Wei-Tang Chang¹, Thomas Witzel², Kevin Wen-Kai Tsai¹, Wen-Jui Kuo³, and Fa-Hsuan Lin^1
1Institute of Biomedical Engineering, National Taiwan University, Taipei, Taiwan, ²Athinoula A. Martinos Center for Biomedical Imaging, Massachusetts General Hospital, Charlestown, MA, United States, ³Institute of Neuroscience, National Yang-Ming University, Taipei, Taiwan

To ensure a good BOLD contrast with TE = 34 ms at 3T, the scanning time of magnetic resonance inverse imaging (InI) can be further shortened to 25 ms per volume by using the echo shifting technique. Here we demonstrated the feasibility of using echo-shifted InI (esInI) with an unprecedented temporal resolution (40 Hz / volume) to detect hemodynamic responses of human visual cortex. Validated by EPI, esInI was found with good spatial localization using the minimum norm estimation (MNE) for volumetric reconstruction.

Kevin Wen-Kai Tsai¹, Aapo Nummenmaa², Thomas Witzel^2,3, Wei-Tang Chang⁴, Wei-Jui Kuo⁵, and Fa-Hsuan Lin^1,2
1Institute of Biomedical Engineering, National Taiwan University, Taipei, Taiwan, ²A. A. Martinos Center, Massachusetts General Hospital, Charlestown, MA, United States,³Harvard-MIT Divisions of Health Sciences and Technique, Charlestown, MA, United States, ⁴Institute of Biomedical Engineering, National Taiwan University, Taipei, Taiwan, Taiwan, ⁵Cognitive Neuropsychology Laboratory, National Yang-Ming University, Taipei, Taiwan, Taiwan

MR inverse imaging (InI) can achieve 100 ms temporal resolution with whole-brain coverage using highly parallel detection at the cost of compromised spatial resolution due to solving ill-posed inverse problems in image reconstruction. Here we propose the multi-projection InI (mInI) method. Using projection data in three orthogonal directions from all RF channels separately can achieve a high temporal resolution without compromising spatial resolution. Results of using mInI to study the hemodynamic responses in human visuomotor system from 12 participants using a 32-channel head coil array at 3T can achieve 100 ms temporal resolution and 4 mm3 isotropic spatial resolution.

Thomas Witzel^1,2, Jonathan R Polimeni¹, FaHsuan Lin^1,3, Aapo Nummenmaa¹, and Lawrence L Wald^1,2
1A.A. Martinos Center MGH Department of Radiology, Harvard Medical School, Boston, MA, United States, ²Harvard-MIT Division of Health Sciences and Technology, Cambridge, MA, United States, ³Biomedical Engineering, National Taiwan University, Taipei, Taiwan

We developed a 64x64x56 matrix, whole-head 3T single-shot EVI sequences for fMRI. We image the whole brain at 8 frames per second and 3.4mm isotropic resolution with the kz phase encoding direction accelerated by a total of 21 fold to reduce distortions in this “slow” phase encoding direction 21 fold. We analyze the spectral composition of BOLD and physiological signals to show that full Nyquist the cardiac frequency is helpful in mitigating their effect on the estimation of the fMRI activation.

Hsu-Lei Lee¹, Benjamin Zahneisen¹, Thimo Grotz¹, Pierre LeVan¹, and Jürgen Hennig^1
1Medical Physics, University Medical Center Freiburg, Freiburg, Germany

Most resting-state network analysis methods assume the networks are stationary during the course of the scan session, usually ranged from 5 to 15 minutes. However it might not be the case. We propose to use a highly under-sampled fast acquisition scheme (shell trajectory) to record images at a 10 Hz sampling rate and use sliding window to track the dynamic change in those coherent networks with a temporal resolution of 20 seconds.

David A Feinberg^1,2, Steen Moeller³, Stephen Smith⁴, Edward Auerbach³, Kamil Ugurbil³, and Essa Yacoub^3
1Advanced MRI Technologies, Sebastopol, CA, United States, ²University of California, Berkeley and San Francisco, CA, United States, ³Center for Magnetic Resonance Research, University of Minnesota, ⁴FMRIB, Oxford University

A multiplexed-EPI (M-EPI) pulse sequence is presented that combines temporal multiplexing (m) utilizing simultaneous echo refocused (SIR) EPI and spatial multiplexing (n) with multibanded RF pulses (MB) to achieve m x n images in an EPI echo train. This resulted in significant increases in temporal resolution for whole brain fMRI evaluated at 0.8s and 0.4s TR in resting state and in substantial reductions in scan time 8.5m in HARDI neuronal fibertracks using 256 b-values. Multiplexed EPI can be used to acquire higher spatial resolutions, increase diffusion encoding, or to investigate temporal dynamics of the fMRI response.

