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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.

No MeSH data available.


Realigned images for each EPI sequence for one participant. (A) SHORT, TR = 700 ms; (B) AVG2, TReffective = 1400 ms; (C) AVG4, TReffective = 2800 ms; (D) REF, TR = 1440 ms. Slices were created using Mango (http://ric.uthscsa.edu/mango/; Jack L. Lancaster and Michael J. Martinez).
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Figure 2: Realigned images for each EPI sequence for one participant. (A) SHORT, TR = 700 ms; (B) AVG2, TReffective = 1400 ms; (C) AVG4, TReffective = 2800 ms; (D) REF, TR = 1440 ms. Slices were created using Mango (http://ric.uthscsa.edu/mango/; Jack L. Lancaster and Michael J. Martinez).

Mentions: The data were preprocessed and analyzed using SPM12 (The Wellcome Trust Centre for Neuroimaging, University College London, London, UK). All participants' images were separately realigned, where the resulting translation and rotation parameters were individually examined to ensure that no participant had either significant head motion exceeding the dimensions of one voxel in any direction or had head motion that was significantly correlated with experimental timings. No data were excluded for either reason. Each participant's realigned EPI images were then coregistered with his/her own T1 anatomical scan. Spatial normalization into Montreal Neurologic Institute (MNI) space was initially performed on each participant's T1 anatomical scan, and these spatial normalization parameters were then applied to each respective functional data set. The spatially normalized images were smoothed with an 8 mm FWHM Gaussian kernel. Selected slices of the realigned EPI images for one participant for each of the four EPI sequences are shown in Figure 2.


Increased fMRI Sensitivity at Equal Data Burden Using Averaged Shifted Echo Acquisition
Realigned images for each EPI sequence for one participant. (A) SHORT, TR = 700 ms; (B) AVG2, TReffective = 1400 ms; (C) AVG4, TReffective = 2800 ms; (D) REF, TR = 1440 ms. Slices were created using Mango (http://ric.uthscsa.edu/mango/; Jack L. Lancaster and Michael J. Martinez).
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Related In: Results  -  Collection

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getmorefigures.php?uid=PMC5120083&req=5

Figure 2: Realigned images for each EPI sequence for one participant. (A) SHORT, TR = 700 ms; (B) AVG2, TReffective = 1400 ms; (C) AVG4, TReffective = 2800 ms; (D) REF, TR = 1440 ms. Slices were created using Mango (http://ric.uthscsa.edu/mango/; Jack L. Lancaster and Michael J. Martinez).
Mentions: The data were preprocessed and analyzed using SPM12 (The Wellcome Trust Centre for Neuroimaging, University College London, London, UK). All participants' images were separately realigned, where the resulting translation and rotation parameters were individually examined to ensure that no participant had either significant head motion exceeding the dimensions of one voxel in any direction or had head motion that was significantly correlated with experimental timings. No data were excluded for either reason. Each participant's realigned EPI images were then coregistered with his/her own T1 anatomical scan. Spatial normalization into Montreal Neurologic Institute (MNI) space was initially performed on each participant's T1 anatomical scan, and these spatial normalization parameters were then applied to each respective functional data set. The spatially normalized images were smoothed with an 8 mm FWHM Gaussian kernel. Selected slices of the realigned EPI images for one participant for each of the four EPI sequences are shown in Figure 2.

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.

No MeSH data available.