Marta Bianciardi¹, Masaki Fukunaga¹, Jacco A de Zwart¹, and Jeff H Duyn^1
1Advanced MRI Section, LFMI, NINDS, National Institutes of Health, Bethesda, MD, United States

The origin of spontaneous fMRI activity (SA-fMRI) of the human brain is still poorly understood, for example if it represents ongoing sensory processing or homeostatic/cognitive functions that depend on brain state. To investigate this, we measured the amplitude of SA-fMRI in the visual cortex and of fluctuations in amplitude of magnetoencephalographic-MEG activity and electro-oculogram-activity, varying independently the brain-attentive-state (eyes-open/closed) and the visual input (presence/absence of light). Amplitude of SA-fMRI changed dynamically with brain state, and was not modulated by visual input. Our results suggest that the level of SA-fMRI may depend on the level of arousal and oculo-motor activity.

Kevin Murphy¹, James Coulson^1,2, Ashley D Harris¹, Marija Fjodorova¹, and Richard G Wise^1
1CUBRIC, School of Psychology, Cardiff University, Cardiff, Wales, United Kingdom, ²Wales Heart Research Institute, Cardiff University, Cardiff, Wales, United Kingdom

Dynamic changes in both blood pressure and arterial CO2 concentration lead to variations in the BOLD signal. Fluctuations in arterial blood pressure are controlled by the sympathetic nervous system through changes in arterial stiffness. Pulse wave velocity (PWV) alters with arterial stiffness and can be used as a surrogate measure of sympathetic activity. In this study, significant variance in resting state BOLD signals was explained by simultaneously recorded PWV traces. A lack of delay between the two signals suggests that the related BOLD fluctuations are associated with flow changes arising from dynamic variations in blood pressure.

Matthew Jon Brookes¹, Joanne Hale¹, Claire Stevenson¹, Johanna Zumer¹, Gareth Barnes², Julia Owen³, Susan Francis¹, Srikantan Nagarajan³, and Peter Morris^1
1Sir Peter Mansfield Magnetic Resonance Centre, University of Nottingham, Nottingham, United Kingdom, ²Wellcome Trust Centre for Neuroimaging, University College London, London, United Kingdom, ³Biomagnetic Imaging Laboratory, University of California San Francisco, San Francisco, California, United States

In this study we employ ultra high field (7T) functional connectivity (fc) MRI and magnetoencephalography (MEG) to explore, in detail, the electrophysiological basis of haemodynamic measures of functional connectivity. We show good agreement between motor cortex connectivity measured independently using these two disparate neuroimaging modalities. We employ three different MEG based functional connectivity metrics to investigate how neural oscillations mediate functional connectivity. Finally, we investigate the temporal dynamics of connectivity, showing that marked changes occur on a timescale accessible to fMRI. Our study has implications to those developing fcMRI methodologies, and to those employing fcMRI to understand functional connectivity.

Changwei W Wu¹, Hong Gu¹, Qihong Zou¹, Hanbing Lu¹, Elliot A Stein¹, and Yihong Yang^1
1Neuroimaging Research Branch, National Institute on Drug Abuse, Baltimore, Maryland, United States

Spatial and spectral effects of T2* were assessed on low-frequency spontaneous fluctuations acquired at 3T. Using a mutlti-echo sequence, broad local (ipsilateral) connections but minimal long-distance (contralateral) connections were found at an ultra-low TE (7.7 ms) in the default-mode network. In frequency domain, the uniform spectral power at low TE indicated minimal T2*-weighted connectivity and the elevated spectral power with long TEs in the frequency range of 0–0.05 Hz, likely due to T2*-mediated neuronal activities. These results characterized the effects of transverse relaxation times on functional connectivity, which would be useful for the interpretation of resting-state fMRI studies.

