摘要:

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

ISSN:0740-3194    

DOI:10.1002/mrm.1910050502

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1987

数据来源: WILEY

摘要:

AbstractWe have introduced the selective Fourier transform technique for spectral localization. This technique allows the acquisition of a high‐resolution spectrum from a selectable location with control over the shape and size of the spatial response function. The shape and size of the spatial response are definedduring data acquisitionand the location is selectable through processing after the data acquisition is complete. The technique uses pulsed‐field‐gradient phase encoding to define the spatial coordinates. In this paper the theoretical basis of the selective Fourier transform technique is developed and experimental results are presented, including comparisons of spectral localization using either the selective Fourier transform method or conventional multidimensional Fourier transform chemical‐shift imaging. © Academic Pr

ISSN:0740-3194    

DOI:10.1002/mrm.1910050503

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1987

数据来源: WILEY

摘要:

AbstractIn vivoT1measurements are usually made from images. In this paper we describe an alternative method in which data are collected from a strip instead of from an entire plane. We will compare the signal‐to‐noise ratios, the time to make a measurement, and the error inT1as well as other aspects of the two methods. We have found that the strip method has less inherent signal‐to‐noise, but that this may be compensated for by taking measurements at more than the usual two repetition rates. The method employs a selective 180° pulse as well as a selective 90° pulse. It is shown that both pulses effectively isolate the region of interest. © Academic

ISSN:0740-3194    

DOI:10.1002/mrm.1910050504

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1987

数据来源: WILEY

摘要:

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 C

ISSN:0740-3194    

DOI:10.1002/mrm.1910050505

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1987

数据来源: WILEY

摘要:

AbstractPhosphorus‐31 (31P) nuclear magnetic resonance (NMR) spectroscopic investigations of the rat stomach were performed utilizing a 1‐cm2, three‐turn, zig‐zag coil. A zig‐zag coil of this dimension produced an effectiveBlfield that extends only within a 4‐mm distance from the plane of the surface coil, rendering it possible to obtain high‐resolution31P spectra localized to the stomach without contamination from surrounding tissues. Normal stomach showed a characteristic spectral pattern with resonances reflecting inorganic phosphate (Pi), phosphocreatine (PCr), and the α‐, β‐, and γ‐phosphates of adenosine triphosphate (ATP). Ischemia‐induced changes inPi, PCr, and ATP resonances were readily followedin vivowith a time resolution of 2.13 min. Indomethacin‐induced ulcer revealed a low intracellular pH and a decrease in the PCr toPiratio indicating the partially ischemic conditions of ulcerative lesions of the stomach as has been previously suggested. The present studies indicate that31P NMR spectroscopy utilizing a zig‐zag coil is a powerful tool to study local pathology of the gastrointestinal (GI) tract. Since zig‐zag coils suitable for fiberscopic devices are easily constructed, clinical applications of the present technique are a

ISSN:0740-3194    

DOI:10.1002/mrm.1910050506

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1987

数据来源: WILEY

摘要:

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 toB0the 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

ISSN:0740-3194    

DOI:10.1002/mrm.1910050507

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1987

数据来源: WILEY

摘要:

AbstractAnin vivo13C NMR study was performed to investigate whether the relaxation properties of the C‐1 carbon of the glucopyranose residues of glycogen changed as the molecule increased in size. There was no change in resonance intensity or linewidth. Therefore, no significant change inT1, orT2was observed. © Academic Press, I

ISSN:0740-3194    

DOI:10.1002/mrm.1910050508

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1987

数据来源: WILEY

摘要:

AbstractA 32‐year‐old woman who had been diagnosed as having pulmonary sarcoidosis 18 months previously presented with thirst and polyuria. The diagnosis of diabetes insipidus was confirmed biochemically and magnetic resonance imaging (MRI) revealed sarcoid involvement of the pituitary stalk. © Academic Press,

ISSN:0740-3194    

DOI:10.1002/mrm.1910050509

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1987

数据来源: WILEY

摘要:

AbstractA new type of double‐resonant coil which takes advantage of the properties of a radio‐frequency transformer is described. Two concentric loops are wound in close proximity to yield a high mutual inductance. The primary side is tuned to 34 MHz for31P and the secondary side is tuned to 85 MHz for protons. A single lead allows program control over frequency without the need to rearrange cabling. Proton and phosphorus spectroscopy are made possible over essentially the same volume of interest without the need for repositioning the sample. © Academic Press,

ISSN:0740-3194    

DOI:10.1002/mrm.1910050510

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1987

数据来源: WILEY

摘要:

AbstractWhen developing new techniques for NMR imaging andin vivospectroscopy it is a major advantage to be able to calculate the magnetization slice profiles, at any point during a pulse sequence in the presence of a field gradient. While this has frequently been done by treating the problem as a number of discrete resonances, it is sometimes necessary to consider the continuous nature of the magnetization profiles. This paper describes a method used to simulate the free‐induction decay at any point during the NMR experiment. © Academic Press, I

ISSN:0740-3194    

DOI:10.1002/mrm.1910050511

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1987

数据来源: WILEY