Swati Rane¹, John T Spear¹, Carlos Faraco¹, Manus Donahue^1,2, and John C Gore^1,3
1Radiology and Radiological Sciences, Vanderbilt University, Nashville, TN, United States, ²Neurology, Vanderbilt University, Nashville, TN, United States,³Biomedical Engineering, Vanderbilt University, Nashville, TN, United States

This work investigates the microvascular specificity of T1_ρ functional magnetic resonance imaging at very low locking fields. Compared to conventional spin and gradient echo, we find that relative to the tissue BOLD contrast, BOLD signal in large vessels is better suppressed with T1_ρ functional imaging.

Laura D Lewis¹, Jonathan R Polimeni², Kawin Setsompop², and Bruce R Rosen^2
1Society of Fellows, Harvard University, Cambridge, MA, United States, ²Athinoula A. Martinos Center for Biomedical Imaging, Department of Radiology, Harvard Medical School, Massachusetts General Hospital, Boston, MA, United States

EEG recordings have demonstrated that neural oscillations above 0.1 Hz are important for cognitive function, but these frequencies are too high to be measured directly with traditional fMRI. We used fast acquisition (TR=246 ms) to study whether fMRI can detect continuous neuronal oscillations at high frequencies. We presented periodic visual stimuli and found that the BOLD signal in V1 matched the input frequency at rates up to 0.33 and 0.5 Hz. The phase of the response depended on stimulus dynamics. We conclude that fMRI can directly measure neural oscillations at the lowest end of the delta (0.25-4 Hz) band.

A Alhamud¹, Paul Taylor^1,2, Jia Fan¹, Ernesta Meintjes¹, and André J.W. van der Kouwe^3
1Human Biology,MRC/UCT Medical Imaging Research Unit, University of Cape Town, Cape Town, Western Cape, South Africa, ²African Institute for Mathematical Sciences (AIMS), Western Cape, South Africa, ³Massachusetts General Hospital, Charlestown, Massachusetts, United States

During fMRI acquisition, magnetic field inhomogeneities may lead to severe signal dropouts and geometric distortions in fMRI images. The inhomogeneities are routinely minimized by shimming prior to fMRI scan. However, factors, which may include breathing, heating of the shim iron coils or subject motion, can alter the static shim and affect the BOLD measures. The purpose of this work is to introduce a technique to measure, report and correct in real-time magnetic field distortions as well as subject motion. This is achieved by acquiring two volumetric navigators to track motion and produce a field map after each fMRI volume acquisition.

Daniel Zaldivar¹, Nikos Logothetis¹, and Jozien Goense^1,2
1Logothetis, Max Planck Institute for Biological Cybernetics, Tuebingen, Baden-Württemberg, Germany, ²Institute of Neuroscience and Psychology, University of Glasgow, Glasgow, United Kingdom

There is still debate whether negative BOLD responses have a neural or vascular origin. Laminar differences in neurovascular coupling have also been observed during the negative-BOLD response. We investigated whether these differences have a neural origin by performing laminar recordings in V1. We positioned two laminar electrodes in V1; one of these was located in the negative-BOLD area whereas the other in the positive-BOLD area. We observed that the middle cortical layers did not decrease their neural activity while all other layers did, suggesting that the negative BOLD response is driven by the neural activity reductions in the supragranular and infragranular layers.

Maria Guidi¹, Laurentius Huber¹, Leonie Lampe¹, Claudine J. Gauthier¹, and Harald E. Möller^1
1Max Planck Institute for Human Cognitive and Brain Sciences, Leipzig, Germany

The Davis model for blood oxygenation level dependent (BOLD) signal changes gives the possibility of estimating cerebral metabolic rate of oxygen consumption (CMRO2) changes noninvasively. The increased resolution offered by ultra-high fields (7T) paved the way for layer dependent studies and for the investigation of CMRO2 distribution across cortical layers. Scaled BOLD and vascular space occupancy (VASO) profiles, together with M and CMRO2 estimates in human primary motor cortex, were obtained at high resolution (0.8x0.8x1.5 mm3) and showed a marked change with cortical depth, implying that the assumption of constant values across the cortex should be decisively called into question.