Anna Leigh Rack-Gomer¹, and Tom T Liu^1
1Bioengineering and Center for Functional MRI, UC San Diego, La Jolla, CA, United States

Prior work has shown that caffeine decreases the amplitude and correlation of resting-state BOLD fluctuations. However, the physiological mechanisms by which caffeine alters spontaneous BOLD fluctuations remain unclear. In this study, we show that the ratio of the amplitudes of resting-state BOLD and cerebral blood flow (CBF) fluctuations in the motor cortex is reduced by caffeine. This finding indicates that caffeine tightens the coupling between resting-state fluctuations in CBF and oxygen metabolism. Tighter flow-metabolism coupling is consistent with the caffeine-induced decrease in the amplitude of spontaneous BOLD fluctuations and may also contribute to the reduced resting-state BOLD connectivity.

Steven Roys¹, Gadi Alon², George Makris³, and Rao Gullapalli^1
1University of Maryland, School of Medicine, Baltimore, MD, United States, ²Physical Therapy, University of Maryland, School of Medicine, ³University of Maryland, School of Medicine

Intracranial electrical brain stimulation has been shown to provide favorable clinical outcomes in various CNS conditions including Parkinson’s disease, stroke, clinical depression and pain. However the mechanisms related to these outcomes are less well understood. In this study we report changes in the resting state motor network following electrical stimulation of the motor cortex using both pulsed and direct current stimulation. We observe persistent, significant changes in the resting state motor network following pulsed electric stimulation. These results suggest that functional connectivity MRI studies can help elucidate the mechanisms responsible for therapeutic effects of electric stimulation.

Najmeh Khalili-Mahani^1,2, Mathiass J. P. Van Osch¹, and Serge A. R. B. Rombouts^1,2
1Radiology, Leiden University Medical Center, Leiden, Netherlands, ²Leiden Institute for Brain and Cognition, Institute of Psychology, Leiden, Netherlands

We have previously shown that different CNS drugs induce distinct and network specific changes in resting state network connectivity. Here we have examined the relationship between changes in resting state connectivity and changes in cerebral blood flow measured in the same subjects.

Maolin Qiu¹, Ramachandran Ramani², Roberto Martuzzi¹, Xiaohui Zhang¹, and R Todd Constable^1,3
1Diagnostic Radiology, Yale University School of Medicine, New Haven, CT, United States, ²Anesthesia, Yale University School of Medicine, New Haven, CT, United States,³Biomedical Engineering, Neurosurgery, Yale University School of Medicine, New Haven, CT, United States

Effects of sevoflurane on rCBF are observed across the brain cortices but are highly region-specific, with increases limited primarily to subcortical structures and insula and decreases observed primarily in neocortical regions. The functional connectivity within sub-neural networks appears to be much less affected by sevoflurane. With the assumption that both the resting state rCBF and functional connectivity are associated with the same underlying neuronal processes, we wanted to test whether a decrease in CBF during anesthesia would lead to a decrease in functional connectivity, and vice versa. Discrepancies between the changes in rCBF and connectivity caused by sevoflurane might suggest the differences in the neuronal processes with which they are associated. This work examined the relationship between local changes in rCBF and BOLD based functional connectivity in the awake and anesthetized state in humans. Regional CBF was significantly altered by sevoflurane across the brain while the network properties as measured using BOLD functional connectivity remained largely undisturbed. These discrepancies in the responses between rCBF and functional connectivity suggest that they are in general not associated with the same functional components of underlying neuronal processes.

R Matthew Hutchison¹, L Stan Leung¹, Seyed M Mirsattari¹, Joseph S Gati², Ravi S Menon², and Stefan Everling^2
1University of Western Ontario, London, Ontario, Canada, ²Robarts Research Institute, London, Ontario, Canada

Independent component analysis of the resting macaque brain revealed homologous large-scale network organization at multiple levels of processing with humans. These included higher-order networks facilitating executive functioning, attentional processing, reward evaluation, and default-mode activity as well as lower-order networks responsible for vision, audition, sensorimotor integration, and motor control. The consistency of RSNs between macaques and humans suggests the same gross topological cortical organization, thereby providing strong support for their use as an animal model in the study of normal and abnormal functional connectivity.

