Artikel
Event-related real-time functional Magnetic Resonance Imaging (erfMRI) at 3T and 7T
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Autoren
Veröffentlicht: | 6. September 2007 |
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Gliederung
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Introduction: New experiments using erfMRI enable self-regulation of brain-activity or optimising learning strategies [Ref. 1],[Ref. 2]. However, real-time statistical analysis is usually less powerful than a full General Linear Model and short stimulus durations (event-related stimuli) decreases the BOLD signal. Therefore, higher field strengths such as 3T or 7T are required.
Methods: For online data export a standard EPI-BOLD sequence was modified. Experiment and data analysis were controlled with a custom-made XML-based parameter/experiment description language (EDL) and a MATLAB application (post-processing, statistical analysis, visualization). t-test and correlation-analysis with a double-gamma function were implemented. Results were displayed to the investigator and the volunteer. erfMRI experiments were conducted at 3T and 7T scanners (both Siemens) with 64x64 matrix, TR=2s, TE=29s (3T) or 20s(7T), 31 slices (3T) or 16 slices (7T). Visual stimulation (10 Hz checkerboard), and finger-tapping were measured. Activation/rest blocks (20s/20s) served to localize activated areas. Subsequently, stimulus duration was shortened from 10 sec to 0.1 sec. A constant window as well as a growing window was used to analyse data online..
Results: Visual areas were detectable at a minimum stimulus duration of 500 ms at 7T and 1 sec at 3T. Motor areas were detected at a minimum stimulus duration of 1 sec at 7T and 2 sec at 3T. Mean signal change was 2-3% (1s stimulus duration) for motor activation at 3T, and 5-6% at 7T. For visual areas mean signal change was of 3-4% at 7T and 2-3% at 3T (500ms stimulus
duration).
Conclusion: The results represent the first successful erfMRI 7T with stimulus duration as short as 500 ms. At 7T the activated clusters were more homogeneous and the mean signal change was larger than at 3T which should allow to detect smaller activated clusters.
References
- 1.
- N. Weiskopf et al., Self-regulation of local brain activity using real-time functional magnetic resonance imaging (fMRI). Journal of Physiology, pages 357–373, 2004
- 2.
- Posse et al., A New Approach to Measure Single-Event Related Brain Activity Using Real-Time fMRI: Feasibility of Sensory, Motor, and Higher Cognitive Tasks. - Human Brain Mapping, 12:25-41, 2001