摘要:

AbstractA method has been developed to reduce a magnetic resonance image artifact arising from the Fourier transformation of data truncated in the phase‐encoding direction. The discontinuity is eliminated between the phase of the complex data sample associated with the maximum negative phase‐encoding gradient and the phase of the maximum positive gradient sample. Images retain sharper edges than if low‐pass filtering is employed. The method is demonstrated on clinical images, then an explanation of the method is presented.© 1985 Academic Pre

ISSN:0740-3194    

DOI:10.1002/mrm.1910020602

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

年代:1985

数据来源: WILEY

摘要:

AbstractUsing a Taylor series expansion of the phase shift of a moving isochromatic spin group in the presence of a magnetic field gradient, the refocusing effects of the Carr‐Purcell‐Meiboom‐Gill pulse sequence on stationary nuclei and those with constant, rectilinear velocity are readily demonstrated. Continuing the analysis to higher orders of motion reveals that nuclei with a constant, rectilinear acceleration have a phase shift at the spin echoes which increases linearly with echo number. Constant, rectilinear jerk (the time rate of change of acceleration) leads to an increase in phase shift from echo to echo which is quadratic in nature with an overlying reduction of the odd‐numbered echoes by a constant amount. Motion parameters may be measured by parameter identification techniques. These principles may be applied to phase‐sensitive NMR imaging.© 1985 Academic

ISSN:0740-3194    

DOI:10.1002/mrm.1910020603

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

年代:1985

数据来源: WILEY

摘要:

AbstractMultislice imaging techniques effectively applicable to inversion‐recovery (IR) imaging are developed and applied to human imaging. These new multislice IR imaging sequences employ the time‐multiplexing (TM) technique conventionally used in the slice‐by‐slice saturation‐recovery (SR) imaging. Two new time‐multiplexed multislice (TMM) IR imaging sequences are proposed and some of the experimental results obtained with the methods are presented.© 1985 Academ

ISSN:0740-3194    

DOI:10.1002/mrm.1910020604

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

年代:1985

数据来源: WILEY

摘要:

AbstractEarly 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

ISSN:0740-3194    

DOI:10.1002/mrm.1910020605

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

年代:1985

数据来源: WILEY

摘要:

AbstractEncoding the Precession phase angle of proton nuclei for Fourier analysis has produced accurate measurement of fluid velocity vector components by MRI. A Pair of identical gradient pulses separated in time by exactly ½ TE, are used to linearly encode the phase of flow velocity vector components without changing the phase of stationary nuclei, Two‐dimensional Fourier transformation of signals gave velocity density images of laminar flow in angled tubes which were in agreement with the laws of vector addition. These Velocity profile images provide a quantitative method for the investigation of fluid dynamics and hemodynamics.© 1985 Academic Press,

ISSN:0740-3194    

DOI:10.1002/mrm.1910020606

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

年代:1985

数据来源: WILEY

摘要:

AbstractAn arrangement of two surface coils was devised to allow phosphours‐31 (31P) NMR spectroscopy of a localized hemispheric brain injury model in the rat. Two elliptical (8×12mm) surface coils are placed parallel to each other (3 mm apart) over each side of the rat head. Spectra are collected from either the normal or the injured side of the head using the appropriate surface coil. A passive detuning method was used to eliminate unwanted coil‐coil interactions.31P imaging results with the two coils on phantoms show excellent isolation (6% signal overlap) between the two coils. The two‐coil set up was then used to follow a time course of injury from the hemispheric injury model.© 1985 Academic Pr

ISSN:0740-3194    

DOI:10.1002/mrm.1910020607

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

年代:1985

数据来源: WILEY

摘要:

AbstractA model system forin vivoproton NMR studies consisting of a transplantable tumor growing on a rat's tail was investigated at 90 MHz using a high‐resolution Fourier transform spectrometer. Spectra were obtained, relaxation times were measured, and the spatial distributions of proton signal intensities were estimated. We conclude that the model could be used for developing both spectroscopy and imaging approaches.© 1985 Academic Press,I

ISSN:0740-3194    

DOI:10.1002/mrm.1910020608

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

年代:1985

数据来源: WILEY

摘要:

AbstractSelective suppression of a given resonance in an NMR image can be obtained with a π/2 pulse whose excitation spectrum in zero at the appropriate chemical shift. The selective π/2 pulse presented here is composed of two nonselective π/2 pulses of opposite phase. The two pulses are separated by a short interval which determines the excitation spectrum.© 1985 Academic Press,

ISSN:0740-3194    

DOI:10.1002/mrm.1910020609

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

年代:1985

数据来源: WILEY

ISSN:0740-3194    

DOI:10.1002/mrm.1910020610

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

年代:1985

数据来源: WILEY

ISSN:0740-3194    

DOI:10.1002/mrm.1910020601

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

年代:1985

数据来源: WILEY