Blood oxygenation level dependent (BOLD) functional magnetic resonance imaging
(fMRI) is the dominant tool used for mapping human brain function because it is
non-invasive, does not use ionizing radiation, and offers relatively high spatial and
temporal resolution compared to other neuroimaging techniques. Unfortunately, conventional
fMRI techniques cannot map brain function in the inferior temporal cortex
(ITC) and orbitofrontal cortex (OFC). These brain regions experience severe magnetic
field distortions due to magnetic susceptibility mismatch with the neighboring
air-filled ear-canals (ITC) or sinus cavities (OFC), causing loss of the fMRI signal.
Functional imaging capability is important for gaining a better understanding of these
brain regions and the diseases that commonly affect them (Alzheimer’s disease and
epilepsy (ITC), Parkinson’s disease and schizophrenia (OFC)).
Balanced steady state free precession (balanced SSFP) is a relatively new fMRI
technique that can measure function in all brain regions. Rather than diffuse signal
loss, balanced SSFP images exhibit signal loss in spatially periodic, narrow bands.
Banding artifacts cannot be eliminated in a single scan, but the phase of the banding
artifacts can be controlled by the experimenter, permitting the combination of two
antiphase balanced SSFP images to produce a single image free of banding artifacts.
Unfortunately, image-corrupting transient signal oscillations limit the rate at which
the banding artifact phase can be modified, such that the banding-artifact-free image
acquisition rate is prohibitively slow for most clinical and neuroscience applications.
This work describes the development of a modified balanced SSFP fMRI technique,
alternating SSFP, which permits rapid, banding-artifact-free balanced SSFP fMRI.
Theoretical modeling was used to find a rapid transition between antiphase balanced
SSFP images with minimal transient signal oscillations. Monte Carlo simulations
were used to optimize alternating SSFP acquisition parameters for BOLD sensitivity,
with comparison to established balanced SSFP acquisitions. Rat fMRI was used to
confirm these predictions. Finally, the ability of alternating SSFP to provide rapid,
banding-artifact-free balanced SSFP fMRI in humans at 4 T was demonstrated.
| Identifer | oai:union.ndltd.org:LACETR/oai:collectionscanada.gc.ca:NSHD.ca#10222/40672 |
| Date | 03 December 2013 |
| Creators | Patterson, Steve |
| Source Sets | Library and Archives Canada ETDs Repository / Centre d'archives des thèses électroniques de Bibliothèque et Archives Canada |
| Language | English |
| Detected Language | English |
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