bluuebunny/crossref_metadata_2025 huggingface dataset:
Variations in slice shape and absorption as artifacts in the determination of tissue parameters in NMR imaging
Authors: Young I. R. , Bryant D. J. , Payne J. A.
Published: March 2007

Existing models for the contrast between one tissue and another in NMR imaging have shown that there are regions of ambiguity particularly in spin‐echo sequences. This paper indicates that there are further problems due to variations in slice formation with tissue parameters, and that it is necessary to be very conservative in assessing the magnitude of T1 in any imaging system. The change in shape affects the appearance of images due, in essence, to adjustments in partial volume effects, with some of the contributions to the signal from lesions with long T1 coming from different regions to those for normal tissue. A simple model for a slice is used because the actual form in a real imaging situation is the result of a number of factors which are usually not accurately enough known.
Vascular Occlusions Detected by Magnetic Resonance Imaging
Authors: Choyke Peter L. , Kressel Herbert Y. , Axel Leon , Gefter Warren , Thickman David , Arger Peter H. , Meranze Steven G.
Published: March 2007

Early experience with magnetic resonance imaging (MRI) indicates that it is well suited as a noninvasive vascular imaging modality. Blood flow at physiologic velocities results in a low signal within the vessel lumen and this property allows the separation of flowing blood from surrounding soft tissues. While flow effects, aneurysms, and mural lesions have been emphasized in the literature, vascular occlusions have received less attention. We evaluated 21 patients with documented venous or arterial occlusions on a 0.12‐T developmental resistive unit. Venous occlusions caused by thrombus generally appeared as focal regions of increased signal. In 3 of 10 cases the venous thrombus itself could not be identified but the absence of a low‐signal lumen in a normal location confirmed the impression of thrombus. In 2 of 17 venous occlusions a rim of low signal was noted around the thrombus. Venous collaterals were commonly seen. Tumor thrombus tended to have signal characteristics similar to the main bulk of the tumor from which it arose. There were four arterial occlusions including two cases of emboli, one arteriosclerotic occlusion, and one case of tumor invasion. Vascular calcifications, clearly evident on plain radiographs, were not seen on MRI. MIR appears to be a potentially useful nonivasive means of detecting vascular occlusions.© 1985 Academic Press,Inc.
Phosphorus‐31 nuclear magnetic resonance measurements of 2, 3‐DPG degradation in human adult and cord blood erythrocytes
Authors: Zwerling Hayward K. , Diamond Joel N. , Levy George C. , Clark David A.
Published: March 2007

We have measured the percent change in 2, 3‐diphosphoglycerate (DPG) concentration in cord blood erythrocytes and adult erythrocytes during incubation at 37°C using 31P nuclear magnetic resonance spectroscopy. DPG concentrations remained unchanged during the first 4.0 ± 0.9 h (mean + SD) for cord blood erythrocytes and 6.0 ± 1.0 h for adult blood erythrocytes. After this plateau phase, cord blood and adult erythrocyte DPG concentrations decreased at a rate of 11.6 ± 0.4 and 11.4 ± 0.5% of the baseline DPG concentration per hour, respectively. There was no statistically significant difference in the percent rate of DPG degradation when comparing cord blood erythrocytes to adult erythrocytes during either the plateau phase or the decay phase. Starting at the onset of the decay phase, the neonate 3‐P DPG resonance shifted downfield at a rate of 0.03 ± 0.006 ppm per hour; the adult 3‐P DPG resonance shifted downfield at a rate of 0.02 ± 0.003 ppm per hour. © 1986 Academic Press, Inc.
Instrumentation for rapid MR image synthesis
Authors: Lee James N. , Riederer Stephen J. , Bobman Stuart A. , Farzaneh Farhad , Wang Henry Z.
Published: March 2007

MR image synthesis has previously been developed as a means of retrospectively optimizing contrast of arbitrary materials in MR images. The first step of this process is to form computed N(H), T1, and T2 images from source images acquired at a variety of echo delay and repetion times. The second step is to take these computed images, along with operatorselected timing parameters, and mathematically generate a synthesized image. Computation is carried out pixel by pixel according to the equation describing the chosen pulse sequence. This paper presents a study of design considerations for a digital image processor capable of rapidly performing the second step, the actual synthesis. In this work the computations inherent to image synthesis are identified, and the feasibility of performing them in highspeed hardware examined. An analysis of the imprecision due to bit‐limited calculations shows that an error bound of 0.4% is possible with a 16‐bit processor design. A method is described which uses a commercially available image processor by which images can be synthesized according to any of the standard pulse sequences in less than 600 ms. © 1986 Academic Press, Inc.
Differentiation of parenchymal lung disorders with in vitro proton nuclear magnetic resonance
Authors: Vinitski Simon , Pearson Michael G. , Karlik Stephen J. , Morgan W. Keith C. , Carey Lewis S. , Perkins Garth , Goto Tohihiro , Befus Dean
Published: March 2007

We investigated in vitro NMR properties of bleomycin‐induced alveolitis and pulmonary fibrosis in 18 Lewis rats (6 controls). When alveolitis or fibrosis had developed, animal lungs were excised and examined histologically and gravimetrically and their T1 and T2 were determined by a NMR spectrometre at 10.7 MHz and 37°C. Clinical diagnosis was confirmed histologically in each case. The NMR signal intensities were siginificantly elevaed in both disease states (P < 0.001). Both T1 and T2 values of alveolitic lungs were about the same as in controls, but were significantly decreased in fibrotic lungs (P < 0.01). Changes in T1 and T2 correlated well (P < 0.001) with changes in water content of discased lungs. © 1986 Academic Press, Inc.
NMR studies of combined lanthanide shift and relaxation agents for differential characterization of 23Na in a two‐compartment model system
Authors: Brown M. A. , Stenzel T. T. , Ribeiro A. A. , Drayer B. P. , Spicer L. D.
Published: March 2007

