RCBI: Rochester Center for Brain Imaging

Past Events

Friday, November 16, 2007, 3:30-4:30pm
"Free breathing cardiac MRI"
Yi Wang, Ph.D.
Department of Radiology Weill Medical College of Cornell University
River Campus - Robert B. Goergen Hall - Room 101

Abstract:

Currently clinical cardiac MRI is performed using the breath-holding 2D acquisition approach, imaging the heart slice by slice through many repetitive breath-holds. The limitations of this breath-hold approach include inapplicability in dyspneic patients, poor image quality with problematic breath-holding, slice misregistration, inadequate spatial resolution and volume coverage. The free breathing approach to address these breath-hold problems have been developed by us and others using the navigator approach that measures motion immediately before data acquisition and uses the measured motion information to compensate for motion artifacts in image data. There is significant interest to expand and optimize free breathing navigator cardiac MRI sequences. The cardiac fat navigator can be used to directly monitor motion of the heart. Navigator scan efficiency can be increased using the simultaneous mulitple volume approach. (Pizza and Pop will be provided)

Monday, June 18, 2007, 12:00am-1:00pm
"Detection of Cortical Vision Loss Using fMRI and Psychophysics"
Mary Jo Maciejewski Ph.D.
Joint MCW & MU Functional Imaging Program MU Department of Biomedical Engineering MCW Department of Radiology Milwaukee, WI 53226
Kresge Room (Meliora 269)

Abstract:

Understanding the validity of functional magnetic resonance imaging (fMRI) blood oxygen level dependent (BOLD) contrast as an indicator of the functional status of brain tissue in the visual cortex is important for both theoretical and clinical purposes. One method to determine the validity is to compare an fMRI-based visual field map with behavioral perimetry. Ideally, these data should be obtained simultaneously to ensure that both measures are closely correlated. To facilitate this goal, a Video Automated Perimeter (VAP) was developed to facilitate visual field testing inside the MRI scanner. To confirm the VAP was comparable with standard automatic perimetry, data were obtained using both the VAP and a conventional Humphrey Field Analyzer (HFA) for 9 patients having stable, localized, cortical visual field defects. The spatial pattern of visual sensitivity matched well in the two tests, with a median spatial cross correlation of 0.71. Thus the VAP system provides visual field maps equivalent to those obtained with HFA, but can be administered while the patient is in the MRI scanner, thus reducing test time and ensuring that both measures are obtained under closely matched conditions. VAP was then used to test the overall validity of fMRI visual field mapping. Forty-eight patients with cortical visual field loss participated in a total of 68 mapping studies. The results of these studies were analyzed, using both automated and manual scoring techniques to compare behavioral sensitivity and visually evoked fMRI responses for individual points and for an array of sectors segmenting out to 24B eccentricity. Overall, the two measures concurred in 68% of the locations tested. However, many of the mismatched points were diagnostically informative. Mismatches where there is an activation loss in the FFMap but vision is preserved in perimetry may represent neurovascular uncoupling caused by direct effects of cortical pathology on the vasculature and BOLD mechanism. Alternatively, mismatches when fMRI activation is preserved and perimetry shows an apparent loss of vision can arise if sensory input to early visual cortex is preserved but higher level processing is impaired, as in attentional neglect. Appreciating the validity of fMRI activation as an indicator of cortical function provides an important scale for weighing theoretical interpretations or clinical decisions, especially when misinterpretation could have important consequences for the patient, such as surgery-induced vision loss.

Thursday, April 5, 2007, 12:00-1:00pm
"Human V1 topography investigated with structural and functional MRI"
Oliver Hinds
Boston University, Department of Cognitive and Neural Systems 677 Beacon Street Boston, MA 02215
Kresge Room (Meliora 269)

Abstract:

Primary visual cortex (V1) contains a well-ordered topographic map of the entire contralateral visual hemifield. In macaque monkey the mapping between visual space and V1 is well described by complex-logarithm models, which require only a few parameters to account for the two-dimensional structure of the mapping, including cortical magnification and the slight local anisotropy in the visual field representation. I will describe an fMRI experiment which establishes that complex-logarithm models generalize to human visual cortex and that there is little intersubject variability in V1 topography. Because stimulating the foveal and peripheral visual field in the MRI scanner is challenging, accurately measuring the topographic map in these regions is not yet practical. However, measuring the shape of V1 can provide information about topography over the entire cortical area. I will present the results of a study where V1 was imaged using high-resolution structural MRI of the stria of Gennari at 7 T in whole ex vivo human hemispheres. A surface mesh representation of V1 was constructed from the MRI data then accurately flattened into the plane to allow statistical shape analysis. V1 shape was found to be nearly invariant across subjects, which is consistent with the results of the in vivo fMRI experiment. Also, the measured shape of V1 was in excellent agreement with the shape predicted by the model of topography. The results of both these studies indicate regularity in the topography of V1 across humans and macaques.

