bluuebunny/crossref_metadata_2025 huggingface dataset:
In Vivo measurement of cerebral oxygen consumption and blood flow using 17O magnetic resonance imaging
Authors: Pekar J. , Ligeti L. , Ruttner Z. , Lyon R. C. , Sinnwell T. M. , van Gerderen P. , Fiat D. , Moonen C. T. W. , McLaughlin A. C.
Published: March 2007

We used 17O NMR imaging techniques to measure the H217O concentration in a 0.8‐ml voxel in the cat brain following injection of an arterial bolus of enriched H217O and during inhalation of enriched 17O2. We also measured the H217O concentration in arterial blood during 17O2 inhalation. The data from the first measurement were used to calculate the blood flow in the voxel. The data from all three measurements were combined to calculate the oxygen consumption in the voxel. The values of cerebral blood flow and oxygen consumption calculated with 17O NMR techniques agree reasonably well with values calculated for a similar region of the cat brain using autoradiographic techniques. © 1991 Academic Press, Inc.
A clinically viable technique of fat suppression for abdomen and pelvis
Authors: Mao Jintong , Bidgood W. Dean , Ang Peter G. P. , Mancuso A. , Yan Hong
Published: March 2007

Chemical‐shift selective imaging with an improved selective presaturation pulse can be used to suppress the fat signal uniformly across the entire abdominal cavity. The required magnetic field homogeneity is no higher than for a routine diagnostic scan. Therefore, no extra setup time for shimming is needed. The technique has been implemented on our clinical system for routine fat suppression scans. © 1991 Academic Press, Inc. © 1991 Academic Press, Inc.
Fatty‐acyl iminopolycarboxylates: Lipophilic bifunctional contrast agents for NMR imaging
Authors: Kim Sung K. , Pohost Gerald M. , Elgavish Gabriel A.
Published: March 2007

New fatty‐acyl contrast agents, N3−2′‐myristoyloxyethyl‐ N6−2′‐hydroxyethyl‐1, 8‐dioxotriethylenetetraamine‐N, N, N′, N′ ‐tetraacetic acid (MHE‐DTTA) and N3, N6‐bis (2′‐myristoyloxyethyl)‐1, 8‐dioxo‐triethylenetetraamine‐N, N, N′, N′‐tetraacetic acid (BME‐DTTA) were prepared by sequential alkylation, acylation, and catalytic hydrogenation from bis(hydroxyethyl)‐ethylenediamine with satisfactory yields (overall 36–46%). The 1:1 gadolinium complexes of the ligands MHE‐DTTA and BME‐DTTA were incorporated into liposomes and their relaxivities in vitro were determined. The relaxivities of both agents were similar and were greater than those of Gd3+ aquoion, Gd(EDTA), and Gd(DTPA) at both 0.23 T and 0.47 T. The relaxivities of these two agents increased from the lower to the higher magnetic field, indicating a positive field dependence. This is advantageous because of the widespread use of high‐field (B0 > 0.5 T) NMR imaging instruments. Stability constants (log K) of Gd(MHE‐DTTA) and Gd(BME‐DTTA) were found to be 15.27 ± 2.21 and 16.78 ± 0.36, respectively. LD50 of both compounds was >0.2 mmol/kg. These stabilities and lower limits of LD50 indicate the possible in vivo application of these agents. © 1991 Academic Press, Inc.
High‐speed STEAM MRI of the human heart
Authors: Frahm J. , Hänicke W. , Bruhn H. , Gyngell M. L. , Merboldt K. D.
Published: March 2007

High‐speed STEAM MR images of the normal human heart were obtained from single cardiac cycles using a 2.0‐T whole‐body system equipped with conventional 10 mT m−1 gradients. The single‐shot 90°‐TE/2–90°‐TM‐(α‐TE/2‐Acq)n pulse sequence acquires n differently phase‐encoded stimulated echoes. Measuring times of 127–254 ms were achieved using a “repetition time” of 3.96 ms in conjunction with data matrices of 32–64 × 128 pixels covering a field‐of‐view of 250–350 mm. The sequence provides easy access to anatomical short‐axis and long‐axis views of the heart by single and double oblique rotation of the image orientation. STEAM images resemble the features of spinecho images with respect to chemical shifts, susceptibilities, and flow. Thus, no additional techniques are required for the suppression of blood signals. EKG‐triggered acquisitions demonstrate that slice‐selective STEAM sequences using short TM intervals allow an unambiguous delineation of those parts of the myocardium that remain stationary within the selected plane throughout the entire imaging process. Neither spins leaving nor entering the slice defined by the initial 90° RF pulses give rise to a stimulated echo and therefore do not contribute to the resulting image. © 1991 Academic Press, Inc.
Echo‐planar time course MRI of cat brain oxygenation changes
Authors: Turner Robert , Bihan Denis Le , Moonen Chrit T. W. , Despres Daryl , Frank Joseph
Published: March 2007

When deoxygenated, blood behaves as an effective susceptibility contrast agent. Changes in brain oxygenation can be monitored using gradient‐echo echo‐planar imaging. With this technique, difference images also demonstrate that blood oxygenation is increased during periods of recovery from respiratory challenge. © 1991 Academic Press, Inc.
High‐dose applications of gadolinium chelates in magnetic resonance imaging
Authors: Runge Val M. , Kirsch John E. , Thomas Greg S.
Published: March 2007

