Abstract: A method of cancelling ghosts from NMR images. The method involves estimating a phase difference function .DELTA. (n.sub.1, n.sub.2) and using that function to solve a linear system of equations to find the magnitudes of the true object densities at the true image and ghost locations x(n.sub.1,n.sub.2) and x(n.sub.1,n.sub.2 +N/2), respectively, where the image has dimensions N.times.N.sub.s. Experimental values of .DELTA. (n.sub.1, n.sub.2) for a variety of objects indicate that its variation along n.sub.1 is considerably larger than along n.sub.2. Thus, for each column n.sub.1, the phase difference function .DELTA. (n.sub.1, n.sub.2) can be modelled as a one-dimensional function of n.sub.2 with two parameters .alpha. (n.sub.1) and .beta. (n.sub.1), which are estimated from the pixels in the 2-D FFT processed reconstructed image Y(n.sub.1,n.sub.2). These parameters are then used to estimate .DELTA. (n.sub.1, n.sub.2), which is ultimately used to de-ghost the image.

Abstract: A method to recover MRI signals resulting from the application of time varying gradients. The raw MRI signal is demodulated, low pass filtered, and digitized using an A/D converter sampling linearly at the Nyquist rate. The samples from the A/D converter are compiled into a vector, which is multiplied by a least squares estimator matrix (H*H).sup.- H*, where H is a matrix whose mkth element, in the case of a sinusoidal gradient, is given by ##EQU1## This multiplication is repeated for each vector of samples from the A/D converter, and the vectors resulting from the multiplication are accumulated to form the columns of a matrix, the rows of which are Fourier transformed to obtain the MRI image.

Abstract: A method of high-speed magnetic resonance imaging in which the object to be imaged is placed in a high static magnetic field. Nuclear spins are excited in an image area by applying a pulse of radio frequency magnetic field. Optionally, a first gradient field, termed a slice selection gradient, may be applied in conjunction with the RF excitation pulse such that spins are excited only in a selected plane of the object. Following an encoding pulse sequence and rephasing of the nuclear spins by the application of a 180.degree. radio frequency pulse, mutually orthogonal phase-encoding and readout gradients are alternatively applied in the image plane to effect a traversal through spatial frequency domain (k-space). In a preferred embodiment of the invention, the readout gradient is applied as a continuous sinusoidal wave, resulting in a slight overlap between the phase-encoding and readout gradients. If phase errors vary slowly in time, only a partial k-space trajectory is required.

Abstract: A method of high-speed magnetic resonance imaging in which the object to be imaged is placed in a high static magnetic field. Nuclear spins are excited in an image area in a selected plane of the object by superimposing a slice-selection gradient along an axis and applying a pulse of radio frequency magnetic field. Following an encoding pulse sequence and rephasing of the nuclear spins by the application of a 180.degree. radio frequency pulse, mutually orthogonal phase-encoding and readout gradients are alternately applied in the image plane to effect a traversal through spatial frequency domain (k-space). In a preferred embodiment of the invention, the readout gradient is applied as a continuous sinusoidal wave, resulting in a slight overlap between the phase-encoding and readout gradients. If phase errors vary slowly in time, only a partial k-space trajectory is required.

Abstract: A method of high-speed imaging is employed in which less than 100% of the spatial frequency domain (k-space) is sampled. In one embodiment, the trajectory extends over the k-space origin, and the information acquired from the extension is used to compensate for any phase errors. If the same number of points are collected as in a full k-space acquisition, signal bandwidth is maintained, and spatial frequency response is increased. In a second embodiment, two or more partial k-space acquisitions are performed and then pieced together in a "mosaic" prior to Fourier transformation. In a further embodiment, partial k-space acquisitions in the direction of the readout gradient are combined with interleaved acquisitions in the direction of the phase-encoding gradient to avoid discontinuities.

Abstract: A method of high-speed magnetic resonance imaging in which the object to be imaged is placed in a high static magnetic field. Nuclear spins are excited in an image area in a selected plane of the object by superimposing a slice-selection gradient along an axis and applying a pulse of radio frequency magnetic field. Following an encoding pulse sequence and rephasing of the nuclear spins by the application of a 180.degree. radio frequency pulse, mutually orthogonal phase-encoding and readout gradients are alternately applied in the image plane to effect a traversal through spatial frequency domain (k-space). If phase errors vary slowly in time, only a partial k-space trajectory is required. Chemical shift is eliminated either by the application of a suppression pulse of RF field or by tailoring the frequency spectrum of the rephasing pulse so as to preclude rephasing of one or other of the chemical moieties.

Abstract: A circuit and method are disclosed for providing high, constant amplitude sinusoidally modulated NMR gradient fields. A capacitor is connected in parallel with the gradient coil, but separated by a switch. A pre-determined amount of energy is stored in the capacitor and then the switch is closed to permit a sinusoidal oscillation of energy between the capacitor and gradient coil. By precharging appropriately, sine wave or cosine wave oscillation can be obtained for the NMR system. The oscillation is terminated by opening the switch at a time when all of the oscillating energy is in the capacitor. In a preferred embodiment of the invention, the switch is a bridge circuit, each of whose sides is a back-to-back thyristor pair, so that the gradient field may be modulated either as a full wave, half-wave rectified or non-rectified sinusoidal oscillation. In one embodiment, a full-wave rectified sine wave is used, and all the oscillating energy is caught in the capacitor during intervals in which 180.degree.

Abstract: A method of cancelling ghosts from NMR images. The method involves estimating a phase difference function .DELTA. (n.sub.1, n.sub.2) and using that function to solve a linear system of equations to find the magnitudes of the true object densities at the true image and ghost locations x(n.sub.2,n.sub.2) and x(n.sub.1,n.sub.2 +N/2), respectively, where the image has dimensions N.times.N.sub.s. Experimental values of .DELTA. (n.sub.1, n.sub.2) for a variety of objects indicate that its variation along n.sub.1 is considerably larger than along n.sub.2. Thus, for each column n.sub.1, the phase difference function .DELTA. (n.sub.1, n.sub.2) can be modelled as a one-dimensional function of n.sub.2 with two parameters .alpha. (n.sub.1) and .beta. (n.sub.1), which are estimated from the pixels in the 2-D FFT processed reconstructed image Y(n.sub.1,n.sub.2). These parameters are then used to estimate .DELTA. (n.sub.1, n.sub.2), which is ultimately used to de-ghost the image.