HALF FOURIER RECONSTRUCTION OF SPIRAL MR IMAGES

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Introduction: Partial sampling of k-space in conventional spin-warp imaging has become a standard way of reducing echo times or total acquisition time. In an analogous way, reconstruction of images from interleaved spiral k-space trajectories is also possible where only half the number of interleaves are acquired. Methods and Discussion: This method relies on the Hermitian conjugate symmetry of the raw data and hence is sensitive to factors influencing this symmetry, such as B0 field inhomogeneity, B1 phase variation, Maxwell terms, etc. Unfortunately, these are all factors which are present in data acquired in the scanner therefore methods of correction are required. Half Fourier reconstruction in spiral imaging relies on putting the spiral undersampling artifact in quadrature to the desired imaged. Unfortunately, in the presence of phase variations in the imaged object, these artifacts appear at some distance from the location of the inhomogeneity. The simplest correction is to use a two dimensional homodyne correction similar to the way it is used in spin warp half Fourier reconstruction but this does not solve the problem of the non-localized image artifacts. Fundamental Nyquist sampling limits are being violated and interpolation of data requires the construction of better interpolation functions bringing into question the accuracy of the gridding algorithm most commonly used in spiral image reconstruction. Conclusion: This technique holds promise for improving the temporal resolution of functional MR imaging studies and other studies employing the spiral imaging sequence.