bluuebunny/crossref_metadata_2025 huggingface dataset:
In vivo high‐resolution volume‐selected proton spectroscopy and T1 measurements in the dog brain
Authors: Galloway Graham J. , Field James , Rose Stephen E. , Haseler Luke J. , Brooks William M. , Brereton Ian M. , Bore Peter J. , Crozier Stuart , Doddrell David M.
Published: March 2007

Successful in vivo NMR spectroscopy requires a combination of techniques to address the problems of volume selection, water suppression, and resolution. All this needs to be done in the very heterogeneous environment found in living organisms. Previously published techniques are used to obtain 1H spectra from a dog brain, observing metabolites with concentrations below 1 mM. Measurements of spin‐lattice relaxation times (T1) are also presented. The 1H relaxation times are long (T1 > 1.0 s) yielding information about the fluidity of the molecular environment. Comments are made concerning the achievable linewidth in vivo and the deficiencies that phase‐encoding spectroscopic methods may have in obtaining high‐resolution 1H spectra. © 1989 Academic Press, Inc.
Comparison of the signal‐to‐noise ratio at 1.5 and 2.0 T using a whole‐body system
Authors: Beckmann N. , Müller S. , Seelig J.
Published: March 2007

Signal‐to‐noise ratios for 1H, 31P, and 13C signals at 1.5 and 2.0 T were compared using a whole‐body system with a fast rampable magnet. Results indicate that SNR lies within the predicted values of linear and 7/4th power dependency with the applied magnetic field, for lossy and lossless samples, respectivety. © 1989 Academic Press, Inc.
A method for direct in vivo measurement of drug concentrations from a single 2H NMR spectrum
Authors: Evelhoch Jeffrey L. , McCoy Cheryl L. , Giri Brij P.
Published: March 2007

The use of 2H‐labeled drugs provides a measure of drug concentration in situ directly from a single 2H NMR spectrum obtained with any antenna by correcting only for differential saturation effects. The limit of detection for a drug labeled with three equivalent deuterons is roughly 0.5 mM. © 1989 Academic Press, Inc.
Use of solvent suppression technique to enhance changes due to susceptibility variations in magnetic resonance imaging
Authors: Hall A. S. , Collins A. G. , Bryant D. J. , Young I. R. , Bydder G. M.
Published: March 2007

This communication describes the use of a binomial pulse sequence designed from solvent suppression in proton spectroscopy to convert the small frequency changes associated with field variations into significant amplitude changes in magnetic resonance images. This technique can be used to demonstrate tissue susceptibility change. © 1989 Academic Press, Inc.
Characterization of fluid flow using low‐spatial‐resolution velocity spectra from NMR images
Authors: Wendt Richard E. , Nitz Wolfgang , Murphy Paul H. , Bryan R. Nick
Published: March 2007

Flow velocity distributions or spectra may be obtained by NMR imaging using an anisotropic three‐dimensional Fourier transform pulse sequence in which the low‐resolution direction encodes perpendicular velocity. Velocity spectra from regions of interest covering the entire lumens of pipes in a flow phantom containing straight sections, a jet, and a constriction suggest that velocity spectra provide useful information even when the vessels are not spatially well‐resolved. The flow in the phantom was characterized and limited measurements were made. © 1989 Academic Press, lnc.
Therapeutic response of breast carcinoma monitored by 31P MRS in situ
Authors: Ng Thian C. , Grundfest Sharon , Vijayakumar Srinivasan , Baldwin Nicholas J. , Majors Anthony W. , Karalis Ipatia , Meaney Thomas F. , Shin Kyu Ho , Thomas Frank J. , Tubbs Raymond
Published: March 2007

In situ phosphorous MRS was employed to study the metabolites of normal and cancerous breasts, and the alterations of tumor response to therapy. In a group of 7 normal volunteers and 12 patients, the total mobile phosphate content of breast carcinomas was found to be at least two to three times higher than that of the normal breast measured off menstruation. The metabolite profiles of normal and tumorous breasts are coarsely similar. In both cases the intracellular pH (pHi) was either neutral or slightly alkaline (pH > 7.0). Prior to treatments, the metabolite levels of phosphoryl monoester‐to‐ATP ratio of breast neoplasms were higher than those of the controls and decreased after the patients received a few treatments while the pHi fluctuated at a value greater than 7.0. The phosphoryl diester‐to‐ATP ratio also demonstrated to a lesser extent a decreasing trend in response to therapy. © 1989 Academic Press, Inc.
Single‐scan volume‐selective editing of NMR spectra with the aid of a split‐pathway technique for homonuclear applications
Authors: üttel A. Kn , Kimmich R.
Published: March 2007

An RF and field‐gradient pulse sequence that permits the recording of localized and edited proton spectra is presented. The editing principle is a technique of splitting and recombining the coherence pathways. While the recombination of the pathways of uncoupled spins is destructive, that of coupled spins can be adjusted to be constructive. © 1989 Academic Press, Inc.
Efficient biphasic spin‐echo magnetic resonance imaging
Authors: Parker Dennis L. , Caputo Gary R. , Frederick Philip R.
Published: March 2007

The concept of temporal echo multiplexing is defined and used to develop rapid bipha‐sic spin‐echo sequences for imaging the heart. Three imaging sequences, based on four‐echo and two‐echo multiplexing and rapid single echo (i.e., conventional spin‐echo imaging), are compared. Preliminary results indicate that two‐echo multiplexing yields a significantly reduced acquisition time window with image quality that is only slightly inferior to single‐echo imaging. Single‐echo biphasic imaging results in the most consistent image quality. © 1989 Academic press, Inc.
Computing material‐selective projection images in MR
Authors: Wright G. A. , Brosnan T. J. , Macovski A. , Nishimura D. G.
Published: March 2007