Administration of gadolinium chclates at doses greater than 0.1 mmol/kg IV can potentially improve both lesion detection and the assessment of tissue perfusion. Preliminary results are presented in clinical patients and two animal models. In human intracranial metastatic disease, administration of 0.3 (cumulative dose) mmol/kg gadoteridol (Gd HP‐DO3A) has permitted detection of additional lesions not visualized at 0.1 mmol/kg. In a rabbit model of focal liver disease, 0.5 mmol/kg IV provided superior enhancement of both normal parenchyma and lesion rim compared to doses of 0.25 and 0.1. Dynamic imaging (T1‐weighted turbo‐FLASH) immediately following bolus injection of 0.5 mmol/kg permitted direct visualization (on unsubtracted images) of an acute perfusion defect in the cat brain not visible on conventional T1‐ and T2‐weighted scans. © 1991 Academic Press, Inc.
Electromagnetic fields of surface coil in vivo NMR at high frequencies
Authors: Keltner J. R. , Carlson J. W. , Roos M. S. , Wong S. T. S. , Wong T. L. , Budinger T. F.
Published: March 2007

A high frequency solution of the electromagnetic field produced by a circular surface coil adjacend to a homogenous conducting, dielectric sphere is used to predict the attainable signal to noise ratio (S/N) and specific absorption rate (SAR) for in vivo 1H NMR spec troscopy experiments from 200 to 430 MHz (4.7–10T). Above 200 MHz the S/N increases more rapidly with frequency and the SAR increases less rapidly compared with the respective S/N and SAR frequency dependence below 200 MHz. The difference in frequency dependence is due to dielectric resonances of the magnetic field inside the sphere at frequencies above 200 MHz. It is predicted that surface coil 1H NMR experiments may be performed on a head‐sized sphere, having conductivity and relative dielectric constant of brain, at frequencies up to 430 MHz without exceeding 8 W/kg local SAR and 3.2 W/kg SAR. The calculations of the S/N and SAR are used to determine optimum surface coil geometries for NMR experments. The power radited by the surface coil in the absence of shielding and asymmetries in the received signal with respect to the plane defined by the surface coil axix and the direction of the static magnetic field are significant at high frequency. Experimental measurements of the magnetic field inside a head‐sized sphere verfy the presence of dielectric resonances at frequencies above 200 MHz. © 1991 Academic Press, Inc.
A localized in vivo detection method for lactate using zero quantum coherence techniques
Authors: Van Dijk J. E. , Bosman D. K. , Chamuleau R. A. F. M. , Bovee W. M. M. J.
Published: March 2007

A method is described to selectively measure lactate in vivo using proton zero quantum coherence techniques. The signal from lipids is eliminated. A surface coil and additionally slice selective localization are used. The resulting spectra demonstrate the good performance of the method. © 1991 Academic Press, Inc.
Spin‐lattice relaxation in murine tumors after in vivo treatment with interferon α/β or tumor necrosis factor α
Authors: Macrì M. A. , Casieri C. , de Luca F. , Maraviglia B. , Belardelli F. , Proietti E. , Carpinelli G. , Podo F.
Published: March 2007

1H NMR spin–lattice relaxation times (T1) were measured in vitro and in vivo in Friend leukemia cell tumors during subcutaneous tumor growth in syngeneic mice and after in vivo administration of either purified murine interferon α/β (IFN) or recombinant tumor necrosis factor α (TNF). Untreated tumors exhibited monoexponential T1 relaxation independently of tumor age at least until Day 16 after implantation. Histological examinations showed that under these conditions tumors were highly homogeneous and substantially free of necrotic areas. Peritumoral administrations of either IFN or TNF did not significantly alter the tumor relaxation properties at early stages of inhibition of tumor growth. The longitudinal relaxation decay became instead clearly biexponential at later stages (more than 7 days of IFN treatment or 2 days after TNF administration). While the T1 relaxation behavior could be unequivocally correlated with the presence of necrotic areas in these tumors, it could not be considered as an early marker of the altered growth capability, induced by administration of either IFN or TNF. © 1992 Academic Press, Inc.
Perfusion imaging
Authors: Detre John A. , Leigh John S. , Williams Donald S. , Koretsky Alan P.
Published: March 2007

Measurement of tissue perfusion is important for the functional assessment of organs in vivo. Here we report the use of 1H NMR imaging to generate perfusion maps in the rat brain at 4.7 T. Blood water flowing to the brain is saturated in the neck region with a sliceselective saturation imaging sequence, creating an endogenous tracer in the form of proximally saturated spins. Because proton T1 times are relatively long, particularly at high field strengths, saturated spins exchange with bulk water in the brain and a steady state is created where the regional concentration of saturated spins is determined by the regional blood flow and regional T1. Distal saturation applied equidistantly outside the brain serves as a control for effects of the saturation pulses. Average cerebral blood flow in normocapnic rat brain under halothane anesthesia was determined to be 105 ± 16 cc. 100 g−1. min−1 (mean ± SEM, n = 3), in good agreement with values reported in the literature, and was sensitive to increases in arterial pCO2. This technique allows regional perfusion maps to be measured noninvasively, with the resolution of 1H MRI, and should be readily applicable to human studies. © 1992 Academic Press, Inc.
Multispectral analysis of uterine corpus tumors in magnetic resonance imaging
Authors: Taxt Torfinn , Lundervold Arvid , Fuglaas Bjørn , Lien Hans , Abeler Vera
Published: March 2007

