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    Changes in MRI signal intensity during hypercapnic challenge under conscious and anesthetized conditions

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    Authors
    Brevard, Mathew E.
    Duong, Timothy Q.
    King, Jean A.
    Ferris, Craig F.
    UMass Chan Affiliations
    Department of Psychiatry
    Document Type
    Journal Article
    Publication Date
    2003-12-20
    Keywords
    Anesthesia
    Animals
    Carbon Dioxide
    Cerebrovascular Circulation
    Consciousness
    Hypercapnia
    *Magnetic Resonance Imaging
    Male
    Models, Animal
    Rats
    Rats, Sprague-Dawley
    Psychiatry
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    Link to Full Text
    http://dx.doi.org/10.1046/j.1528-1157.2003.61002.x
    Abstract
    Most functional magnetic resonance imaging (fMRI) studies in animals are conducted under anesthesia to minimize motion artifacts. However, methods and techniques have been developed recently for imaging fully conscious rats. Functional MRI studies on conscious animals report enhanced BOLD signal changes as compared to the anesthetized condition. In this study, rats were exposed to different concentrations of carbon dioxide (CO(2)) while conscious and anesthetized to test whether cerebrovascular reactivity may be contributing to these enhanced BOLD signal changes. Hypercapnia produced significantly greater increases in MRI signal intensity in fully conscious animals (6.7-13.3% changes) as when anesthetized with 1% isoflurane (3.2-4.9% changes). In addition, the response to hypercapnia was more immediate in the conscious condition (< 30s) with signal risetimes twice as fast as in the anesthetized state (60s). Both cortical and subcortical brain regions showed a robust, dose- dependent increase in MRI signal intensity with hypercapnic challenge while the animals were conscious but little or no change when anesthetized. Baseline variations in MRI signal were higher while animals were conscious but this was off set by greater signal intensity changes leading to a greater contrast-to-noise ratio, 13.1 in conscious animals, as compared to 8.0 in the anesthetized condition. In summary, cerebral vasculature appears to be more sensitive to hypercapnic challenge in the conscious condition resulting in enhanced T2* MRI signal intensity and the potential for better BOLD signal changes during functional imaging.
    Source
    Magn Reson Imaging. 2003 Nov;21(9):995-1001.
    Permanent Link to this Item
    http://hdl.handle.net/20.500.14038/45820
    PubMed ID
    14684202
    Related Resources
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