We detail a robust, general method for computing projection images of individual materials in a volume as linear combinations of MR projection images with different material‐dependent weightings. Signal per unit volume for each material in each raw image is acquired directly for accurate cancellation of undesired, overlapping materials. The weighted sum of the input images is determined to maximize the signal‐to‐noise ratio (SNR) and minimize inhomogeneity effects in the material‐selective images. We tested the implementation experimentally in both phantom and human studies, producing selective images with reasonable SNRs and material isolation. With further develop ment of sequences to rapidly acquire input images having greater material differentiability, we envision the application of the selective projection imaging format to screening studies searching over large volumes for diseased tissues. © 1989 Academic Press, Inc.
Metabolism of tumor regression from angiogenesis inhibition: 31P magnetic resonance spectroscopy
Authors: Hoffer Fredric A. , Taylor George A. , Spevak Melissa , Ingber Donald , Fenton Terry
Published: March 2007

31P NMR spectroscopy was used to analyze the in vivo metabolism of reticulum cell sarcoma of mice. The ratio of high‐ to low‐energy phosphates ATPB/(Pi + PME) was measured to reflect the relative metabolic state in the tumor. Of the 34 mice studied, 26 were treated with an antiangiogenesis regimen of heparin and cortisone. Eighty‐two percent of the tumors treated eventually decreased in volume (P < 0.01 ). Volumes and spectroscopic information of 20 tumors were analyzed. Although the average untreated volume was similar to the volume after 3 days of treatment, the average ATPB/(Pi + PME) ratio rose from 0.34 ± 0.10 to 0.47 + 0.07 (P = 0.02). However, after 6 days of treatment, the volume significantly decreased (P < 0.0001) but the ratio did not significantly rise further (P = 0.06). The rise in the high‐energy phosphate preceded a significant decrease in volume of the tumors. In addition, the replenishment of the high‐energy stores with tumor regression coincided with the histologic findings of a decrease in the number of tumor cells, a decrease of the mitotic index, and a decrease of the number of necrotic cells present with ongoing treatment. Our data suggest that noninvasive methods of assessing early biochemical response of tumor regression may be possible.
Study of proton spin‐lattice relaxation variation induced by paramagnetic antibodies
Authors: Macr M. A. , De Luca F. , Maraviglia B. , Polizio F. , Garreffa G. , Cavallo S. , Natali P. G.
Published: March 2007

A murine anti‐human melanoma monoclonal antibody fragment was labeled with gadolinium and its proton relaxation efficiency compared to controls at frequencies ranging from 2 to 300 MHz. Relaxation time variations were about 30–40% in 10–15 μM solutions. The labeled fragment showed proton relaxation enhancement relative to free gadolinium, while preserving its immunoreactivity. A tentative labeling of a melanoma pellet by means of the fragment, just at the borderline of a minimum expected T1 variation, gave no detectable diffemm.
1H COSY spectra of superfused brain slices of rat: Ex vivo direct assignment of resonances
Authors: Gillet B. , Mergui S. , Beloeil J‐C. , Champagnat J. , Fortin G. , Jacquin T.
Published: March 2007

Realization of 1 D 1H spectra of superfused brain slices of rats is described. Two‐dimensional 1H− 1H COSY spectra have been used for the direct assignment of resonances on living tissue (lactate, GABA, N‐acetyl aspartate, aspartate, glutamine/glutamate, creatine/phosphocreatine, taurine, inositol, choline/ethanolamine). Utilization of the SUPERCOSY sequence permits simultaneously the enhancement of off‐diagonal signals for small metabolites and the reduction of the signals for water and macromolecules.
Continuous‐flow 13C‐filtered 1H NMR spectroscopy of ethanol metabolism in rat liver perfusate
Authors: Albert Klaus , Sudmeier James L. , Sawkat Anwer M. , Bachovchin William W.
Published: March 2007

Using a 188.5‐μl continuous‐flow dual probe 1H{13C} spin‐echo difference spectra of rat liver perfusate were acquired. The conversion of [1−13C]ethanol to [1−13C]‐ acetaldehyde was readily monitored as a function of time. In combination with 1‐1 water nonexcitation and WALTZ 13C decoupling, this method proved to be superior in sensitivity and selectivity to direct 1H or 13C detection.
Two‐dimensional correlated spectroscopy (COSY) of intact frog muscle: Spectral pattern characterization and lactate quantitation
Authors: Alonso Julio , Arús Carlos , Westler William M. , Markley John L.
Published: March 2007

Two‐dimensional scalar‐correlated 1H spectra (COSY) were recorded from a model solution containing varying amounts of lactate and a fixed concentration of carnosine as the reference compound. The integrated volume of the lactate methyl to methine cross peak in the magnitude‐calculated spectra showed a linear increase with respect to lactate concentration. Accordingly, the COSY cross‐peak integral volume should be a useful parameter for the quantitative study of metabolism in intact tissue. We have tested this assumption in excised gastrocnemius frog muscle. Lactate, carnosine, and creatine/ phosphocreatine cross peaks have been assigned in the spectrum of summer frog muscle. The change in concentration of lactate and phosphorylated compounds upon anaerobic storage of excised frog muscle has been followed by interleaving one‐dimensional ( 1 D) 1H and 31P spectra with 2D homonuclear 1H COSY spectra. The lactate concentration in the excised muscle derived from COSY agreed well with that determined from muscle extracts. Qualitative changes in the COSY pattern of the excised muscles under caffeineinduced contracture were detected. Furthermore, seasonal variations were observed in the COSY spectral pattern: winter frog muscle was found to differ from summer frog muscle by the appearance of cross peaks from phosphodiesters and mobile fatty acids.
in vitro NMR characterization of mammalian myocardium: Effect of specimen integrity on relaxation times
Authors: Scholz Thomas D. , Fleagle Steven R. , Skorton David J.
Published: March 2007

