A study of a spiral scan echo planar method in the presence of static field inhomogeneities is presented. The approach consists of obtaining the samples over the Fourier plane trajectory of the spiral scan, as modified by the inhomogeneities. The resulting images are compared to a Cartesian scan echo-planar method also subjected to inhomogeneities in the static field. The conclusion is that the spiral scan is more sensitive to this type of inhomogeneity. The possibility of compensating for the inhomogeneities during the reconstruction procedure is suggested by a preliminary experimental result.

An interpolation method useful for reconstructing an image from its Fourier plane samples on a linear spiral scan trajectory is presented. This kind of sampling arises in NMR imaging. We first present a theorem that enables exact interpolation from spiral samples to a Cartesian lattice. We then investigate two practical implementations of the theorem in which a finite number of interpolating points are used to calculate the value at a new point. Our experimental results confirm the theorem's validity and also demonstrate that both practical implementations yield very good reconstructions. Thus, the theorem and/or its practical implementations suggest the possibility of using direct Fourier reconstruction from linear spiral-scan NMR imaging.

Absrrucr-The pinned sine transform (PST) coder described is a practical approximation to the pinned KLT coder. The image is partitioned into two fields: a bounduryfield, which depends only on the coded block boundaries, and a pinned field, which vanishes at the boundaries and is subsequently sine transformed and compressed. The reconstructed image is continuous across the block boundaries and "blocking effects" are hardly visible. Simulation results are given for fixed and adaptive compression schemes with fair image quality at low hit rates down to 0.3 hits/pel.

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