Microsoft Word - ISMRM2005-002196.DOC
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Y. Yang, H. Gu, E. A. Stein Neuroimaging Research Branch, National Institute on Drug Abuse, Baltimore, MD, United States Introduction Functional MRI (fMRI) techniques based on BOLD (blood oxygenation level-dependent) and CBF (cerebral blood flow) (1,2) contrasts have been used extensively for mapping functional neuroanatomy. Recently, an fMRI technique based on cerebral blood volume (CBV) change or vascular space occupancy (VASO) contrast during brain activation was proposed (3). These MRI signals have different characteristics in terms of sensitivity and specificity in detecting brain activity. In general, BOLD imaging has higher sensitivity than ASL and CBV imaging, whereas ASL and VASO techniques provide better spatial localization by targeting signal changes more closely related to neuronal activity. Simultaneous detection of multiple fMRI signals may have a number of advantages, including efficient acquisition of multiple functional images and minimal temporal variations between the images. A combination of these complementary functional signals may offer a better understanding of the physiological and/or biophysical transduction mechanisms between neuronal activity, hemodynamics and MRI signals. Methods Simultaneous VASO, ASL and BOLD Acquisitions. Both VASO and ASL techniques use inversion recovery (IR) sequences. An IR sequence with multiple excitations may incorporate these two signals into a single-shot technique. For an IR sequence with two 90° excitations (Fig.1), the steady-state MR signal intensities acquired at inversion time TI1 and TI2 can be described as
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تاریخ انتشار 2005