Cortical Depth-Dependent Function Analysis in the Native EPI Space Based on BISEPI at 7T

Poster No:

2082 

Submission Type:

Abstract Submission 

Authors:

Guoxiang Liu1,2, Adnan Shah1,2, Takashi Ueguchi1,2

Institutions:

1CiNet, NICT, Osaka, Japan, 2Graduate School of Frontier Biosciences, Osaka University, Osaka, Japan

First Author:

Guoxiang Liu  
CiNet, NICT|Graduate School of Frontier Biosciences, Osaka University
Osaka, Japan|Osaka, Japan

Co-Author(s):

Adnan Shah  
CiNet, NICT|Graduate School of Frontier Biosciences, Osaka University
Osaka, Japan|Osaka, Japan
Takashi Ueguchi  
CiNet, NICT|Graduate School of Frontier Biosciences, Osaka University
Osaka, Japan|Osaka, Japan

Introduction:

BISEPI [1] allows us to investigate submillimeter-level brain activity without the need of an additional anatomical scan using a different sequence. Based on BISEPI, in OHBM 2019, we presented a procedure for generating T1w-Like anatomy based on image inversion, tissue segmentation and image fusion of the submillimeter-resolution distortion and resolution matched (DRM) anatomy [2]. In this work, we propose a novel imaging and analysis strategy for investigating cortical depth-dependent function analysis in the native EPI space. Functional ribbons from BOLD activity on the grey matter structure can be determined at distinct cortical depths. Using boundary shrinkage of the GMWM mask generated from the acquired DRM anatomical slices, the proposed method is demonstrated to recover distinct depth-dependent activity in the native EPI space in high-resolution fMRI at 7T.

Methods:

Two adult human participants were scanned using BISEPI sequence on a Siemens MAGNETOM 7T scanner with a 32-channel phased array head coil (Nova Medical, MA, USA) to obtain imaging data in two experiments, where 48 fMRI volumes each at a spatial resolution of 0.7×0.7×2.0 mm3 were acquired. The acquisition parameters for functional scans were as follows: TR = 3000 ms, TE = 23 ms, flip angle (FA) = 90º, number of segments = 6, number of shots in block = 16, PF = 6/8. A bilateral finger tapping task was performed in experiment 1 on subject 1 and only a right finger tapping task was performed in experiment 2 on subject 2 using BISEPI design [1] with ON and OFF for 12 s each. Experiment 2 utilized a TR = 4 s. In both experiments, functional scans were followed by six slices for anatomical imaging with variable inversion recovery for each slice generated by an IR-sweep with varying inversion time (TI) across slices (TI=100-2400ms) [3]. The obtained anatomical volumes were used to generate T1-maps after T1-fitting. These T1-maps were post-processed for generating T1w-Like anatomical images based on image inversion and image fusion [2]. For cortical depth dependent analysis in the native EPI space, first masks were generated based on a step-wise shrinkage of GM/pial boundary. The obtained masks were then used to extract functional ribbons from the task-related functional maps obtained by GLM analysis in BrainVoyager 21.4 after data pre-processing that includes mean intensity correction, interscan slice time correction, motion correction, and high-pass filtering. The proposed imaging and analysis strategy allows investigating cortical depth dependent responses in the native EPI space and avoids interpolation, spatial transformation and spatial smoothing of functional activity providing benefits for analysing high-resolution fMRI. The proposed analysis strategy improves the specificity of functional activity in high-resolution fMRI at 7T.

Results:

Figure 1 (A) to the left shows fMRI BOLD activity in experiment 1 overlaid on two different axial slices of the reconstructed T1w-Like DRM anatomy. The associated cortical depth-dependent functional responses in these slices moving from GM/pial boundary (Depth 1) to GM/WM interface (Depth 4) are shown in sub-figures to the right. Figure 1 (B) shows the zoomed-in view of functional activity sampled at these distinct cortical depths. Figure 2 shows the result of experiment 2 with TR = 4 s, where activity is sampled at two distinct cortical depths. The overall response and cortical depth-dependent responses are shown in sub-figure to the right in this figure.
Supporting Image: f1_final2.png
   ·Figure 1
Supporting Image: f3_final2.png
   ·Figure 2
 

Conclusions:

Based on BISEPI technique, functional activity ribbons of the cortical GM structure in the native EPI space are generated based on tissues segmented from distortion and resolution matched (DRM) anatomy. The obtained functional ribbons reveal distinct depth-dependent activity in the native EPI space preserving the voxel-wise dynamics in high-resolution fMRI at 7T. The proposed method can be used to improve localization of brain activity in high-resolution fMRI studies.

Modeling and Analysis Methods:

Activation (eg. BOLD task-fMRI) 2
Methods Development
Segmentation and Parcellation

Novel Imaging Acquisition Methods:

Anatomical MRI
BOLD fMRI 1

Keywords:

Cortical Layers
Data analysis
Data Registration
FUNCTIONAL MRI
HIGH FIELD MR
Other - Submillimeter-resolution fMRI at 7T

1|2Indicates the priority used for review

My abstract is being submitted as a Software Demonstration.

No

Please indicate below if your study was a "resting state" or "task-activation” study.

Task-activation

Healthy subjects only or patients (note that patient studies may also involve healthy subjects):

Healthy subjects

Was any human subjects research approved by the relevant Institutional Review Board or ethics panel? NOTE: Any human subjects studies without IRB approval will be automatically rejected.

Yes

Was any animal research approved by the relevant IACUC or other animal research panel? NOTE: Any animal studies without IACUC approval will be automatically rejected.

Not applicable

Please indicate which methods were used in your research:

Functional MRI
Structural MRI

For human MRI, what field strength scanner do you use?

7T

Which processing packages did you use for your study?

SPM
Brain Voyager
FSL

Provide references using author date format

[1] Liu G, Shah A, Ueguchi T. Block-Interleaved segmented EPI for voxel-wise high-resolution fMRI studies at 7T. Proceedings of the International Society for Magnetic Resonance in Medicine Joint Annual Meeting ISMRM-ESMRMB. 2018;5450.
[2] Shah A, Liu G, Ueguchi T. EPI based distortion- and resolution-matched T1-Like anatomy for submillimeter-resolution fMRI at 7T. 25th Annual Meeting of the Organization for Human Brain Mapping. 2019;2591.
[3] Panchuelo RS, Turner R, Mougin O, Francis S. A 2D multi-shot inversion recovery EPI (MS-IR-EPI) sequence for high spatial resolution T1-mapping at 7T. Proceedings of the International Society for Magnetic Resonance in Medicine. 2018;60.