Tuesday, April 3, 2007, 12:30-1:45pm
"Lunch Talk"
Merry Mani
RCBI Research Technical Associate Candidate
BME/RCBI Conference Room (Annex 2.A224)

Wednesday, December 13, 2006, 12:30-2:00pm
"Location Processing and Object Identification in Deaf Signers: an fMRI Study"
JILL WEISBERG
Center for the Study of Learning Georgetown Medical Center Washington, DC
BME/RCBI Conference Room (Annex 2.A224)

Thursday, November 16, 2006, 1:00-2:30pm
"New Frontiers in Arterial Spin Labeling Perfusion MRI"
JIONGJIONG WANG, PhD.
Research Assistant Professor of Radiology and Neurology University of Pennsylvania, 3 W Gates, 3400 Spruce Street Philadelphia, PA 19104 Phone: 215-614-0631 Fax: 215-349-8260 Email: Jiongjiong.Wang@uphs.upenn.edu
Natapow Conference Room (URMC 1-9545)

Abstract:

ASL is an emerging neuroimaging method that provides noninvasive and absolute quantification of perfusion. Its widespread applications have been limited by the small labeling effect. Latest technical advances including high magnetic field, array imaging, novel spin labeling scheme and image acquisition have brought ASL to the frontier of practical clinical and neuroscience applications. Some interesting clinical applications include tumor grading, cerebrovascular disease and pediatric stroke. Compared to functional MRI studies based on the BOLD contrast, ASL has the advantages of absolute quantification, stable noise characteristics and resistance to magnetic field inhomogeneity effects, therefore is particularly suited for visualizing sustained changes in brain function. Representative perfusion fMRI studies of motor learning, natural vision, mood and psychological stress are reviewed. Finally, perfusion fMRI results have recently been compared and validated with PET metabolic mapping.

Thursday, November 2, 2006, 1:00-2:30pm
"Diffusion Imaging: Technical Developments and Their Applications to Neuro-oncology"
Xiaohong Joe Zhou, PhD.
Associate Professor of Radiology, Neurosurgery, and Bioengineering University of Illinois Medical Center Chicago, Illinois E-mail: xjzhou@uic.edu http://www.cmrr.uic.edu/
Northeastern Conference Room (URMC 1-9525)

Abstract:

Diffusion MRI is one of the rapidly growing areas in medical imaging. This talk will focus on technical developments of diffusion imaging and their clinical applications to brain tumors. Discussion on techniques will include several new data acquisition strategies and image analysis techniques, all aimed at providing improved imaging tools for detecting and characterizing abnormal brain tissues. Neuro-oncologic applications of diffusion imaging will be demonstrated through a number of examples, such as evaluation of treatment efficacy, assessment of tumor cell infiltration, characterization of benign versus malignant lesions, and surgical planning for brain tumor resection. The talk will conclude by a brief discussion of the new opportunities in diffusion imaging afforded by ultra-high magnetic field.

Wednesday, May 31, 2006, 12:30-2:00pm
"CVS/RCBI Talk"
THOMAS MCKEEFF
Department of Psychology, Princeton University
BME/RCBI Conference Room (Annex 2.A224)

Abstract:

TOPIC: Attention can alter the temporal capacity of object processing in high-level visual areas Attention has an important role in our ability to individuate objects across variations in both space and time. Many studies have investigated how attention can dynamically alter the spatial tuning properties of visual neurons, but much less is known about whether attention can alter the temporal properties of the visual system. Previously, we have shown that temporal tuning functions of individual human visual areas can be reliably measured with fMRI. Here, we investigated whether spatial attention can enhance the temporal processing capacity of cortical visual areas during object processing. Subjects were instructed to attend to one of two simultaneously presented RSVP sequences of face and houses, which were presented to the left and right of central fixation. Presentation rate varied from 2-30 items/second. Spatial attention led to an overall increase in response amplitudes in early areas V1-V3, but did not alter the temporal frequency response profile of these areas. In V4v, the fusiform face area, and parahippocampal place area, attention not only led to enhanced response amplitudes but also led to a rightward shift in the temporal frequency response profile, indicating a shift in peak sensitivity toward higher temporal rates. Our results suggest that spatial attention is capable of altering the temporal processing capacity of some high-level visual areas. These results may be of functional significance when an observer must identify an object under temporally demanding conditions.

