Brain mapping: preoperative planning with functional MRI

Interview with Dr. Alexander Smirnov, Neuroradiology Department, "N.N. Burdenko National Medical Research Center of Neurosurgery", Moscow

01/04/2019

A surgery already begins before the patient is lying on the operating table – namely with the planning. For example, if brain surgery is imminent, the brain must first be mapped. This makes the activity level of certain brain areas visible. Functional magnetic resonance imaging makes this possible.

Dr. Alexander Smirnov

In an interview with MEDICA-tradefair.com, Dr. Alexander Smirnov explains what can be measured with functional magnetic resonance imaging, what its advantage is and what needs to be considered when mapping the brain.

Dr. Smirnov, what is functional magnetic resonance imaging? What insights can be gained with it?

Dr. Alexander Smirnov: fMRI is a type of magnetic resonance imaging, which is performed to measure hemodynamic reactions. These are changes in blood flow by blood oxygen level-dependent (BOLD) effect caused by the neural activity of the human brain. So it makes possible to determine the activation of a specific region of the brain during its normal functioning under the influence of various physical factors and under various pathological conditions.

fMRI is mainly used in preoperative mapping of the cerebral cortex, and also to determine the lateralization of speech areas, for example, in patients with epilepsy Also the method is applied in assessing changes in patients with neurodegenerative processes and in psychiatric practice.

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Image: tb-fMRI Scan; Copyright: A. Smirnov

With the fMRI, images of at least two states must be taken and compared – in the activity state at the desired stimulus situation (tb-fMRI) and in the rest state without stimulus (rs-fMRI).

Image: rs-fMRI Scan; Copyright: A. Smirnov

Thanks to the various images, it is possible to see which brain regions were addressed by the stimulus situation. This allows conclusions to be drawn about brain function.

You have just mentioned the use of fMRI for planning brain operations or mapping the brain. To what extent is the fMRI suitable for this?

Smirnov: Task-based fMRI (tb-fMRI) allows us to evaluate individual localization of eloquent brain areas, e.g. language, hand, or leg areas. But worldwide research data reports a large percentage of discrepancies between fMRI and intraoperative brain cortex stimulation mapping (CSM). A big advantage of the fMRI compared to the CSM is that it is non-invasive and allows you to more accurately identify the localization of brain areas according to structural image (T1/T2 sequences).

Why is this such a big challenge?

Smirnov: Concerning the task-based fMRI, the patient must follow certain instructions in the MR tomograph exactly in order to obtain accurate results in the identification of eloquent brain areas. And the better the research instructions are followed, the better the results will be.

Despite the advantages, the tb-fMRI method has a disadvantage: the results directly depend on the patient's ability to perform the task; do not use sedatives; more scanning time to determine several functionally eloquent areas. Thus we try to combine tb-fMRI and resting-state fMRI (rs-fMRI).

Image: Close-up of a woman lying in an MRI device; Copyright: panthermedia.net/Craig Robinson

With functional MRI, the activity level of certain brain areas can be made visible.

For which patients is the fMRI therefore not suitable? Where would you see limits?

Smirnov: All risks or limits remain the same as for regular MRI. Therefore the fMRI is not suitable for patients with metal implants, pacemakers or claustrophobia. It is also worth noting that not every patient is able to follow the instructions for tb-fMRI or to lie without movement for about 12 minutes for rs-fMRI. This includes, for example, children or psychiatric patients.

In your opinion, how could preoperative planning (in neurology) change or improve in the future?

Smirnov: Today the method is widely used for preoperative planning, in conjunction with the CSM. Our hope for the future is that the development and further study of the method will allow further avoidance invasive procedures and will give a more complete picture of the functioning of the brain.