Abstract: A method whereby motion can be detected in real time during the acquisition of MRI data. This enables the implementation of several algorithms to reduce or eliminate this motion from an image as it is being acquired. The method is an extension of the acceptance/rejection method algorithm called the diminishing variance algorithm (DVA). With this method, a complete set of preliminary data is acquired along with information about the relative motion position of each frame of data. After all the preliminary data is acquired, the position information is used to determine which lines are most corrupted by motion. Frames of data are then reacquired, starting with the most corrupted frame. The position information is continually updated in an iterative process, therefore each subsequent reacquisition is always done on the worst frame of data. The algorithm has been implemented on several different types of sequences, and preliminary in vivo studies indicate that motion artifacts are dramatically reduced.

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: A high resolution NMR signal is obtained for a thin slice through a body by combining signals in which excitation k-space is covered in two or more excitations. An RF excitation pulse is applied along with an oscillating (e.g. triangular, trapezoidal, sinusoidal) wave modulated magnetic gradient with the RF pulse having nulls corresponding to zero values of the gradient. The RF pulse is applied a second time with the magnetic gradient inverted NMR signals detected following the application of the RF excitation pulses are summed. Minimum phase RF pulses can be employed to reduce signal dropout and reduce artifacts.

Abstract: Disclosed is a method of obtaining magnetic resonance signals from a body which are spatially and spectrally selective comprising the steps of applying a static magnetic field (Bo) to said body thereby aligning nuclear spins, applying a modulated magnetic gradient (G(t)) to said body, applying an RF excitation pulse (B(t)) to said body to tip said nuclear spins, said RF excitation pulse being related to said modulated magnetic gradient whereby resulting magnetic resonance signals are spatially and spectrally dependent, and detecting said magnetic resonance signals. The steps can be repeated in a multi-slice or multi-spectral acquisition mode. The steps can be repeated in a rapid gradient echo pulse sequence.