The goal of this prospective study was to evaluate multispectral analysis techniques for automatic recognition of uterine cancer in magnetic resonance (MR) imaging. The first part of this study was an open training phase in which the statistical parameters of the various normal and pathological tissue types were estimated. This was followed by a test phase that was done as a blind experiment. Results from an extensive pathological examination of the surgically removed organs served as the reference for the diagnosis and various geometric measurements of the lesions. A radiological examination of the MR images was also performed. All malignant test tumors were correctly or close to correctly classified. However, parts of normal endometrium and other mucosal linings were also classified as adenocarcinomas. In addition, parts of some of the malignant tumors were classified as normal endometrium. The geometrical extension of the tumor and its relationship to the surroundings were slightly better predicted than those obtained by the radiologist. The results indicate that it is possible to differentiate and determine the local extension of some types of uterine malignancies based on the information present in MR images. © 1992 Academic Press, Inc.
On the precision of diffusion/perfusion imaging by gradient sensitization
Authors: Pekar James , Moonen Chrit T. W. , van Zijl Peter C. M.
Published: March 2007

Computer simulation is used to assess the precision and accuracy of diffusion and perfusion parameters derived from a set of gradient‐sensitized images. Under ideal experimental conditions, a moderate signal‐to‐noise level (ca. 40) suffices to estimate diffusion coefficients to within 20% relative precision. However, estimation of a typical cerebral perfusion fraction of 5% to within 20% relative precision requires signal‐to‐noise levels of ca. 400. Simulations also show that systematic errors in perfusion fraction estimation, as well as understimation of the uncertainties in perfusion parameters (by X‐squared analysis), will be found at moderate signal‐to‐noise levels. © 1992 Academic Press, Inc.
Diffusion imaging of the human brain in vivo using high‐speed STEAM MRI
Authors: Merboldt Klaus‐Dietmar , Hänicke Wolfgang , Bruhn Harald , Gyngell Michael L. , Frahm Jens
Published: March 2007

This paper describes a new method for diffusion imaging of the human brain in vivo that is based on a combination of diffusion‐encoding gradients with high‐speed STEAM MR imaging. The single‐shot sequence 90°‐TE/2‐90°‐TM‐(α‐TE/2‐STE)n generates n = 32–64 differently phase‐encoded stimulated echoes STE yielding image acquisition times of 576 ms for a 48 ×128 data matrix. Diffusion encoding is performed during the first TE/2‐interval as well as during each readout period. Phantom studies reveal a quantitative agreement of calculated diffusion coefficients with literature values. EKG triggering completely eliminates motion artifacts from diffusion‐weighted single‐shot STEAM images of human brain in vivo. While signal attenuation of the cerebrospinal fluid (CSF) is predominantly due to flow, that observed for gray and white matter results from diffusion. Evaluated diffusion coefficients yield (1.0 ± 0.1) × 10−5 cm2 s−1 for gray matter, (0.5 ± 0.1) × 10−5 cm2 s−1 for white matter with the diffusion encoding parallel to the main orientation of the myelin sheath of the neurofibrils, and (0.3 ± 0.1) × 10−5 cm2 s−1 for white matter and a perpendicular orientation. All studies were performed at 2.0 T using a conventional 10 mT m−1 gradient system. © 1992 Academic Press, Inc.
Effects of RF amplifier distortion on selective excitation and their correction by prewarping
Authors: Chan Frandics , Pauly John , Macovski Albert
Published: March 2007

In a magnetic resonance imaging system, an RF power amplifier is employed to boost an RF pulse to sufficient strength to excite the nuclear spins in a subject. The nonideal behavior of this amplifier distorts a selective‐excitation pulse, and this distortion in turn degrades the slice profile. We have found two types of nonideal behavior particularly troublesome: nonlinearity and incidental phase modulation. One of their effects is the introduction of an unwanted “skirt” in the out‐of‐slice region of a slice profile. We present an effective method of correction in which a selective‐excitation pulse is prewarped to compensate for the distortion. © 1992 Academic Press, Inc.
Correction of chemical‐shift artifacts in 19F imaging of PFOB: A robust signed magnitude method
Authors: Lee H. K. , Nalcioglu O. , Buxton R. B.
Published: March 2007

This paper describes a method for correcting the chemical‐shift artifacts in 19F NMR imaging of perfluoroctylbromide emulsion (PFOB) by utilizing the two spectral peaks of PFOB which have a long T2 value in conjunction with the Dixon method. Corrected images are obtained from the magnitude of the measured images using the sign determined from the phase images. The method was tested in the presence of several phase deformation factors, such as static magnetic field inhomogeneity and inaccurate time shift of the π refocusing pulse, which affect the phase errors of each pixel in the reconstructed image. The advantage of the signed magnitude method is demonstrated experimentally by comparing it with the currently used complex and magnitude summation/subtraction methods. © 1992 Academic Press, Inc.
Measurement of the T2 relaxation time of ethanol and cerebral metabolites, in vivo
Authors: Rose Stephen E. , Crozier Stuart , Brereton Ian M. , Moxon Leith N. , Galloway Graham J. , Bore Peter , Doddrell David M.
Published: March 2007

