This file was created by the Typo3 extension sevenpack version 0.7.14 --- Timezone: CEST Creation date: 2013-05-25 Creation time: 00-36-24 --- Number of references 7 article CavusogluPBU2012 Magnetic Resonance in Medicine 2013 2 69 2 524–530 Most experiments assume a global transit delay time with blood flowing from the tagging region to the imaging slice in plug flow without any dispersion of the magnetization. However, because of cardiac pulsation, nonuniform cross-sectional flow profile, and complex vessel networks, the transit delay time is not a single value but follows a distribution. In this study, we explored the regional effects of magnetization dispersion on quantitative perfusion imaging for varying transit times within a very large interval from the direct comparison of pulsed, pseudo-continuous, and dual-coil continuous arterial spin labeling encoding schemes. Longer distances between tagging and imaging region typically used for continuous tagging schemes enhance the regional bias on the quantitative cerebral blood flow measurement causing an underestimation up to 37% when plug flow is assumed as in the standard model. http://www.kyb.tuebingen.mpg.de http://www.kyb.tuebingen.mpg.de http://www.kyb.tuebingen.mpg.de Department Scheffler http://onlinelibrary.wiley.com/doi/10.1002/mrm.24278/pdf 10.1002/mrm.24278 mustafaMCavusoglu rolfRPohmann burgerHCBurger kuludagKUludag article CavusogluBYU2011 NeuroImage 2012 2 59 4 4044–4054 Cortical representations of the visual field are organized retinotopically, such that nearby neurons have receptive fields at nearby locations in the image. Many studies have used blood oxygenation level-dependent (BOLD) fMRI to non-invasively construct retinotopic maps in humans. The accuracy of the maps depends on the spatial extent of the metabolic and hemodynamic changes induced by the neural activity. Several studies using gradient-echo MRI at 1.5 T and 3 T showed that most of the BOLD signal originates from veins, which might lead to a spatial displacement from the actual site of neuronal activation, thus reducing the specificity of the functional localization. In contrast to BOLD signal, cerebral blood flow (CBF) as measured using arterial spin labeling (ASL) is less or not at all affected by remote draining veins, and therefore spatially and temporally more closely linked to the underlying neural activity. In the present study, we determined retinotopic maps in the human brain using CBF as well as using BOLD signal in order to compare their spatial relationship and the temporal delays of each imaging modality for visual areas V1, V2, V3, hV4 and V3AB. We tested the robustness and reproducibility of the maps across different sessions, calculated the overlap as well as signal delay times across visual areas. While area boundaries were relatively well preserved, we found systematic differences of response latencies between CBF and the BOLD signal between areas. In summary, CBF data obtained using ASL allows reliable retinotopic maps to be constructed; this approach is, therefore, suitable for studying visual areas especially in close proximity to large veins where the BOLD signal is spatially inaccurate. http://www.kyb.tuebingen.mpg.de http://www.kyb.tuebingen.mpg.de http://www.kyb.tuebingen.mpg.de Department Scheffler Department Logothetis http://www.sciencedirect.com/science/article/pii/S1053811911012201 10.1016/j.neuroimage.2011.10.056 mustafaMCavusoglu abartelsABartels barisBYesilyurt kuludagKUludag article 5689 Magnetic Resonance Imaging 2009 10 27 8 1039-1045 Arterial spin labeling (ASL) using magnetic resonance imaging (MRI) is a powerful noninvasive technique to investigate the physiological status of brain tissue by measuring cerebral blood flow (CBF). ASL assesses the inflow of magnetically labeled arterial blood into an imaging voxel. In the last 2 decades, various ASL sequences have been proposed which differ in their ease of implementation and their sensitivity to artifacts. In addition, several quantification methods have been developed to determine the absolute value of CBF from ASL magnetization difference images. In this study, we evaluated three pulsed ASL sequences and three absolute quantification schemes. It was found that FAIR-QUIPSSII implementation of ASL yields 10–20% higher signal-to-noise ratio (SNR) and 18% higher CBF as compared with PICORE-Q2TIPS (with FOCI pulses) and PICORE-QUIPSSII (with BASSI pulses). In addition, quantification schemes employed can give rise to up to a 35% difference in CBF values. We conclude that, although all quant itative ASL sequences and CBF calibration methods should in principle result in the similar CBF values and image quality, substantial differences in CBF values and SNR were found. Thus, comparing studies using different ASL sequences and analysis algorithms is likely to result in erroneous intra- and intergroup differences. Therefore, (i) the same quantification schemes should consistently be used, and (ii) quantification using local tissue proton density should yield the most accurate CBF values because, although still requiring definitive demonstration in future studies, the proton density of blood is assumed to be very similar to the value of gray matter. http://www.kyb.tuebingen.mpg.de http://www.kyb.tuebingen.mpg.de http://www.kyb.tuebingen.mpg.de Department MRZ http://www.sciencedirect.com/science?