A novel technique called "Noquist" is introduced for the acceleration of dynamic cardiac magnetic resonance imaging (CMRI). With the use of this technique, a more sparsely sampled dynamic image sequence is reconstructed correctly, without Nyquist foldover artifact. Unlike most other reduced field-ofview (rFOV) methods, Noquist does not rely on data substitution or temporal interpolation to reconstruct the dynamic image sequence. The proposed method reduces acquisition time in dynamic MRI scans by eliminating the data redundancy associated with static regions in the dynamic scene. A reduction of imaging time is achieved by a fraction asymptotically equal to the static fraction of the FOV, by omitting acquisition of an appropriate subset of phase-encoding views from a conventional equidistant Cartesian acquisition grid. The theory behind this method is presented along with sample reconstructions from real and simulated data. Noquist is compared with conventional cine imaging by retrospective selection of a reduced data set from a full-grid conventional image sequence. In addition, a comparison is presented, using real and simulated data, of our technique with an existing rFOV technique that uses temporal interpolation. The experimental results confirm the theory, and demonstrate that Noquist reduces scan time for cine MRI while fully preserving both spatial and temporal resolution, but at the cost of a reduced signal-tonoise ratio (SNR). Magn Reson Med 51:331-342, 2004.
A novel cardiac magnetic resonance imaging (MRI,) acceleration strategv called "NoQuist " is presented here. Using this new technique, a more sparsely sampled dynamic image sequence is correctly reconstructed without Nyquist foldover artifact by reductions in the size of'the Fourier model of the k-space data for the dynamic image. It does not rely either on substitution or interpolation to arrive at a data set sufficient for reconstruction of the dynamic sequence.The proposed "NoQuist" method allows reduction of' acquisition time in dynamic MRI scans by eliminating the data redundancy that is associated with the presence of static regions in the dynamic scene. A reduction of acquisition time can be achieved, asymptotically equal to the tatic fraction of thefield-of-view (FOV), by omitting acquisition of a strategically selected subset of' phase encoding views from a conventional equidistant Cartesian acquisition grid. IntroductionIn cardiac imaging of a patient with a severe cardiovascular disease, the shorter breath hold time required to complete a whole movie will increase the success rate in imaging it. This fact, associated with the constant motion of the heart, are the main problems still encountered in cardiac MRI.Thus, faster acquisition is desirable since it allows the same image to be acquired in a shorter breath hold. Alternatively, it also allows higher-resolution images in the same breath hold time, or complete multi-slice coverage of anatomy in fewer breath holds. This is why a reduction of imaging time remains of great interest in many applications of dynamic MRI, and mainly in cardiac imaging.A repeated acquisition of image planes in which only part of the field-of-view (FOV) changes over time is involved in many important dynamic MR imaging applications. A clear example is cine-imaging of the heart, where in a breath-held acquisition, the heart moves during the cardiac cycle, but the lungs and shoulders do not move. For each image of a conventional dynamic acquisition technique, all the raw data space, called kspace, will be acquired. Various approaches have been proposed to trade the associated redundancy for reduction in acquisition time or, alternatively, increase temporal resolution. These existing techniques have in common the fact that improvement of acquisition efficiency is achieved by reduction of spatial sampling density, followed by one form or another of temporal interpolation or filtering of the data points in order to eliminate the foldover artifact [ 1-41. A common feature of most reduced FOV techniques to date is the associated time savings. If the size of the dynamic region represents a fraction 1iK of the total FOV, the proposed techniques all offer acquisition efficiency improvement by a factor exactly or approximately exactly equal to K.The novel acceleration strategy introduced here does not rely on substitution or interpolation. A more sparsely sampled dynamic image sequence is correctly reconstructed without Nyquist foldover artifact by reductions in the size of the Fourie...
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