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Further evaluation of the initial negative response in functional magnetic resonance imaging
Author(s) -
Yacoub Essa,
Le Tuong Huu,
Ugurbil Kamil,
Hu Xiaoping
Publication year - 1999
Publication title -
magnetic resonance in medicine
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.696
H-Index - 225
eISSN - 1522-2594
pISSN - 0740-3194
DOI - 10.1002/(sici)1522-2594(199903)41:3<436::aid-mrm2>3.0.co;2-#
Subject(s) - interstimulus interval , blood oxygenation , nuclear magnetic resonance , contrast effect , functional magnetic resonance imaging , stimulus (psychology) , magnetic resonance imaging , physics , contrast (vision) , neuroscience , optics , psychology , medicine , cognitive psychology , radiology , stimulation
The initial negative response (i.e., the dip) in the functional MR signal at stimulus onset has aroused much interest. Such a response is consistent with optical imaging data and can be potentially mapped to generate spatially more specific maps. However, there are still controversies regarding the exact origin of the initial response. In particular, experimental reports of its echo‐time dependence have been inconsistent. Furthermore, several investigators have suggested the possibility of an apparent dip that may arise artifactually when the interstimulus interval (ISI) is not sufficiently long. The present study investigates the echo‐time dependence of the initial response and the effect of the ISI on the initial response. Experimental results obtained at TEs of 21, 30, and 45 msec demonstrate that the initial dip has a TE dependence that is in agreement with a T2* contrast, and thereby consistent with a blood oxygenation level‐dependent origin. At an ISI of 90 sec, a statistically significant initial negative response was detected and shown to be indistinguishable from that observed at an ISI of 45 sec, which was used in our previous studies, indicating that the initial negative response observed at 4 T is not a consequence of short ISI. Magn Reson Med 41:436–441, 1999. © 1999 Wiley‐Liss, Inc.