The SPACE volume selection technique was combined with a spin‐echo sequence to measure the transverse relaxation time of the resonances of ethanol and cerebral metabolites in the dog brain, in vivo. The method was extended to measure brain metabolite T2, values in the rat using 1H NMR microspectroscopy. The T2 decays for the resonances of the metabolites N‐acetylaspartate, creatine/phosphocreatine, and choline/phosphorylcholine were found to be biexponential with long T2 components of 490, 260, and 350 ms for the dog and 490, 220, and 355 ms for the rat brain, respectively. The existence of a second T2 component may originate from J‐coupled nonresolved metabolite resonances. The relaxation decay for the ethanol triplet could be fitted to a single exponential giving a T2 relaxation time of 335 ms. However, given the large errors in the measurement of ethanol peak intensities at short echo times because of overlapping lipid signal and the effects of J‐modulation, a biexponential decay with a long T2 component of 335 ms cannot be ruled out. Ambiguities regarding the reported partial detection of the 1H NMR signal of ethanol in the brain are discussed. © 1992 Academic Press, Inc.
The effect of postinfarction intramyocardial hemorrhage on transverse relaxation time
Authors: Lotan Chaim S. , Miller Sandra K. , Cranney Gregory B. , Pohost Gerald M. , Elgavish Gabriel A.
Published: March 2007

1H NMR imaging has been used to define zones of myocardial infarction (MI), which appear as areas of relatively increased signal intensity (SI). However, zones of decreased SI have been observed within or around the areas of infarction in NMR images acquired at high magnetic fields. To determine the cause of these areas of reduced SI, ex vivo spin‐echo 1H NMR imaging at 1.5 T was performed in eight dogs following 72 h of coronary artery occlusion. In all dogs, a zone of increased SI (122 ± 7% compared to control myocardium; P < 0.01) was observed in the territory of the occluded coronary artery. In seven of the dogs, additional zones were also seen, within or around the central zone of increased SI, which displayed SI that was reduced in comparison with the local enhanced intensity, but was similar to the intensity of normal myocardium (97± 7% compared to control; P = NS). Gross inspection and histological assessment of sliced myocardium disclosed hemorrhage in these regions characterized by locally decreased NMR SI. Image‐derived calculation of T2 in the various infarct regions revealed a significant shortening of T2, in the hemorrhagic infarct zones characterized by decreased SI, in comparison with the nonhe‐morrhagic infarct zones characterized by increased SI (59 ± 7 ms vs 73 ± 10 ms, P < 0.05). No difference was found, however, between the observed T2 of hemorrhagic infarct and of control tissue (57 ± 4 ms). Using a biexponential analysis of T2 from the hemorrhagic infarct zones, the intrinsic T2 of water protons affected by hemorrhage was determined to be 43 ± 9 ms, significantly reduced in comparison with the values obtained with the standard monoexponential fit. The reduction in T2 in the hemorrhagic zone is consistent with the paramagnetic effects of deoxyhemoglobin associated with intramyocardial hemorrhage. Thus the apparent T2, measured in hemorrhagic infarct tissue, represents the result of an averaging effect of infarct and hemorrhage on T2 relaxation times. These observations improve our understanding of the changes in NMR SI within the infarcted regions, and may provide a noninvasive method for the detection and quantitative assessment of intramyocardial hemorrhage. © 1992 Academic Press, Inc.
Theory of paramagnetic contrast agents in liposome systems
Authors: Barsky D. , Pütz B. , Schulten K. , Magin R. L.
Published: March 2007

We develop a theoretical description of nuclear spin relaxation mediated by MRI contrast agents and transport processes in liposome systems. Such systems compartmentalize the physical space such that paramagnetic contrast agents, which enhance relaxation, are trapped in some subvolume. Due to diffusive transport across compartmental barriers, i.e., across liposome membranes, nuclear spins in the whole volume exhibit fast relaxation. The description developed is based on the diffusion–Bloch equations for the nuclear magnetization with appropriate boundary and continuity conditions. From this set of equations a new inhomogeneous differential equation for the local relaxation times is derived. For simple geometries of compartmentalized spaces the equation can be solved analytically. A simple formula for average relaxation times in liposome systems is presented. The resulting relaxation times agree well with observations. © 1992 Academic Press, Inc.
Measurement of relative regional tumor blood flow in mice by deuterium NMR imaging
Authors: Evelhoch Jeffrey L. , McDouall Jacqueline B. Larcombe , Mattiello James , Simpson Nicholas E.
Published: March 2007

A noninvasive method to measure relative regional tumor blood flow (rTBF) throughout murine tumors which uses deuterium NMR imaging to observe regional uptake of HOD after bolus iv injection of D2O is introduced. HOD uptake images are formed by subtraction of a background (preinjection) image from 94‐s gradient‐refocused deuterium NMR images acquired starting 30 s and 10 min after D2O injection. The pixel intensity in the HOD uptake image acquired starting 30 s after injection is directly related to rTBF with a limit of detection estimated at 7 ml/(100 g‐min). The image acquired 10 min after D2O injection extends the estimated limit of detection for rTBF to 3 ml/(100 g‐min). Heterogeneity in rTBF and regional effects of photodynamic therapy within RIF‐1 tumors are readily perceived. This method may provide a valuable tool to further our understanding of the relationship between blood flow and therapeutic response in tumors. © 1992 Academic Press, Inc.
Investigation of the magnetic properties of iron oxide nanoparticles used as contrast agent for MRI
Authors: Pouliquen D. , Perroud H. , Calza F. , Jallet P. , Le Jeune J. J.
Published: March 2007