Paola Valsasina¹, Maria Assunta Rocca¹, Gianna Riccitelli¹, Andrea Falini², Giancarlo Comi³, and Massimo Filippi^1
1Neuroimaging Research Unit, Institute of Experimental Neurology, Division of Neuroscience, San Raffaele Hospital, Milan, Milan, Italy, ²Department of Neuroradiology, San Raffaele Hospital, Milan, Milan, Italy, ³Department of Neurology, San Raffaele Hospital, Milan, Milan, Italy

In this study, we assessed gender-related differences in the entity of resting state (RS) fluctuations in a large cohort of healthy subjects (48 males, 56 males, mean age=23.1 years). Voxel-based morphometry was also run to investigate the correspondence between functional and structural differences. RS activity was found to be increased in males vs. females in several regions of the temporal and parietal lobes, whereas females had a higher RS activity than males in the frontal lobes, the cerebellum and several visual and auditory areas. Gender-related RS functional differences had only a minimal overlap with gray matter volume differences.

Pan Lin¹, Nicola De Pisapia¹, and Jorge Jovicich^1,2
1Center for Mind Brain Sciences,University of Trento, Mattarello, Trento, Italy, ²Department of Cognitive and Education Sciences,University of Trento, Rovereto, Trento, Italy

The default mode network (DMN) is an intrinsic brain system that participates in internal modes of cognition. Neural activity and connectivity within the default network , which are correlated with cognitive ability even at rest. However, what remain unclear is the key issue of whether the inter-region functional connectivity within DMN is related to task performance. Here, we hypothesized that the strength of the functional connectivity (FC) within DMN is an index of the degree of regulation of task performance during attention task state. We found that some inter-region FC within DMN showed the significant negative correlations to reaction time during attention task. These results would suggest the important role of the inter-region FC within DMN can predict attention task performance.

Bob L Hou¹, Alison Smith², Jason Chong², Julie Brefczynski-Lewis¹, and Marc Haut^2
1Radiology, West Virginia University, Morgantown, WV, United States, ²Behavioral Medicine & Psychiatry, West Virginia University, Morgantown, WV, United States

We presented our study applying rfMRI data to evaluate the impacts of attention training on healthy highly educated subjects and to examine our hypothses: 1) Brain attention function is linked with rest-state brain attention network; 2) the improvement of attention due to ~{!0~}training~{!1~}results from the increase in the network connectivity.

Lei Jiang¹, Zhihao Li¹, Claire Coles², Mary Lynch², and Xiaoping Hu^1
1Department of Biomedical Engineering, Emory University and Georgia Institute of Technology, Atlanta, GA, United States, ²Department of Psychiatry and Behavioral Sciences, Emory University School of Medicine, Atlanta, GA, United States

Children and adolescents prenatally exposed to cocaine are at high risk not only for attention/arousal dysregulation and possible inefficiencies in some cognitive functions, but also for problems such as antisocial behavior, substance abuse, and emotional disorders. Because functional brain networks detected in resting-state fMRI have a small-world architecture that reflects a robust functional organization of the brain, here we examined whether this functional organization is disrupted in prenatal cocaine exposure (PCE) by employing a wavelet analysis method. The results show that dysfunctional integrations occur in the brains of PCE individuals during the resting state. Differences between sub-bands were also observed in the small-world analysis. Our findings highlight the need to consider different frequency bands and the usefulness of wavelets in functional connectivity analyses of resting state fMRI.

Chong-Yaw Wee¹, Pew-Thian Yap¹, Kevin Denny², Lihong Wang², and Dinggang Shen^1
1Radiology, University of North Carolina, Chapel Hill, North Carolina, United States, ²Brain Imaging and Analysis Center, Duke University Medical Center, Durham, North Carolina, United States

We introduce an effective network-based multivariate classification algorithm, using multi-spectral connectivity networks derived from resting-state functional MRI, to accurately identify MCI patients from normal controls. Classification accuracy given by our approach is 86.5%, which is at least an 18.9% increment from methods using a single frequency band. The AUC value of our method is 0.863, indicating good diagnostic power. Significant improvements and promising results indicate that the proposed framework can potentially serve as a complementary approach to clinical diagnosis of alteration in brain functions associated with cognitive impairment, especially at early stages.

