Meeting Banner
Abstract #4255

B0 field mapping inaccuracies at 7T and their effect on shim estimation and EPI distortion

Claire Lucas1, Susan T Francis1, and Adam Berrington1
1Sir Peter Mansfield Imaging Centre, University of Nottingham, Nottingham, United Kingdom

Synopsis

Keywords: Shims, Artifacts, brain, multi-coil shim array, EPI, distortion, eddy current

Motivation: Inconsistencies in B0-maps may lead to bias in shimming and acquisition, yet their extent is unclear.

Goal(s): Determine the repeatability of standard dual-echo B0-mapping sequences and the impact of bias fields at 7T.

Approach: 2D and 3D B0-maps were acquired in vivo and the bias field introduced by frequency-encoding, phase-encoding and slice-select gradients were measured using gradient flipping. The impact on B0 shimming was calculated and demonstrated for EPI.

Results: 2D was more robust than 3D B0-mapping. Averaging gradient flipped acquisitions created an ‘unbiased’ B0-map, removing eddy current fields which were shown to generate compensatory shim terms that led to distortions in EPI.

Impact: Inconsistencies in B0-maps lead to poor shimming at 7T, increased linewidths in MRS and distortion artefacts in MRI. This work recommends use of a 2D B0-mapping protocol along with the acquisition of an ‘unbiased’ B0-map for image-based shimming.

How to access this content:

For one year after publication, abstracts and videos are only open to registrants of this annual meeting. Registrants should use their existing login information. Non-registrant access can be purchased via the ISMRM E-Library.

After one year, current ISMRM & ISMRT members get free access to both the abstracts and videos. Non-members and non-registrants must purchase access via the ISMRM E-Library.

After two years, the meeting proceedings (abstracts) are opened to the public and require no login information. Videos remain behind password for access by members, registrants and E-Library customers.

Click here for more information on becoming a member.

Keywords