Spin relaxation and chemical shifts by lanthanide chelate complexes are used to distinguish 23Na singnals in a simulated two‐compartment model. Both effects are significant in EDTA, DTPA, and TPP complexes of Gd and in the TPP complex of Dy. The simultaneous measurement of these properties is illustrated and represents a promising method for monitoring sodium concentrations and fluxes including fast transport components. © 1986 Academic Press, Inc.
A new method for flow velocity measurement: Frequency encoded NMR
Authors: Caprihan A. , Davis J. G. , Altobelli S. A. , Fukushima Eiichi
Published: March 2007

We demonstrate a new rapid NMR method to measure the average velocity and the velocity distribution of a flowing fluid. We use a truncated Carr‐Purcel‐Meiboom‐Gill pulse sequence, π/2‐T‐π‐2T‐π‐T‐echo, in the presence of a static magnetic field gradient. The π/2 pulse is selective and tags a narrow slice of nuclei. The second echo from the tagged nuclei is Fourier transformed after the nuclei have evolved for a time 4T to give the velocity distribution modified by the initial slice selection profile. In this way, average velocities up to 54 cm/s were measured for water flowing in a plastic tube with either a plug or a developed velocity distribution. Each measurement required about 20 ms but this could be reduced with larger field gradients. Thus, this method is fast enough to apply to such problems as measuring pulsatile flow in arteries. © 1986 Academic Press, Inc.
Contrast‐enhanced MRI of periarticular soft‐tissue changes in experimental arthritis of the rat
Authors: Terrier François , Revel Didier , Reinhold Charles E. , Levine Jon , Grodd Wolfgang , Genant Harry K. , Brasch Robert C.
Published: March 2007

This study was to determine if manipulation of magnetic resonance signal intensity by means of an intravenously injected paramagnetic contrast agent is useful for the detection and characterization of periarticular inflammation. Arthritis was induced in 20 rats by means of intradermal injection of Freund's complete adjuvant. MR imaging was performed with a resistive magnet operating at 0.35 T. A double spin‐echo technique with TE's of 28 and 56 ms and TR's of 0.5 and 2.0 s was used. The hindpaws of the adjuvant‐injected rats were imaged on Day 8, Day 11, or Day 15 following injection of the adjuvant. The images were obtained in the transverse plane before and after intravenous injection of gadolinium‐DTPA (0.2 mmol/kg). Because of their long T2 relaxation time, inflammatory lesions were characterized by high MR signal intensity on precontrast images obtained with long TR and long TE (T2‐weighted images). On the other hand, because of their long T1 relaxation time, the inflammatory lesions were of relatively low intensity and not easily recognized on precontrast images obtained with short TR and short TE (T1‐weighted images). Postcontrast T1‐weighted images were also sensitive in detecting periarticular inflammation as a result of T1 shortening by the gadolinium‐DTPA. However, in our particular model, the data did not indicate any greater MR sensitivity for detecting arthritis by means of gadolinium‐DTPA enhancement. © 1986 Academic Press, Inc.
Effect of induced field inhomogeneity on transverse proton NMR relaxation in tissue water and model systems
Authors: Kurland Robert J. , Ngo Frank Q. H.
Published: March 2007

The effect of induced field inhomogeneity (IFI) on transverse NMR relaxation of water protons in tissue has been investigated by examining the field dependence of the effective transverse relaxation rates (1/T2 eff) for in vitro canine brain tissue samples. At fields of 0.47, 2.35, 7.05 T (corresponding to 20, 100, and 300 MHz, respectively) the transverse relaxation rates for both white and gray matter samples follow a field dependence of the form 1/T2 eff = C0 + C1 B0, where B0 is the applied field. The linearly dependent term, C1 B0, which reflects the IFI contribution, does not contribute much (i. e., less than 20%) at fields less than 2.0 T. However, at greater field strengths the contribution is appreciable, e. g., greater than 60% at 7.0 T. Results from model systems of glass beads are also reported to illustrate IFI effects. For both the model systems and canine brain tissue samples, the effects of restricted diffusion are qualitatively evident in Hahn spin‐echo experiments. © 1986 Academic Press, Inc.
31P NMR detection of mobile dog brain phospholipids
Authors: Cerdan S. , Subramanian V. Harihara , Hilberman M. , Cone J. , Egan J. , Chance B. , Williamson J. R.
Published: March 2007

The in vivo dog brain 31P NMR spectrum has a large peak in the phosphodiester region accounting for more than 35% of the total observable phosphorus metabolites. It is possible to reduce the intensity of this peak by off‐resonance saturation. To characterize the nature of this peak, extracts of dog brain frozen in situ were analyzed by high resolution 31P NMR. ATP, phosphocreatine, inorganic phosphate, and phosphomonoesters were recovered in appropriate amounts in the methanol: HCI extract. However, acid soluble phosphodiesters accounted for only 8% of the observable phosphorus. More NMR observable phosphodiesters were selectively recovered following CHCI3:methanol extraction of phospholipids. These results suggest that the in vivo phosphodiester resonance has substantial contributions from a fraction of mobile brain phospholipids. © 1986 Academic Press, Inc.
Optimum acquisition times of two spin echoes for MR image synthesis
Authors: Lee James N. , Riederer Stephen J.
Published: March 2007