Superparamagnetic iron oxide particles, a new class of contrast agents for MRI, are extremely good enhancers of proton relaxation. However, the development of such particle systems has resulted in a wide range of preparations whose physico‐chemical properties differ greatly. We have conducted a set of physical experiments: X ray diffraction analysis, relaxivity measurements, susceptibility determinations, and thermomagnetic cycling on different preparations of superparamagnetic particles. Our results demonstrate a good correlation between susceptibilities measured in liquid samples at room temperature and the R2/RI ratio. Susceptibility measurements between liquid nitrogen temperature and room temperature show three different types of behavior dependent on the size of iron oxide crystals. Comparison of heating and cooling curves from strong field thermomagnetic cycles provides information about the maghemite/magnetite crystal content. The information on magnetic properties reported in this study may help to characterize and to select these materials for use as MRI contrast agents. © 1992 Academic Press, Inc.
Radial scanning technique for volume selective 31P spectroscopy
Authors: Rim C. Y. , Ra J. B. , Cho Z. H.
Published: March 2007

An interlaced radial scanning method that is ideally suited for 31P spectroscopy with short T2 components and a wide spectral range is presented. The proposed method, which uses an additional radial gradient and radial scans in the k‐space, minimizes T2 decay during the selection time and also optimizes the volume selectivity in a given gradient field strength. Simulation and experimental results with a short selection time of 2 ms demonstrate that the proposed method is suitable for volume selective 31P spectroscopy. © 1992 Academic Press, Inc.
In vivo T1 values from guinea pig brain depend on body temperature
Authors: Youl B. D. , Hawkins C. P. , Morris J. K. , Duboulay E. P. G. H. , Tofts P. S.
Published: March 2007

T1 and T2 values were calculated from guinea pig brain in vivo at 0.5 T. T1 values showed significant dependence on body temperature, but the effect varied significantly from animal to animal and from one tissue type to another. Mean dependencies were 8.2 ms/°C for corpus callosum, 14.7 ms/°C for gray matter, and 21.5 ms/°C for hemispheric white matter (1.7, 2.6, and 4.5%/°C, respectively), all with respect to core temperature. These findings suggest that body temperature monitoring and control may be needed when sensitive measurements of T1 are being made. There was evidence for regulation of brain temperature within the hyperthermic range of body temperature. © 1992 Academic Press, Inc.
Liver tissue characterization by in vitro NMR: Tissue handling and biological variation
Authors: Moser Ewald , Holzmueller Peter , Gomiscek Gregor
Published: March 2007

The extraction of reliable and useful relaxation time data for tissue characterization by NMR requires strict protocols, optimized for each type of biological tissue, which include parameters like storage duration and temperature as well as measurement parameters. Spin‐lattice relaxation times in liver tissue vary not only with NMR frequency but also with their “time‐after‐excision characteristics,” while spin‐spin relaxation times are almost independent of most parameters which influence T1 at 20 MHz in normal liver tissue (e.g., species, sex, circadian rythm, starvation). T2, however, being more sensitive to water content and pH changes, is well suited for detecting nonspecific tissue alterations (e.g., due to ischemia, chemical toxins). Following the suggestions outlined herein, investigation of at least 120 min of time‐after‐excision (storage) effects allows the significant distinguishing of various physiological differences in normal liver tissue as well as improvement of early detection of liver pathologies. © 1992 Academic Press, Inc.
Experimental design and fabrication of birdcage resonators for magnetic resonance imaging
Authors: Vullo Thomas , Zipagan Raymond T. , Pascone Romeo , Whalen Joseph P. , Cahill Patrick T.
Published: March 2007

Although the birdcage resonator has been theoretically described for single‐ and multinuclear operation, this study provides the basic experimental guidelines needed for the fabrication and testing of such coils for various geometries and resonant frequencies from 10 to 95 MHz. The correlation of coil dimensions and resonant frequencies with individual inductance elements, L1, and L2, is also shown. Experimentally derived algorithms are presented for the determination of the capacitance needed for low‐pass resonators based on measurements of the coil's “global” inductance. Ten low‐pass birdcage coils with eight legs were evaluated and their four resonant frequencies were within 4% of theoretical predictions. © 1992 Academic Press, Inc.
A data adaptive reprojection technique for MR angiography
Authors: Korosec F. R. , Weber D. M. , Mistretta C. A. , Turski P. A. , Bernsteins M. A.
Published: March 2007

Inability to detect vessel overlap and vascular loops can compromise the interpretation of magnetic resonance angiograms. A data‐adaptive ray tracing (DART) technique was developed to produce the appropriate variations in signal intensity at points of vessel overlap in order to simulate the standard angiographic representation of vessels. In this technique a threshold is utilized to identify vessels in the image slices composing a 3D angiographic data set. A mask, which defines regions slightly larger than the vessel boundaries, is obtained by blurring the vessel information surviving the initial threshold. This mask is converted to binary form prior to multiplication by the original angiographic data set. Following application of an additional threshold to the masked data, line integrals through the regions defined by the mask are performed to obtain an angiographic signal proportional to the integrated vessel signal as in conventional angiography. This integrated reprojection is then uniquely combined with a maximum intensity pixel (MIP) reprojection to produce the final DART image. The application of the DART technique to 2D time‐of‐flight and 3D phase‐contrast angiograms successfully enabled the identification of overlapping vessels and vascular loops. DART was also found to produce less vessel narrowing than the MIP technique. © 1992 Academic Press, Inc.
Creatine kinase activity in rat skeletal muscle with intermittent tetanic stimulation
Authors: Le Rumeur E. , Le Moyec L. , De Certaines J. D.
Published: March 2007

