ISMRM 21st Annual Meeting & Exhibition 20-26 April 2013 Salt Lake City, Utah, USA

Novel fMRI Acquisition Methods & Contrast Mechanisms
Wednesday 24 April 2013
Room 255 BC  10:00 - 12:00 Moderators: Fa-Hsuan Lin, Wietske van der Zwaag

10:00 0409.   Blipped-CAIPI Spiral for Simultaneous Multi-Slice BOLD FMRI
Benjamin Zahneisen1, Benedikt A. Poser1, Thomas Ernst2, and Victor Andrew Stenger1
1Department of Medicine, John A. Burns School of Medicine, University of Hawaii, Honolulu, Hawaii, United States, 2Department of Medicine, John A. Burns School of Medicine, University of Hawaii at Manoa, Honolulu, Hawaii, United States

Sub-second whole brain fMRI is advantageous since it resolves physiological signal fluctuations, virtually freezes head motion, has greater statistical power, and allows the detection of subtle HRF shifts or delays. Recently, the “blipped-CAIPI” EPI method was introduced as a means to reduce the g-factor penalty in simultaneous multi-slice (SMS) imaging. However, the approach is limited to Cartesian trajectories with their unique fold-over artifact. Here, we present a new framework for SMS imaging based on 3D Fourier encoding of simultaneously excited slices. We show that the blipped-CAIPI approach can be generalized to non-Cartesian trajectories and SENSE-like reconstructions including a new design for blipped-CAIPI spiral trajectories. Spiral has a more efficient gradient utilization and shorter readouts are possible.

10:12 0410.   Characterization of Artifactual Correlation in Highly-Accelerated Simultaneous Multi-Slice (SMS) fMRI Acquisitions
Kawin Setsompop1,2, Jonathan R. Polimeni1,2, Himanshu Bhat3, and Lawrence L. Wald1,2
1A.A. Martinos Center for Biomedical Imaging, MGH, Charlestown, MA, United States, 2Harvard Medical School, Boston, MA, United States, 3Siemens Medical Solutions, Charlestown, MA, United States

Simultaneous Multi-Slice (SMS) acquisition with blipped-CAIPI scheme has enabled dramatic reduction in imaging time for fMRI acquisitions, enabling high-resolution whole-brain acquisitions with short repetition times. The characterization of SMS acquisition performance is crucial to wide adoption of the technique. In this work, we examine an important source of artifact: spurious thermal noise correlation between aliased imaging voxels. This artifactual correlation can create undesirable bias in fMRI resting-state functional connectivity analysis. Here we provide a simple method for characterizing this artifactual correlation, which should aid in guiding the selection of appropriate slice- and inplane-acceleration factors for SMS acquisitions during protocol design.

10:24 0411.   An Approach to 3-Dimensional Multi-Band Acquisition
Bruno Riemenschneider1, Jakob Assländer1, and Jürgen Hennig1
1Dept. of Radiology, Medical Physics, University Medical Center Freiburg, Freiburg, Germany

Multi-band excitation in conjunction with a 3-dimensional read-out helps to overcome the limitation in number of slices that can be resolved with parallel imaging techniques. Other than slab-wise excitation, it leads to exploitation of the coil sensitivities in all three dimensions and inhomogeneities at the interface between adjacent slabs are avoided. The feasibility of the approach is demonstrated by a sample measurement with a 32-channel headcoil. The field of view of (0.192 m)³ with voxel size 3mm was measured in 400 ms.

10:36 0412.   
Simultaneous SE-BOLD and T2* Measurement by Functional MRS of Water Signal
Peng Cao1,2, Jevin W. Zhang1,2, Victor B. Xie1,2, Iris Y. Zhou1,2, and Ed X. Wu1,2
1The University of Hong Kong, Hong Kong, Hong Kong SAR, China, 2Department of Electrical and Electronic Engineering, Hong Kong, Hong Kong SAR, China

Blood-oxygen-level-dependent (BOLD) contrast is known to be modulated by vascular origins such as intravascular, extravascular, venular and capillary. The relative contributions of these factors to BOLD signal are dependent of magnetic field strength and whether spin echo or gradient echo detection is used. MRS voxel selective excitation method (e.g. PRESS) can measure the SE-BOLD (i.e., amplitude of SE BOLD signal) and T2* (i.e., the FID decay rate) directly simultaneously. With this approach, we simultaneously acquired SE-BOLD signals and T2* and quantitatively compared their characteristics.

10:48 0413.   
T2- Prepared Blood-Oxygenation-Level-Dependent (BOLD) fMRI Using Single-Shot 3D Fast Gradient Echo (GRE) Sequence with Whole Brain Coverage at 7T
Jun Hua1,2, Craig K. Jones1,2, Qin Qin1,2, and Peter C.M. van Zijl1,2
1Neurosection, Div. of MRI Research, Dept. of Radiology, Johns Hopkins University School of Medicine, Baltimore, Maryland, United States, 2F.M. Kirby Research Center for Functional Brain Imaging, Kennedy Krieger Institute, Baltimore, Maryland, United States

We introduce a new acquisition scheme for T2-weighted BOLD fMRI. It employs a T2-preparation module to generate the BOLD contrast, followed by a single-shot 3D fast gradient echo readout. We implemented it on 7T human scanners with whole brain coverage (2.5mm voxel, 55 slices). In fMRI experiments of simultaneous visual and sensory stimulation, this sequence showed comparable sensitivity as the conventional 2D SE-EPI, and advantages of minimal geometric distortion and signal dropouts, lower power deposition, and greater spatial coverage. This approach would be particularly useful for fMRI studies that require whole brain coverage, or focus on regions near air cavities.