Spin‐echo images can be synthesized at arbitrary values of echo time TEs if two images are acquired at the same repetition time and two different echo times TEI and TE2. Depending on the value of TEs, the noise in the synthetic images can either be greater or less than the acquisition noise. This note shows that if the time between the acquired echoes TE2‐TE1 is equal to T2, the noise level in the synthetic images is no larger than the acquisition noise for TEs ⩾ TE1. This is the lowest possible noise bound for two‐echo acquisition. Also, the noise bound for images synthesized with O ⩽ TEs ⩽ TE1 is minimized by making TE1 as short as possible. © 1986 Academic Press, Inc.
Reproducibility of relaxation and spin‐density parameters in phantoms and the human brain measured by MR imaging at 1.5T
Authors: Breger Robert K. , Wehrli Felix W. , Charles H. Cecil , MacFall James R. , Haughton Victor M.
Published: March 2007

The reproducibility of T1, T2, and proton density, measured in phantoms and the human brain was evaluted by proton imaging techniques. The sequence used to derive T1 and density values was a multiple‐saturation recovery which consists of four pairs of 90° pules, followed by a 180° phase reversal pulse, generting four T2‐weighted images. The data were analyzed by fitting the pixel intensities to the respective equations by means of nonlinear multi‐parameter least‐squares analysis. Short‐term reproductibility between four consecutive scans was evaluted to b 1–40% depending on location with a covering the entire span of physiological T1 and T2 values. A second phantom containing a series of identiical samples served to study the depeendence of the apparment T1 and T2 on position, both radially and axially, with respect to magnet isocneter. Reproducibility across the field of view was found to be better than 7% (T1 and T2). This phantom was further used to evaluate effects of long‐term reproductibility, which at each location varied from 5–14% (T1) and 2–10% (T2). Finally, interinstrument reprducibilty, tested by means of the same protcol on three different insturments, all operating at the same magnetic field and using largely indentical hardware for each location, was found to be 1–14% (T1) and 2–10% (T2). The positional dependence of the apparent relaxation times appears to be systematic and may be due to variations in the effective field, caused by magnet and rf inhomogeneity. Finally, brain tissue relaxation and spin‐density data were determined using the same protocol in 37 scans performed on 27 normal volunteers. The tissues analyzed were putamen, thalamus, caudate nucleus, centrum semiovale, internal capsule, and corpus callosum. Excellent accordance was further obtained between left and right hemispheres. © 1986 Academic Press, Inc.
Currents and fields of thin conductors in rf saddle coils
Authors: Carlson J. W.
Published: March 2007

The current distribution on thin conductors and rf field homogeneity for rf coils is described theoretically. After a pedagogical introduction to the techniques and an exact solution for the current or an isolated strip conductor, this article describes current distribution and field uniformity for a variety of conventional and quadrature rf coil designs. © 1986 Academic Press, Inc.
Relaxation of water protons in the intra‐ and extracellular regions of blood containing Gd(DTPA)
Authors: Koenig Seymour H. , Spiller Marga , Brown Rodney D. , Wolf Gerald L.
Published: March 2007

The magnetic field dependence of the longitudinal relaxation rates 1/T1 (NMRD profiles) of blood and plasma from rabbits before and after injection of Gd(DTPA) are reported as a function of magnetic field strength from 0.01 to 50 MHz. Over 100 values along the time‐dependent magnetization were recorded for each 1/T1 and analyzed for multiple exponentials. From these data, which indicate a single exponential, from the measured Gd content of each sample, and the NMRD profiles, we show that Gd is in the extracellular space only and is present as rotationally mobile Gd(DTPA), uncomplexed with protein or blood cells; and that the water protons exchange rapidly between the intra‐ and extracellular regions. © 1986 Academic Press, Inc.
Surface‐coil T1 images
Authors: Hardy C. J. , Edelstein W. A. , Mueller O. M.
Published: March 2007

A method for producing calculated T1 images with high signal‐to‐noise ratio and good spatial resolution using surface coils is presented. Separate transmit and receive rf coils with electronic decoupling are employed to insure uniform B1 excitation. The sensitivity profile of the receiver coil is normalized out of the image by the T1 calculation. T1 values determined by this method show close agreement with previously reported values. © 1986 Academic Press, Inc.
An evaluation of the effect of fasting on the exercise‐induced changes in pH and Pi/PCr from skeletal muscle
Authors: Lunt J. A. , Allen P. S. , Brauer M. , Swinamer D. , Treiber E. O. , Belcastro A. , Eccles R. , King E. G.
Published: March 2007

The changes in the response of skeletal muscle to maximal dynamic exercise were investigated in going from a fasted state to a refed state by means of 31P NMR spectroscopy. It was found that in the fasted state, exercise‐induced changes in Pi/PCr and in pH were both inhibited, in comparison with those in the refed state. © 1986 Academic Press, Inc.
Effects of calcium antagonists on high‐energy phosphates in ischemic rat brain measured by 31P NMR spectroscopy
Authors: Sauter André , Rudin Markus
Published: March 2007

The effects of various calcium antagonists on the ATP, PCr, and Pi levels as well as intracellular pH in normal and ischemic rat brain were examined by 31P NMR spectroscopy using a surface coil. None of the calcium antagonists tested showed any effect in the nonischemic rat brain. However, when global ischemia was induced by cardiac arrest, the ensuring rapid decrease of ATP and PCr and concomitant increase of pi were significantly retarded by dihydropyridine calcium antagonists, but not by verapamil. The fall in pH caused by ischemia was not affected by either drug. Barbiturates showed effects similar to calcium antagonists, whereas calcium agonists showed the opposite. These results suggest that dihydropyridine calcium antagonists, similar to barbiturates, decrease the high‐energy phosphate consumption of the brain, which might be beneficial in instances where their production is severely hampered, e.g., during ischemia. © 1987 Academic Press, Inc.
Localized magnetic resonance imaging with oscillating gradients
Authors: Feig Ephraim
Published: March 2007