Elisa Canu¹, Federica Agosta¹, Paola Valsasina¹, Nilo Riva², Alessandro Prelle³, Giulia Longoni¹, Giancarlo Comi², and Massimo Filippi^1
1Neuroimaging Research Unit, Institute of Experimental Neurology, Division of Neuroscience, Scientific Institute and University Hospital San Raffaele, Milan, Italy,²Department of Neurology, Scientific Institute and University Hospital San Raffaele, Milan, Italy, ³3Ospedale Fatebenefratelli e Oftalmico, Milan, Italy

Using resting state functional MRI (RS fMRI), the default mode (DMN), fronto-parietal, executive, and salience networks were explored in 16 patients with amyotrophic lateral sclerosis (ALS) with no cognitive impairment and 15 healthy controls. Compared to controls, ALS patients showed a decreased connectivity of the DMN and fronto-parietal networks in the frontal cortex, but enhanced connectivity in the parietal regions. In non-demented ALS patients, the pattern of network abnormalities mirrors that observed in patients with frontotemporal dementia (FTD). RS fMRI may contribute to shed light on to the overlap between ALS and FTD.

zhiqun wang¹, xiuqin jia¹, peipeng liang¹, and kuncheng li^1
1radiology department, xuanwu hospital of Capital Medical University, Beijing, Beijing, China, People's Republic of

Problem: Recently, resting-state functional MRI (fMRI) has attracted increasing attention. Most studies have focused on the hippocampus and posterior cingulate cortex (PCC) connectivity regarding their crucial roles in cognitive function, while less attention has been devoted to the potential role of subcortical nuclei such as thalamus. Methods: Resting state fMRI was used to examine changes in thalamus connectivity in mild cognitive impairment (MCI), which presented a neuro-disconnection syndrome. Results: Functional connectivity between the thalamus and a set of regions was decreased in MCI. We also found increased functional connectivity between the left and the right thalamus in MCI. Conclusions: This study offered a clue to the reduced integrity and compensation in thalamus-related network in MCI.

Benedikt A Poser¹, Cungeng Yang¹, Weiran Deng¹, Vijayanand Alagappan^2,3, Lawrence L Wald^2,4, and V Andrew Stenger^1
1University of Hawaii, John A. Burns School of Medicine, Honolulu, Hawaii, United States, ²A.A. Martinos Center for Biomedical Imaging, Department of Radiology, Massachusetts General Hospital, Boston, Massachusetts, United States, ³Department of Biomedical Engineering, Tufts University, Medford, Massachusetts, United States,⁴Harvard-MIT Division of Health Sciences and Technology, Cambridge, Massachusetts, United States

Signal loss remains the most obdurate problem in gradient-echo BOLD fMRI. Here we address the issue by merging two highly promising techniques, parallel-transmission z-shimming and multi-echo EPI acquisition. ME-EPI has previously been shown to increase BOLD sensitivity over the entire brain; however it does not actively compensate for through-plane dephasing. This makes multi-channel transmission for the application of local corrective z-shims is highly complementary. The combined method is found to be more effective in reducing susceptibility artifacts than each individual approach; In vivo experiments reveal improved sensitivity in the frontal lobe, demonstrating the method’s potential for fMRI application.

Christoph Barmet¹, Bertram Jakob Wilm¹, Lars Kasper¹, Christian C Ruff², Klaas Enno Stephan^2,3, and Klaas Paul Pruessmann^1
1Institute for Biomedical Engineering, University and ETH Zürich, Zurich, Zurich, Switzerland, ²Laboratory for Social and Neural Systems Research, University of Zurich, Zurich, Zurich, Switzerland, ³Wellcome Trust Centre for Neuroimaging, University College of London, London, London, United Kingdom

In fMRI it is attractive to precisely know the spatio-temporal magnetic field evolution in the imaging volume during the scan. On the one hand, such knowledge can be taken into account for image reconstruction; on the other hand, it could be a useful means of subject surveillance and of monitoring the course of a study for retrospective analysis. Recent advances in field monitoring hardware and methods actually promise to offer such capability. The present work aims to explore this proposition, using recent concurrent magnetic monitoring technology.

