Abstract
Introduction:
B0-fluctuations induced by breathing and body motion lead to artifacts for certain brain imaging sequences at ultra-high
field (7T). A promising solution is to monitor the B0-fluctuations during the scan using external field probes, and update the
shim currents in real-time (1). It is a fundamental challenge, however, that the B0 measurements are spatially sparse (e.g. 16
probes), and performed outside the brain. Typically, the field is modelled by a linear combination of the spatial shim fields that
the scanner can produce (such as spherical harmonics up to 3rd order), and the coefficients for these spatial terms are determined
by least square fitting to the field probe measurements. The probes must be placed carefully to ensure that the spherical
harmonics can be distinguished using these few samples, and they must be placed close to the head so that the spatial field model
is valid and to have good SNR. Here, we provide a simulation of breathing-induced B0-fluctuations inside and around the head
and use this simulated field to test different sets of probe positions. We also formulate two optimization problems to guide
placement of the field probes.
B0-fluctuations induced by breathing and body motion lead to artifacts for certain brain imaging sequences at ultra-high
field (7T). A promising solution is to monitor the B0-fluctuations during the scan using external field probes, and update the
shim currents in real-time (1). It is a fundamental challenge, however, that the B0 measurements are spatially sparse (e.g. 16
probes), and performed outside the brain. Typically, the field is modelled by a linear combination of the spatial shim fields that
the scanner can produce (such as spherical harmonics up to 3rd order), and the coefficients for these spatial terms are determined
by least square fitting to the field probe measurements. The probes must be placed carefully to ensure that the spherical
harmonics can be distinguished using these few samples, and they must be placed close to the head so that the spatial field model
is valid and to have good SNR. Here, we provide a simulation of breathing-induced B0-fluctuations inside and around the head
and use this simulated field to test different sets of probe positions. We also formulate two optimization problems to guide
placement of the field probes.
| Originalsprog | Engelsk |
|---|---|
| Publikationsdato | 2015 |
| Antal sider | 1 |
| Status | Udgivet - 2015 |