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• W2157575452 abstract "Introduction Theoretical considerations as well as experimental studies have suggested that imaging at high fields is advantageous for fMRI. Specifically: 1) the signal to noise ratio (SNR) of the images is expected to increase; 2) the contrast to noise ratio (CNR) of the BOLD response is expected to increase; and 3) the specificity of BOLD response to the gray matter is expected to improve. The anticipated increase in SNR and CNR, and the decrease in signal from the blood vessels are supposed to bring about a high degree of reproducibility of the BOLD response at high field. In this study we have investigated the reproducibility of the BOLD response obtained from the human brain at high-resolution at 7 Tesla. Methods: fMRI Three healthy volunteers participated in this study. Imaging was performed at 7 Tesla (magnet: Magnex, console: Varian) using a quadrature RF surface coil (10x12 cm). A segmented gradient echo EPI sequence was used with the following parameters: matrix 128x128, FOV 12.8x12.8 cm2, 4 segments, 2-3 sagittal slices 2-3 mm thick, TR 150 msec per segment per slice, and TE 20 msec. A visual stimulation paradigm was used to activate a portion of the visual field. The pattern of stimulus was a ring that subtended an eccentricity angle of 8°-15° of the visual field. The ring was composed of flickering (6 Hz) high-contrast checkers. A block stimulation paradigm (16-sec stimulus on, 21-sec stimulus off) was used. A test and re-test study was performed for each subject during the same session, at an average time difference of 20 min. Analysis: Activated pixels were defined by correlating the measured time course with the stimulation time course convolved with the pattern of the hemo-dynamic response (Boynton et al., 1996). A correlation threshold of 0.20 was used for deriving the maps of activated voxels. In addition, a spatial cluster size threshold of 8 voxels was applied. Results Fig. 1 presents the reproducibility of BOLD response as obtained from one of the subjects. Bright-bluish voxels represent those voxels that exhibited significant BOLD response in both the test and the re-test. Dark-reddish voxels passed the threshold during the test or the re-test but not during both. 70.5% of all activated voxels presented reproducible response (bright bluish voxels), while the rest 29.5% did not (dark reddish voxels). Table 1 summarizes the results obtained from all three subjects. Discussion The result of this study revealed a high degree of reproducibility of fMRI as measured at high-resolution at 7 Tesla. It should be noted that the actual reproducibility may depend on the SNR in the data and the statistical threshold used in the analysis. With the high spatial resolution used in this study, the SNR in the data was only 30 to 40. A previous study performed at 4 Tesla (Tegeler et al., 1999) reported an average fraction of 0.41±0.16 of voxels presenting reproducibility (using t-test) across three scans. The average fraction of reproducible voxels across two scans in the current study was 0.61±0.08. The present data reveal a similar degree of reproducibility at 7 Tesla, although the voxel size used in the 4 Tesla study was 35 times the one used in the current study. Note, however, that this comparison is only qualitative and by no means well controlled due to different modalities, stimulation paradigms and analysis methods that were used. At this point, while our results do indicate that there is a high degree of reproducibility at 7 Tesla, a systematic comparison is needed to fully establish the superiority of the 7 Tesla instrument. Figure 1. Reproducibility of BOLD response as measured at 7 Tesla (2 sagittal slices, subject SR). References 1. Boynton GM, Engel SA, Glover GH, Heeger DJ (1996) Linear systems analysis of functional magnetic resonance imaging in human V1. J Neurosci. 16:4207-21. 2. Tegeler C, Strother SC, Anderson JR, Kim SG (1999) Reproducibility of BOLD-based functional MRI obtained at 4T. Human Brain Mapping 7:267-283." @default.
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• W2157575452 date "2001-04-01" @default.
• W2157575452 modified "2023-09-27" @default.
• W2157575452 title "Reproducibility of the BOLD response in the human brain as measured at high-resolution at 7 Tesla" @default.
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