Nonlinear estimation of BOLD signals with the aid of cerebral blood volume imaging

Abstract

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