We systematically evaluated three different methods of preparing canine myocardium for NMR relaxometry: using whole specimens, specimens sliced into approximately 2‐mm3 pieces, and specimens minced into pieces <2 mm3. NMR relaxation times were determined at 20 MHz. TI relaxation time and water content were not different among the three methods. However, T2 values differed significantly between whole and sliced samples (mean ± SEM = 51.2 ± 2.2 ms (whole) vs 54.3 ± 2.7 ms (sliced); P < 0.05). Minced myocardium showed a similar increase that was not statistically significant. We conclude that tissue preparation methods must be controlled when performing NMR relaxometry studies.
Differential flow imaging by NMR
Authors: Xiang Q. S. , Nalcioglu O.
Published: March 2007

A new method for spatially resolved NMR flow measurements, named differential flow imaging (DFI), is introduced and experimentally verified. The DFI technique is based on the fact that flow velocity in any direction may cause a pixel position shift in the phase‐encoding direction of a 2DFT NMR image. In this method two flow‐influenced magnitude images are obtained by properly encoding and/or compensating the flow velocity. A spatial map of the desired component of the flow velocity can consequently be calculated from these two images. Since the DFI technique uses only the magnitude information of the complex images, it is not sensitive to systematic phase errors in contrast to other methods which are based on the phase measurements. On the other hand, the DFI technique can be combined with the phase measurement methods to perform multidimensional flow measurements in a shorter data acquisition time when the phase errors are small or corrected. © 1989 Academic Press, Inc.
Piezoelectric‐controlled tuning capacitor for surface coils
Authors: Hyde James S. , Rilling Robert J. , Jesmanowicz A. , Kneeland J. Bruce
Published: March 2007

The design of a piezoelectric‐controlled trimmer capacitor and its use as a tuning element of an MRI surface coil at 63.8 MHz are described. It is found that image quality does not depend strongly on match of the coil to the transmission line but that tuning can be a significant factor. The work is intended to lead eventually to an automatic frequency control circuit in which the capacitor serves as the active element in holding the resonant frequency of the nuclei and the resonant frequency of the coil in coincidence. © 1989 Academic Press, Inc.
Phosphodiesters in the Liver: The Effect of Field Strength on the 31P Signal
Authors: Bates Timothy E. , Williams Stephen R. , Gadian David G.
Published: March 2007

31P NMR spectra of the rat liver were recorded in vivo at 2.35 and 8.5 T. There was a large peak in the phosphodiester region of spectra obtained at 2.35 T which was much reduced at 8.5 T. The peak at 2.35 T is unlikely to be primarily from free cytosolic phosphodiesters, which would not be expected to display such a marked field dependence. © 1989 Academic Press, Inc.
Baseline deconvolution, phase correction, and signal quantification in fourier localized spectroscopic imaging
Authors: Derby K. , Hawryszko C. , Tropp J.
Published: March 2007

Lineshapes of spectra obtained through chemical‐shift imaging are often distorted due to the delay in sampling necessary for application of phase‐encoding gradients. We have developed an automated fitting procedure which simultaneously performs signal quantification, phase correction, and baseline deconvolution of such spectra. The fit is based on the maximum likelihood method and can be implemented in either the time or the frequency domain. © 1989 Academic Press, Inc.
Proton‐decoupled, overhauser‐enhanced, spatially localized carbon‐13 spectroscopy in humans
Authors: Bottomley Paul A. , Hardy Christopher J. , Roemer Peter B. , Mueller Otward M.
Published: March 2007

Spatially localized, natural abundance, carbon (13C) NMR spectroscopy has been combined with proton (1H) decoupling and nuclear Overhauser enhancement to improve I3C sensitivity up to five‐fold in the human leg, liver, and heart. Broadband‐decoupled 13C spectra were acquired in 1 s to 17 min with a conventional 1.5‐T imaging/ spectroscopy system, an auxiliary 1H decoupler, an air‐cooled dual‐coil coplanar surface probe, and both depth‐resolved surface coil spectroscopy (DRESS) and one‐dimensional phase‐encoding gradient NMR pulse sequences. The surface coil probe comprised circular and figure‐eight‐shaped coils to eliminate problems with mutual coupling of coils at high decoupling power levels applied during I3C reception. Peak decoupler RF power deposition in tissue was computed numerically from electromagnetic theory assuming a semi‐infinite plane of uniform biological conductor. Peak values at the surface were calculated at 4 to 6 W/kg in any gram of tissue for each watt of decoupler power input excluding all coil and cable losses, warning of potential local RF heating problems in these and related experiments. The average power deposition was about 9 mW/kg per watt input, which should present no systemic hazard. At 3 W input, human 13C spectra were decoupled to a depth of about 5 cm while some Overhauser enhancement was sustained up to about 3 cm depth, without ill effect. The observation of glycogen in localized natural abundance 13C spectra of heart and muscle suggests that metabolites in the citric acid cycle should be observable noninvasively using 13C‐labeled substrates. © 1989 Academic Press, Inc.
Monitoring therapeutic response of human superficial tumors using phase‐encoded spectroscopy
Authors: Majors Anthony W. , Ng Thian C. , Xue Min , Meaney Thomas F.
Published: March 2007

