The exact, hardware-constrained design of a spiral k-space trajectory requires the solution of a differential equation, thereby making real-time prescription difficult on scanners with limited computational power. This study describes a closed-form approximate solution for interleaved Archimedian spiral trajectories that closely matches the exact design. Both slew rate-limited and amplitude-lim...

K. Borsuk in 1979, at the Topological Conference in Moscow, introduced concept of the capacity of a compactum and asked some questions concerning properties of the capacity ofcompacta. In this paper, we give partial positive answers to three of these questions in some cases. In fact, by describing spaces homotopy dominated by Moore and Eilenberg-MacLane spaces, the capacities of a Moore space $...

In real-world sampling of k-space data, one generally makes a stochastic error not only in the value of the sample but in the effective position of the drawn sample. We refer to the latter as imprecise sampling and apply this concept to the fourier-based acquisition of magnetic resonance data. The analysis shows that the effect of such imprecisely sampled data accounts for contributions to nois...

PURPOSE To investigate the performance of the recently introduced spatiotemporal parallel imaging technique called parallel MRI with extended and averaged generalized autocalibrating partially parallel acquisitions (GRAPPA) kernels (PEAK-GRAPPA) for myocardial perfusion measurements. MATERIALS AND METHODS A study with 11 patients with myocardial infarction was performed to compare nonaccelera...

Introduction: We present a method to compute the fastest possible gradient waveforms for a given k-space trajectory. In our design, we exploit the fact that each gradient set has its own limitation. This is an extension of our previous method described in [1]. In that solution, the worst-case magnitude gradient and slew constraints were considered. This has the advantage of resulting in wavefor...

PROPELLER MRI (periodically rotated overlapping parallel lines with enhanced reconstruction) provides images with significantly fewer B(0)-related artifacts than echo-planar imaging (EPI), as well as reduced sensitivity to motion compared to conventional multiple-shot fast spin-echo (FSE). However, the minimum imaging time in PROPELLER is markedly longer than in EPI and 50% longer than in conve...

We present an index for top-k most frequent document retrieval whose space is |CSA|+o(n)+D log n D+O(D) bits, and its query time is O(log k log 2+ n) per reported document, where D is the number of documents, n is the sum of lengths of the documents, and |CSA| is the space of the compressed suffix array for the documents. This improves over previous results for this problem, whose space complex...

We show that isomorphism testing of k-trees is in the class StUSPACE(log n) (strongly unambiguous logspace). This bound follows from a deterministic logspace algorithm that accesses a strongly unambiguous logspace oracle for canonizing k-trees. Further we give a logspace canonization algorithm for k-paths.

Surface plasmon resonators can drastically redistribute incident light over different output wave vectors and polarizations. This can lead for instance to sub-diffraction sized nanoapertures in metal films that beam and to nanoparticle antennas that enable efficient conversion of photons between spatial modes, or helicity channels. We present a polarimetric Fourier microscope as a new experimen...