Jürgen Finsterbusch^1,2, and Falk Eippert^1,2
1Department of Systems Neuroscience, University Medical Center Hamburg-Eppendorf, Hamburg, Germany, ²Neuroimage Nord, University Medical Centers Hamburg-Kiel-Lübeck, Hamburg-Kiel-Lübeck, Germany

BOLD-based spinal cord imaging suffers from the magnetic field inhomogeneities induced by the different susceptibilities of the vertebrae and the surrounding tissue. In T2*-weighted acquisitions, these inhomogeneities cause a signal dephasing that varies between different transverse sections. In this study, it is shown that applying slice-specific gradient compensation moments reduce the signal variations and drop outs which could help to improve the detectability and reliability of BOLD-based functional neuroimaging of the spinal cord.

Kwan-Jin Jung¹, and Tiejun Zhao^2
1Scientific Imaging Brain Research (SIBR), Department of Psychology, Carnegie Mellon University, Pittsburgh, PA, United States, ²MR R&D Collaborations, Siemens Medical Solutionsn USA, Siemens Healthcare, Pittsburgh, PA, United States

Parallel imaging with acceleration was noted to pronounce the ripple artifact near the susceptibility-affected region in the gradient echo EPI for BOLD fMRI. Using the extended EPI sequence, which collected extended readouts outside the regular data acquisition window, the pronounced ripple artifact was analyzed and found to be caused by an increased echo shift in the pre-TE period in accelerated parallel imaging. This was also confirmed by theoretical derivation of the echo shift due to the magnetic field susceptibility. A new EPI sequence was developed to reduce the ripple artifact as well as to restore the signal level to the level of un-accelerated parallel imaging by applying the acceleration asymmetrically only to the post-TE period. The un-accelerated portion in the pre-TE period utilized the delay for the optimum BOLD sensitivity at 3T, maintaining the same slice coverage as the conventional acceleration in both pre- and post-TE periods.

Wei Lin¹, Enrico Simonotto¹, Feng Huang¹, Charles Saylor¹, George R Duensing¹, and Arne Reykowski^1
1Invivo Corporation, Philips Healthcare, Gainesville, FL, United States

A recently proposed rapid k-space-based parallel imaging method for variable-density (VD) spiral, Generalized GRAPPA for wider spiral bands (GROWL) is applied to fMRI. When compared with standard EPI images acquired with identical scan parameters, VD spiral-in images shows significantly less signal dropout in the frontal orbital region. A second potential advantage is to achieve higher temporal/spatial resolution and larger volume coverage with highly undersampled VD spiral trajectories.

Jochen Rick¹, Oliver Speck², Jürgen Hennig¹, and Maxim Zaitsev^1
1Dept. of Radiology, Medical Physics, University Medical Center Freiburg, Freiburg, Germany, ²Biomedical Magnetic Resonance, Otto-von-Guericke University, Magdeburg, Germany

Anatomy-related susceptibility gradients in the human head lead to artefacts in echo planar imaging (EPI). The use of a slice-dependent template-based gradient compensation method improves BOLD sensitivity (BS) in areas affected by strong susceptibility-induced field gradients. Here, an evaluation of BS changes is performed for a compensated measurement in relation to an uncompensated measurement. It is shown that the ratio of signal loss to signal gain is well balanced, but the method allows the sensitivity to be optimized in target areas. These results are affirmed in a functional experiment and shows that the method can be used for event-related functional experiments.

Jaemin Shin¹, Sinyeob Ahn¹, and Xiaoping P Hu^1
1Biomedical Engineering, Georgia Tech/Emory University, Atlanta, GA, United States

Susceptibility-induced field inhomogeneity is a major cause of signal loss in functional MRI. Z-shimming has been widely used in the slice selection (SS) direction. Shimming technique has been extended to the phase encoding (PE) direction. However, the gradient of a fixed amplitude in PE direction may not achieve the optimal signal recovery of whole brain. In this work, we describe a single shot EPI sequence that can optimally compensate for the inhomogeneity in both SS and PE directions. Signal recovery with only Z- shimming was only 38% of the optimal shimming in the two directions. In conclusion, multi directional shimming is better than Z-shimming alone for signal recovery in fMRI.