Hinshaw's sensitive‐point method and Macovski's post‐filtering localization techniques are analyzed under very general imaging conditions. It is shown that one can obtain an expression for the FID signal induced by all resonating particles at any particular point in the imaged object. Contributors to the signal may have different relaxation behaviors, spin rates, and velocity components. In fact, in the case of flows, different nuclei contribute to the signal at different times during the observation. Localization enables us to impose local assumptions on our model rather than global ones, as is usually done in MRI. Applications to imaging slow and fast flows and in vivo spectroscopy are discussed. © 1987 Academic Press, Inc.
Small animal imaging with a clinical magnetic resonance imager
Authors: Henkelman R. Mark , van Heteren John G. , Bronskill Michael J.
Published: March 2007

Any clinical whole‐body MR imager can be adapted for experimental small animal imaging. The design of an if receiver coil and an efficient magnified imaging technique are presented. Application of this small animal imaging technique is illustrated using a study of paramagnetic contrast enhancement of a tumor in the mouse. © 1987 Academic Press, Inc.
Flow velocity measurement with ac gradients
Authors: Walton J. H. , Conradi Mark S.
Published: March 2007

Two NMR experiments are described that use ac field gradients to measure flow velocities. Both experiments perform no spacial localization; instead, fluid velocity is converted to a resonance frequency shift. Thus, by Fourier transformation of a single FID or echo train the distribution of velocities is available. The first experiment uses only one of pulse but requires a homogeneous static field. The second experiment uses the CPMG multiple‐pulse sequence to refocus the effects of field inhomogeneity and chemical shifts. Results are shown for both experiments using a simple flowing phantom. Applications of the techniques to time‐resolved blood flow measurement are discussed. © 1987 Academic Press, Inc.
Simplified mathematical description of longitudinal recovery in multiple‐echo sequences
Authors: Conturo Thomas E. , Beth Albert H. , Arenstorf Richard F. , Price Ronald R.
Published: March 2007

The intensity of multiple echoes separated by a time 2τ has been modeled using the closed form of a finite geometric series. This eliminates long exponential series, introduces the number of echoes as an independent parameter, and corrects for the net T1 relaxation during the echo train. Other sequences having echo trains can be modeled similarly. © 1987 Academic Press, Inc.
Spin‐echo proton NMR spectroscopy of urine samples. Water suppression via a urea‐Dependent T2 relaxation process
Authors: Connor S. , Everett J. , Nicholson J. K.
Published: March 2007

Spin‐echo methods have been used to effect solvent suppression during the collection of 400 and 500 MHz 1H NMR spectra of urine samples containing urea in the concentration range 0.7–1.2 M. There was a marked trough of water T values in the pH* range 2.6 to 4.1, due to acidcatalyzed proton exchange between urea and the solvent water. Minimum values of T (9 ms at 500 MHz) of water were obtained at about pH* 3.2 in urine samples containing 1.2 M urea. However, good solvent suppression factors were obtained with endogenous urea concentrations of only 0.7 M. There was a strong field dependence on the water, T2 over the pH range 2 to 4. Attenuation of the water signal was estimated to be at least an order of magnitude greater at 500 MHz rather than at 400 MHz. Using the Cam‐Purcell‐Meiboom‐Gill spin‐echo pulse sequence, water signals broader than 13 Hz were attenuated by factors of > 103, and factors of > 104 were possible with water linewidths greater than 20 Hz, thus allowing the signals from metabolites in the sample to be efficiently digitized. This approach allowed metabolite signals at or near the water resonance to be observed without serious distortion of their intensities. The utility of this approach to solvent suppression in real systems is illustrated by observation of paracetamol and benzyl penicillin metabolites in human urine samples. © 1987 Academic Press, Inc.
The fate of inorganic phosphate and pH in regional myocardial ischemia and infarction: A noninvasive 31P NMR study
Authors: Bottomley P. A. , Smith L. S. , Brazzamano S. , Hedlund L. W. , Redington R. W. , Herfkens R. J.
Published: March 2007

To determine the characteristic appearance of phosphorus (31P) nuclear magnetic resonance spectra in acute and chronic myocardial infarction in situ. cardiac‐gated depth‐resolved surface coil spectroscopy (DRESS) at 1.5 T was used to monitor 31P NMR spectra from localized volumes in the left anterior canine myocardium for up to 5 days following permanent occlusion of the left anterior descending coronary artery. Coronary occlusion initially produced regional ischemia manifested as significant reductions in the phosphocreatine (PCr) to inorganic phosphate (Pi) ratios and intracellular pH (P < 0.05, Student's t test) in endocardially displaced spectra acquired in periods as short as 50 to 150 s postocclusion. Spectra acquired subsequently revealed either (i) restoration of near‐normal phosphate metabolism sometime between 10 and about 50 min postocclusion or (ii) advancing ischemic phosphate metabolism at about an hour postocclusion, and/or (iii) maintenance of depressed PCI/P1 ratios for up to 5 days postocclusion with a return of the apparent pH to near normal values between 6 and 15 h postocclusion. Postmortem examination of animals exhibiting the first type of behavior revealed the existence of coronary collateral vessels. The last type of behavior indicates that P1 remains substantially localized in damaged myocardium for days following infarction. The location and size of infarctions were determined postmortem by staining excised hearts. The smallest infarctions detected by 31P DRESS weighed 4.9 and 7.5 g. The most acidic pH measured in vivo was 5.9 ± 0.2. Infarctions aged 1/2 day to 5 days were characterized by elevated but broad P1 resonances at 5.1 ± 0.2 ppm relative to PCr and significantly depressed PCr/P1 ratios (P < 0.002, Student's t test) relative to preocclusion values. Contamination of P1 resonances by phosphomonoester (PM) components is a significant problem for preocclusion P1 and pH measurements. These results should be applicable to the detection and identification of human myocardial infarction using 31P NMR and DRESS. © 1987 Academic Press, Inc.
Noise reduction in wide‐bore magnets using a patient cage
Authors: Ceckler Toni L. , Bryant Robert G. , Hornak Joseph P.
Published: March 2007

