Simultaneous multi-slice inverse imaging of the human brain

Yi-Cheng Hsu, Ying-Hua Chu, Shang-Yueh Tsai, Wen-Jui Kuo, Chun-Yuan Chang, Fa-Hsuan Lin
2017 Scientific Reports  
Ultrafast functional magnetic resonance imaging (fMRI) can measure blood oxygen level dependent (BOLD) signals with high sensitivity and specificity. Here we propose a novel method: simultaneous multi-slice inverse imaging (SMS-InI) -a combination of simultaneous multi-slice excitation, simultaneous echo refocusing (SER), blipped controlled aliasing in parallel imaging echo-planar imaging (EPI), and regularized image reconstruction. Using a 32-channel head coil array on a 3 T scanner, SMS-InI
more » ... hieves nominal isotropic 5-mm spatial resolution and 10 Hz sampling rate at the whole-brain level. Compared with traditional inverse imaging, we found that SMS-InI has higher spatial resolution with lower signal leakage and higher time-domain signal-to-noise ratio with the optimized regularization parameter in the reconstruction. SMS-InI achieved higher effective resolution and higher detection power in detecting visual cortex activity than InI. SMS-InI also detected subcortical fMRI signals with the similar sensitivity and localization accuracy like EPI. The spatiotemporal resolution of SMS-InI was used to reveal that presenting visual stimuli with 0.2 s latency between left and right visual hemifield led to 0.2 s relative hemodynamic response latency between the left and right visual cortices. Together, these results indicate that SMS-InI is a useful tool in measuring cortical and subcortical hemodynamic responses with high spatiotemporal resolution. There is accumulating evidence suggesting the advantage of collecting BOLD signals with sub-second sampling rate. First, we can monitor and suppress cardiac-and respiratory-related physiological noise 1 more efficiently 2-5 . Second, the fine timing information related to neuronal activity in the range of a few hundreds of milliseconds can be detected in hemodynamic response 6,7 . Third, the functional connectivity in the resting-state networks involving visual and motor cortices is more stably detected in both spatial and temporal domains when the sampling frequency is higher than 0.1 Hz 8 . Fourth, with improved sampling rate, we can measure the effective connectivity between the visual and motor system more reliably, demonstrating the advantage of characterizing inter-regional information flow in simple visuo-motor tasks 9,10 . Lastly, with the high sampling rate, the time series can be cleaned using large number of regressors and achieve higher statistical power in resting state network estimation 11,12 . There are currently different methods to achieve fMRI measurements with a high sampling rate. Parallel detection methods can achieve 10 Hz sampling rate with millimeter spatial resolution and whole-brain coverage. These include, for example, MR-encephalography (MREG) 13 and inverse imaging (InI) 14, 15 . Targeting at a more homogeneous spatial resolution, MREG uses non-Cartesian 16 trajectories at the cost of more complicated image reconstruction, where volumetric image voxels are coupled in a large linear system. On the other hand, InI uses a simpler rectilinear k-space trajectory to allow the 3D image reconstruction separated into multiple linear systems of a much smaller size. However, InI has rather anisotropic resolution because the sensitivity information from the coil array is not sufficient to separate spatially aliased image voxels 14 . Recently, parallel-accelerated simultaneous multi-slice (SMS) imaging 17 using blipped controlled aliasing (CAIPI) EPI has been introduced 18 . This method was further integrated with simultaneous echo refocusing (SER) to achieve a 2.5 Hz volumetric sampling rate in fMRI experiments 7,19 . Using a 32-channel head coil array on 3 T, blipped-CAIPI-EPI provides acquisitions with about 2-3 mm isotropic spatial resolution at a volumetric sampling interval in the range of 300 ms to 600 ms. However, the quality of fMRI time series was found poor if the Published: xx xx xxxx OPEN www.nature.com/scientificreports/
doi:10.1038/s41598-017-16976-0 pmid:29208906 pmcid:PMC5717110 fatcat:frvuc4pb2ba7lfvggiavrary3u