Journal
MAGNETIC RESONANCE IN MEDICINE
Volume 59, Issue 1, Pages 221-227Publisher
JOHN WILEY & SONS INC
DOI: 10.1002/mrm.21473
Keywords
z-shim; SENSE; spiral; fMRI; susceptibility
Funding
- NINDS NIH HHS [NS 50329, NS 4132] Funding Source: Medline
- NATIONAL INSTITUTE OF NEUROLOGICAL DISORDERS AND STROKE [R01NS050329] Funding Source: NIH RePORTER
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Blood oxygenation level-dependent (BOLD) functional MRI (fMRI) can be severely hampered by signal loss due to susceptibility-induced static magnetic field (B-0) inhomogeneities near air/tissue interfaces. A single-shot spiral-in/out sequence with a z-shim gradient embedded between the two acquisitions was previously proposed to efficiently recover the signal. However, despite promising results, this technique had several limitations, which are addressed here as follows. First, by adding a second z-shim gradient before the spiral-in acquisition and optimizing both z-shim gradients slice-by-slice, a significantly more uniform signal recovery can be achieved. Second, by acquiring a B-0 map, the optimal z-shim gradients can be directly, efficiently, and accurately determined for each subject. Third, by complementing the z-shimming approach with sensitivity encoding (SENSE), the in-plane spatial resolution can be increased and, hence, susceptibility artifacts further reduced, while maintaining a high temporal resolution for fMRI applications. These advantages are demonstrated in human functional studies.
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