A one‐dimensional phase‐encoded spectroscopy sequence was implemented on a GE 1.5‐T Signa imager and the feasibility of its application to monitor the 31P metabolities of superficial tumors was demonstrated. Serial 31P spectra of I‐cm slices with adequate signal‐to‐noise ratio and insignificant T2 weighting can be obtained in 28 min. The degree of “bleeding” effect was reduced with increased phase‐encoding steps. © 1989 Academic Press, Inc.
Proton relaxation enhancement of albumin, immunoglobulin g, and fibrinogen labeled with gd‐dtpa
Authors: Paajanen Hannu , Reisto Timo , Hemmilä Ilkka , Komu Markku , Niemi Pekka , Kormano Martti
Published: March 2007

Bovine serum albumin, immunoglobulin G, and fibrinogen were labeled with Gd‐DTPA using a bifunctional chelating agent DTPA anhydride. The protein‐(Gd‐DTPA) conjugates had 1.4‐ to 2.0‐fold greater longitudinal relaxivities at 0.02 and 0.44 T than the relaxivity of plain Gd‐DTPA. The increase of longitudinal relaxivity was not directly related to the size of carrier protein. Up to 50 Gd‐DTPA chelates per protein, longitudinal relaxivity of the conjugates was proportional to the concentration of Gd and independent of the Gd/protein ratio.
Nmr and esr study of liposome delivery of mn2+ to murine liver
Authors: Bacic G. , Niesman M. R. , Magin R. L. , Swartz H. M.
Published: March 2007

The mechanism of tissue relaxation of liposome‐delivered Mn2+ as a contrast agent for magnetic resonance imaging (MRI) was examined using magnetic resonance and electron spin resonance (ESR) techniques. It is known that liposomes of the size and composition used in this study are taken up by fixed liver macrophages (Kupffer cells). It was determined that Mn2+ must be released from the liposomes in order to affect the water proton relaxation rate in the liver. As long as the Mn2+ was confined to the Kupffer cells, no substantial changes in the relaxation of the majority of the liver water were observed. Unlike other contrast agents delivered to the Kupffer cells (for example, Gd‐starch microspheres or magnetite), once the Mn2+ is delivered and released into the Kupffer cells, it can diffuse from the Kupffer cells and be rapidly taken up by the hepatocytes. This seems to be the mechanism for selective relaxation enhancement in the liver. A consequence of this behavior is that the time at which maximum contrast enhancement occurs for MRI can be varied by the choice of liposome phospholipid composition. ESR techniques were used to directly determine the state of Mn2+ and the integrity of liposomes in various stages of processing.
In vivo13c nuclear magnetic resonance investigations of choline metabolism in rabbit brain
Authors: Tunggal Budi , Hofmann Kay , Stoffel Wilhelm
Published: March 2007

The metabolism of choline in rabbit brain was studied by the noninvasive approach of in vivo 13C NMR spectroscopy. 13C‐Enriched precursors were introduced into the brain. Surgery of the head skin was avoided through controlled localization of the surface coil. For long‐term accumulation studies in brain, repeated subcutaneous injections proved to be advantageous over other forms of application. The resorption kinetics was calculated to be zero order which suggests slow delivery from the subcutaneous depots. Choline metabolism was studied by two approaches: [N‐13CH3] choline and S‐[ 13CH3 ] methionine were administered separately to adult and myelinating rabbits (Days 5 to 32), respectively, over 4 weeks. [ N‐ 13CH3] Choline and the 13CH3 group of methionine were incorporated into lecithin and sphingomyelin of brain myelin. In vivo kinetic studies of the turnover of these labeled structures were carried out. Choline and methionine are readily transported through the blood‐brain barrier and utilized by the myelinating brain for the biosynthesis of its phospholipids.
Investigations concerning the potential for using 1h nmr relaxometry or high‐resolution spectroscopy of plasma as a screening test for malignant lung disease
Authors: Schuhmacher Jochen H. , Conrad Dorothea , Manke Hans G. , Clorius John H. , Matys Edmund R. , Hauser Harald , Zuna Ivan , Maier‐Borst Wolfgang , Hull William E.
Published: March 2007

In 158 plasma samples, obtained from patients with lung carcinoma, lung metastases, and infectious or inflammatory lung diseases and from healthy controls, the NMR relaxation times T1, and T2 of water protons were measured at a resonance frequency of 20 MHz by pulsed NMR techniques and adjusted to a standardized total plasma protein concentration. For one‐third of these samples water‐suppressed 500‐MHz 1H NMR spectroscopy at 37°C was used (a) to determine the widths of the composite lipid methyl and methylene signals, and (b) to quantitate individual lipid methylene signal components that could be detected in resolution‐enhanced spectra. In addition, hematological parameters and the plasma levels of several acute phase proteins and apolipoprotein‐A were monitored. No diagnostically significant differences between lung carcinoma patients and patients with nonmalignant lung disease could be found for any of the plasma NMR parameters, nor could T1, or lipid line width data distinguish between any patient group and healthy controls. However, the mean T2, was significantly shortened by about 15% for any kind of lung disease compared to healthy controls. Similar but less significant results were found for apolipoprotein‐A levels. A linear discriminant function, calculated from the apolipoprotein‐A and T2, data, did not improve the differentiation between malignant and nonmalignant lung disease but did improve the discrimination between tumor patients and healthy controls up to a sensitivity and specificity of 80 and 96.5%, respectively. T, correlates inversely with plasma fibrinogen levels and the blood sedimentation rate and, therefore, appears to monitor a general inflammatory status of a tumor patient rather than the presence or absence of cancer. For all groups except healthy pregnant women, the lipid methylene composite signal line width correlates inversely with the fraction of mobile triglyceride present (mainly as VLDL), as estimated from resolution‐enhanced spectra.
0.3‐second flash mri of the human heart
Authors: Frahm J. , Merboldt K. D. , Bruhn H. , Gyngell M. L. , Hänicke W. , Chien D.
Published: March 2007