Jonathan Rizzo Polimeni¹, Kyoko Fujimoto¹, Boris Keil¹, Douglas N. Greve¹, Bruce Fischl^1,2, and Lawrence L. Wald^1,3
1A. A. Martinos Center for Biomedical Imaging, Department of Radiology, Harvard Medical School, Massachusetts General Hospital, Charlestown, MA, United States,²Computer Science and AI Lab (CSAIL), Massachusetts Institute of Technology, Cambridge, MA, United States, ³Harvard-MIT Division of Health Sciences and Technology, Massachusetts Institute of Technology, Cambridge, MA, United States

Here we provide characterization of the radial independence of the fluctuations at each depth below a given cortical location. This radial correlation length of resting state fluctuations was measured using gradient echo and spin echo EPI. The radial correlation length is strongly affected by the removal of confounding physiological signals in a counter-intuitive way--namely the global signals regressed out do not seem to produce an artifactual high-correlation between layers, but rather mask the presence of correlations between different depths. Similarly, the spin echo acquisition, which is also expected to remove relatively global fluctuations also uncovers additional underlying radial correlations.

Rankin Williams McGugin¹, Christopher Gatenby^2,3, and Isabel Gauthier^1
1Psychology, Vanderbilt University, Nashville, TN, United States, ²Radiology & Radiological Sciences, Vanderbilt University Medical Center, Nashville, TN, United States,³Radiology, University of Washington, Seattle, Washington, United States

We imaged the inferior temporal lobe in humans at 7T, using built-in realtime fMRI analysis in combination with the 3D FFE-SENSE sequence to allow for bilateral imaging of the Fusiform Face Area (FFA). We demonstrate robust and reliable functional heterogeneity of the fine-grain neural architecture of bilateral FFA, such that clusters of voxels maximally responsive to non-face categories (irrespective of hemisphere) are spatially interdigitated amongst regions showing maximal response to faces. We demonstrate that a functionally-defined region that appears to be homogenously face-selective at standard resolution (~3mm isotropic) is, in fact, functionally heterogeneous when explored at HR.

Matthew Man Hin Cheung^1,2, Joe S. Cheng^1,2, Iris Y Zhou^1,2, Kevin C. Chan^1,2, Condon Lau^1,2, and Ed X. Wu^1,2
1Laboratory of Biomedical Imaging and Signal Processing, The University of Hong Kong, Pokfulam, Hong Kong SAR, China, People's Republic of, ²Department of Electrical and Electronic Engineering, The University of Hong Kong, Pokfulam, Hong Kong SAR, China, People's Republic of

The inferior colliculus (IC) is an important auditory relay center for ascending pathways and the central nucleus of IC receives input from lower auditory centers and projects to the medial geniculate body in a strictly tonotopic manner. In this study, a novel approach was proposed to map the tonotopic organization in IC with fMRI by using (1) periodic frequency-modulated auditory stimulus with linearly sweeping frequency; and (2) distortion-free balanced steady state free precession (bSSFP) sequence. Tonotopic mapping in IC by fMRI was here demonstrated successfully for the first time in animals or humans.

Jeroen Cornelis Willem Siero^1,2, Natalia Petridou^1,2, Johannes Marinus Hoogduin^1,2, Peter R Luijten², and Nick F Ramsey^1
1Rudolf Magnus Institute, University Medical Center Utrecht, Utrecht, Netherlands, ²Radiology, University Medical Center Utrecht, Utrecht, Netherlands

The BOLD specificity to the cortical vascular architecture was investigated in the human brain, at 7T: temporal dynamics (delay and width) of the BOLD response were characterized across cortical depth in the primary motor and visual cortices. Faster and narrower (<4s) BOLD responses corresponded to the deeper gray matter, and these temporal properties increased in an orderly manner toward the cortical surface. A pooling time of oxygenated blood from the deeper cortex to the pial surface was estimated <~1s. These findings matched the known vascular organization across cortical depth, and may lead to new insights in neurovascular coupling in humans.

Junjie V Liu¹, Matthew Huberty¹, and Afonso C Silva^1
1NINDS, National Institutes of Health, Bethesda, MD, United States

We conducted systematic measurements of BOLD fMRI responses to unilateral electrical stimulation, in both the contralateral and the ipsilateral primary somatosensory cortex (SI) of awake non-human primates (marmosets). Taking advantage of T1 mapping co-registered with fMRI, we found many interesting differences between the responses in low-T1 and high-T1 regions within area 3b of SI, specifically regarding to their relationships with stimulus frequency, duration and intensity. Because T1 is correlated with density of thalamic inputs, with our results the ipsilateral SI responses driven mainly by corticocortical neural inputs can be distinguished from the contralateral SI responses driven mainly by thalamic inputs.