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Increased fMRI Sensitivity at Equal Data Burden Using Averaged Shifted Echo Acquisition

View Article: PubMed Central - PubMed

ABSTRACT

There is growing evidence as to the benefits of collecting BOLD fMRI data with increased sampling rates. However, many of the newly developed acquisition techniques developed to collect BOLD data with ultra-short TRs require hardware, software, and non-standard analytic pipelines that may not be accessible to all researchers. We propose to incorporate the method of shifted echo into a standard multi-slice, gradient echo EPI sequence to achieve a higher sampling rate with a TR of <1 s with acceptable spatial resolution. We further propose to incorporate temporal averaging of consecutively acquired EPI volumes to both ameliorate the reduced temporal signal-to-noise inherent in ultra-fast EPI sequences and reduce the data burden. BOLD data were collected from 11 healthy subjects performing a simple, event-related visual-motor task with four different EPI sequences: (1) reference EPI sequence with TR = 1440 ms, (2) shifted echo EPI sequence with TR = 700 ms, (3) shifted echo EPI sequence with every two consecutively acquired EPI volumes averaged and effective TR = 1400 ms, and (4) shifted echo EPI sequence with every four consecutively acquired EPI volumes averaged and effective TR = 2800 ms. Both the temporally averaged sequences exhibited increased temporal signal-to-noise over the shifted echo EPI sequence. The shifted echo sequence with every two EPI volumes averaged also had significantly increased BOLD signal change compared with the other three sequences, while the shifted echo sequence with every four EPI volumes averaged had significantly decreased BOLD signal change compared with the other three sequences. The results indicated that incorporating the method of shifted echo into a standard multi-slice EPI sequence is a viable method for achieving increased sampling rate for collecting event-related BOLD data. Further, consecutively averaging every two consecutively acquired EPI volumes significantly increased the measured BOLD signal change and the subsequently calculated activation map statistics.

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Related in: MedlinePlus

Post-hoc results for repeated measures ANOVAs for BOLD percent signal change and GLM-calculated T-statistics for the ROI mask containing only task-related regions extracted from the FSL Harvard-Oxford Atlas. As described in the text, SHORT, TR = 700 ms; AVG2, TReffective = 1440 ms; AVG4, TReffective = 2800 ms; REF, TR = 1440 ms. Percent signal change values were calculated from the beta weights estimated during the GLM. **Indicates a post-hoc difference at p < 0.05, Bonferroni corrected for comparing across the four different EPI sequences. *Indicates a post-hoc difference at p < 0.05, uncorrected.
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Figure 6: Post-hoc results for repeated measures ANOVAs for BOLD percent signal change and GLM-calculated T-statistics for the ROI mask containing only task-related regions extracted from the FSL Harvard-Oxford Atlas. As described in the text, SHORT, TR = 700 ms; AVG2, TReffective = 1440 ms; AVG4, TReffective = 2800 ms; REF, TR = 1440 ms. Percent signal change values were calculated from the beta weights estimated during the GLM. **Indicates a post-hoc difference at p < 0.05, Bonferroni corrected for comparing across the four different EPI sequences. *Indicates a post-hoc difference at p < 0.05, uncorrected.

Mentions: A trend-level omnibus repeated-measures effect was noted when comparing the calculated percent signal change across all sequences [F(2, 9) = 3.41, p < 0.08]. Planned comparisons revealed that the AVG2 sequence had a significantly higher percent signal change than both the SHORT and AVG4 sequences. No other significant post-hoc comparisons were noted. A significant within-subjects effect was also noted [F(3, 30) = 4.2, p < 0.03], indicating that this pattern of results was held across all subjects. Results are summarized in Table 1 and Figure 6.


Increased fMRI Sensitivity at Equal Data Burden Using Averaged Shifted Echo Acquisition
Post-hoc results for repeated measures ANOVAs for BOLD percent signal change and GLM-calculated T-statistics for the ROI mask containing only task-related regions extracted from the FSL Harvard-Oxford Atlas. As described in the text, SHORT, TR = 700 ms; AVG2, TReffective = 1440 ms; AVG4, TReffective = 2800 ms; REF, TR = 1440 ms. Percent signal change values were calculated from the beta weights estimated during the GLM. **Indicates a post-hoc difference at p < 0.05, Bonferroni corrected for comparing across the four different EPI sequences. *Indicates a post-hoc difference at p < 0.05, uncorrected.
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Related In: Results  -  Collection

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getmorefigures.php?uid=PMC5120083&req=5

Figure 6: Post-hoc results for repeated measures ANOVAs for BOLD percent signal change and GLM-calculated T-statistics for the ROI mask containing only task-related regions extracted from the FSL Harvard-Oxford Atlas. As described in the text, SHORT, TR = 700 ms; AVG2, TReffective = 1440 ms; AVG4, TReffective = 2800 ms; REF, TR = 1440 ms. Percent signal change values were calculated from the beta weights estimated during the GLM. **Indicates a post-hoc difference at p < 0.05, Bonferroni corrected for comparing across the four different EPI sequences. *Indicates a post-hoc difference at p < 0.05, uncorrected.
Mentions: A trend-level omnibus repeated-measures effect was noted when comparing the calculated percent signal change across all sequences [F(2, 9) = 3.41, p < 0.08]. Planned comparisons revealed that the AVG2 sequence had a significantly higher percent signal change than both the SHORT and AVG4 sequences. No other significant post-hoc comparisons were noted. A significant within-subjects effect was also noted [F(3, 30) = 4.2, p < 0.03], indicating that this pattern of results was held across all subjects. Results are summarized in Table 1 and Figure 6.

View Article: PubMed Central - PubMed

ABSTRACT

There is growing evidence as to the benefits of collecting BOLD fMRI data with increased sampling rates. However, many of the newly developed acquisition techniques developed to collect BOLD data with ultra-short TRs require hardware, software, and non-standard analytic pipelines that may not be accessible to all researchers. We propose to incorporate the method of shifted echo into a standard multi-slice, gradient echo EPI sequence to achieve a higher sampling rate with a TR of &lt;1 s with acceptable spatial resolution. We further propose to incorporate temporal averaging of consecutively acquired EPI volumes to both ameliorate the reduced temporal signal-to-noise inherent in ultra-fast EPI sequences and reduce the data burden. BOLD data were collected from 11 healthy subjects performing a simple, event-related visual-motor task with four different EPI sequences: (1) reference EPI sequence with TR = 1440 ms, (2) shifted echo EPI sequence with TR = 700 ms, (3) shifted echo EPI sequence with every two consecutively acquired EPI volumes averaged and effective TR = 1400 ms, and (4) shifted echo EPI sequence with every four consecutively acquired EPI volumes averaged and effective TR = 2800 ms. Both the temporally averaged sequences exhibited increased temporal signal-to-noise over the shifted echo EPI sequence. The shifted echo sequence with every two EPI volumes averaged also had significantly increased BOLD signal change compared with the other three sequences, while the shifted echo sequence with every four EPI volumes averaged had significantly decreased BOLD signal change compared with the other three sequences. The results indicated that incorporating the method of shifted echo into a standard multi-slice EPI sequence is a viable method for achieving increased sampling rate for collecting event-related BOLD data. Further, consecutively averaging every two consecutively acquired EPI volumes significantly increased the measured BOLD signal change and the subsequently calculated activation map statistics.

No MeSH data available.


Related in: MedlinePlus