bluuebunny/crossref_metadata_2025_split huggingface dataset:
Modified crossed‐ellipse radiofrequency coil for MRI
Authors: de Luca F. , Crescenzi A. , Luzzi M. , De Simone B. C. , Campanella R. , Casieri C. , Maraviglia B. 
Published: March 2007

AbstractNew coil geometries obtained by computer simulations from the crossed‐ellipse rf coil are reported. These geometries with elliptical transverse section improve the signal‐to‐noise ratio with respect to the classic ellipse and saddle coils. The increase of signal‐to‐noise ration is mainly due to the reduction of coil losses and to the better B1 efficiency and distribution. © 1986 Academic Press, Inc.
Counter rotating current local coils for high‐resolution magnetic resonance imaging
Authors: Froncisz W. , Jesmanowicz A. , Kneeland J. Bruce , Hyde James S. 
Published: March 2007

AbstractA type of local coil (or surface coil) for magnetic resonance imaging and spectroscopy is described in which two circular loops of the same diameter are disposed axially with respect to each other and in which counter rotating currents (CRC) are supported in the two loops. This type of coil has been used for localized reception in a uniform circularly polarized excitation field produced by a whole‐body coil of an imager functioning at 1.5 T. The CRC coil is decoupled from the transmitter coil by a combination of intrinsic (or geometrical) isolation (which functions during both excitation and reception) plus passive decoupling (which functions only during excitation). CRC coils of 7.5, 10, 12.5, and 15 cm diameter have been compared on a bench test setup with conventional surface coils of these diameters. Sensitivities are very similar. Q's have been measured as a function of coil diameter and both Q's and frequency shifts have been measured as a function of distance from a saline tank. The CRC coil appears to have advantages with respect to tuning and matching. A high‐resolution image of the rotator cuff is shown as an illustration of coil performance. © 1986 Academic Press, Inc.
The intrinsic signal‐to‐noise ratio in NMR imaging
Authors: Edelstein W. A. , Glover G. H. , Hardy C. J. , Redington R. W. 
Published: March 2007

AbstractThe fundamental limit for NMR imaging is set by an intrinsic signal‐to‐noise ratio (SNR) for a particular combination of rf antenna and imaging subjects. The intrinsic SNR is the signal from a small volume of material in the sample competing with electrical noise from thermally generated, random noise currents in the sample. The intrinsic SNR has been measured for a number of antenna‐body section combinations at several different values of the static magnetic field and is proportional to B0. We have applied the intrinsic and system SNR to predict image SNR and have found satisfactory agreement with measurements on images. The relationship between SNR and pixel size is quite different in NMR than it is with imaging modalities using ionizing radiation, and indicates that the initial choice of pixel size is crucial in NMR. The analog of “contrast‐detail‐dose” plots for ionizing radiation imaging modalities is the “contrast‐detail‐time” plot in NMR, which should prove useful in choosing a suitable pixel array to visualize a particular anatomical detail for a given NMR receiving antenna. © 1986 Academic Press, Inc.
Multiple‐spin‐echo imaging with a 2D Fourier method
Authors: Graumann R. , Oppelt A. , Stetter E. 
Published: March 2007

AbstractIn 2D Fourier imaging the normal Carr‐Purcell multiple‐echo sequence generally leads to center line and mirror artifacts caused by imperfect rotations by the rf pulses. We describe a method to avoid these distortions using a phase alternating‐phase shift (PHAPS) sequence which also allows multiple‐slice and multiple‐echo imaging at the same time. Measuring phantoms with calibrated T2 values, we have shown that the PHAPS imaging sequence leads to an accuracy of quantitative T2 determinations of better than 10%. Contrast‐enhanced images are presented which we calculated from multiple‐echo images and extrapolated to arbitrary echotimes, including negative ones. We believe that these improvements in T2 imaging will result in a significant reduction of patient investigation time in magnetic resonance imaging. © 1986 Academic Press, Inc.
The field dependence of NMR imaging. II. Arguments concerning an optimal field strength
Authors: Hoult D. I. , Chen C‐N. , Sank V. J. 
Published: March 2007