Thursday, April 27, 2006, 12:30-1:45pm
"fMRI Studies of Semantic Processing"
Jeffrey R. Binder, MD
Medical College of Wisconsin Department of Neurology
Kresge Room (Meliora 269)

Abstract:

Over a lifetime, people amass extensive perceptual and linguistic knowledge about the world. The neural mechanisms for storage and retrieval of this knowledge can be called semantic processes. Evidence will be presented concerning the location of these processes in the human brain, suggesting that they occupy a large extent of the temporal and inferior parietal lobe neocortex. The discussion will focus on several fMRI experiments aimed at clarifying the organization of this complex system. The first study addresses how knowledge about concrete objects is represented, how this knowledge is related to perceptual experience, and how perceptual theories of object knowledge can account for category-related dissociations in brain damaged individuals. The second study addresses the topic of abstract concepts (e.g., process, semantics, knowledge), which have no direct perceptual attributes. Evidence will be presented for both inter-hemispheric asymmetries and intra-hemispheric dissociations in the processing of abstract and concrete concepts. The final study addresses how combinations of distinct concepts are jointly processed, as commonly occurs during sentence comprehension. The claim will be made that building a complex representation of meaning through conceptual combination is one of the primary tasks of the human temporal and inferior parietal association cortex.

Tuesday, March 14, 2006, 12:30-1:30pm
"Internal representation of reward modulates episodic memory formation"
R. Alison Adcock, MD, PhD
Department of Psychiatry, Gabrieli Cognitive Neuroscience Laboratory, Stanford University, UCSF
Kresge Room (Meliora 269)

Monday, February 13, 2006, 12:00-1:30pm
"Decoding Consciousness"
Geraint Rees, MRCP, PhD
Wellcome Senior Clinical Fellow & Consultant Neurologist (Hon)
Kresge Room (Meliora 269)

Abstract:

The simplicity and directness with which we have conscious experience of the world around us belies the complexity of the underlying neural mechanisms, which remain incompletely understood. This talk will review recent work from our laboratory in two key areas. First, we have been attempting to decode spatial patterns of activity in visual cortex in order to predict conscious and unconscious perception. Second, we have been studying in depth the neural correlates of fluctuations in perception during binocular rivalry. Taken together, our findings point to new and potentially exciting data concerning neural correlates of human consciousness; and suggest novel possibilities for how functional MRI might be used to study both human consciousness and cognition more generally.

Thursday, December 8, 2005, 12:00-1:30pm
"Connecting the Hemifields: Human Occipital Callosal Fiber Tracks "
Bob Dougherty, PhD
Stanford Institute for Reading and Learning (SIRL)
Northeastern Conference Room (URMC 1-9525)

Abstract:

In-vivo measurement of visual field maps in individual human subjects using functional MRI is now routine. It is also possible to measure long-range neural connections through the white matter using diffusion tensor imaging (DTI). I combined these techniques to create a functional map of posterior callosal pathways: visual field maps were measured with fMRI and callosal connections between right and left visual areas were tracked using using DTI. As expected, the occipital-callosal connections pass through the lower-half of the splenium. I will also show that pathways connecting ventral-medial occipital cortex pass through the inferior-anterior corner of the splenium; pathways connecting dorsal regions form a large band of fibers that comprises much of the lower-half of the splenium. The left and right occipital pole and lateral-occipital regions are connected through a bundle of fibers just superior to the dorsal conenctions. Damage to this part of the splenium can lead to alexia. These results suggest that callosal connections between the left and right occipital pole (which represents the fovea) and/or left and right lateral-occipital cortex are important for reading proficiency. Bob Dougherty's research focus is on the functional organization of the human brain. He uses functional and structural MRI as well as behavioral measures to study brain organization. He also studies children with these techniques in order to understand how the functional and structural organization of the brain develops.

