Background: The hemodynamic balloon model describes the change in coupling\nfrom underlying neural activity to observed blood oxygen level dependent (BOLD)\nresponse. It plays an increasing important role in brain research using magnetic resonance\nimaging (MRI) techniques. However, changes in the BOLD signal are sensitive\nto the resting blood volume fraction (i.e., V0) associated with the regional vasculature.\nIn previous studies the value was arbitrarily set to a physiologically plausible value to\ncircumvent the ill-posedness of the inverse problem. These approaches fail to explore\nactual V0 value and could yield inaccurate model estimation.\nMethods: The present study represents the first empiric attempt to derive the actual\nV0 from data obtained using cerebral blood volume imaging, with the aim of augmenting\nthe existing estimation schemes. Bimanual finger tapping experiments were\nperformed to determine how V0 influences the model estimation of BOLD signals\nwithin a single-region and multiple-regions (i.e., dynamic causal modeling). In order to\nshow the significance of applying the true V0, we have presented the different results\nobtained when using the real V0 and assumed V0 in terms of single-region model estimation\nand dynamic causal modeling.\nResults: The results show that V0 significantly influences the estimation results within\na single-region and multiple-regions. Using the actual V0 might yield more realistic and\nphysiologically meaningful model estimation results.\nConclusion: Incorporating regional venous information in the analysis of the hemodynamic\nmodel can provide more reliable and accurate parameter estimations and\nmodel predictions, and improve the inference about brain connectivity based on fMRI\ndata.
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