AbstractSome of the factors involved in the choice of field strength for NMR imaging are examined. The influences of relaxation times and chemical shift upon image quality and signal‐to‐noise ratio are highlighted, and power deposition is introduced as a significant factor which may limit the flexibility and information available at higher fields as long as 180° echo pulses continue to be necessary. Chemical‐shift imaging is examined and found wanting as a means of coping with chemical‐shift artifacts, and the use of multiple echoes (albeit with research) in conjunction with multiple‐slice techniques is advocated as representing an efficient data‐gathering scheme which can improve image signal‐to‐noise ratio. With such use, a medium field strength (0.5–1 T) is presented as representing, for general purpose imaging of head and torso, the best current compromise when imaging time is of major importance, with the important caveat that new techniques may always invalidate this conclusion. © 1986 Academic Press, Inc.
In vitro proton T1 and T2 studies on rat liver: Analysis of multiexponential relaxation processes
Authors: Barthwal R. , Höhn‐berlage M. , Gersonde K. 
Published: March 2007

AbstractAt 37°C and 20 MHz, the T1 and T2 proton relaxation processes in intact rat liver tissue are multiexponential functions which in the majority of cases were decomposed into a major (α* ≈ 90%, T = 374 ms, T = 58 ms) and a minor (α** ≈ 10%, T = 130 ms, T = 181 ms) component. Both, T1 and T2, are temperature‐dependent with a temperature shift of ΔT1 = 1.5 ms/°C and ΔT2 = 0.5 ms/°C, respectively. Storage of liver tissue at 4°C and 37°C led to remarkable changes of the T1 and T2 values. For T2 these changes occurred after a shorter storage time than for T1, but they are more pronounced for T1, To avoid such influences the relaxation measurements were performed within one hour after excision of the tissue. Even at 4°C, long‐term storage (>3h) must be avoided. A method for the quantitative determination of the fat content in liver based on multiexponential analysis of the T1 relaxation process was evaluated employing mixtures of triolein with liver homogenate. Triolein is a two‐component system with T = 144 ms (α* = 62%) and T = 355 ms (α** = 38%). Finally, liver‐specific protocol conditions were defined for in vitro relaxation studies. © 1986 Academic Press, Inc.
T1,T2, and relative proton density at 0.35 T for spleen, liver, adipose tissue, and vertebral body: Normal values
Authors: Nyman Rickard , Ericsson Anders , Hemmingsson Anders , Jung Bo , Sperber Göran , Thuomas Karl Åke 
Published: March 2007

AbstractAn MRI installation (Magnetom, Siemens, software version B1 of NUMARIS) working at 0.35 T was used to estimate T1, T2, and relative proton density in the spleen, liver, adipose tissue, and vertebral body in 14 healthy volunteers. Two double‐echo sequences were applied for all subjects: TR = 500 ms, TE1 = 35 and TE2 = 70 ms; and TR = 1600 ms, TE1 = 35 and TE2 = 70 ms. The images were sampled in regions of interest and appropriate relaxation expressions fitted to the ROI data yielding relaxation parameters and relative proton densities. Relaxation expressions, included in standard software (Siemens), were compared to more elaborate functions, developed in parallel to this study. The latter were found more appropriate, especially for high T1 values, and gave the following mean values for the four tissues (estimated uncertainty of mean in parentheses) T1 (ms) 915(36), 428(5), 261(7), and 501(11); T2(ms) 79.7(8.8), 51.0(0.2), 59.8(1.0), and 64.7(0.8); and corresponding relative proton density (ρ, arbitrary units) 2088(136), 2182(10), 2915(49), and 2136(21). The uncertainty in the values was estimated in the fitting procedure and does not include systematic errors. The relative noise in the ROIs was about 9% and the reproducibility of the ROI mean values about 8%. © 1986 Academic Press, Inc.
Measurement of solute proton spin‐lattice relaxation times in water using the 1,3,3,1 sequence
Authors: Sankar S. S. , Molé P. A. , Coulson R. L. 
Published: March 2007

Abstract1H NMR spin‐lattice relaxation times (T1) of the NCH3 proton resonances of phosphocreatine (PCr) and creatine (Cr) in water solutions were obtained using the 1,3,3,1 pulse sequence. These T1 values were equivalent to those obtained in D2O and water using either the conventional inversion‐recovery experiment or the 1,3,3,1 pulse sequence. Thus, the 1,3,3,1 sequence of proton NMR can provide an independent means along with phosphorous NMR for assess PCr and for the study of the creatine kinase reaction (PCr + ADP ⇌ ATP + Cr) in aqueous solutions and perhaps in biological preparations. © 1986 Academic Press, Inc.
The utilization of two frequency‐shifted sinc pulses for performing volume‐selected in vivo NMR spectroscopy
Authors: Doddrell David D. , Galloway Graham J. , Brooks William M. , Bulsing J. Mark , Field James C. , Irving Michael G. , Baddeley Hiram 
Published: March 2007