ATP synthesis from PCr through creatine kinase reaction was measured in vivo in rat leg muscle using 31P NMR magnetization transfer and progressive saturation. Both techniques determined a spin‐lattice relaxation time for PCr of 3 s at rest and an identical forward rate constant of 0.22‐0.26 s−1. In stimulated muscles, magnetization transfer showed that flux was not changed with a steady‐state PCr of 54% of initial level. During stimulation inducing a PCr decrease to 38% of initial value, flux was significantly lowered by 30%. These findings could result from an accumulation of ions and water increases or from compartmentation of ATP and PCr in different pools either in the muscle cell or in the different muscle fibers. In addition, these results could reinforce the hypothesis against a crucial role for creatine kinase shuttle in the ATP supply in skeletal muscle. © 1992 Academic Press, Inc.
MRI susceptometry: Image‐based measurement of absolute susceptibility of MR contrast agents and human blood
Authors: Weisskoff Robert M. , Kiihne Suzanne
Published: March 2007

We present a novel NMR imaging technique that allows absolute determination of the magnetic susceptibility constant, χ, of a solution. By comparing the phase difference of MR images produced with an instant (echo planar) “offset” spin‐echo sequence, we obtain a direct measure of the magnetic field perturbations caused by the solution. We demonstrate this method with Gd(DTPA), Dy(DTPA), human red blood cells, and superparamagnetic iron oxide particles. © 1992 Academic Press, Inc.
Scan time reduction in snapshot flash MRI
Authors: Jakob P. M. , Haase A.
Published: March 2007

We describe the speeding up of snapshot FLASH MRI by placing a slice selection experiment before the whole imaging sequence. In conventional snapshot FLASH slice selection is made in every projection, thus consuming a great deal of experimental time. This problem can be overcome by applying only one slice‐selective procedure before starting the imaging. The idea is to make a selective saturation of the outer volume and to interrogate the unaffected slice by a train of rapid, hard, low‐angle pulses. By this new method the measuring times of snapshot FLASH can be further reduced. © 1992 Academic Press, Inc.
Concurrent quantification of tissue metabolism and blood flow via 2h/31P NMR in Vivo. 11. validation of the deuterium nmr washout method for measuring organ perfusion
Authors: Neil Jeffrey J. , Song Sheng‐kwei , Ackerman Joseph J. H.
Published: March 2007

The deuterium washout technique of measuring tissue blood flow is based upon NMR detection of HOD (administered as D2O saline, but typically detected as HOD because of rapid proton‐deuteron exchange) as a freely diffusible tracer. Though this method is coming into more general use, it has not yet been rigorously validated in vivo against an accepted, independent measure of tissue blood flow. To this end, simultaneous radiolabeled micro‐sphere and HOD washout blood flow measurements were made in rat gastrocnemius muscle. D2O saline was administered either intramuscularly or intraarferially (near the aortic bifurcation), and the sciatic nerve was electrically stimulated to increase the muscle blood flow rate. Over a range of flows of 2 to 80 ml/(100 g. min), comparison of micro‐sphere and HOD washout measurements showed good agreement, with r = 0.92 (n = 16) for intramuscular administration and r = 0.91 (n = 12) for intraarterial administration. These data strongly suggest thatthe HOD washout technique provides accurate blood flow measurements in skeletal muscle.
Intensity artifacts in MRI caused by gradient switching in an animal‐size NMR magnet
Authors: Hughes D. G. , Robertson S. , Allen P. S.
Published: March 2007

The switching of magnetic field gradients in MRI gives rise to eddy currents in the structural components of superconducting magnet systems. The associated magnetic fieldscause intensity artifacts which are particularly severe in some animal‐size systems. We treat theoretically three mechanisms which cause intensity artifacts in one‐dimensional projection images obtained by a spin‐echo technique. The first is an off‐resonance effect, caused by applying the refocusing pulse before the read compensation gradient pulse has decayed sufficiently. The other two mechanisms are caused by a spatial dependence of the phase accumulated by the spins at the time of formation of the echo. as a result of the eddy current fields. First, interference causes aloss of transverse magnetization because of a variation in the phase of spins which lieon the same isochromat during the read gradient pulse. Second, a variation of the phaseof the spins in a direction orthogonalto the isochromats causes spins throughout the sample to refocus at different times. These two mechanisms are fundamentally different, since interference can occur even if the main magnetic field is homogeneous, whereas improper refocusing does not. It is shown that there is no loss of intensity by the interference mechanism if phase encoding is used to form two‐dimensional images. This maywell be a major reason why images obtained by 2DFT have been found to be generally superior to thoseobtained by projection reconstruction. Experimentally, the distributionof intensity in one‐dimensional projection images of a square slice phantom is compared with theoretical intensities, estimated using eddy current fields reported in the preceding paper.
Decrease of glucose in the human visual cortex during photic stimulation
Authors: Merboldt Klaus‐Dietmar , Bruhn Harald , Hanicke Wolfgang , Michaelis Thomas , Frahm Jens
Published: March 2007

Localized proton NMR spectroscopy was used to study cerebral metabolism in the visual cortex of healthy adults during rest and photic stimulation. Basal lactate levels showed considerable interindividual differences ranging from below detectability (mM) to about 1 mM without consistent alterations during photic stimulation. Local brain glucose levels were significantly reduced (≈ 50%) during the entire period of photic stimulation and recovered to resting levels (≈0.8 mM)within 10 minafter the end of stimulation. This decrease reflects the establishment of a new equilibrium due to enhanced delivery (blood flow) and enhanced consumption. The absence of lactate accumulation supportsthe hypothesis of a rapid efflux of lactate from brain tissue under activated conditions.
Application of self‐refocusing band selective RF pulses for spectroscopic localization
Authors: Marshman Margaret F. , Brereton Ian M. , Rose Stephen E. , O'Connor Anthony J. , Doddrell David M.
Published: March 2007