Thomas Le Paine^1,2, and Brad P Sutton^1,2
1Bioengineering, University of Illinois Urbana-Champaign, Urbana, IL, United States, ²Beckman Institute, University of Illinois Urbana-Champaign, Urbana, IL, United States

Magnetic susceptibility differences between air and tissues lead to magnetic field inhomogeneity in the brain that can cause artifacts during functional neuroimaging using the BOLD mechanism. When a gradient echo acquisition is used, gradients in the magnetic field inhomogeneity can cause effective echo time shifts that result in spatial variations in the sensitivity of BOLD. With a measured field map, these variations can be calculated and used to calibrate BOLD maps. We show BOLD maps from a breath hold task for four different acquisition trajectories on the same subject and compare them to the expected BOLD sensitivity maps.

Pål Erik Goa^1,2, Benedikt Andreas Poser^2,3, and Markus Barth^2,3
1Department of Medical Imaging, St.Olav University Hospital, Trondheim, Norway, ²Erwin L. Hahn Institute for Magnetic Resonance Imaging, University Duisburg-Essen, Essen, Germany, ³Donders Institute for Brain, Cognition and Behaviour, Radboud University Nijmegen, Nijmegen, Netherlands

Navigator phase correction is used in GRE sequences to remove respiration induced global phase variations. Non-balanced Steady-state free precession might also benefit from phase correction. Here we investigate the phase variation in S1 and S2 signals individually and evaluate two different navigator methods. Results show that the S2 phase is different from S1 phase and cannot be corrected using a single S1 navigator. An interleaved scheme where navigator echoes for both S1 and S2 are sampled every m TR will successfully correct both signals individually. BOLD-fMRI experiments on 7T shows significant increase in number of activated voxels using the interleaved scheme.

Qi Peng^1,2, Yi Zhang^1,2, Oscar San Emeterio Nateras^1,2, and Timothy Q Duong^1,2
1Radiology, UT Health Science Center at San Antonio, San Antonio, TX, United States, ²Research Imaging Institute, UT Health Science Center at San Antonio, San Antonio, TX, United States

Pass-band balanced steady-state free precession (pbSSFP) fMRI offers high BOLD sensitivity and is less susceptible to physiological noise compared to traditional gradient echo planar imaging sequences. However, the contrast mechanism is still under investigation, and the impact of TE on commonly used short-TR (<10ms) pbSSFP on BOLD sensitivity has not been experimentally investigated at 3.0T. In this study, we demonstrated that a TE/TR ratio approaching unity had much higher BOLD compared to the same pbSSFP with TE/TR¡Ü0.5. Therefore, k-space trajectories leading to larger TE have advantages in short-TR pbSSFP fMRI studies to obtain high BOLD sensitivity.

Rob Hendrikus Tijssen¹, Thomas William Okell¹, and Karla Loreen Miller^1
1FMRIB Centre, Oxford University, Oxford, Oxon, United Kingdom

Low distortion and high signal-to-noise ration make Steady-state free precession (SSFP) FMRI an attractive pulse sequence for high resolution brainstem FMRI. Unfortunately the multi-shot character of the readout makes the sequence highly susceptible to flow-induced instabilities that correlate with the cardiac cycle. We present a readout method that achieves real-time cardiac synchronization without varying frame rate, based on GRAPPA and partial-Fourier reconstruction. This method significantly improves temporal stability in the brainstem.

Iris Yuwen Zhou^1,2, Matthew M. Cheung^1,2, Kevin C. Chan^1,2, Condon Lau^1,2, and Ed X Wu^1,2
1Laboratory of Biomedical and Signal Processing, The University of Hong Kong, Hong Kong SAR, China, People's Republic of, ²Department of Electrical and Electronic Engineering, The University of Hong Kong, Hong Kong SAR, China, People's Republic of

The major challenges in EPI-fMRI are the image distortions and constraint in spatial resolution, thus limiting accurate and high resolution mapping of brain functions especially in small animals at high fields. To overcome these limitations and also to achieve high CNR and robust signal changes, we investigated the feasibility of fMRI using bSSFP together with intravascular susceptibility contrast agent MION in rodent brains. We also compared with the conventional SE-EPI and GE-EPI based fMRI. The results demonstrated that bSSFP in combination with intravascular contrast agent provides a robust CBV based fMRI approach. Such brain functional mapping is distortion free and can be of high resolution, and it is particularly suited for high field fMRI study of animal models.