AbstractA new approach to volume‐selected in vivo NMR spectroscopy uses two frequencyshifted sinc pulses, in conjunction with pulsed field gradients, to destroy the coherence of the unwanted signals. A hard π/2 pulse can then be used to read the z magnetization in the region of interest. This method is independent of T2, provides complete volume selection in a single acquisition, and can be readily implemented on most high‐field commercial imaging/spectroscopy systems. © 1986 Academic Press, Inc.
In vivo proton spin‐lattice relaxation times of normal and dystrophic muscles
Authors: Narayana P. A. , Brey W. W. , Kulkarni M. V. , Misra L. K. 
Published: March 2007

AbstractIn vivo spin‐lattice relaxation times (T1) of water and lipid protons were measured in normal and dystrophic chicken pectoralis muscles at different ages. Values were obtained with a surface coil used as both a receiver and a transmitter. A 2θ‐T1‐θ‐Acquisition sequence was used for these measurments. Accuracy was verified with an inversion‐recovery method using a slotted tube resonator as the transmitter and a surface coil as the receiver. It was observed that (1) the T1 values of water protons in normal muscles decrease with age, (2) the T1 values of water protons do not change with age in dystrophic muscles, and (3) the T1 values of lipid protons increase with age in normal and dystrophic muscles. These results indicate a failure of the normal maturation of dystrophic muscles. © 1987 Academic Press, Inc.
Echo acquisition during frequency‐selective pulse trains for proton spectroscopy of metabolites in vivo
Authors: Meyer Ronald A. 
Published: March 2007

AbstractSuppression of water and fat in proton spectra of rat skeletal muscle was achieved by acquisition of the spin echoes formed in the steady state after a series of frequency‐selective composite pulses of constant amplitude, phase, and interpulse interval. The method enables observation of lactate in the presence of fat without resorting to difference spectroscopy, and on spectrometers which permit data acquisition immediately prior to a pulse, enables much faster data accumulation compared to standard echo sequences. © 1987 Academic Press, Inc.
Analysis of spin‐echo rephasing with pulsatile flow in 2D FT magnetic resonance imaging
Authors: Katz J. , Peshock R. M. , McNamee P. , Schaefer S. , Malloy C. R. , Parkey R. W. 
Published: March 2007

AbstractThe effects of pulsatile flow on spin phases in spin‐echo magnetic resonance imaging are considered. General expressions for the spin phases of the first four echoes are derived in terms of the Fourier coefficients of flow. These expressions are valid for any time‐dependent acceleration and, hence, are not restricted to constant acceleration. The derived expressions are then theoretically evaluated for aortic flow and examined at different points in the cardiac cycle. Our results show that rephasing may occur at certain points in the cardiac cycle for either even or odd echoes depending upon the particular Fourier coefficients of the velocity function and the spin‐echo delay time. However, even‐echo rephasing is not always necessarily valid. Furthermore, the possibility of determining the flow velocities in the body with an appropriate series of imaging studies is also discussed. © 1987 Academic Press, Inc.
MRI: The development of T2 contrast with rapid field echo sequences
Authors: Young I. R. , Payne J. A. , Collins A. G. , Bydder G. M. 
Published: March 2007

AbstractThe soft tissue contrast obtained in fast imaging using rapidly repeated partial saturation sequences is usually based on differences in T1. We describe here an extension of the method which results in the development of clinically useful T2‐based contrast. © 1987 Academic Press, Inc.
A comparison of some gradient‐encoded volume‐selection techniques for in vivo NMR spectroscopy
Authors: Galloway Graham J. , Brereton Ian M. , Brooks William M. , Field James , Irving Michael , Baddeley Hiram , Doddrell David M. 
Published: March 2007

AbstractFour of the techniques proposed for in vivo volume‐selected NMR spectroscopy have been compared using a simple phantom with a large background water signal which was outside the region of interest. The methods VSE, SPACE, SPARS, and DIGGER all use pulsed field gradients for spatial encoding and were tested with a symmetric and an asymmetric phantom. SPACE was used to obtain volume‐selected 1H NMR spectra of a human leg, demonstrating excellent discrimination between bone marrow and muscle. © 1987 Academic Press, Inc.
Even‐echo rephasing and constant velocity flow
Authors: Katz J. , Peshock R. M. , Malloy C. R. , Schaefer S. , Parkey R. W. 
Published: March 2007