W. Scott Hoge^1,2 and Jonathan R Polimeni^2,3
1Dept. of Radiology, Brigham and Women's Hosp, Boston, MA, United States, ²Harvard Medical School, Boston, MA, United States, ³Dept. of Radiology, Athinoula A. Martinos Center for Biomedical Imaging, Massachusetts General Hospital, Charlestown, MA, United States

EPI is widely used in neuroimaging applications. However, many imaging artifacts are inherent in the method, with Nyquist ghosting one of the most prominent. Conventional methods to correct the sampling errors that give rise to Nyquist ghosts typically model only linear and constant phase error terms. In this work, we present a Dual-Polarity GRAPPA method to address the limitations of conventional Nyquist ghost correction. In-vivo results are shown that demonstrate the ability of the method to correct higher-order phase errors in EPI data. .

Nadine N Graedel¹, Mark Chiew¹, Jennifer A McNab², and Karla L Miller^1
1FMRIB Centre, University of Oxford, Oxford, Oxfordshire, United Kingdom, ²Department of Radiology, Stanford University, California, United States

We propose the use of a 3D hybrid radial-Cartesian trajectory for functional MRI, in which the readout EPI planes are rotated around kz according to an angle scheme based on the golden ratio. This acquisition strategy facilitates correction for many sources of temporal fluctuation (such as motion and physiological noise) and allows flexible post-acquisition definition of spatio-temporal resolution. We implemented example corrections for motion and physiological noise, which allowed recovery of data corrupted by severe motion. Additionally we show visual fMRI data reconstructed at different temporal resolutions.

Yi He^1,2, Hellmut Merkle³, and Xin Yu^1,2
1Research Group of Translational Neuroimaging and Neural Control, High-Field Magnetic Resonance, Max Planck Institute for Biological Cybernetics, Tuebingen, Baden-Wuerttemberg, Germany, ²Graduate School of Neural Information Processing, University of Tuebingen, Tuebingen, Baden-Wuerttemberg, Germany,³Laboratory of Functional and Molecular Imaging, National Institute of Neurological Disorders and Stroke, National Institutes of Health, Bethesda, MD, United States

In contrast to the traditional T2*-weighted EPI-fMRI signal, the T2* fMRI signal is more specific with less temporal noise interference. We developed a multi-Echo Line-Scanning fMRI (MELS-fMRI) method to map T2* signal in a block design stimulation paradigm with 100ms sampling rate. Individual penetrating venules can be directly identified from the raw image with 100x100¦Ìm spatial resolution. The spatial pattern of single-venule fMRI signal was detected from 3 ms to 20.5 ms with 3.5ms interval. It is the first step to decipher the millisecond scale fMRI signal propagation across cerebrovasculature in the deep layer cortex.

Tiffany Jou¹, Joseph Y Cheng², Chris Bowen³, Michael Lustig⁴, and John M Pauly^1
1Electrical Engineering, Stanford University, Stanford, CA, United States, ²Radiology, Stanford University, Stanford, CA, United States, ³Radiology, Dalhousie University, Halifax, NS, Canada, ⁴Electrical Engineering and Computer Sciences, UC Berkeley, Berkeley, CA, United States

By using RF catalyzation to alternate between two RF phase-cycling steady states, Alternating-SSFP (alt-SSFP) suppresses banding artifacts in conventional Passband Balanced-SSFP (pb-SSFP) and allows for whole-brain fMRI in a single functional run. In this work, we demonstrate that due to the offset banding patterns of different phase-cycling, the coil sensitivity maps of alternate phase-cycling volumes can be used as additional maps to enhance the conditioning of the parallel imaging reconstruction of the alt-SSFP phase-cycled images. This increases temporal SNR for alt-SSFP fMRI in highly accelerated cases.

Deng Mao¹ and Hanzhang Lu^1
1Advanced Imaging Research Center, Univ of Texas Southwestern Medical Center, Dallas, TX, United States

Quantification of venous oxygenation is a critical component for understanding brain metabolism. The present study aimed to develop a non-invasive, efficient and reproducible technique to map brain venous oxygenation in 3D. Our method has utilized phase contrast principle to isolate pure blood signal and measure its T2* from its signal decay in multi-echo gradient echo by mono-exponetial fitting. The fitted blood T2* can be converted into oxygenation level though in vitro calibration curve.This novel T2-base oximetry implementation has successfully provided a 3D map of blood T2* and oxygenation and demonstrated excellent reproducible.