Many event-related functional magnetic resonance imaging paradigms performed so far have been designed to study a limited part of the brain with high temporal resolution. However, event-related paradigms can be exploratory, therefore requiring whole brain scans and so repetition times (TR) of several seconds. For these large TR values, the slice acquisition order may have an important effect on the detection of event-related activation. Indeed, when the scanning is interleaved, the temporal delay between the acquisition of two contiguous slices can reach a few seconds. During this time, the subject is likely to move, and the haemodynamic response will vary significantly. In this case, the interpolation applied between contiguous slices for motion correction induces a temporal smoothing between voxels that are spatially close but temporally sampled a few seconds apart. This should modify the frequency structure of the response and may impair the detection of short events. We, therefore tested the effect of three acquisition schemes (sequential, sequential with gap and interleaved, INT) at two repetition times (TR = 3 and 6 s on six and seven subjects, respectively) on activation detection and frequency content in a visual motion event-related paradigm. Unexpectedly, for large TR (6 s), results were found in favour of the INT acquisition scheme (P < 0.05). For smaller TR, no strong bias could be found. Generally, intra-subject variability (across acquisition schemes) is found to be much smaller than inter-subject variability, confirming the importance of multi-subjects analyses. Our study also shows that important physiological information is carried by high frequency components that should not be filtered out.
|Original language||English (US)|
|Number of pages||10|
|Journal||Magnetic Resonance Materials in Physics, Biology and Medicine|
|State||Published - 2001|
Bibliographical noteFunding Information:
This work would not have been possible without the help of Valerie Cornilleau-Pérès who provided the visual stimuli. We are deeply in debt to Oliver Josephs and Chris Clark for their careful reading and commenting of this manuscript. We also thank our colleagues for their help during this work, especially, Ute Leonards, Emmanuel Gérardin and Anne Darquié for their help in acquiring the data. ALP was funded by CEA and IFSBM.
- Event-related functional magnetic resonance imaging
- Statistical analysis