Room 255 BC

10:00 - 12:00

Moderators:

Fa-Hsuan Lin, Wietske van der Zwaag

Benjamin Zahneisen¹, Benedikt A. Poser¹, Thomas Ernst², and Victor Andrew Stenger^1
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.

Kawin Setsompop^1,2, Jonathan R. Polimeni^1,2, Himanshu Bhat³, and Lawrence L. Wald^1,2
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.

Bruno Riemenschneider¹, Jakob Assländer¹, and Jürgen Hennig^1
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.

Peng Cao^1,2, Jevin W. Zhang^1,2, Victor B. Xie^1,2, Iris Y. Zhou^1,2, and Ed X. Wu^1,2
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.

Jun Hua^1,2, Craig K. Jones^1,2, Qin Qin^1,2, and Peter C.M. van Zijl^1,2
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.

Philipp Ehses^1,2, Juliane Budde¹, Gunamony Shajan¹, and Klaus Scheffler^1,2
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.

Deqiang Qiu¹, Thomas Christen¹, Wendy W. Ni¹, Heiko Schmiedeskamp¹, Greg Zaharchuk¹, and Michael E. Moseley^1
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.

Tomokazu Tsurugizawa¹, Boucif Djemai¹, Luisa Ciobanu¹, and Denis Le Bihan^1
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.

Tsen-Hsuan Lin¹, William M. Spees^2,3, Robert Mikesell⁴, Anne H. Cross^3,5, and Sheng-Kwei Song^2,3
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.

Padmavathi Sundaram¹, William Wells², Darren B. Orbach¹, Daniel Orringer³, Mukund Balasubramanian¹, Robert Mulkern¹, and Yoshio Okada^4
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.