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Resting state BOLD functional connectivity at 3T: spin echo versus gradient echo EPI.

Chiacchiaretta P, Ferretti A - PLoS ONE (2015)

Bottom Line: Main results showed that, within subject, the GE sensitivity is overall larger with respect to that of SE, but to a less extent than previously reported for activation studies.Noteworthy, the reduced sensitivity of SE was counterbalanced by a reduced inter-subject variability, resulting in comparable group statistical connectivity maps for the two sequences.Future studies should clarify if these features of the SE BOLD signal can be beneficial to distinguish subtle variations of functional connectivity across different populations and/or treatments when vascular confounds or regions affected by signal dropout can be a critical issue.

View Article: PubMed Central - PubMed

Affiliation: Department of Neuroscience, Imaging and Clinical Sciences, University "G. d'Annunzio" of Chieti, Chieti, Italy; Institute for Advanced Biomedical Technologies (ITAB), University "G. d'Annunzio" of Chieti, Chieti, Italy; Bioengineering Unit, IRCCS Neuromed, Pozzilli (IS), Italy.

ABSTRACT
Previous evidence showed that, due to refocusing of static dephasing effects around large vessels, spin-echo (SE) BOLD signals offer an increased linearity and promptness with respect to gradient-echo (GE) acquisition, even at low field. These characteristics suggest that, despite the reduced sensitivity, SE fMRI might also provide a potential benefit when investigating spontaneous fluctuations of brain activity. However, there are no reports on the application of spin-echo fMRI for connectivity studies at low field. In this study we compared resting state functional connectivity as measured with GE and SE EPI sequences at 3T. Main results showed that, within subject, the GE sensitivity is overall larger with respect to that of SE, but to a less extent than previously reported for activation studies. Noteworthy, the reduced sensitivity of SE was counterbalanced by a reduced inter-subject variability, resulting in comparable group statistical connectivity maps for the two sequences. Furthermore, the SE method performed better in the ventral portion of the default mode network, a region affected by signal dropout in standard GE acquisition. Future studies should clarify if these features of the SE BOLD signal can be beneficial to distinguish subtle variations of functional connectivity across different populations and/or treatments when vascular confounds or regions affected by signal dropout can be a critical issue.

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Correlation values for the different node-seed functional connections as measured with GE and SE.The r-values were first averaged across voxels inside a node on individual correlation maps and then averaged across subjects. Error bars are standard errors.
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pone.0120398.g002: Correlation values for the different node-seed functional connections as measured with GE and SE.The r-values were first averaged across voxels inside a node on individual correlation maps and then averaged across subjects. Error bars are standard errors.

Mentions: The mean correlation values across subjects for the different node-seed connections are shown in Fig. 2. As expected, the larger sensitivity of GE acquisition to the BOLD signal fluctuations yielded larger correlation values with respect to SE acquisition (about a factor of 2.5 for SMN, 1.9 for ECN, 1.9 for SN, 1.6 for DAN and 1.2 for DMN). However, SE correlation coefficients exhibited a lower intersubject variability as shown by the smaller standard errors. As a consequence, the statistical significance in the group level connectivity maps was comparable for the two sequences (the one sample t-test values are shown in Fig. 3).


Resting state BOLD functional connectivity at 3T: spin echo versus gradient echo EPI.

Chiacchiaretta P, Ferretti A - PLoS ONE (2015)

Correlation values for the different node-seed functional connections as measured with GE and SE.The r-values were first averaged across voxels inside a node on individual correlation maps and then averaged across subjects. Error bars are standard errors.
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4352074&req=5

pone.0120398.g002: Correlation values for the different node-seed functional connections as measured with GE and SE.The r-values were first averaged across voxels inside a node on individual correlation maps and then averaged across subjects. Error bars are standard errors.
Mentions: The mean correlation values across subjects for the different node-seed connections are shown in Fig. 2. As expected, the larger sensitivity of GE acquisition to the BOLD signal fluctuations yielded larger correlation values with respect to SE acquisition (about a factor of 2.5 for SMN, 1.9 for ECN, 1.9 for SN, 1.6 for DAN and 1.2 for DMN). However, SE correlation coefficients exhibited a lower intersubject variability as shown by the smaller standard errors. As a consequence, the statistical significance in the group level connectivity maps was comparable for the two sequences (the one sample t-test values are shown in Fig. 3).

Bottom Line: Main results showed that, within subject, the GE sensitivity is overall larger with respect to that of SE, but to a less extent than previously reported for activation studies.Noteworthy, the reduced sensitivity of SE was counterbalanced by a reduced inter-subject variability, resulting in comparable group statistical connectivity maps for the two sequences.Future studies should clarify if these features of the SE BOLD signal can be beneficial to distinguish subtle variations of functional connectivity across different populations and/or treatments when vascular confounds or regions affected by signal dropout can be a critical issue.

View Article: PubMed Central - PubMed

Affiliation: Department of Neuroscience, Imaging and Clinical Sciences, University "G. d'Annunzio" of Chieti, Chieti, Italy; Institute for Advanced Biomedical Technologies (ITAB), University "G. d'Annunzio" of Chieti, Chieti, Italy; Bioengineering Unit, IRCCS Neuromed, Pozzilli (IS), Italy.

ABSTRACT
Previous evidence showed that, due to refocusing of static dephasing effects around large vessels, spin-echo (SE) BOLD signals offer an increased linearity and promptness with respect to gradient-echo (GE) acquisition, even at low field. These characteristics suggest that, despite the reduced sensitivity, SE fMRI might also provide a potential benefit when investigating spontaneous fluctuations of brain activity. However, there are no reports on the application of spin-echo fMRI for connectivity studies at low field. In this study we compared resting state functional connectivity as measured with GE and SE EPI sequences at 3T. Main results showed that, within subject, the GE sensitivity is overall larger with respect to that of SE, but to a less extent than previously reported for activation studies. Noteworthy, the reduced sensitivity of SE was counterbalanced by a reduced inter-subject variability, resulting in comparable group statistical connectivity maps for the two sequences. Furthermore, the SE method performed better in the ventral portion of the default mode network, a region affected by signal dropout in standard GE acquisition. Future studies should clarify if these features of the SE BOLD signal can be beneficial to distinguish subtle variations of functional connectivity across different populations and/or treatments when vascular confounds or regions affected by signal dropout can be a critical issue.

Show MeSH
Related in: MedlinePlus