A new self‐refocusing slice selection 90° pulse is presented and its incorporation in the Space localization sequence described. Experimental comparisons are made with the self‐refocusing pulse reported by Geen (H. Geen, S. Wimperis and R. Freeman, J. Magn. Reson. 85, 620 (1990)). The main source of localization error in the Space sequence is traced to the hard π/2 pulse and the development of a shaped‐pulse version of the sequence is described. This required the calculation of a slice‐selective pulse capable of rotating coherent transverse magnetization to the z‐axis. The RF power requirements for these experiments are also discussed. © 1992 Academic Press, Inc.
Chemical shift imaging with phase‐encoding RF pulses
Authors: Hennig J.
Published: March 2007

An inherent problem of conventional chemical shift imaging is signal contamination into adjacent voxels. This is especially severe in proton spectroscopy of the central nervous system, where the lipid signal from the skull is several orders of magnitude higher than the metabolite resonances from the brain. The reason for the contamination lies in the fact that the distribution of spins does not coincide with the discrete sampling matrix of the discrete Fourier transformation if a continuous phase‐encoding scheme using magnetic field gradients is being used. This problem can be overcome if phase encoding is performed by appropriately phase‐modulated RF pulses. It is demonstrated that contamination free spectra can be acquired from voxels immediately adjacent to the skull. Using small voxels of 1 × 1 × 2‐ml regional variations of N‐acetyl aspartate in the cerebellum of patients with oligopontine cerebellar atrophy could be observed. © 1992 Academic Press, Inc.
In vivo7Li NMR imaging and localized spectroscopy of rat brain
Authors: Ramaprasad S. , Newton J. E. O. , Cardwell D. , Fowler A. H. , Komoroski R. A.
Published: March 2007

Lithium‐7 in vivo NMR spectroscopy and imaging techniques have been developed at 4.7 T for rat head. The pharmacokinetics of lithium (Li) uptake in rat head has been measured using STEAM localized spectroscopy for the whole brain, which showed relatively rapid uptake of Li and a steady level of Li from about 5 to 20 h. Localized spectroscopy on brain sections revealed no differences in Li concentration among the front, middle, and rear of the brain. The spin‐lattice relaxation time showed a single exponential decay for the head. The spin‐spin relaxation time for head showed a biexponential behavior. Using a 1H‐7Li double coil assembly,7Li images were generated for rat head, as was the corresponding 1H image for anatomic localization. The 7Li image (7‐mm slice thickness, 4‐mm in‐plane resolution) recorded after the last dose in a multiple ip dose protocol shows the Li distribution in the head and neck. Based on 7Li images, the Li level in muscle was about twice that in the brain. Variations of 7Li intensity level across the brain were typically small. © 1992 Academic Press, Inc.
Experimental analysis of T1 imaging with a single‐scan, multiple‐point, inversion‐recovery technique
Authors: Zhang Y. T. , Yeung H. N. , Carson P. L. , Ellis J. H.
Published: March 2007

Look and Locker's single‐scan, multiple‐point, T1 determination technique modified for imaging applications was evaluated experimentally for its accuracy and reliability with respect to the pulse sequence parameters. in particular. to the interpulse delay, TD, and the tip angle, α. T1 imaging experiments were performed with a 0.5‐T imaging system on a phantom which consisted of an array of vials containing 2% agarose gels doped with various amount of Mn2+ using different combinations of the parameter set {TD. α}. T1, results obtained with this technique were compared with those measured by a conventional inversion‐recovery procedure using the same spectrometer. Strategic choice of pulse sequence parameters to minimize experimental errors and the criteria for these choices will be discussed. © 1992 Academic Press, Inc.
Magnetization transfer time‐of‐flight magnetic resonance angiography
Authors: Pike G. Bruce , Hu Bob S. , Glover Gary H. , Enzmann Dieter R.
Published: March 2007

Time‐of‐flight (TOF) angiography based on inflow enhancement is limited by the steady‐state signal differences between blood and the surrounding stationary tissues. We present a new TOF sequence in which magnetization transfer contrast is used to supplement wash. in effects. Angiograms demonstrating the superior performance of this technique are presented. © 1992 Academic Press, Inc.
An aqueous gastrointestinal contrast agent for use in echo‐planar MR imaging
Authors: Hahn Peter F. , Saini Sanjay , Cohen Mark S. , Goldberg Mark , Reimer Peter , Mueller Peter R.
Published: March 2007

Four volunteers were imaged with echo‐planar imaging before and after ingesting a dilute barium preparation. The contrast material improved bowel visibility by increasing lumen signal intensity, without increasing noise. Long T2 gastrointestinal contrast material can be used in T2‐weighted imaging when motion artifacts are suppressed by ultrashort acquisitions. © 1992 Academic Press, Inc.
Time course EPI of human brain function during task activation
Authors: Bandettini Peter A. , Wong Eric C. , Hinks R. Scott , Tikofsky Ronald S. , Hyde James S.
Published: March 2007

Using gradient‐echo echo‐planar MRI, a local signal increase of 4.3 ± 0.3% is observed in the human brain during task activation, suggesting a local decrease in blood deoxyhemoglobin concentration and an increase in blood oxygenation. Images highlighting areas of signal enhancement temporally correlated to the task are created. © 1992 Academic Press, Inc.
31P magnetization transfer studies in the monkey brain
Authors: Mora Bassem N. , Narasimhan P. T. , Ross Brian D.
Published: March 2007