Thursday, November 10, 2005, 12:30-1:45pm
"Diffusion Tensor Imaging (DTI) of Stroke in Nonhuman Primates"
Alex de Crespigny, PhD
Martinos Center, Massachusetts General Hospital Charlestown, MA, USA
Kresge Room (Meliora 269)

Abstract:

The recent failure of many clinical trials of neuroprotective compounds may in part be due to poor animal models of human stroke. We have developed an endovascular stroke model in nonhuman primates that is compatible with serial magnetic resonance imaging (MRI) monitoring. Using cynomologous macaques, a microcatheter is navigated transarterially (under X-ray fluoroscopic guidance) into the middle cerebral artery (MCA) where is wedged in a distal MCA branch for a period of 3 hours, to cause focal cerebral ischemia. During occlusion, reperfusion, and for 30 days afterwards, animals are scanned with MRI (including diffusion tensor imaging (DTI) and perfusion weighted imaging (PWI)) and the imaging findings compared to the stained brains sections. Further, coregistration of the serial MRI data acquired from the hyperacute through to the chronic time points reveals differing patterns of stroke evolution (i.e. heterogeneity) within stroke lesions. In an attempt to bridge the gap between the in vivo MRI and the very high resolution histological sections we have acquired high resolution 3D structural MRI, DTI and Q-space (DSI- diffusion spectrum imaging) scans of the formalin fixed brains prior to sectioning and staining. Ex vivo diffusion MRI tractography reveals the complex fiber structure in both white matter and cortical gray matter in normal brain tissue, as well as abnormalities due to the stroke lesion.

Wednesday, November 9, 2005, 2:00-2:00pm
"Decoding conscious and unconscious perception from dynamic brain patterns "
John-Dylan Haynes, PhD
Max Planck Institute, Leipzig
Kresge Room (Meliora 269)

Abstract:

Because the spatial scale of orientation columns is below the spatial resolution of conventional fMRI, it has long been considered impossible to directly study orientation-selective processing in humans. However, simulations show that due to slight anisotropies in the V1 orientation map, each small fMRI "voxel" will sample a slightly different proportion of cells with different tuning properties. This creates a weak but reliable sampling bias, that can be accumulated across all voxels of V1 using multivariate analyses (Haxby et al., 2001; Kamitani & Tong, 2005; Haynes & Rees, 2005). This provides a measure of orientation selective processing that is so powerful that the orientation of a stimulus can be recovered with high accuracy from single fMRI images acquired every 1.3 sec. This approach can also be used to reveal orientation-selective processing of stimuli in V1 even when they are rendered completely invisible due to masking, suggesting that V1 can have information about stimulus features that is not available for conscious access. We also applied multivariate analyses to data obtained under binocular rivalry. When conflicting, unfusable stimuli are presented to the two eyes, perception alternates in a quasi-stochastic fashion between the two conflicting inputs. Using multivariate analysis we were able to track the individual, stochastic timecourses of rivalry with high precision from brain activity alone. This demonstrates that even conventional fMRI images contain much more information about the dynamics of conscious perception than commonly appreciated.

Thursday, November 3, 2005, 12:30-1:45pm
Allen Song, PhD
Associate Director for Functional Brain Imaging
Associate Professor of Radiology, Duke University
Associate Professor of Biomedical Engineering, Duke University
Kresge Room (Meliora 269)

Tuesday, June 21, 2005, 12:30-2:00pm
Antoine Shahin, PhD
Experimental Psychology & Department of Medical Physics and Department of Psychology, McMaster University
West Conference Room (URMC 1-9654, Kornberg Building)

Abstract:

In the current study, we investigated brain activations due to semantic and acoustic processing during speech discrimination tasks in 10 healthy subjects. The acoustic task was to detect words spoken in a female voice in a train of words spoken in a male voice. The semantic task was to detect words of animate meaning in a train of words of inanimate meaning. We used Electroencephalography (EEG) and Functional Magnetic Resonance Imaging (fMRI). EEG records the electrical activity of the brain from sensors on the scalp, while fMRI takes pictures showing the activated regions of the brain, stemming from changes in the blood flow of these areas. EEG and fMRI both provide us with information of what is happening in the brain when a human subject perceives the world and initiate behavior. However, using EEG or fMRI independently has its disadvantages. For example, although EEG can tell us exactly when a certain brain activity is taking place, it lacks in determining where this activation is occurring in the brain. On the contrary, fMRI can tell us the exact location of the activation in the brain but it is unable to provide us with accurate timing of the activity. Our results show a network of activations of a distinct temporal and spatial dynamics evoked during the semantic and acoustic tasks. Both tasks revealed similar activations in the supratemporal and inferior parietal regions with the semantic condition provoking additional activations in the inferior and middle frontal regions. The time course of activities proceeded from the initial auditory processing in the super temporal gyrus, to the middle and inferior frontal gyri (specific to semantic synthesis) and finally to the inferior parietal lobes