Flow‐suppressed FLASH MR images of the human heart have been recorded within a measuring time of 0.3 s using a 2.0‐T whole‐body research system (Siemens Magnetom) equipped with a conventional 10 mT m−1 gradient system. Subsecond imaging times have been achieved by reducing the repetition time to TR = 4.8 ms and by lowering the spatial resolution to 64 × 128 measured data points. The flip angle of the slice‐selective radiofrequency (rf) pulses was adjusted to 10o. Cardiac chambers, ventricular walls, and valves are well delineated in images from a single cardiac cycle using a field of view of 250 mm and a slice thickness of 8 mm. No motion artifacts were observed as a consequence of the short echo time of TE = 2.8 ms. Distinction between flowing blood and solid structures has been achieved by spatial presaturation of adjacent slices using two slice‐selective 90° rf pulses preceding the entire imaging sequence.
Optimization of survey protocols for mri
Authors: Mcveigh Elliot R. , Mark Henkelman R. , Bronskill Michael J.
Published: March 2007

A method for evaluating the sensitivity of MRI protocols to changes in an arbitrary number of tissue parameters over a broad range of parameter values is presented. This analysis is useful for choosing an optimal basis set of images for either a “survey” protocol or tissue segmentation algorithms. A survey protocol is required when searching for a lesion of unknown type or location. Segmentation requires unique signal signatures for tissues that may cover a broad range of tissue parameter values. Data acquisition is modeled as a mapping of a domain of tissue parameter values into a signal manifold in a signal strength space defined by the MRI protocol. The efficacy of the protocol is evaluated by investigating the characteristics of the signal manifold. A figure of merit which maximizes the probability of discriminating each point in the domain of tissue parameters from all others is developed.
The use of laboratory microcomputers to hold nmr data bases
Authors: Moore T. A. , Morris P. G.
Published: March 2007

Computer‐based data bases are essential tools for NMR spectroscopists working with complex mixtures such as tissue extracts. Algorithms are described which are easily implemented on a small laboratory microcomputer and which can be used to make, edit, and query personalized laboratory data files. The data are stored in a series of small files accessed by pointers to overcome inherent redundancy in the information. Performance times are tabulated for a BBC Model B microcomputer working in the BASIC language and using 5.25‐in. floppy discs as virtual memory.
1h nmr observation of tissue myoglobin: an indicator of cellular oxygenation in vivo
Authors: Jue T. , Anderson S.
Published: March 2007

Cellular oxygen status is a critical parameter. To measure the oxygen tension in vivo, however, demands extant techniques to surmount two experimental difficulties: invasive experimental protocols and imprecise tissue localization. NMR techniques have the potential to overcome these obstacles. Indeed we show in this study that cellular myoglobin is NMR visible and its proximal histidyl NH signal in the deoxy state can be used to monitor changes in cellular oxygenation. Coupled with recent advances in NMR signal localization, this 1H NMR strategy promises to lead directly to cellular oxygen measurement in specific tissue regions in vivo.
Why MEM does not work in MR image reconstruction
Authors: Constable R. T. , Henkelman R. M.
Published: March 2007

This paper discusses the theory and application of the Maximum Entropy Method (MEM) to the reconstruction of Magnetic Resonance (MR) images. It is shown that the MEM is inappropriate for MR image reconstruction and that the usual heuristic justification is invalid in this case. The application of the MEM in MR image reconstruction is characterized as merely one of many constrained regularization approaches. © 1990 Academic Press, Inc.
CNR enhancement in the presence of multiple interfering processes using linear filters
Authors: Brown D. G. , Lee J. N. , Blinder R. A. , Wang H. Z. , Riederer S. J. , Nolte L. W.
Published: March 2007

Given several images of the same slice, a linear filter can produce an image in which the contrast‐to‐noise ratio (CNR) between pathological and normal tissues is greater than in any of the initial images. To distinguish the pathology from more than one tissue, the filter should optimize the set of CNRs between the pathology and each of the interfering tissues. We define the optimal filter as the one which provides the largest value for the minimum CNR in the set and show how it is selected from a field of only four possibilities. The filter is demonstrated with both experimental phantom studies and clinical cases. Filter performance is compared with that of other techniques for distinguishing a desired feature from more than one interfering process. © 1990 Academic Press, Inc.
Analysis of T2 limitations and off‐resonance effects on spatial resolution and artifacts in echo‐planar imaging
Authors: Farzaneh Farhad , Riederer Stephen J. , Pelc Norbert J.
Published: March 2007

Several aspects of blipped echo‐planar imaging (EPI) are treated mathematically. An expression relating the necessary readout gradient strength and sampling time to the spatial resolution and readout duration is derived. It is shown how the net spatial resolution may be limited by the object's T2 characteristics and Bo field homogeneity, irrespective of the number of sampled points. Additionally, off‐resonance effects result in a loss of spatial resolution and image distortion to a considerably greater degree than in conventional two‐dimensional Fourier transform imaging. The extent of these effects is directly related to the time required to acquire the data matrix, and is therefore amplified when EPI is implemented on a standard commercial whole‐body system which because of limited gradient performance uses necessarily longer sampling durations. Specific hardware modifications to a standard commercial imager are considered to allow successful EPI implementation. EPI image characteristics are compared quantitatively with those of conventional methods. © 1990 Academic Press, Inc.
A13C NMR study of the application of [U‐13C] succinate for metabolic investigations in rabbit renal proximal convoluted tubular cells
Authors: Jans Arnold W. H. , Willem Rudolph
Published: March 2007