AbstractIt has been shown previously that for constant magnetic field gradients, constant velocity flow leads to even‐echo rephasing for all echo delay times. We show that for flow which is not pluglike, even‐echo rephasing also occurs for the pulsed readout gradients used in magnetic resonance imaging if and only if the gradients begin at the time the 90° pulse is applied. We also show for these gradients that even‐echo rephasing for all echo delay times in the case of nonpluglike flow implies a constant flow velocity at the point considered. Furthermore, it suffices to assume the vanishing of the spin‐echo phase for any even echo, since the vanishing of any even echo for all echo delay times implies that all other even echoes also vanish identically. The odd echoes are then all equal to each other and proportional to the flow velocity. If acceleration is present, it may then be seen that for nonpluglike flow, even‐echo rephasing may only be present for some but not all echo delay times.However, for the typicall slice selection gradients used in magnetic resonance imaging or for usual readout gradients starting after the 90° pulse is applied, it is shown that for constant velocity flow the even‐echo phases do not vanish identically. Hence, rephasing cannot always ocur for nonpluglike flow in either of these situations. Furthermore, the spin‐echo phases are proportional to the flow in velocity. The converse is also showh; namely, if the phase of any even echo at given point is proportional to the velocity at the point considered for all echo delay times, then the flow velocity is constant at the point. Furthermore, the phases of all even echoes are also equal to each other and proportional to the flow velocity at that point. In addition, the odd echoes are then also equal to each other and proportional to the flow velocity, but with a proportionally constant different from that of the even echoes. © 1987 Academie Press, Inc.
Magnetic resonance imaging of parasitic tapeworm larvae Taenia crassiceps cysticerci in the peritoneal cavity of mice
Authors: Haselgrove John , Grun James , Owen Charles S. , Larralde Carlos 
Published: March 2007

AbstractBecause of their long T2 relaxation time (400 ms), larvae of the tapeworm Taenia crassiceps can be distinctly imaged in the mouse peritoneal cavity by NMR. An echo time of 400 ms sharply contrasted the parasites against the surrounding abdominal organs. A rapid, quantitative assay for parasite load can be obtained by recording the amplitude of a spin echo with no applied gradients at an echo time of 400–1000 ms. The T2 of the vesicular fluid of the human parasite Taenia solium was also long (600 ms), indicating that the same approach (long TE and long TR) can be used to image this parasite for diagnosis of human cysticercosis by NMR imaging. © 1987 Academic Press, Inc.
NMR investigation of hydroxyethyl starch‐induced aggregation of human erythrocytes
Authors: Caines G. Herbert , Goldstein J. H. 
Published: March 2007

AbstractAggregation of human erythrocytes at physiological hematocrit by hydroxyethyl starch (HES) was investigated with a 1H nuclear magnetic resonance method which measures the erythrocyte mean water exchange time, τa. A relationship that takes into account the effect of the aggregate as the water‐exchanging unit was used to transform τ. values into the number of cells per aggregate, n. The procedure permits the determination of the time course of aggregation as well as its initial and equilibrium status. The values of n at equilibrium range from about 2 to 4 cells over the concentration of 1 to 5% HES in isotonic saline. The aggregation of erythrocytes in the presence of HES was found to follow first‐order kinetics. The feasibility of this technique for application in the study of diseased states is indicated. © 1987 Academic Press, Inc.
Magnetic resonance imaging of midline brain tumors using inversion recovery sequences at 0.08 T (3.4 MHz)
Authors: Smith F. W. 
Published: March 2007

AbstractThe use of inversion recovery sequences to highlight intracranial tumors in children is illustrated. The effect of changing the inversion time (TI) to produce the best spatial resolution and to highlight the contrast resolution between different tumors and normal brain is analyzed. The normal appearances and clinical examples in the central nervous system are used to illustrate the options that are available using IR sequences. Variation of TI for providing a means of differentiating short T1 lesions from long T1 lesions is discussed, short TI sequences being best for demonstrating gliomas and astrocytomas whilst medium/ long TI sequences are best for demonstrating vascular abnormalities and short T, tumors. Inversion recovery imaging is considered to be an accurate alternative to spin‐echo imaging as Currently applied. © 1987 Academic Press, Inc.
Surface coil holder for Signa
Authors: Bárány Michael , Mertz George T. , Ivicic Joseph , Mok Evelyn , Spigos Dimitrios G. , Kleps Robert A. 
Published: March 2007

