Room: Exhibit Hall | Forum 8
Purpose: A lightweight low-cryogen compact 3T (C3T) MRI scanner has been developed to image the brain and extremities, which is equipped with high performance gradient to achieve 80-mT/m magnitude and 700-T/m/s slew-rate simultaneously. The gradient has been demonstrated to reduce echo-planar-imaging (EPI) distortion. In this work, we investigate the benefit of high performance gradient on functional MRI (fMRI) and demonstrate the improvement by comparing the fMRI results with a conventional whole-body 3T MRI scanner (GE 750, 50-mT/m and 200-T/m/s).
Methods: Under IRB-approved protocol, routine EPI-based resting-state (rs) fMRIs were obtained with a 32-channel Nova head-coil on the C3T on 12 subjects. To further demonstrate the benefit of the high gradient performance, 2 subjects were scanned with high spatial resolution on both the C3T and the 750 scanner (Table 1). The fMRI time series were pre-processed and registered to the anatomical images with AFNI[3,4]. Coverage ratio was calculated with FreeSurfer ROIs and EPI-brain-mask for evaluation of the local distortions. Temporal SNR (tSNR) and Z-scores converted from correlation coefficients with seeds placed in left and right fusiform gyri were calculated.
Results: Routine rs-fMRI on the C3T can detect rs-networks(Fig.1). When compared with whole-body scanner, the high gradient performance on the C3T reduced the TR and echo-spacing in EPI, which resulted in higher temporal resolution and reduced signal dropouts in both the temporal and frontal lobes(Fig.2). Therefore, both the coverage ratio and tSNR were improved on the C3T in these high-susceptibility regions(Fig.3&4). The C3T detected greater pixel correlation in the Z-score map(Fig.4).
Conclusion: The high performance gradient on the C3T scanner improves the temporal resolution and reduces geometric distortion leading to higher tSNR in the corresponding areas for the fMRI data when compared with the conventional whole-body scanner. Improved brain network analysis can be derived from the less-distorted brain regions.
Funding Support, Disclosures, and Conflict of Interest: This work was supported in part by NIH Grant U01-EB024450.
Functional Imaging, Geometric Distortion, Echo Planar Imaging