The fate of the 13C label arising from [ U‐13C ] succinate in rabbit renal proximal convoluted tubular (PCT) cells, incubated with [U‐13C]succinate, was investigated by 13C NMR spectroscopy of the perchloric acid extracts of the cell pellets. The 13C label of [U‐13C] succinate was predominantly metabolized into glutamate, glutamine, and into glucose, lactate, and alanine, which is the consequence of a carbon efflux of the label from the Krebs cycle at the stage of α‐ketoglutarate and oxaloacetate, respectively. © 1990 Academic Press, Inc.
Flow artifact reduction in MRI: A review of the roles of gradient moment nulling and spatial presaturation
Authors: Ehman Richard L. , Felmlee Joel P.
Published: March 2007

In the past, flow artifacts and inconsistent depiction of vascular anatomy have represented significant problems in clinical MRI. These difficulties are now generally well addressed by the techniques of gradient moment nulling and spatial presaturation. Gradient moment nulling (GMN) is an effective method for eliminating flow artifacts in gradient echo images, while presaturation is more applicable to the same task in spin echo acquisitions. The GMN technique also has useful applications in spin echo imaging such as combating the effects of tissue and CSF motion in long TE sequences. In contrast to presaturation, however, GMN is not suitable for suppressing artifacts due to pulsatile blood flow in spin echo images. © 1990 Academic Press, Inc.
Moving average improves the signal‐to‐noise ratio of kinetic studies in magnetic resonance spectroscopy
Authors: Seguin F. , Berthiau F. , Le Pape A. , Grivet J. P.
Published: March 2007

Moving average can be used to improve the signal‐to‐noise ratio of NMR kinetic studies. The method was tested on simulated spectra with time‐dependent intensities or peak positions. It was then applied to a series of in vivo spectra, showing the pharmacological effect of heptaminol on the intracellular pH of perfused hearts. © 1990 Academic Press, Inc.
31P NMR studies of ATP concentrations and Pi–ATP exchange in the rat kidney in Vivo: Effects of inhibiting and stimulating renal metabolism
Authors: Shine Nancy , Xuan Ai , Weiner Michael W.
Published: March 2007

Previous investigators found that cyanide (CN−) is a potent inhibitor of renal Na+ transport, while the uncoupling agent 2,4‐dinitrophenol (DNP) and fructose (both which lower ATP levels) are weak transport inhibitors. To examine the disparate effects of these substances measurements of ATP were performed, using 31P NMR, while simultaneously monitoring renal Na+ transport. Infusion of CN−, DNP, and fructose lowered whole kidney ATP levels by about the same extent (30%) while only CN− inhibited Na+ transport. This may be due to the fact that CN− has a potent action on the thick ascending limb of Henle, while fructose and DNP may have a more proximal action. Alternatively, ATP turnover may be a more important determinant of transport than ATP concentrations. Saturation transfer experiments were performed to measure Pi–ATP flux. Unilateral nephrectomy, high protein feeding, and methylprednisolone were used to stimulate metabolism and transport. The rate of Pi‐ATP flux was 20.1 μmol/min/g. However, because oxygen consumption was stimulated, the ATP/O ratio was 0.85, considerably less than the theoretical value of 3. Finally, atrial natriuretic factor, which increased Na+ transport, had no effect on Pi‐ATP flux. The results raise the possibility that the saturation transfer technique does not detect all Pi‐ATP flux, especially when renal metabolism is Stimulated. © 1990 Academic Press, Inc.
Real‐time interactive magnetic resonance imaging
Authors: Holsinger Anna E. , Wright Ronald C. , Riederer Stephen J. , Farzaneh Farhad , Grimm Roger C. , Maier Joseph K.
Published: March 2007

We describe a system for performing interactive MRI in real time. Using a TR/TE 7.1/ 3.5 ms sequence, the operator may alter a scan parameter and observe the effects of the alteration on the image within a few hundred milliseconds. With this system, we can interactively control the oblique scan slice orientation and, using inversion pulses, the image Contrast. © 1990 Academic Press, Inc.
3‐D MR angiography with scanning 2‐D images—simultaneous data acquisition of arteries and veins (SAAV)
Authors: Kim J. H. , Cho Z. H.
Published: March 2007

A 3‐D MR angiography using a scanning 2‐D planar imaging technique with the 90° flip angle steady‐state free precession sequence is presented. This method, in essence, is the rapid scanning of 2‐D images to form a 3‐D volume image. The method is then extended to the simultaneous acquisition of the separated images of the arteries and veins. Using the proposed method a set of separate angiograms of 3‐D artery and vein of a volunteer's head of imaging volume of 220 × 220 × 120 mm was obtained with total imaging time of 16.5 min. © 1990 Academic Press, Inc.
In vivo MRS measurement of deoxymyoglobin in human forearms
Authors: Wang Zhiyue , Noyszewski Elizabeth A. , Leigh John S.
Published: March 2007

