Abstract
Differing noise variance across study populations has been shown to cause artifactual group differences in functional connectivity measures. In this study, we investigate the use of short echo time functional MRI data to correct for these noise sources in blood oxygenation level dependent (BOLD)-weighted time series. A dual‐echo sequence was used to simultaneously acquire data at both a short (TE = 3.3 ms) and a BOLD-weighted (TE = 35 ms) echo time. This approach is effectively “free,” using dead-time in the pulse sequence to collect an additional echo without affecting overall scan time or temporal resolution. The proposed correction method uses voxelwise regression of the short TE data from the BOLD-weighted data to remove noise variance. In addition to a typical resting state scan, non-compliant behavior associated with patient groups was simulated via increased head motion or physiological fluctuations in 10 subjects. Short TE data showed significant correlations with the traditional motion-related and physiological noise regressors used in current connectivity analyses. Following traditional preprocessing, the extent of significant additional variance explained by the short TE data regressors was significantly correlated with the average head motion across the scan in the resting data (r2 = 0.93, p < 0.0001). The reduction in data variance following the inclusion of short TE regressors was also correlated with scan head motion (r2 = 0.48, p = 0.027). Task-related data were used to demonstrate the effects of the short TE correction on BOLD activation time series with known temporal structure; the size and strength of the activation were significantly decreased, but it is not clear whether this reflects BOLD contamination in the short TE data or correlated changes in blood volume. Finally, functional connectivity maps of the default mode network were constructed using a seed correlation approach. The effects of short TE correction and low-pass filtering on the resulting correlations maps were compared. Results suggest that short TE correction more accurately differentiates artifactual correlations from the correlations of interest in conditions of amplified noise.
Highlights
The utility of fMRI in investigating the workings of the brain is determined by our ability to capture and isolate appropriate signal contrast
Relative to the Rest scan results, the Breathing data set showed significantly more voxels correlated with the respiration volume per time (RVT) regressors, while the Rest + Motion data set showed fewer voxels correlated with certain RETROICOR regressors (p b 0.05, paired t-test, corrected for multiple comparisons)
This shows that more physiological noise is present in the short TE data of the Breathing scan, related to the respiratory challenges, but less physiological noise is observed in the Rest+ Motion data, where gross head movement artifacts may overwhelm more subtle pulsatory motion
Summary
The utility of fMRI in investigating the workings of the brain is determined by our ability to capture and isolate appropriate signal contrast. Blood oxygenation level dependent (BOLD) contrast is the dominant method for identifying activated areas of the brain (Bandettini et al, 1992; Kwong et al, 1992; Ogawa et al, 1990). These signal changes reflect a complex coupling between local blood volume, blood flow and concentrations of deoxygenated hemoglobin, all of which are altered by neural activity (for a review, see Buxton, 2012). This is problematic when comparing children or patient populations with young healthy
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
