of deuteration at the above fields. For the samples containing D2O, T1 for deuterium was also measured at fields 2 and 7 T. The deuterium measurements were used to estimate water rotational correlation times which were in turn used to estimate the contribution of so‐called “hydrodynamic effects” of macromolecules to proton relaxation. The proton relaxation rates at full deuteration were compared with those in protonated solvent (water) to obtain a second, direct measurement of this effect. Both measurements provide quantitation of the hydrodynamic effects, free from the contributions of other effects that are transparent to deuteration, and results from both measurements agree with each other reasonably well. The cross‐relaxation rate between solute and solvent protons, and the contribution of paramagnetic impurities in the samples were also obtained from the proton T1studies. The experimental results show that the hydrodynamic effects (intramolecular and intermolecular water‐water interactions) are about the same magnitude in all the proteins studied as well as in rat liver. However, the cross‐relaxation rate generally increases with increasing protein molecular weight. Measurements in soaked rat liver indicate that the cross‐relaxation rate per unit mass of solute is much higher in tissues than in simple solutions of proteins of similar mean molecular weight. The results challenge the prevailing concept that the relaxation properties of biological tissues may be treated as a simple superposition of the properties of their Constituents.
Echo‐planar imaging of the human fetus in utero
Authors: Stehling M. K. , Mansfield P. , Ordidge R. J. , Coxon R. , Chapman B. , Blamire A. , Gibbs P. , Johnson I. R. , Symonds E. M. , Worhington B. S. , Coupland R. E.
Published: March 2007

We have demonstrated that echo‐planar imaging can be used to produce high‐quality snapshot images of the human fetus in utero in a fraction of a second. These images are free of motional artifact or blurring and allow detailed depiction of fetal structures in normal and pathological pregnancies.
A continuously variable field of view surface coil
Authors: Duensing R. , Fitzsimmons J. , Sanford D. , Vazquez J.
Published: March 2007

A new type of surface coil is described which allows the user to continuously vary the size of the field of view. This utilizes a modified radiofrequency trombone for size adjustment that results in a stable frequency over a wide range of dimensions. Results show that the coil may be increased in area by as much as 60% while maintaining frequency stability to ca. 1 MHz at 63.5 MHz. Images of the human spine are presented to demonstrate the clinical utility of the new design.