Advances in Spiral fMRI: A High-resolution Study with Single-shot Acquisition

Spiral fMRI has been put forward as a viable alternative to rectilinear echo-planar imaging, in particular due to its enhanced average k-space speed and thus high acquisition efficiency. This renders spirals attractive for contemporary fMRI applications that require high spatiotemporal resolution, such as laminar or columnar fMRI. However, in practice, spiral fMRI is typically hampered by its reduced robustness and ensuing blurring artifacts, which arise from imperfections in both static and dynamic magnetic fields.Recently, these limitations have been overcome by the concerted application of an expanded signal model that accounts for such field imperfections, and its inversion by iterative image reconstruction. In the challenging ultra-high field environment of 7 Tesla, where field inhomogeneity effects are aggravated, both multi-shot and single-shot 2D spiral imaging at sub-millimeter resolution was demonstrated with high depiction quality and anatomical congruency.In this work, we further these advances towards a time series application of spiral readouts, namely, single-shot spiral BOLD fMRI at 0.8 mm in-plane resolution. We demonstrate that spiral fMRI at 7 T is not only feasible, but delivers both competitive image quality and BOLD sensitivity, with a spatial specificity of the activation maps that is not compromised by artifactual blurring. Furthermore, we show the versatility of the approach with a combined in/out spiral readout at a more typical resolution (1.5 mm), where the high acquisition efficiency allows to acquire two images per shot for improved sensitivity by echo combination.HighlightsThis work reports the first fMRI study at 7T with spiral readout gradient waveforms.We achieve spiral fMRI with sub-millimeter resolution (0.8 mm, in-plane FOV 230 mm), acquired in a single shot.Spiral images exhibit intrinsic geometric congruency to anatomical scans, and spatially highly specific activation patterns.Image reconstruction rests on a signal model expanded by measured trajectories and static field maps, inverted by cg-SENSE.We assess generalizability of the approach for spiral in/out readouts, providing two images per shot (1.5 mm resolution).

Calibration of spiral-readout image-plate detectors

An improved method for intensity-uniformity calibration of diffraction data collected on spiral-readout image-plate (IP) systems is described. This technique is applicable to all types of spiral-readout IP detectors. The procedure utilizes an attenuated direct-beam scan of the IP to generate a radial-sensitivity calibration table. Exposure and scanning of the calibration frame are done on the same time scale as typical data collections, and require no additional equipment. Specific examples are presented for use with Mac Science DIP2000 systems. The new radial calibration is shown to reduce significantly structure-basedRfactors. The improved radial calibration is also shown to lowerRmergewhen the IP is offset from the beam center. In addition to improving data quality and statistics, this method provides a quick and simple diagnostic tool to monitor changes in the sensitivity of the IP detector as a function of age.