Simultaneous Functional Magnetic Resonance and Two-Dimensional Optical Imaging Spectroscopy

Abstract

The blood oxygenation level-dependent (BOLD) functional magnetic resonance imaging (fMRI) signal is a biophysical consequence of the hemodynamic response to neuronal activity. Intrinsic optical imaging spectroscopy (2D-OIS) is an invasive imaging method that can provide detailed two-dimensional information of this underlying hemodynamic response. Here, methods for the combination of fMRI and 2D-OIS in the rodent model are described. One of the numerous advantages of this simultaneous methodology is that 2D-OIS provides an independent hemodynamic measure to help interpret evoked or spontaneous BOLD signals. This is important when imaging animal models of disease where abnormal BOLD responses could result and thus be difficult to interpret without such an independent measure. From a more mathematical perspective the concurrent hemodynamic data can be used to help refine and/or test biophysical models of the BOLD fMRI signal—such models are important for the interpretation of human BOLD data in terms of the underlying neuronal activity. This has obvious benefits for calibrated BOLD studies heavily reliant on such models. The reverse is also true: using biophysical models the concurrent BOLD data can be used as an indicator of the hemodynamic response. This would allow modification of algorithms of light transport through tissue in optical imaging spectroscopy to better predict the hemodynamic response and which in turn could be used in the analysis of the BOLD fMRI signal. With all the above in mind, a final (but equally important) benefit of collecting multimodal data is that the number of animals needed for a specific study can be substantially reduced.