Significant rf noise reduction is demonstrated by enclosing the patient in a conducting cage grounded to the magnet bore in a 22‐cm‐bore spectrometer system capable of examining magnetic images and spectroscopy of human limbs. This method of noise reduction was found to be reliable, simple, and efficient for dealing with ambient rf noise in an unshielded room. © 1987 Academic Press, Inc.
Spectral resolution in clinical magnetic resonance spectroscopy
Authors: Cox I. Jane , Bryant David J. , Ross Brian D. , Young Ian R. , Gadian David G. , Bydder Graeme M. , Williams Stephen R. , Busza Albert L. , Bates Timothy E.
Published: March 2007

We observe linewidths of 0.1–0.4 ppm in 31P spectra of human muscle, liver, and brain. T2 measurements of muscle phosphocreatine, together with previous brain studies, indicate that further improvements in linewidth to 0.02–0.05 ppm might often be achieved, but in same lesions magnetic susceptibility variations may limit spectral resolution. © 1987 Academic Press, Inc.
General solution to the NMR excitation problem for noninteracting spins
Authors: Ngo J. Thomas , Morris Peter G.
Published: March 2007

The design of an NMR excitation scheme, whether selective or nonselective, is essentially the simultaneous inversion of an array of Bloch equations driven by magnetic fields which differ according to well‐defined constraints. We find that if relaxation effects are negligible, nearly exact inversion of the Bloch equations is straightforward when performed in a special time‐varying frame of reference. Repeated inversions of the Bloch equations for small perturbations provide the basis for arbitrarily large, optimal adjustments of the magnetization response to an applied time‐varying magnetic field. Choice of the target response to be sought at each iteration is not trivial if overall adjustments of more than one‐half rotation are required. We present the analysis both formally and in geometric terms and show how it leads to a general algorithm for the optimization of NMR excitation schemes. The unprecedented efficiency of the algorithm and its ability to generate novel pulses from distant starting approximations are demonstrated in the optimization of slice‐selective π/2 pulses for inversion and refocusing, and a prefocused slice‐selective π/2 pulse. Other applications are discussed, including use of the algorithm to compensate for instrumental imperfections such as radiofrequency inhomogeneity. © 1987 Academic Press, Inc.
Real‐time movie imaging from a single cardiac cycle by NMR
Authors: Chapman B. , Turner R. , Ordidge R. J. , Doyle M. , Cawley M. , Coxon R. , Glover P. , Mansfield P.
Published: March 2007

Using a 1‐m‐bore super conductive magnet at 0.1 T, whole‐body transverse images through adult humans have been obtained at repetition times of 57 ms. The techniques used were minor variations of echo‐planar imaging (EPI) employing large pulsed gradients to provide complete coverage of the plane in phase space, and low‐angle RF excitation sequences allowing rapid repetition of the experiment. In addition active magnetic screening of the gradient coils was implemented to protect the surrounding magnet from the eddy currents induced by the necessarily fast switching of the large gradient fields. © 1987 Academic Press, Inc.
The Development of a pH‐sensitive contrast agent for NMR 1H imaging
Authors: Helpern Joseph A. , Curtis Jeff C. , Hearshen David , Smith Jmichael B. , Welch Kenneth M. A.
Published: March 2007

Fe(III)meso‐tetra(4‐sulfonatophenyl)porphine (Fe‐TPPS,) has been investigated as a potential pH‐sensitive nuclear magnetic resonance (NMR) proton image contrast agent. Relaxation rates (1/T1, and 1/T2) of water protons were measured as a function of pH and concentration of Fe‐TPPS, in phosphate‐buffered isotonic saline. Transverse relaxation rates (1/T2) did not change appreciably with pH above 6.0. Longitudinal relaxation rates (1/T1) increased significantly between pH 7.75 and 5.75. This effect was more pronounced with the increasing concentration of Fe‐TPPS, from 0.1 to 1. 5 mM and is attributed to a pH‐dependent equilibrium between the high‐spin (S = 5/2) Fe–TPPS4 monomer at low pH and the antiferromagnetically coupled μ‐oxodimer O–(FeTPPS4)2 at high pH. The efficacy of this pH‐dependent contrast agent is demonstrated in vitro. © 1987 Academic Press, Inc.
Measurement of lactate accumulation by in Vivo proton NMR spectroscopy during global cerebral ischemia in rats
Authors: Richards T. L. , Keniry M. A. , Weinstein P. R. , Pereira B. M. , Andrews B. T. , Murphy E. J. , James T. L.
Published: March 2007