In vivo MRS measurement of deoxymyoglobin (deoxy‐Mb) in human forearms was performed by observing the N‐δ proton of F8 proximal histidine. The concentration of deoxy‐Mb reflects the oxygen level in the muscle. In resting muscles, the deoxy‐Mb level was below the detection sensitivity. When ischemia was introduced by arterial occlusion, the time‐resolved NMR spectra (with 1 min resolution) was recorded to follow the change in the deoxy‐Mb signal. The result shows that deoxy‐Mb signal builds up and levels off within 6 min. This technique may be used to study bioenergetics of muscle during exercise and under pathological conditions. © 1990 Academic Press, Inc.
Measurement of ATP synthesis rates by 31P‐NMR spectroscopy in the intact myocardium in vivo
Authors: Robitaille Pierre‐Marie , Merkle Hellmut , Sako Edward , Lang Gregory , Clack Rose Marie , Bianco Richard , From Arthur H. L. , Foker John , Uǧurbil Kǎmil
Published: March 2007

The ability to measure ATP synthesis rates using 31P‐NMR spectroscopy is demonstrated in the normal, ischemic, and postischemic myocardium in vivo. Cardiopulmonary bypass (CBP) was employed to induce 20 min of global myocardial ischemia, and to conduct magnetization transfer measurements during the ischemic episode and following reperfusion and return to normal circulation. For the first few minutes of ischemia, transfer of magnetization from ATPγ to P1 was extensive and the resultant fractional reduction (ΔM/Mo) in the Pi resonance intensity reached approximately 100%. Subsequent to reperfusion and stabilization off CPB and on normal circulation, both the fractional reduction and the spin‐lattice relaxation time, T, of the Pi resonance were determined when ATP, spins were saturated. Under these conditions, the unidirectional ATP synthesis rate was 0.41 ± 0.09 (SEM, N = 4) μmol/s/g wet wt. The data suggest that in the canine myocardium in vivo, glycolytic enzymes mediate a very rapid exchange between Pi and ATP γ‐phosphates during early phases of ischemia; in the postischemic reperfused myocardium, however, the glycolytic contribution to the unidirectional Pi → ATP rate measured by NMR in vivo is relatively small compared to that observed in glucose‐perfused, postischemic rat hearts. © 1990 Academic Press, Inc.
Effect of repetitive brief episodes of cardiac ischemia on 31P magnetic resonance spectroscopy in the cat
Authors: Holt William W. , Wendland Michael F. , Derugin Nikita , Finkbeiner Walter E. , Higgins Charles B.
Published: March 2007

Angina is characterized by brief periods of ischemia followed by reperfusion; the cumulative effect of these episodes on energetics of the myocardium has not been fully elucidated. This study used an in vivo feline model for the assessment of high‐energy phosphate compounds during brief sequential periods of ischemia and reperfusion. Nine adult, open‐chest, anesthetized cats were prepared with a reversible occluder around the proximal left anterior descending artery and a 1.2‐cm‐inside diameter coil sutured on the myocardial surface in the distribution of the left anterior descending coronary artery. Levels of PCr, Pi and ATP (β‐phosphate signal) were measured by 31P MRS in a GE CSI 2‐T NMR spectrometer/imager. Measurements were obtained during a control period and during three successive occlusion‐deocclusion periods of roughly 12 and 20 min' duration, respectively. The last deocclusion period was observed for 60 min. Electron microscopy was performed in two animals. PCr declined (P < 0.01) rapidly following each occlusion to 51 ± 5.2% (occlusion 1), 53 ± 5.8% (occlusion 2), and 48 ± 5.7% (occlusion 3) of the control value by 6 min. Pi rose (P < 0.01) with the three sequential occlusions to 253 ± 46, 288 ± 57, and 277 ± 46%, respectively. PCr and Pi returned to baseline promptly with reperfusion, while ATP showed a gradual decline throughout the experiment, decreasing to 77 ± 7.2% of control at the end of the last reperfusion (P < 0.05). Although PCr returned to baseline during reperfusion, ATP did not, suggesting a reduction in the nucleotide pool. These findings indicate that the repeated episodes of ischemia, which are insufficient to produce necrosis, can have an effect on myocardial high‐energy phosphate metabolism as evidenced by mild depletion of ATP. © 1990 Academic Press, Inc.
Three‐dimensional magnetization‐prepared rapid gradient‐echo imaging (3D MP RAGE)
Authors: Mugler John P. , Brookeman James R.
Published: March 2007

A new three‐dimensional imaging technique which is applicable for 3D MR imaging throughout the body is introduced. In our preliminary investigations we have acquired high‐quality 3D image sets of the abdomen showing minimal respiratory artifacts in just over 7 min (voxel size 2.7 × 2.7 × 2.7 mm3), and 3D image sets of the head showing excellent gray/white contrast in less than 6 min (voxel size 1.0 × 2.0 × 1.4 mm3). © 1990 Academic Press, Inc.
High‐resolution NMR spectroscopy of cerebral white matter in multiple sclerosis
Authors: Sappey‐Marinier Dominique
Published: March 2007

Multiple sclerosis (MS) lesions have been shown by conventional methods to have major alterations in water and myelin lipid contents. To characterize these abnormalities more efficiently, NMR spectroscopy was used to evaluate water content by measuring relaxation times at 0.5 and 2.0 T. Subsequently, cholesterol content was obtained by using 1H NMR spectroscopy, while 31P NMR spectroscopy allowed measurement of the four main phospholipids and the inorganic phosphate concentrations in normal and pathological cerebral white matter samples. The relaxation times were significantly prolonged in MS lesions relative to normal white matter. Measured in different sample types, T 1 and T2 times increased with water content. Moreover, the T2 of normal‐appearing white matter was considerably lengthened. Analysis of white matter lipid composition using this method gave accurate values, which showed a significant decrease in phospholipids and cholesterol content in MS samples. © 1990 Academic Press, Inc.
NMR imaging in the earth's magnetic field
Authors: Stepišnik J. , Eržen V. , Kos M.
Published: March 2007