_ob=PdfDownloadURL&_uoikey=B6T9D-4WK4B0Y-1&_tockey=%23toc%235112%239999%23999999999%2399999%23FLA%23&_orig=search&_acct=C000003178&_version=1&_userid=29041&md5=13320c9280bc9acec40024e4b0368f Biologische Kybernetik Max-Planck-Gesellschaft en 10.1016/j.mri.2009.04.002 mustafaMCavusoglu josefJPfeuffer KUgurbil kuludagKUludag poster CavusogluBU2012 2012 5 20 578 http://www.kyb.tuebingen.mpg.de http://www.kyb.tuebingen.mpg.de http://www.kyb.tuebingen.mpg.de Department Scheffler Department Logothetis http://www.ismrm.org/12/Session57.htm Melbourne, Australia 20th Annual Meeting and Exhibition of the International Society for Magnetic Resonance in Medicine (ISMRM 2012) mustafaMCavusoglu abartelsABartels kuludagKUludag poster 5686 2008 5 16 1930 324 Three different ASL schemes (Q2TIPS, FAIR-QUIPSSII and PICORE-QUIPSSII with asymmetric BASSI pulses) were compared measuring absolute cerebral blood flow (CBF) in the human brain at 3T. Signal-to-noise ratios (SNR), magnetization difference between control and tag images and three different absolute CBF quantification schemes were evaluated. For identical sequence parameters and voxels, it was found that a) FAIR-QUIPSSII has the highest SNR b) FAIR-QUIPSSII yields slightly higher CBF values c) absolute CBF values depend on the quantification scheme utilized. One possible explanation for the findings is that effective labeling efficiency and physiological noise contamination are different for the tagging procedures used. http://www.kyb.tuebingen.mpg.defileadmin/user_upload/files/publications/ISMRM-2008-01930.pdf http://www.kyb.tuebingen.mpg.de http://www.kyb.tuebingen.mpg.de Department MRZ http://www.ismrm.org/08/ Biologische Kybernetik Max-Planck-Gesellschaft Toronto, Canada 16th Scientific Meeting and Exhibition of the International Society of Magnetic Resonance in Medicine (ISMRM 2008) en mustafaMCavusoglu KUgurbil kuludagKUludag conference 7082 2010 10 11 13 Arterial Spin Labeling (ASL) is a magnetic resonance imaging (MRI) method to map the cerebral blood flow (CBF). ASL present a non-invasive alternative to the contrast agent and ASL techniques are capable of providing quantitative information about local tissue blood flow by tracking the inflow of magnetically labeled arterial blood into an imaging slice. Retinotopy describes the correspondence between visual field locations and their cortical representations. Many studies have used blood oxygenation level-dependent (BOLD) fMRI to non-invasively reveal retinotopic maps. Their accuracy therefore depends on the spatial extent of the metabolic and hemodynamic changes induced by the neural activity. Many studies using gradient-echo MRI at 1.5T and 3T showed that most of the BOLD signal originates from macroscopic veins which might lead to a spatial displacement from the actual site of neuronal activations reducing the specificity for functional localization. In this study we performed perfusion contrast based retinotopic mapping of the human brain at 3T by using arterial spin labeling (ASL) which provides improved sensitivity and better functional localization relative to the BOLD signal. We determined retinotopic maps from both of the fMRI imaging modalities, tested their robustness and replicability across different sessions, and calculated the overlap of the resulting visual areas V1, V2, V3, hV4, V3A/B obtained between the two imaging modalities. Velocity selective ASL (VS-ASL) is a specific form of ASL methods which labels the blood below or above a certain velocity threshold by using velocity selective RF pulses instead of a spatial selection. Here we will describe the ASL methods in basics, retinotopy of the human brain with perfusion contrast as an application and the implementation of VS-ASL as a specific pulse sequence. http://www.kyb.tuebingen.mpg.de http://www.kyb.tuebingen.mpg.de http://www.kyb.tuebingen.mpg.de Department MRZ Abstract Talk http://www.neuroschool-tuebingen-nena.de/fileadmin/user_upload/Dokumente/neuroscience/AbstractbookNeNa2010u.pdf Biologische Kybernetik Max-Planck-Gesellschaft Heiligkreuztal, Germany 11th Conference of Junior Neuroscientists of Tübingen (NeNa 2010) en mustafaMCavusoglu conference Cavusoglu2009 2009 11 10 15 Arterial Spin Labeling (ASL) is a magnetic resonance imaging (MRI) method to map the cerebral blood flow (CBF). ASL present a non-invasive alternative to the contrast agent and ASL techniques are capable of providing quantitative information about local tissue blood flow by tracking the inflow of magnetically labeled arterial blood into an imaging slice. The delivery of the tagged water to each image voxel is measured. Because ASL is completely noninvasive, the tagging can be repeated many times to obtain a high signal-to-noise ratio (SNR). ASL produces perfusion maps of human brain with higher spatial and temporal resolution than any other existing technique. Furthermore, ASL techniques are an important tool to study the physiological basis of functional neuroimaging techniques such as BOLD signal. Retinotopy describes the spatial organization of the neuronal responses to visual stimuli. In many locations within the brain, adjacent neurons have receptive fields that include slightly different, but overlapping portions of the visual field. The position of the center of these receptive fields forms an orderly sampling mosaic that covers a portion of the visual field. fMRI retinotopic mapping provides detailed information about the correspondence between the visual field and its cortical representation in the individual subjects. In this study, we present the possibilty to map the retinotopic organization of the visual areas by using perfusion contrast measured with the arterial spin labeling fMRI. http://www.kyb.tuebingen.mpg.de http://www.kyb.tuebingen.mpg.de http://www.kyb.tuebingen.mpg.de Department MRZ Abstract Talk http://www.neuroschool-tuebingen-nena.de/ Ellwangen, Germany 10th Conference of Junior Neuroscientists of Tübingen (NeNa 2009) mustafaMCavusoglu