Resting-State fMRI

Resting-State fMRI is a functional MRI (fMRI) technique in which, unlike in task-based fMRI, the patient is not stimulated by any paradigm. The techniques makes it possible to study the functional connectivity of the brain.

Resting-state fMRI is based on spontaneous low frequency fluctuations (0.1 Hz) in the BOLD signal (Biswal et al. 1995). Studying correlations between variations of the BOLD signal, it can identify regions which activate synchronously with each other (Lee et al. 2012).

Resting-State fMRI Protocol

Like for task-based fMRI, a T2*-weighted gradient-echo EPI sequence is used to acquire the images (pixel size: approx. 3*3*3 mm³) every few seconds (e.g. TR = 3s) during approximately 6 minutes (Van Dijk et al. 2010). Eyes are open, with a fixation target. ECG, breathing and refluxed CO2 are sometimes recorded in order to eliminate physiological noise.

Resting-State fMRI Analysis

The pre-processing of resting-state fMRI images is similar to the one of standard fMRI images: slice-timing correction, motion correction, spatial and temporal filtering, and normalization. In the seed-based analysis, ROIs are manually drawn and their temporal signals are correlated with each others and with other voxels in the brain. Another approach, which requires less a priori assumptions, uses independent component analysis, in which the user must select the relevant components. Alternative analysis methods include graphs theory, clustering algorithms, and multivariate pattern classification.

Resting-State Networks

The functional network which has been the most studied by resting-state fMRI is the default mode network. This network has been shown to be spontaneously activated without stimulation, and linked with mind wandering (Christoff et al. 2009). On the contrary, some other systems are task-based, such as the somatosensory, visual, auditory, language, attention and cognitive control networks.

Clinical Applications of Resting-State fMRI

For patients with neurological disabilities, resting-state fMRI is less demanding than task-based fMRI, which requires cooperation. However, clinical applications of resting-state fMRI are still at an early stage (Lee et al. 2013). Studies have used the technique to identify functional networks for neurosurgical planning (Hart et al. 2016). It has also been used to identify epileptogenic networks in epileptic patients. Studies have shown that resting-state networks characteristics could identify patients with Alzheimer disease and distinguish patients with mild cognitive impairment from controls. Patients with disorders of consciousness and psychiatric patients may also benefit from the technique (Vanhaudenhuyse et al. 2010).

Combo-fMRI

Resting-state fMRI is looking for correlations of these fluctuations in different brain regions, making it possible to identify functional networks, such as the default mode network, the auditory network, etc. Combo-fMRI substracts these fluctuations from the task-based fMRI signal, in order to purify it, leading to less noisy activation maps.

Resting-State fMRI: References

  • Biswal et al. Functional connectivity in the motor cortex of resting human brain using echo-planar MRI. Magn Reson Med. 1995, 34:537-541.
  • Christoff et al. Experience sampling during fMRI reveals default network and executive system contributions to mind wandering. PNAS 2009, 106:8719-8724.
  • Hart et al. Functional connectivity networks for preoperative brain mapping in neurosurgery. J Neurosurg. 2016, 26:1-10.
  • Lee et al. Resting-State fMRI: A Review of Methods and Clinical Applications. AJNR 2013, 34:1866-1872.
  • Van Dijk et al. Intrinsic functional connectivity as a tool for human connectomics: theory, properties, and optimization. J Neurophysiol. 2010, 103:297-321.
  • Vanhaudenhuyse et al. Default network connectivity reflects the level of consciousness in non-communicative brain-damaged patients. Brain 2010, 133:161-171

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