Feasibility of spiral fMRI based on an LTI gradient model

Nadine N Graedel,Lars Kasper,Maria Engel,Jennifer Nussbaum,Bertram J Wilm,Klaas P Pruessmann,S Johanna Vannesjo

doi:10.1016/j.neuroimage.2021.118674

Nadine N Graedel, Lars Kasper + Show 5 more

Open Access

https://doi.org/10.1016/j.neuroimage.2021.118674

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Abstract

Spiral imaging is very well suited for functional MRI, however its use has been limited by the fact that artifacts caused by gradient imperfections and B0 inhomogeneity are more difficult to correct compared to EPI. Effective correction requires accurate knowledge of the traversed k-space trajectory. With the goal of making spiral fMRI more accessible, we have evaluated image reconstruction using trajectories predicted by the gradient impulse response function (GIRF), which can be determined in a one-time calibration step.GIRF-predicted reconstruction was tested for high-resolution (0.8 mm) fMRI at 7T. Image quality and functional results of the reconstructions using GIRF-prediction were compared to reconstructions using the nominal trajectory and concurrent field monitoring.The reconstructions using nominal spiral trajectories contain substantial artifacts and the activation maps contain misplaced activation. Image artifacts are substantially reduced when using the GIRF-predicted reconstruction, and the activation maps for the GIRF-predicted and monitored reconstructions largely overlap. The GIRF reconstruction provides a large increase in the spatial specificity of the activation compared to the nominal reconstruction.The GIRF-reconstruction generates image quality and fMRI results similar to using a concurrently monitored trajectory. The presented approach does not prolong or complicate the fMRI acquisition. Using GIRF-predicted trajectories has the potential to enable high-quality spiral fMRI in situations where concurrent trajectory monitoring is not available.

Highlights

Blood Oxygen Level Dependent (BOLD) functional magnetic resonance imaging requires fast imaging, for which acquisitions with Echo Planar Imaging (EPI) readouts are currently used as the gold standard
Spiral imaging is very well suited for functional MRI, its use has been limited by the fact that artifacts caused by gradient imperfections and B0 inhomogeneity are more difficult to correct compared to EPI
With the goal of making spiral functional magnetic resonance imaging (fMRI) more accessible, we have evaluated image reconstruction using trajectories predicted by the gradient impulse response function (GIRF), which can be determined in a one-time calibration step

Summary

Introduction

Blood Oxygen Level Dependent (BOLD) functional magnetic resonance imaging (fMRI) requires fast imaging, for which acquisitions with Echo Planar Imaging (EPI) readouts are currently used as the gold standard. Spiral sampling is more amenable to high undersampling factors, as the point spread function results in relatively incoherent aliasing (Wright et al, 2014), which can be less detrimental to image quality compared to coherent aliasing, which occurs in undersampled EPI. Despite these advantages spiral imaging has not yet become a mainstream fMRI acquisition strategy. It is common to perform a delay correction in spiral imaging (Bhavsar et al, 2014; Börnert et al, 1999; Robison et al, 2010) This typically requires extra calibration scans, and is usually not as effective as the EPI delay correction. Spiral fMRI images have often been blurry, especially around the air-tissue interfaces in the frontal sinuses and ear canals

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