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Blood-oxygen-level-dependent imaging, or BOLD-contrast imaging, is a method used in functional magnetic resonance imaging (fMRI) to observe different areas of the brain or other organs, which are found to be active at any given time. [1]
The physiological blood-flow response largely decides the temporal sensitivity, that is how accurately we can measure when neurons are active, in BOLD fMRI. The basic time resolution parameter (sampling time) is designated TR; the TR dictates how often a particular brain slice is excited and allowed to lose its magnetization.
Because this response is a smooth continuous function, sampling with faster TRs helps only to map faster fluctuations like respiratory and heart rate signals. [17] While fMRI strives to measure the neuronal activity in the brain, the BOLD signal can be influenced by many other physiological factors other than neuronal activity.
The hemodynamic response is the basis for the BOLD (blood oxygen level dependent) contrast in fMRI. [5] The hemodynamic response occurs within seconds of the presented stimuli, but it is essential to space out the events in order to ensure that the response being measured is from the event that was presented and not from a prior event.
There are different fMRI techniques that can pick up a functional signal corresponding to changes in each of the previously mentioned components of the haemodynamic response. The most common functional imaging signal is the blood-oxygen-level dependent signal (BOLD), which primarily corresponds to the concentration of deoxyhemoglobin. [13]
The use of fNIRS as a functional neuroimaging method relies on the principle of neuro-vascular coupling also known as the haemodynamic response or blood-oxygen-level dependent (BOLD) response. This principle also forms the core of fMRI techniques. Through neuro-vascular coupling, neuronal activity is linked to related changes in localized ...
This finding has an important implication for the interpretation of BOLD fMRI data where this high baseline activity is generally ignored and response to the task is shown as independent of the baseline activity. 13 C MRS studies indicate that this approach can misjudge and even completely miss the brain activity induced by the task. [37]
Functional magnetic resonance imaging is enabled by the detection of the BOLD signal. Event-related functional magnetic resonance imaging can be used to detect changes in the Blood Oxygen Level Dependent (BOLD) hemodynamic response to neural activity in response to certain events.