The most important and very expensive part of a magnetic resonance imaging set‐up is the magnet, which is capable of generating a constant and highly homogeneous magnetic field. Here a new MR imaging technique without the magnet is introduced. This technique uses the earth's magnetic field instead of a magnetic field created by a magnet. This new method has not yet reached the stage of medical application, but the first images obtained by MRIE (magnetic resonance imaging in the earth's field) show that the resolution is close to that expected based on sensitivity estimations. © 1990 Academic Press, Inc.
The effect of cardiopulmonary bypass on brain and heart metabolism: A 31P NMR study
Authors: Swain Julie A. , Robbins Robert C. , Balaban Robert S. , McDonald Thomas J. , Schneider Benjamin , Groom Robert C.
Published: March 2007

The development of a large animal preparation using 31P nuclear magnetic resonance (NMR) spectroscopy for the study of cerebral and myocardial metabolism during cardiopulmonary bypass (CPB) is reported. The effect of normothermic CPB on myocardial and cerebral metabolism was evaluated. Adolescent sheep were used which have low levels of 2,3 ‐diphosphoglycerate, a compound which can interfere with the calculation ofintra‐cellular pH and inorganic phosphate content. CPB was performed using standard procedures modified for the presence of a high magnetic field and limited access to the animal. High quality 31P NMR data were obtained from the brains and hearts of these animals before and during normothermic CPB. These results demonstrate that the initiation of normothermic CPB does not change high energy phosphate levels or intracellular pH. In particular, the decreased myocardial oxygen demand associated with CPB is not associated with improvement in the levels of adenosine triphosphate or phosphocreatine. The measurements of energy metabolism and intracellular pH of the brain and heart during CPB were possible within the constraints of the NMR experiment without compromising the CPB procedure. Combining NMR and CPB techniques permits future studies of cerebral and myocardial metabolism, especially those relating to ischemia. © 1990 Academic Press, Inc.
The role of membrane water permeability in characterization of pathologically altered human stomach tissues: NMR studies
Authors: Srejić Radivoje , Popov Danica V. , Boričić Ivan , Žuvela Marinki
Published: March 2007

Comparative NMR studies of normal and pathologically altered human stomach tissues were performed on the basis of proton T1 relaxation time measurements in the presence of high external concentrations of relaxation (contrast) agents manganese ethylenediaminetetraacetic acid (Mn‐EDTA) and gadolinium diethylenetriaminepentaacetic acid (Gd‐DTPA). Diffusion permeability of the cell membrane to water, Pd, was determined by measuring the longest proton T1 component sensitive to the exchange of water molecules through the cell membrane. Pathologically altered tissues showed substantially higher (2 to 10 times) average cell membrane permeabilities to water. © 1990 Academic Press, Inc.
1H MR imaging of anatomical compartments within the finger flexor muscles of the human forearm
Authors: Jeneson J. A. L. , Taylor J. S. , Vigneron D. B. , Willard T. S. , Carvajal L. , Nelson S. J. , Murphy‐Boesch J. , Brown T. R.
Published: March 2007

Fast T2‐weighted 1H MRI following exercise allows investigation of the location of muscle fiber activity within skeletal muscle. Using this method, we have demonstrated that the finger flexor muscles of the human forearm consist of anatomical compartments, located at various depths, which are involved individually in flexion of the index, middle, or ring and little fingers. The results of this study indicate that the exercise protocol in 31P MRS studies of the finger flexor muscles of the human forearm, in which a small surface coil is used for detection, should be carefully reviewed. © 1990 Academic Press, Inc.
Double EPI sequence with 180° RF pulses
Authors: Hennel F. , Jasinski A. , Tomanek B.
Published: March 2007

Rapid imaging can be performed in the magnetic field of low homogeneity using 180° RF pulses instead of gradient reversals to form a series of differently phase‐encoded echoes. A modified version of π‐pulsed EPI which samples the data in two complementary shots was designed. Its advantage for objects of short T2 is illustrated by phantom images. © 1990 Academic Press, Inc.
The relation of low frequency restoration methods to the gerchberg‐papoulis algorithm
Authors: Yan Hong , Mao Jintong
Published: March 2007

In magnetic resonance imaging, low frequency components can be allowed to saturate the analog to digital converter to reduce the quantization noise. These components can be estimated using least squares error estimation based low frequency restoration methods or the iterative Gerchberg‐Papoulis algorithm. In this paper, we show the relationship between the closed form estimation methods and the iterative algorithm, propose a method for improving the speed of iteration, and discuss the advantages and disadvantages of two types Of methods. © 1990 Academic Press, Inc.
Viability testing of transplantation donor liver by 1H NMR relaxometry
Authors: Holzmueller P. , Reckendorfer H. , Burgmann H. , Moser E.
Published: March 2007

We present preliminary results of water proton relaxation time measurements on perfused, cold‐stored rat livers as a basis of a simple method for testing the viability of human donor livers in liver transplantation surgery. Proton T1 and T2 data correlated strongly (p < 0.01) with bile flow measurements, indicating that relaxation times reflect organ viability and therefore might be used for rapid testing of donor livers shortly before transplantation. © 1990 Academic Press, Inc.
Flow velocity quantitation using inversion tagging
Authors: Salonerand David , Anderson Charles M.
Published: March 2007

A method for quantitating flow velocities is presented. The technique tags multiple boli of magnetization in transit across a thick selection slab using of inversion pulses. Results in phantoms andin vivodemonstrate that the method is robust and can provide velocity determinations in tortuous vessels. © 1990 Academic Press, Inc.