The forward and reverse rates through the creatine‐kinase (CK) catalyzed reaction, phosphocreatine + ADP + H+ \documentclass{article}\pagestyle{empty}\begin{document}$\'\mathop \mathbin{\lower.3ex\hbox{$\buildrel\textstyle\rightarrow\over {\smash{\leftarrow}\vphantom{_{\vbox to.5ex{\vss}}}}$}} \limits_{kr}^{kr} \{$\end}document} creatine + ATP in the in vivo monkey brain were measured using the techniques of saturation transfer (ST) and inversion transfer (IT) 31P nuclear magnetic resonance (NMR) spectroscopy. Independent checks on the ST apparent longitudinal relaxation (τ) data could be obtained from the parameters determined from the IT analyses. At near‐equilibrium it is assumed that the forward‐to‐reverse flux ratio lies close to 1.0. In the monkey brain the value for the forward‐to‐reverse flux ratio obtained is 1.37 ± 0.26 calculated from ST with average τ values from IT initial slopes, a value which is not significantly different from unity. The present NMR data point to the CK reaction in the living monkey brain being maintained at or near equilibrium.
A fast gradient‐recalled MRI technique with increased sensitivity to dynamic susceptibility effects
Authors: Moonen Chrit T. W. , Liu Guoying , Gelderen Peter Van , Sobering Geoffrey
Published: March 2007

A fast imaging method that is based on gradient‐recalled echoes of spins whose excitation and echo formation are separated by more than one TR period is presented. This method does not incorporate chemical‐shift refocusing and thus results in drastically increased sensitivity to dynamic susceptibility erects, while maintaining a short total imaging time. The efficiency of the new technique is demonstrated in dynamic contrast‐enhanced experiments (bolus tracking) in the cat brain using a duration of 600 ms for each image. Blood volume maps are derived with expected contrast between white and gray matter.
The impact of the ISIS experiment order on spatial contamination
Authors: Burger C. , Buchli R. , Mckinnon G. , Meier D. , Boesiger P.
Published: March 2007

When performing volume‐localized spectroscopy measurements, the amount of spatial contamination is an important quality criterion. With the ISIS localization technique contamination cannot only arise from the transition regions around the volume of interest, but also from remote regions of the sample. The latter contamination component is a consequence of inhomogeneous excitation pulses, if short repetition times TR are used. Its severity depends both on the order of the eight phase cycling experiments needed for an ISIS measurement, and on the ratio TR/T1. Here it is theoretically discussed from which regions of the sample contamination can arise for a specific phase cycling order. For the worst orders the contaminating regions are almost three times as large as for the optimal orders. The ratio for the effectively measured contamination, however, can be moderated in real experiments, because cancellation effects occur due to the phase distribution of the contaminating signals. 31P phantom experiments clearly demonstrate that contamination is present even if adiabatic excitation pulses are applied and that spatial contamination can be reduced to about a third by an optimal choice of the phase cycling order.
Dynamic studies of gadolinium uptake in brain tumors using inversion‐recovery echo‐planar imaging
Authors: Gowland P. , Mansfield P. , Bullock P. , Stehling M. , Worthington B. , Firth J.
Published: March 2007

Echo‐planar imaging has been used to observe the dynamics of Gd‐DTPA uptake in brain tumors. It has been possible to examine both vascular uptake and diffusion across the blood‐brain barrier in a single experiment, by using the IR‐MBEST echo‐planar sequence which combines a high temporal resolution (approximately 3 s) with strong T1 weighting. To model the uptake it is necessary to know the arterial concentration of Gd‐DTPA; in this study the signal in the sagittal sinus was measured to avoid the need to take repeated blood samples. The time constant for transfer across the blood‐brain barrier was measured to be between 20 and 1050 s for different tumors. The results of the modeling correlated with the results of other assessments of tumor vascularity.
Recursive RF excitation
Authors: Christy P. S. , Grimm R. C. , Greenleaf J. F. , Ehman R. L.
Published: March 2007

We have investigated the properties of a recursive process in which the output signal from a given RF excitation pulse may be used as the input (excitation) pulse of a subsequent iteration. This recursive excitation technique increases contrast and improves feature segmentation for the purpose of motion tracking.
Breast coil design for low‐field mri
Authors: Komu Markku , Kormano Martti
Published: March 2007

Four double‐breast coils were designed for the low‐field resistive magnet MR imaging of female breasts at 0.02, 0.04, and 0.1 T. The signal‐to‐noise ratio is optimized by shaping the coils, by constructing two different size coils at 0.02 T, and by using special wire for the turns of the solenoidal coils. The approximate linear dependence of the SNR on the Larmor frequency is estimated.
T1values of phosphomonoester and phosphocreatine of brain show no significant change during development
Authors: Hida Kazutoshi , Kwee Ingrid L. , Nakada Tsutomu
Published: March 2007

Changes in apparent 31P spin‐lattice relaxation times (T1) associated with brain development were investigated in rat pups. While analysis of variance showed strong age dependency in [PME]/[ATP] and [PCr]/[ATP], the T1 values of PME, PCr, and ATP did not show any age dependency. The studies indicate that in contrast to the data which indicated aging‐related changes in the T1 values of PME, the observed changes in PME during neonatal development are likely to be quantitative in nature.