Minimizing dead-periods in flow-encoded or -compensated pulse sequences while imaging in oblique planes

A technique is developed to minimize magnetic resonance pulse sequence dead-periods, with first and higher moment requirements, while imaging in oblique planes. Dead-period requirements of starting amplitude, ending amplitudes, area, and other moment requirements are transformed from the image coordinate system to the physical gradient coordinate system, where the waveforms are then designed. With this technique, the full capabilities of the gradient hardware are utilized. An online algorithm is presented to perform dead-period minimization and gradient waveform design when the first moment and area of the dead-period are specified. The algorithm is then used to implement three-axis flow-compensation in a fast spoiled gradient-echo sequence. This results in a minimal increase in TE and TR over an equivalent non-flow-compensated sequence, and little variation in the minimum TR over the entire range of oblique slice orientations. Applications of this algorithm extend to the optimization of any pulse sequence in which the first moment is important and oblique imaging is required. J. Magn. Reson. Imaging 1999;10:183-192.