Optimizing interleaved KY -phase encoding in magnetic resonance angiography

In Fourier encoded magnetic resonance time-of-flight angiography, blood vessels are imaged by selectively suppressing the magnetic resonance signal within a region and detecting the signal of blood as it flows through this region. Large imaging volumes are acquired as multiple overlapping slabs in order to exploit the tradeoffs between the superior signal-to-noise ratio thick slabs and the improved inflow enhancement of thin slabs. Slab selection profiles, flow signal saturation within slabs, and patient motion can produce a slab boundary artifact in the final image volume.;In a clinical setting, this artifact can significantly interfere with image interpretation and hence the diagnosis of the presence or absence of vascular disease. Recently, a sophisticated interleaving technique was developed to address the slab boundary artifact. The method applies the Fourier encoding technique, making it relatively straightforward to implement. The order of Fourier encoding is modified so as to eliminate the presence of slab boundaries. Reduction of the artifact simplifies image interpretation and increases the clinical relevance of the interleaved acquisition.;Traditional multiple slab, the new interleaving, and modified interleaving techniques were assessed through numerical simulations and experiments with cylinders of water and with human subjects. The Bloch equations were solved numerically and used to simulate the acquisition of images. The source and extent of image errors in each of the techniques were quantified. The signal and noise performance of the three techniques were assessed through simulation and measurement along imaged vessels. Finally, qualitative comparisons were made between images.;The interleaving technique can reduce by more than 70% the slab boundary artifact observed in the multiple slab acquisitions. Yet the interleaving method suffers an inherent limitation that prevents the further reduction of image artifacts. One modified interleaving method described here eliminates practically 100% of the slab boundary artifact. The same approach ranks 9 out of 14 when measured by signal-to-noise ratio as compared with traditional and other interleaving methods. A modified interleaving technique was developed that reduced the slab boundary artifact by 71% and that had signal, noise, and efficiency values comparable to traditional multiple slab acquisition.