11:00 0414.   
T2-Weighted BOLD fMRI at 9.4 T Using a S2-SSFP-EPI Sequence
Philipp Ehses1,2, Juliane Budde1, Gunamony Shajan1, and Klaus Scheffler1,2
1High-Field MR Center, Max Planck Institute for Biological Cybernetics, Tübingen, Germany, 2Dept. of Biomedical Magnetic Resonance, University of Tübingen, Tübingen, Germany

It has been hypothesized that T2-weighted BOLD fMRI at ultra-high field shows higher spatial specificity than T2*-weighted BOLD, since the main signal contribution is expected to come from the extravascular spins of the microvasculature. Unfortunately, the number of slices that can be acquired in multi-slice SE-EPI is limited at ultra-high field due to SAR constraints. T2-weighted steady-state sequences, such as S2-SSFP, have been previously used as an alternative to spin-echo based BOLD fMRI. In this work, we present a 3D S2-SSFP sequence that is accelerated using an EPI readout and show first results from finger tapping experiments at 9.4 T.

11:12 0415.   Simultaneous Spin Echo and Gradient Echo for fMRI Using the USPIO Agent Ferumoxytol in Humans: Enhanced Sensitivity and Potentials for High Resolution Mapping
Deqiang Qiu1, Thomas Christen1, Wendy W. Ni1, Heiko Schmiedeskamp1, Greg Zaharchuk1, and Michael E. Moseley1
1Radiology, Stanford University, Stanford, CA, United States

In this paper, we present the study of the use of ultrasmall superparamagnetic iron particle (USPIO) for fMRI (termed ICE-BVI) using both gradient and spin echo methods. The contrast to noise ratio (CNR) of ICE-BVI was found to be of up to a factor of 3.8 higher than BOLD for gradient echo based method, and the gain is about a factor of 2 for spin echo based method. ICE-BVI has the potential of increasing robustness and accuracy for presurgical mapping and enhanced sensitivity in studying cognitive neuroscience.

11:24 0416.   Diffusion fMRI Can Detect Neural Activation When the BOLD fMRI Response Is Abolished by Nitroprussiate
Tomokazu Tsurugizawa1, Boucif Djemai1, Luisa Ciobanu1, and Denis Le Bihan1
1Neurospin/CEA, Gif-sur-Yvette, Essonne, France

Diffusion-weighted functional MRI (DfMRI) has been shown to be sensitive to neural activation, however, its vascular or non-vascular origin has been a subject of controversy. We have compared the DfMRI and BOLD responses at 7T in the rat brain during forepaw electrical stimulation with and without nitroprussiate, a neurovascular coupling inhibitor, and compared these responses with recorded neural activity. Under the nitroprussiate infusion, while the BOLD signal was completely suppressed, the neuronal activation and DfMRI signal were conserved, demonstrating that DfMRI includes a genuine diffusion component which directly reflects neuronal activation.

11:36 0417.   
Diffusion fMRI Detects White-Matter Dysfunction in Mice with Acute Optic Neuritis
Tsen-Hsuan Lin1, William M. Spees2,3, Robert Mikesell4, Anne H. Cross3,5, and Sheng-Kwei Song2,3
1Physics, Washington University, St. Louis, MO, United States, 2Radiology, Washington University School of Medicine, St. Louis, MO, United States, 3The Hope Center for Neurological Disorders, Washington University School of Medicine, St. Louis, MO, United States, 4Neurology, Washington University School of Medicine, St. Louis, MO, United States, 5Neurology, Washington University in St. Louis, St. Louis, MO, United States

Our previous investigation in healthy mice has shown that visual stimulation caused a significant (~27%) drop in the apparent diffusion coefficient for water perpendicular to the axonal fibers (ADCƒÎ) in optic nerve. In the current study, we have extended these diffusion fMRI measurements in a mouse experimental autoimmune encephalomyelitis (EAE) model at the onset of optic neuritis to investigate the functional integrity of white matter. Our results show that visual stimulation produced a significant 25% decrease in ADCƒÎ in EAE sham optic nerves, while only a 5% decrease in ADCƒÎ was seen in EAE mice. Histological results of SMI31, MBP, and SMI32 staining show axonal swelling and injury distorted myelin sheaths in EAE optic nerves. This suggests that diffusion fMRI could be used as a non-invasive approach to localizing axons with impaired functional integrity.

11:48 0418.   Magnetic Resonance Imaging of Neuronal Currents in an in Vitro Turtle Cerebellum
Padmavathi Sundaram1, William Wells2, Darren B. Orbach1, Daniel Orringer3, Mukund Balasubramanian1, Robert Mulkern1, and Yoshio Okada4
1Radiology, Children's Hospital Boston, Harvard Medical School, Boston, MA, United States, 2Radiology, Brigham and Women's Hospital, Harvard Medical School, Boston, MA, United States,3Neurosurgery, University of Michigan, Ann Arbor, MI, United States, 4Neurology, Children's Hospital Boston, Harvard Medical School, Boston, MA, United States

This work investigates the relationship between neuronal currents and MR signals in an in vitro bloodless turtle cerebellum (Cb). While prior work has demonstrated sensitivity of MR signals to currents, the spatiotemporal relationship between MR phase and neuronal currents remains to be characterized in brain tissue. We use the turtle Cb because: (1) there are no signal contributions from blood, respiration or motion, (2) the cellular circuit is intact, (3) the preparation can withstand anoxia and is physiologically functional for several hours, and (4) it is a flat tissue with the principal neurons oriented parallel to each other.