Abstract: In an MRI imaging system each portion of k-space is sequentially scanned, transformed and separately demodulated. Instead of adding the k-space regions, as is the practice in the prior art, the demodulated portions are added, each representing spectral portions of the image. Each k-space portion is scanned with closely spaced lines which substantially satisfy the sampling requirement to avoid aliasing. In this way, distortion resulting from phase changes between k-space scans is avoided.

Abstract: In an MRI imaging system each portion of k-space is sequentially scanned, transformed and separately demodulated. Instead of adding the k-space regions, as is the practice in the prior art, the demodulated portions are added, each representing spectral portions of the image. Each k-space portion is scanned with closely spaced lines which substantially satisfy the sampling requirement to avoid aliasing. In this way, distortion resulting from phase changes between k-space scans is avoided.

Abstract: A pulsed strong magnetic field, created with a superconductive coil, is applied to a selected region of the anatomy. Following the pulse a relatively low readout field is used along with a set of spatially orthogonal gradient fields parallel to the readout field. The readout field is chosen such that the noise arises primarily from body losses, and results in negligible susceptibility effects. Following excitation, the resultant signals from the precessing moments are detected, processed and used to make magnetic resonance images of the object. The field pulsing is made efficient using energy recovery.

Abstract: In applications where a tuned coil is used as a receiving antenna, the coil's resistance can produce excessive noise. If a low-loss coil is used, such as with cooled or supercoductive wire, the resulting Q results in inadequate bandwidth. To provide the desired bandwidth without additional losses the coil and its tuning capacitor are periodically de-energized using one or two switches. This sets the signal to substantially zero where it starts again to build up, effectively widening the bandwidth. The resulting signal is synchronously detected to provide the in-phase and quadrature signals. In an NMR system this enables the performance to be limited by sample or object noise. In MRI systems using an oscillating readout bias, the shorting is timed with the transition of the bias waveform.

Abstract: Continuous fluoroscopic data is acquired using magnetic resonance imaging by applying magnetic gradients to excited nuclei whereby emitted magnetic resonance signals traverse interleaved spirals in k-space. The spirals can have tighter loops near the origin of k-space to emphasize lower frequencies.

Abstract: A long train of spin echoes is produced using a RARE excitation pulse sequence, and during each spin echo an annular segment of a long k-space spiral as determined by read-out magnetic gradients is detected. At the end of the echo train the entire k-space spiral will have been covered. Each of the segments can be a unique annular portion of the k-space spiral. Alternatively, fewer annular segments of the spiral can be provided, with the fewer annular segments rotated in k-space and replayed to cover interleaved paths in k-space. The imaging gradients are refocused at the time of each spin-echo pulse in order to permit the long echo pulse trains of RARE imaging. Each spiral segment is surrounded by gradient lobes that move out from the k-space origin to the beginning of the segment, and move back to the origin from the end of the segment. Advantageously, the magnetic gradient lobes can be produced concurrently with parasitic echo crusher gradients at the beginning and end of each spin-echo pulse.

Abstract: Disclosed is a method for automatically removing blur in magnetic resonance image signals introduced due to inhomogeneity in the magnetic field and variations in magnetic susceptibility of an object being imaged. Detected signals are demodulated at several different frequencies and reconstructed to create a series of base images. The amount of blur is determined by establishing a focusing measure for each point or part in each base image, and a composite image is then constructed using only the unblurred regions from each base image. Focusing criterion can include minimization of the imaginary part of the complex MRI after removal of constant and low frequency phase information.

Abstract: In an MRI imaging system using a pulsed field to polarize the magnetic moments, a gradient field is applied prior to the collapse of the pulsed field. When the pulsed field turns off, the magnetic moments are spatially varying in the vicinity of the null plane of the gradient field. In one embodiment the gradient field is in quadrature with the pulsed field, enabling the imaging gradient coils to be used to provide an excited slab. In another embodiment the selection gradient field is parallel to the pulsed field and enables sharper slices by subtracting images acquired with different null planes.

Abstract: A high frequency oscillatory signal is added to the gradient waveform to provide a blurring or convolution prior to sampling. The received signal can be modulated to provide the desired space-limiting function and thus avoid aliasing. The received signal is filtered prior to sampling to remove these high frequency signals.