Tao Jin¹, and Seong-Gi Kim^1
1Neuroimaging laboratory, Department of Radiology, University of Pittsburgh, Pittsburgh, PA, United States

The spin-lattice relaxation time in the rotating frame (T1rho) has been applied in many pathological studies, including cartilage degradation, cerebral ischemia, and neurodegeneration diseases. Recently, it has also been reported that the T1rho contrast can detect dynamic changes in the tissue microenvironment induced by hypercapnia, hyperoxia challenges, or neuronal activation. T1rho is most sensitive to molecular fluctuations with correlation times close to the inverse of Rabi frequency of the applied spin-locking (SL) pulse. Thus, the T1rho relaxation time, measured with different SL frequencies, which is termed T1rho dispersion, provides valuable information about the underlying physiological mechanisms. Previous studies have demonstrated that the chemical exchange between labile protons of proteins and the bulk water may be an important contributor to T1rho dispersion in biological tissues in the low-frequency range of below several kHz. In order to gain more insight about the underlying mechanisms of dynamic T1rho changes, we investigated the T1rho response during hypercapnia and hyperoxia for two different SL frequencies.

Tao Jin¹, and Seong-Gi Kim^1
1Neuroimaging laboratory, Department of Radiology, University of Pittsburgh, Pittsburgh, PA, United States

Recently, diffusion-weighted fMRI (DfMRI) signals of brain water were reported to increase with the degree of diffusion sensitization during human visual stimulation, indicating a decrease of the apparent water diffusivity; however, the interpretation of the signal origin was controversial. Le Bihan et al. attributed the activation-induced change of the apparent water mobility to a functional expansion of neuronal cell membrane. Miller et al. found similar DfMRI signal change during a hypercapnia challenge, which was also dependent on the direction of diffusion-sensitizing gradients, thus suggesting that the DfMRI signal change might be due to residue intravascular signals. In this preliminary study, we measured the direction-dependent change of DfMRI signal i) during intravascular susceptibility change without changes in vascular physiology by the intravascular injection of a small amount of iron oxide nanoparticle, and ii) during global hypercapnia and hyperoxia stimulations in anesthetized rats after the suppression of the intravascular signals.

Umesh Suryanarayana Rudrapatna¹, Maurits P A van Meer¹, Annette Van der Toorn¹, and Rick M Dijkhuizen^1
1Image Sciences Institute, University Medical Center Utrecht, Utrecht, Netherlands

As diffusion-based functional imaging schemes are being introduced as alternatives to BOLD fMRI, it is imperative to assess their resilience to hemodynamic effects. We report our findings from a cerebrovascular challenge study in rats, where DTI was applied with relatively high diffusion-weighting. Data reveal that hemodynamic changes significantly influence signals in diffusion-weighted data even at high b-values, in gray as well as white matter. The changes were similar in different directions, suggesting a common vascular origin. This highlights the difficulty of discriminating hemodynamic and cellular responses with diffusion-weighted fMRI during stimulus-induced brain activation.

Sung-Yeon Park¹, Dae-Hoon Kang¹, Se-Hong Oh¹, Myoung-Kyun Woo¹, Joshua H. Park¹, Jun-Young Chung¹, Young-Bo Kim¹, Zang-Hee Cho¹, and Seong-Gi Kim^2
1Neuroscience Research Institute, Gachon University of Medicine and Science, Incheon, Korea, Republic of, ²Radiology, University of Pittsburgh, United States

Recently a magnetization transfer (MT)-varied fMRI technique was proposed to simultaneously measure stimulus-induced arterial CBV (CBVa) change and BOLD response. In previous 9.4-T animal MT fMRI contradicts to previous 1.5-T human MT studies, in which MT reduced the percentage signal change (i.e., increased MTR). This discrepancy can be due to different magnetic field (9.4 T vs. 1.5 T), different spatial resolution (0.3 mm vs. 3.7 mm), different MT pulse scheme (long CW vs. one short pulse), or different species. Thus, in order to investigate the source of discrepancy, we performed MT fMRI with high spatial resolution in humans at 7 T.