In vivo 1H NMR spectral editing techniques were used to monitor cerebral lactate production during remotely controlled temporary forebrain ischemia in rats. The lactate/N‐acetylaspartate (NAA) ratio correlated with survival after ischemia and subsequent reperfusion. The lactate/NAA ratio that predicted death after ischemia in rats was estimated to be approximately 1.3. © 1987 Academic Press, Inc.
Fast three‐dimensional imaging of cerebrospinal fluid
Authors: Hennig J. , Friedburg H. , Ott D.
Published: March 2007

The RARE method is based on the principle of echo imaging to generate images with high T2 contrast. Since RARE is a fast imaging method, it can be used to acquire a high‐resolution three‐dimensional data set in less than 15 min. Thin slices from such a three‐dimensional data set provide detailed information about the ventricular system. © 1987 Academic Press, Inc.
RLSQ: T1, T2, and ρ calculations, combining ratios and least squares
Authors: in den Kleef J. J. E. , Cuppen J. J. M.
Published: March 2007

A method is proposed for calculating images of spin density p and relaxation times T1 T2 from MR imaging sequencies with the following characteristics:

it avoids nonlinear iterative techniques and is consequently sufficiently fast to allow calculation ofp, T1 and T2 on a pixel by pixel basis routinely;

it uses all available data simultaneously in an approximately optimal fashion.

The method is applied to the combined SE + IR sequence but can be used for other acquisition Schemes as Well. © Academic Press, Inc.
Triple nuclear NMR studies of cerebral metabolism during generalized seizure
Authors: Schnall M. D. , Yoshizaki K. , Chance B. , Leigh J. S.
Published: March 2007

Noninvasive NMR spectroscopy of 1H, 31P, and 23Na is performed simultaneously to study brain metabolism during grand mal seizures. Decreases in PCr and increases in lactate associated with seizure as well as an intracellular shift of the Na+ ion pool are demonstrated. A close correlation between the phosphate potential and the intensity of the seizure, as well as the intra/extracellular ionic gradient, is shown. © 1988 Academic Press, Inc.
An analysis of fast imaging sequences with steady‐state transverse magnetization refocusing
Authors: Zur Yuval , Stokar Saul , Bendel Peter
Published: March 2007

Recently, several groups have proposed and demonstrated the use of rapid imaging methods, using short pulse repetition times and gradient‐reversal echoes. Here, we analyze the behavior of the magnetization and the resulting image contrasts in such sequences for the case where the pulse repetition time TR is of the order of, or shorter than, the transverse relaxation time T2, and the transverse magnetization is not destroyed between phase‐encoding cycles. Exact analytical expressions describing the signal evolution between the pulses are derived, taking into account the effects of resonance offsets and flip angles, and examining the influence of constant‐phase or alternate‐phase RF pulse trains. It is shown that for typical imaging sequences two distinct echo signals will develop between pulses, which may have a detrimental effect on image quality if they partially overlap within the sampling window. It is shown that artifact‐free images can be obtained only if the two echo signals overlap precisely, which seems technically close to impossible to achieve, or if they are sufficiently separated in time to allow sampling of only one of the signals. © 1988 Academic Press, Inc.
FADE–A new fast imaging sequence
Authors: Redpath T. W. , Jones R. A.
Published: March 2007

A series of rapid, equally spaced rf pulses of constant amplitude produces two distinct components of transverse magnetization. FADE (fast acquisition double echo) is a new Fourier steady‐state free precession (SSFP) imaging sequence which images both components separately in each interpulse interval. The first component gives more signal than the second but lacks contrast while the second is strongly T2 weighted. © 1988 Academic Press, Inc.
A simple high‐frequency antenna for NMR imaging
Authors: Sergiadis George
Published: March 2007

The classic whole‐body or head antennas for NMR imaging do not resonate properly at higher frequencies. The high‐frequency antenna presented is constructed from segments of transmission lines and is treated as a distributed parameter system. It has an RF magnetic response similar to that of the classic saddle‐shaped antenna, has low exposed impedance to avoid dielectric losses in the patient, and does not disturb the magnetic field gradients. The implementation of a whole‐body antenna for 64 MHz is described and tested. © 1988 Academic Press, Inc.
Nuclear magnetic resonance relaxation in experimental brain edema: Effects of water concentration, protein concentration, and temperature
Authors: Kamman R. L. , Go K. G. , Brouwer W. , Berendsen H. J. C.
Published: March 2007

Proton relaxation times T1 and T2 of macromolecular solutions, bovine brain tissues, and experimental cat brain edema tissues were studied as a function of water concentration, protein concentration, and temperature. A linear relation was found between the inverse of the weight fraction of tissue water and the spin‐lattice relaxation rate, R1, based on a fast proton exchange model for relaxation. This correlation was also found for the spin‐spin relaxation rate, R2, of gray matter samples and macromolecular solutions at low concentrations. Concentrated solutions of protein‐water samples showed an enhanced relaxation due to viscosity effects. The T2 of white matter was considerably lengthened with elevated water concentration, but showed no straightforward relation with the total tissue water content. The relaxation times of all samples increased with temperature, supporting the assumption of fast proton exchange in the model for relaxation. This was not found for white matter, in which T2 decreased with increasing temperature, which indicated that intermediate or even slow exchange was present. The relation found between relaxation times and tissue water content can be used to predict the amount of and/or increase in tissue water due to water‐elevating processes such as edema. © 1988 Academic Press, Inc.
Multifrequency selective rf pulses for multislice MR imaging
Authors: Müller S.
Published: March 2007