Friday, June 17, 2005, 1:00-2:30pm
Kate Watkins, PhD
Experimental Psychology & FMRIB Centre University of Oxford, UK
Louise Slaughter Room (URMC 1-9555)

Abstract:

Historically, the analysis of brain morphometry was stimulated by the landmark study of Geschwind and Levitsky (1968)1, which provided evidence of a structural brain asymmetry in the planum temporale. The asymmetry favoured the left hemisphere correlating, therefore, with the well-established functional specialization of the left hemisphere for language. Subsequent findings of abnormally symmetric plana temporale in individuals with dyslexia2 provided much of the impetus for morphometric studies of developmental disorders. In disorders, such as dyslexia, autism, schizophrenia and specific language impairment, no gross structural abnormalities are visible on brain images. Abnormalities associated with these disorders are likely to be subtle and, as such, their detection may be greatly enhanced by the use of computational analyses of high-resolution brain images.

I will describe our studies of brain morphometry in a large family with a developmental disorder of speech and language3,4. The disorder is associated with motor speech deficits and a mutation in the FOXP2 gene5. We used a whole-brain analysis, known as voxel-based morphometry6, which is completely reproducible and does not require interactions with the user. The analysis is designed to identify regions of anatomical variation between groups of subjects, who may differ with respect to disease state, sex, or age7. It has also been adapted to examine structural brain asymmetries8. Because this method allows analysis of the whole brain, it is of particular use in guiding the investigator’s attention to regions of specific interest. In our study, voxel-based morphometry revealed an abnormal amount of grey matter in the caudate nucleus, which was confirmed by a region-of-interest analysis. Recent studies in rats9, mice and humans10, have reported expression of FOXP2 mRNA in the developing striatum. These results demonstrate how the analysis of brain morphometry in developmental disorders can contribute to our understanding of neurodevelopmental disorder.

Monday, May 16, 2005, 3:30-5:00pm
"Methods and Applications for Probabilistic Diffusion MRI Fibre Tracking "
Geoff Parker
Research Fellow, Faculty of Human and Medical Sciences
Honorary Lecturer, Division of Imaging Science and Biomedical Engineering
University of Manchester
Louise Slaughter Room (URMC 1-9555)

Abstract:

Diffusion MRI provides the means to extract cerebral anatomical connectivity information. However, extracting this information is non-trivial, and a range of novel techniques are being developed to improve the robustness of the process. This presentation will outline some current methodological developments and illustrate their efficacy in normal brain studies and preliminary clinical application.

Thursday, February 24, 2005, 1:00-2:00pm
"Functional imaging of the human lateral geniculate nucleus and superior colliculus "
Keith Schneider

Northeastern Conference Room (URMC 1-9525)

Abstract:

Functional magnetic resonance imaging (fMRI) has provided intriguing insights into the topography and functional organization of visual cortical areas in the human brain. However, human subcortical nuclei have not been extensively studied. I will describe recent work using high-resolution fMRI to investigate the structure and attentional modulation of the human lateral geniculate nucleus (LGN) and superior colliculus (SC). The retinotopic organization of the LGN is similar to that in the macaque, but the horizontal meridian of the visual field is significantly overrepresented relative to the vertical meridian, and the representation of the fovea is expanded, similar to that described for human V1. The magnocellular (M) and parvocellular (P) regions of the LGN can be distinguished based upon their sensitivities to stimulus contrast. The M regions, similar to the SC, respond well to low contrast stimuli. In an attentional tracking task, SC activity was strongly modulated by attention. In the LGN, both the M and P divisions were modulated by attention, with the M modulation being somewhat larger. Finally, I will demonstrate a superresolution technique in which inadvertant subject head motion during the course of an fMRI experiment can be utilized to improve the spatial resolution of the functional images.