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Free keywords:
Reduced field-of-view; Parallel imaging; BOLD imaging; fMRI; Outer-volume suppression; Ultrahigh field
Abstract:
Echo-planar imaging is the most widely used imaging
sequence for functional magnetic resonance imaging (fMRI)
due to its fast acquisition. However, it is prone to local distortions,
image blurring, and signal voids. As these effects scale
with echo train length and field strength, it is essential for
high-resolution echo-planar imaging at ultrahigh field to
address these problems. Partially parallel acquisition methods
can be used to improve the image quality of echo-planar imaging.
However, partially parallel acquisition can be affected by
aliasing artifacts and noise enhancement. Another way to
shorten the echo train length is to reduce the field-of-view
(FOV) while maintaining the same spatial resolution. However,
to achieve significant acceleration, the resulting FOV becomes
very small. Another problem occurs when FOV selection is
incomplete such that there is remaining signal aliased from the
region outside the reduced FOV. In this article, a novel
approach, a combination of reduced FOV imaging with partially
parallel acquisition, is presented. This approach can address
the problems described above of each individual method, enabling
high-quality single-shot echo-planar imaging acquisition,
with submillimeter isotropic resolution and good signal-tonoise
ratio, for fMRI at ultrahigh field strength. This is demonstrated
in fMRI of human brain at 7T with an isotropic
resolution of 650 mm.