A method is described for multislice imaging by means of rf pulses which contain a multifrequency excitation spectrum. These pulses label each slice by an individual signal phase and allow the separation of the signals from all the slices by subsequent add/substract procedures. The image sensitivity corresponds to the total number of acquisitions. Sequences for the imaging of an arbitrary number of slices with a minimum number of experiments are described. © 1988 Academic Press, Inc.
High‐resolution H NMR spectral signature from human atheroma
Authors: Pearlman Justin D. , Zajicek Jaroslav , Merickel Michael B. , Carman Charles S. , Ayers Carlos R. , Brookeman James R. , Brown Michael F.
Published: March 2007

Coronary artery disease due to atherosclerosis takes the lives of approximately 550,000 Americans each year—an enormous toll. Put in economic terms, the cost to the United States alone has been estimated to exceed 60 billion dollars annually. We have found that well‐resolved proton (1H) NMR spectra can be obtained from human atheroma (fatty plaque), despite its macroscopic solid appearance. The fraction of the total spectral intensity corresponding to the sharp 1H NMR signals is temperature dependent and approaches unity at body temperature (37°C). Studies of the total lipids extracted from atheroma and cholesteryl esters were conducted to identify the chemical and physical origin of the spectral signature. The samples were characterized through assignment of their chemical shifts and by measurement of their T1 and T*2 relaxation times as a function of magnetic field strength. The results suggest that the relatively sharp 1H NMR signals from human atheroma (excluding water) are due to a mixture of cholesteryl esters, whose liquid‐crystalline to isotropic fluid phase transition is near body temperature. Preliminary applications to NMR imaging of human atheroma are reported, which demonstrate early fatty plaque formation within the wall of the aorta. These findings offer a basis for noninvasive imaging by NMR to monitor early and potentially reversible stages of human atherogenesis. © 1988 Academic Press, Inc.
Metabolic changes in human muscle denervation: Topical 31P NMR spectroscopy studies
Authors: Zochodne D. W. , Thompson R. T. , Driedger A. A. , Strong M. J. , Gravelle D. , Bolton C. F.
Published: March 2007

Metabolic changes in human forearm flexor muscle following partial or complete denervation were studied using 31P nuclear magnetic resonance spectroscopy. In resting muscle, patients with electromyographically verified forearm flexor denervation had a lower ratio of PCr/Pi than healthy controls [4.76 ± 2.50 (SD) versus 6.50 ± 1.55 (SD); P < 0.01] and a higher intracellular pH [7.09 ± 0.06 versus 7.05 ± 0.04 (SD); P < 0.01]. These changes were more apparent when the diseased arm was compared to the contralateral healthy arm in patients with strictly unilateral denervation. Five patients with severe denervation had the lowest PCr/Pi ratio (1.94 ± 0.70) and the highest pH (7.15 ± 0.04). Four patients with intact innervation and disuse atrophy as a result of a forearm fracture did not exhibit these changes immediately following removal of the forearm cast. The findings show that denervation leads to a reduction in PCr/P, within muscle and a rise in intracellular pH, and that these changes correlate with the degree of denervation and improve with recovery. 31P MRS may be useful to follow the course of denervation atrophy. © 1988 Academic Press, Inc.
Application of a T2,‐filtered COSY experiment to identify the origin of slowly relaxing species in normal and malignant tissue
Authors: Williams P. G. , Saunders J. K. , Dyne M. , Mountford C. E. , Holmes K. T.
Published: March 2007

The 1H NMR spectrum of whole cells consists of many overlapping resonances which are difficult to resolve into individual components. We have developed a modification of the COSY pulse sequence which filters out resonances on the basis of their T2 relaxation rate. When applied to malignant cells, this technique has helped to identify fucose as the origin of the slowly relaxing species associated with their metastatic capacity. The technique can also be used to obtain T2 relaxation rates for individual resonances in a broad envelope of lines. © 1988 Academic Press, Inc.
Gadolinium‐labeled liposomes containing paramagnetic amphipathic agents: Targeted MRI contrast agents for the liver
Authors: Kabalka G. W. , Buonocore E. , Hubner K. , Davis M. , Huang L.
Published: March 2007

Unique paramagnetic liposomal contrast agents were synthesized and utilized for se lective augmentation of TI MR imaging of the livers of normal Balb/c mice. Amphipathic gadolinium complexes, which mimic phospholipids, were incorporated into the lamella of small unilamellar liposomes (SUV) such that they became an integral part of its surface. T 1 signal enhancement of normal liver approached 150% after iv administra‐ tion of the paramagnetic liposomes, determined by experiments performed on a 1.9‐T, experimental whole‐body MRI unit. Tracer studies utilizing gadolinium‐ 153‐tagged SUV revealed that the agents exhibited excellent in vivo stability, compared to liposomal preparations in which paramagnetic agents are simply entrapped in the aqueous core of the liposome vesicle. © 1988 Academic Press, Inc.
Magnetic resonance angiography by selective inversion recovery using a compact gradient echo sequence
Authors: Nishimura Dwight G. , Macovski Albert , Jackson John I. , Hu Robert S. , Stevick C. Andrew , Axel Leon
Published: March 2007

We have studied a pulse sequence using compact imaging gradients for MR angiography by selective inversion recovery. By acquiring signals approaching a half‐echo, we achieve significant immunity to artifacts from flow‐induced dephasing. Initial clinical results on carotid arteries accurately depict stenoses without the problems of signal dephasing. © 1988 Academic Press, Inc.
In vivo31P NMR studies of rat salivary glands at 6.3 tesla
Authors: Heerschap A. , van Vaals J. J. , Bergman A. H. , den Boef J. H. , van Gerwen P. H. J. , Gravenmade E. J.'S
Published: March 2007