AbstractA surface coil holder is described for the General Electric Signa spectrometer. This allows for accurate positioning of the 31P coil relative to that of the 1H coil used for tissue slice localization. © 1987 Academic Press, Inc.
31P NMR studies on recovery from hypoxia of human tumor cells
Authors: West‐Jordan J. A. , Smith A. , Myint S. , Gardner J. A. , Abraham R. J. , Edwards R. H. T. , Warenius H. M. 
Published: March 2007

AbstractWe describe the use of 31P NMR spectroscopy in the study of metabolic changes related to hypoxia in cultured human tumor cells in vitro. The 31P NMR spectrum can easily distinguish between metabolically active cells, metabolically inactive “dormant” cells, and necrotic cells. A crucial observation was that of the ability of the “dormant” cells to resume active metabolism on incubation with oxygen after long periods of hypoxia. © 1987 Academic Press. Inc.
RAPID—A new method for fast imaging using a single slice of 2‐magnetization
Authors: Brooks William M. , Brereton Ian M. , Doddrell David M. 
Published: March 2007

AbstractA single slice of z‐magnetization is used to generate high‐speed images. The slice selection step is achieved using two sin–sinc pulses. This procedure eliminates the need for continual slice gradient reversal, a requirement for the FLASH technique. The RAPID imaging method has less inherent T1 and/or T2 dependence than current fast imaging methods and is more sensitive. © 1987 Academic Press, Inc.
A complication in prescan strategy when using surface coils
Authors: Jesmanowicz A. , Froncisz W. , Hyde James S. 
Published: March 2007

AbstractThe “prescan” process for setting the gain of an MRI scanner can be confounded by an effect arising from the spatial variation of the angle between the vector reception field of a local or surface coil and the excitation field of a whole‐body coil. It is most pronounced when the phase‐encoding direction is parallel to the plane of the coil but not along the magnetic field. The largest signal is shown to reside in a data row that is shifted from the one that corresponds to zero phase‐encoding gradient. The effect depends on the field‐of‐view and the dimensions of the receiving coil. Strategies are suggested by which manufacturers of scanners can cope with this intrinsic problem. In the meantime, users of surface coils should be aware of the difficulty. © 1987 Academic Press, Inc.
31P magnetic resonance spectroscopy of traumatic spinal cord injury
Authors: Vink Robert , Knoblach Susan M. , Faden Alan I. 
Published: March 2007

Abstract31P magnetic resonance spectroscopy (MRS) was applied in vivo to study metabolic changes in spinal cord after experimental traumatic injury. Severe trauma, resulting in spastic paraplegia, caused an early and sustained loss of high energy phosphates with profound intracellular acidosis. Early metabolic changes after traumatic spinal injury may predict irreversible tissue damage. © 1987 Academic Press, Inc.
MR microscopy on rats in vivo at 4.7 T using surface coils
Authors: Rudin Markus 
Published: March 2007

AbstractMR microscopy on intact rats using a single surface coil is reported. The use of the same coil for excitation and detection is experimentally very simple and results in a smaller field‐of‐view than the conventional setup using homogeneous excitation (whole‐body coil or a large surface coil) and a small receiver surface coil. Images at 4.7 T with 60 × 60‐m̈m pixels and an 800‐m̈m slice thickness have been obtained from the eye and ankle joint of a living rat with good anatomical definition. This corresponds to a four‐ to eightfold reduction in voxel size as compared to high‐resolution images obtained with a 30‐mm resonator probe. Many of the basic MRI experiments (spin‐echo, FLASH, chemical‐shift selective MRI) may be carried out in a straightforward way with this one‐coil setup. Sequences relying on a homogeneous flip angle distribution require a whole‐body excitation Coil. © Academic Press, Inc.
Surface coil for MR imaging of the skin
Authors: Hyde James S. , Jesmanowicz A. , Kneeland J. Bruce 
Published: March 2007

AbstractA strategy for the design of surface coils for the imaging of extended superficial planar anatomic structures including skin and subcutaneous fat is presented. The central concept is to create an array of closely spaced coplanar radiofrequency current filaments parallel to B0 the polarizing field, with opposite current directions in adjacent filaments. A specific coil design with four such filaments for imaging at 1.5 T is presented. It consists of two pairs of counterrotating current (CRC) coils. Phantom images as well as representative images of normal skin are shown. © Academic Press, Inc.