Abstract: Following the polarizing of the magnetic moments in an object using a pulsed field the moment distribution is imaged in the rotating frame by exciting the magnetic moments using a radio-frequency gradient field and a radio-frequency bias field whose phase is cyclically oscillated to prevent the loss of signal due to inhomogeniety. To increase the signal-to-noise ratio coils are used to pick up the signals at quadrature positions. A constant gradient is used for spatial selectivity through saturation.

Abstract: Signals from precessing magnetic moments are received in the presence of a cyclically varying bias field to avoid the phase error buildup due to inhomogeniety. The bias field has substantially a zero average value and can either use a pulse or a symmetrical waveform. The demodulating signal is based on the frequency of the cyclical variations.

Abstract: The response of color television are improved by adding a high frequency luminance component which is proportioned to the color-difference signal so as to provide color signals with correct transitions. A control function which minimizes the means square error of the luminance and color difference signals is used to weight the amplitude of the added luminance component. This control function becomes the ratio of the cross correlation of the luminance and color-difference signals to the autocorrelation of the luminance signal. In a television communications system, the control signal can be transmitted as a narrow band signal.

Abstract: The aspect ratio of a television system is increased by reducing the number of active lines in the vertical direction and using those lines to insert information for increasing the width of horizontal lines. The added information is superimposed at or near black level so that conventional receivers will merely see a shorter image without the increased width. To minimize the visibility of the added information, the high-energy low frequencies can be reduced. Alternatively the low frequency information for lengthening the horizontal lines can be placed in compressed form on either side of the normal horizontal lines without being seen on conventional receivers or used to modulate a high-frequency burst placed in the inactive lines. The increased aspect ratio receiver decodes the information in the inactive vertical lines, adds it to the decoded low frequency information, and displays it as an increased aspect ratio image in HDTV receivers.

Abstract: A pulsed strong magnetic field is applied to an object creating a magnetic moment distribution. Following the pulse a set of spatially orthogonal gradient fields pointed normal to the magnetic moments are used to cause the magnetic moments to precess around the axis of the gradient fields, producing time-varying magnetic fields indicative of the spatial distribution of the magnetic moments. These are then detected, processed and used to make magnetic resonance images of the object.

Abstract: A two-dimensional projection image of the NMR activity within a volume is obtained. The signals due to static material are not excited and do not appear in the projection image. The signals due to moving blood in vessels produce an isolated image of the vessels with the superimposed structure removed. Excitation systems are used which excite only moving material and return static material to equilibrium.

Abstract: The amplitude of specific spectroscopic components are measured by first finding their frequency in the presence of inhomogeneity. A large stable component, usually the water line, is used as a frequency standard to determine the amount of frequency shift in each voxel. The frequency standard is used to determine the relative frequencies of each of the desired spectroscopic components. In one approach the entire hydrogen spectrum is envelope detected with the beats between the water line and the spectroscopic components used to provide a stable spectrum, immune to inhomogeneity.

Abstract: Magnetic resonance signals are received using a plurality of coils, each sensitive to different but overlapping regions of the volume being studied. The signals are combined so as to cancel in undesired regions of the body and receive net signals from only desired parts of the volume to enhance the signal-to-noise ratio for imaging and spectroscopy.

Abstract: In a multiple-measurement system, a weighted sum of the measurements is used to provide a selective image. An additional weighted sum is used to provide an increased signal-to-noise ratio image. An improved selective image is formed by combining the low frequency portions of the selective image and the correct high frequency componenets from the increased signal-to-noise ratio image. To provide the correct high frequency components the error between the selective image and the improved selective image is minimized. The low-noise high-frequency image is weighted by the ration of the cross correlation of the selective andlow noise images divided by the autocorrelation of thelow noise image.

Abstract: A two-dimensional projection image of the NMR activity within a volume is obtained. The signals due to static material are not excited and do not appear in the projection image. The signals due to moving blood in vessels produce an isolated image of the vessels with the superimposed structure removed. Excitation systems are used which excite only moving material and return static material to equilibrium. A 180.degree. excitation provides immunity to inhomogeneity.

Abstract: The magnetic resonance activity of a region of a volume is imaged using a time varying gradient whose integral provides a constant velocity spiral in the spatial frequency domain. To provide high fidelity for relatively low values of T.sub.2, high SNR for relatively high values, and a T.sub.2 sensitive image, the spiral is retraced back to the origin. The gradient requirements are minimized using a sequence of interleaved spirals using separate excitations. For further time reduction, only half the spatial frequency domain can be scanned, using inversion excitations to reduce the effects of inhomogeneity.