Activation analysis of T2* time-series from multi-echo fMRI data

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Abstract Submission 

Anezka Kovarova^1,2, Michal Mikl²

¹Masaryk University, Faculty of Medicine, Brno, Czech Republic, ²CEITEC Masaryk University, Brno, Czech Republic

Anezka Kovarova  
Masaryk University, Faculty of Medicine|CEITEC Masaryk University
Brno, Czech Republic|Brno, Czech Republic

Michal Mikl  
CEITEC Masaryk University
Brno, Czech Republic

The multi-echo fMRI acquisition provides enhanced sensitivity to the Blood Oxygenation Level Dependent (BOLD) signal by capturing multiple echoes within a single imaging sequence. Moreover, this advanced approach introduces the possibility of incorporating T2* mapping principles into every time point of the imaging data. This abstract explores the pilot study of the multi-echo multi-band (ME MB) fMRI approach coupled with the principles of T2* mapping, as a synergistic strategy for advancing the field of fast functional imaging. This combination may have the potential to enhance the robustness and stability of processed ME MB fMRI data.

Data was collected from 49 healthy volunteers aged 20-38 without any neurological, psychiatric, or mental disorder. The study protocol was approved by the Masaryk University Ethics Committee. The measurements were performed on the Siemens Prisma 3T MR whole-body scanner with 64-channel head-neck coil. The acquisition consisted of high-resolution anatomical images (MPRAGE, voxel size 1 x 1 x 1 mm, FOV 224 x 224x 240 mm) and then 7 different BOLD runs with block design combining visual stimulation and motor activity (pressing buttons). The acquisition time of each run was 6 minutes, echo times (TE) were 17, 35 and 52 ms, voxel size was 3 x 3 x 3 mm. Repetition times (TR), number of scans and flip angles (FA) were different for every run as follows: 1) 3.05 s / 120 / 80°; 2) 3.05 / 120 / 45°; 3) 0.8 s / 450 / 45°; 4) 0.8 s / 450 / 20°; 5)0.6 s / 600 / 45°; 6) 0.6 s / 600 / 20°; 7) 0.4 s / 900 / 20°. Acquired data was processed in as composite ME model data the optimal combinations weighted by the contrast-to-noise ratio in the standard way in SPM12. The second model was calculated as T2* estimation of the same data. The results of activation were verified by using GLM models on single-subject and group levels. We mainly focused on activation level and power of statistics, so we evaluated the differences between multi-echo and T2* models by assessing the number of active voxels, variance of residuals, percent signal change (PSC) and the power of t-statistics. We explored both global and local metrics which were chosen according to the level of activation.

The comparison of ME MB data and T2* data was done using several metrics. For the global level of activation, we computed the number of active voxels, where the T2* model provided similar values as ME model and in runs 3 and 5 the T2* yielded even higher values than ME and these differences were statistically significant (shown in fig. 1). The variance of residuals was slightly worse in T2* model. We also evaluated data in chosen ROIs based on activation and then picked top 50 voxels from each ROI. When comparing the t-values, the T2* model outperformed ME model in some ROIs as shown in fig. 2 (Left precentral gyrus), especially in runs 3,4,5,6 where the difference was statistically significant. However, in some other ROIs the T2* model provided slightly worse results than ME model. Both models provided similar values of PSC in most ROIs, like in the ROI shown in fig. 2, where the T2* model performed significantly better in runs 5, 6 and 7.

The pilot comparison study of ME MB data and T2* mapping showed promising results in terms of acquiring the same or even higher level of data quality in observed metrics. We hope that T2* as a quantitative parameter could contribute to the robustness and stability of the fast fMRI data processing. Although some ROIs gave slightly worse results of T2* than ME model, the overall activation in our data appears to be comparable. We are also planning to verify our theory and results on event-related data or other types of fMRI task data.

Activation (eg. BOLD task-fMRI) ¹

Methods Development

Motion Correction and Preprocessing

Univariate Modeling

BOLD fMRI ²

Data analysis

FUNCTIONAL MRI

Statistical Methods

Other - multi-echo; T2*