High-field MRI of brain cortical substructure based on signal phase
- Jeff H. Duyn†,
- Peter van Gelderen,
- Tie-Qiang Li,
- Jacco A. de Zwart,
- Alan P. Koretsky, and
- Masaki Fukunaga
- Laboratory for Advanced MRI, Laboratory of Functional and Molecular Imaging, National Institute of Neurological Disorders and Stroke, National Institutes of Health, Building 10, Room B1D-728, 9000 Rockville Pike, Bethesda, MD 20892-1065
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Edited by Leslie G. Ungerleider, National Institute of Mental Health, Bethesda, MD, and approved May 1, 2007 (received for review December 11, 2006)
Abstract
The ability to detect brain anatomy and pathophysiology with MRI is limited by the contrast-to-noise ratio (CNR), which depends on the contrast mechanism used and the spatial resolution. In this work, we show that in MRI of the human brain, large improvements in contrast to noise in high-resolution images are possible by exploiting the MRI signal phase at high magnetic field strength. Using gradient-echo MRI at 7.0 tesla and a multichannel detector, a nominal voxel size of 0.24 × 0.24 × 1.0 mm3 (58 nl) was achieved. At this resolution, a strong phase contrast was observed both between as well as within gray matter (GM) and white matter (WM). In gradient-echo phase images obtained on normal volunteers at this high resolution, the CNR between GM and WM ranged from 3:1 to 20:1 over the cortex. This CNR is an almost 10-fold improvement over conventional MRI techniques that do not use image phase, and it is an ≈100-fold improvement when including the gains in resolution from high-field and multichannel detection. Within WM, phase contrast appeared to be associated with the major fiber bundles, whereas contrast within GM was suggestive of the underlying layer structure. The observed phase contrast is attributed to local variations in magnetic susceptibility, which, at least in part, appeared to originate from iron stores. The ability to detect cortical substructure from MRI phase contrast at high field is expected to greatly enhance the study of human brain anatomy in vivo.
Footnotes
- †To whom correspondence should be addressed. E-mail: jhd{at}helix.nih.gov
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Author contributions: J.H.D. designed research; J.H.D., P.v.G., T.-Q.L., J.A.d.Z., A.P.K., and M.F. performed research; P.v.G., T.-Q.L., J.A.d.Z., A.P.K., and M.F. contributed new reagents/analytic tools; J.H.D., P.v.G., T.-Q.L., J.A.d.Z., A.P.K., and M.F. analyzed data; and J.H.D. wrote the paper.
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The authors declare no conflict of interest.
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This article is a PNAS Direct Submission.
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See Commentary on page 11513.
- Abbreviations:
- SNR,
- signal-to-noise ratio;
- CNR,
- contrast-to-noise ratio;
- GM,
- gray matter;
- WM,
- white matter;
- CSF,
- cerebrospinal fluid;
- GRE,
- gradient-echo;
- MP-RAGE,
- magnetization-prepared rapid gradient-echo;
- TR,
- repetition time;
- TE,
- echo time;
- TI,
- inversion time.
- © 2007 by The National Academy of Sciences of the USA
