RESUMO
New, rapid two- and three-dimensional imaging sequences based on steady-state gradient echoes and projection-reconstruction (PR) techniques are proposed. Quantitative studies show that fast PR sequences and classical, fast gradient-echo Fourier transform sequences lead to identical contrasts. In order to minimize inhomogeneity effects, a particular focus has been placed on echo-time reduction. The use of a weighting window permits one to acquire severely truncated echoes; partial k-space scanning may be considered.
Assuntos
Processamento de Imagem Assistida por Computador , Imageamento por Ressonância Magnética/métodos , Processamento de Sinais Assistido por Computador , Animais , Análise de Fourier , Humanos , Modelos Estruturais , OvinosRESUMO
Simultaneous imaging of proton and fluorine nuclei distributed in a unique sample has been performed by multiplexing the receiver coil's frequency for nmr signal acquisition. Implementation of the technique and modifications of a conventional spectrometer are described for operating at 0.13 T.
Assuntos
Flúor/química , Hidrogênio/química , Espectroscopia de Ressonância Magnética/métodos , Conversão Análogo-Digital , Espectroscopia de Ressonância de Spin Eletrônica , Desenho de Equipamento , Espectroscopia de Ressonância Magnética/instrumentação , PrótonsRESUMO
In magnetic resonance imaging and spectroscopy, knowledge of the magnetic field gradient behavior is very important. This work describes a simple way to characterize the temporal and spatial dependence of the main magnetic field when a gradient is switched. Records are performed with a home-built magnetometer. This device is controlled by a personal computer for recording and processing the NMR signals from an array of small probes spatially distributed and switched by the magnetometer. We present results of measurements on a 2-T superconducting magnet. These results show the residual defects of an active shielded gradient coils system.