http://www.nitrc.org/forum/forum.php?forum_id=6331 <table border="0" width="100%"><tr><td align="left"/></tr></table> <p><b>Magnetic susceptibility-induced echo-time shifts: Is there a bias in age-related fMRI studies?</b></p> <p>J Magn Reson Imaging. 2016 Jun 14;</p> <p>Authors: Ngo GC, Wong CN, Guo S, Paine T, Kramer AF, Sutton BP</p> <p>Abstract<br/> PURPOSE: To evaluate the potential for bias in functional magnetic resonance imaging (fMRI) aging studies resulting from age-related differences in magnetic field distributions that can impact echo time and functional contrast.<br/> MATERIALS AND METHODS: Magnetic field maps were taken on 31 younger adults (age: 22 ± 2.9 years) and 46 older adults (age: 66 ± 4.5 years) on a 3T scanner. Using the spatial gradients of the magnetic field map for each participant, an echo planar imaging (EPI) trajectory was simulated. The effective echo time, time at which the k-space trajectory is the closest to the center of k-space, was calculated. This was used to examine both within-subject and across-age-group differences in the effective echo time maps. The blood oxygenation level-dependent (BOLD) percent signal change resulting from those echo time shifts was also calculated to determine their impact on fMRI aging studies.<br/> RESULTS: For a single subject, the effective echo time varied as much as ±5 msec across the brain. An unpaired t-test between the effective echo time across age groups resulted in significant differences in several regions of the brain (P &lt; 0.01). The difference in echo time was only ∼1 msec, however, which is not expected to have an important impact on BOLD fMRI percent signal change (&lt;4%).<br/> CONCLUSION: Susceptibility-induced magnetic field gradients induce local echo-time shifts in gradient echo fMRI images, which can cause variable BOLD sensitivity across the brain. However, the age-related differences in BOLD signal are expected to be small for an fMRI study at 3T. J. Magn. Reson. Imaging 2016.<br/> </p><p>PMID: 27299727 [PubMed - as supplied by publisher]</p> en-us Copyright 2000-2026 NITRC OSI Tue, 05 May 2026 0:53:10 GMT http://blogs.law.harvard.edu/tech/rss NITRC RSS generator