In vivo31P NMR spectra of rat submandibular glands were obtained. The glands were exposed, leaving the neurovascular system intact, and placed in a solenoidal coil. Resonances of nine phosphate metabolites were identified in the spectra and metabolite concentrations were estimated from the corresponding integrals ([ATP] = 3.4 ± 0.7 mM). Tissue pH, as deduced from the chemical shift ofthe inorganic phosphate resonance, was 7.26 (±0.07). T1 relaxation times of ATP, phosphocreatine, inorganic phosphate, and phosphomonoester 31P spin systems were examined. The effect of hypoxia was followed as a function of time. 31P NMR spectra of the glands have also been obtained noninvasively by the use of a surface coil, adapted to the dimensions of the glands, and depth pulses. © 1988 Academic Press, Inc.
Fast limited flip angle mr subtraction angiography
Authors: Tasciyan Talin A. , Lee James N. , Riederer Stephen J. , Decastro Jose B. , Hedlund Laurence W. , Herfkens Robert J. , Spritzer Charles E.
Published: March 2007

A fast MR angiography method is introduced that is capable of generating difference images of blood vessels in scan times of 10–20 s. This is an order of magnitude faster than many previous methods. The fundamental concept ofthis approach is to use cardiac gating and acquire several phase encodings at least twice during each cardiac cycle using limited flip angles (LFAs) and repetition times in the 20 to 50 ms range. The encodings acquired during diastole are subtracted from those acquired during systole to generate the difference image. The contrast in the difference image is due both to the influx of unsaturated spins and to the loss of phase coherence of systolic blood moving at high velocity along a magnetic gradient. The systolic peak of the cardiac cycle is determined during reconstruction by shifting the systolic and diastolic “windows” until the difference signal is maximized. Ghost artifacts due to pulsatile flow are eliminated by a phase reordering technique similar in concept to those developed for suppression of breathing artifacts. Arteries in thick slices are successfully imaged and initial in vivo results are presented. © 1988 Academic Press, Inc.
Serial changes in nuclear magnetic resonance relaxation times after myocardial infarction in the rabbit: Relationship to water content, severity of ischemia, and histopathology over a six‐month period
Authors: Johnston Donald L. , Homma Shunichi , Liu Peter , Weilbaecher Donald G. , Rokey Roxann , Brady Thomas J. , Okada Robert D.
Published: March 2007

To determine the serial changes in T1 and T2 relaxation times of myocardial infarction, and their relationship to observed changes in water content, regional myocardial blood flow, and histopathology, rabbits were studied at 14 time intervals ranging from 30 min to 6 months after coronary artery ligation. All values were compared to a control group. Hearts were subdivided into infarct and normal segments for measurement of blood flow, water content, and relaxation times (20‐MHz spectrometer); other hearts were excised intact for histopathologic studies. T1 relaxation time of infarcted myocardium did not change significantly compared to control over the 6‐month study period. T2 relaxation time increased (P < 0.0001) at 3 days and returned to baseline by 2 months. Consonant with the increase in T2 of infarct, nuclear magnetic resonance (NMR) images at 3 days demonstrated an increase in signal intensity of infarct compared to surrounding normal myocardium. At 6 months, marked myocardial thinning was observed without changes in signal intensity. Changes in T2 of infarcted myocardium were not related to changes in water content or seventy of ischemia, but correlated best with infarct healing and scar formation as detected on histopathology. In conclusion, the findings of this study indicate that T2 relaxation time of the infarcted myocardium increases markedly at 3 days and remains elevated for 2 months. These changes correlate best with the onset and progression of infarct healing. These data demonstrate the potential of T2‐weighted NMR imaging for assessing healing patterns following ischemic myocardial injury. © 1988 Academic Press, Inc.
NMR characteristics of “visible” intracellular myocardial potassium in perfused rat hearts
Authors: Burstein Deborah , Litt Harold I. , Fossel Eric T.
Published: March 2007

Nuclear magnetic resonance (NMR) spectroscopy provides a unique view of ions through its noninvasive character and relaxation time measurements. Several previous studies have demonstrated that only approximately 20% of cardiac intracellular potassium is visible with current NMR techniques. This study investigates the NMR visible intracellular potassium in a perfused rat heart preparation. When shift reagents were used to separate the intra‐ and extracellular signals, an intracellular T1 of 11.8 ± 0.6 ms, and an intracellular T2 with two time constants of 1.3 ± 0.6 ms (33 ± 8%) and 10.1 ± 1.9 ms (67 ± 4%) were measured. Curve stripping techniques used to separate the intra‐ and extracellular components of a bulk relaxation decay yielded an intracellular T1 of 8.4 ± 0.3 ms and an intracellular T2 with two time constants of 1.1 ± 0.6 ms (38 ± 10%) and 8.0 ± 1.6 ms (62 ± 12%). These results demonstrate that there are at least two distinct pools of potassium within the cardiac cell in slow exchange with each other on the NMR time scale. Studies with an enriched 41K perfusate demonstrated that the exchange rate for the visible intra‐ and extracellular potassium is on the order of 15 min. © 1989 Academic Press, Inc.
A fast method for T1 fitting
Authors: Sperber G. O. , Ericsson A. , Hemmingsson A.
Published: March 2007

When NMR signal amplitudes achieved from spin‐echo sequences with several different repetition times are used to calculate T1, this can be done rapidly by calculating the time coordinate of the center of gravity of the data and determining which T1 should theoretically give this value. In particular, when a large number of similar calculations are made, the time gain may be massive. Simulations suggested that this procedure is only slightly less accurate than least‐squares fitting, and far more rapid. The procedure may also be useful in other types of T1 determination. © 1989 Academic Press, Inc.