Functional MR imaging maps brain function and plasticity

Functional MRI is increasingly being used preoperatively to improve the safety of surgery that will remove brain tumors or locate epileptogenic foci by mapping motor, somatosensory, and language functions, at least in larger teaching and university hospitals.

The technique is being applied clinically in about 60 academic medical centers throughout Europe, said Dr. Christoph Stippich of the University of Heidelberg in Germany.

Presurgical blood oxygen level-dependent fMRI language localization in patient with left superior temporal glioma. (Provided by C. Stippich)

The procedure has not yet become a standard diagnostic routine, however. It is not widely used in smaller community hospitals, and because there are no medically approved software tools for the procedure, fMRI is performed largely in the framework of scientific trials.

A role for fMRI nevertheless is emerging to fill a void in the assessment of patients destined for brain surgery. Although electroencephalography and magnetoencephalography (MEG) do measure somatosensory or language function, the examinations are not easy to complete in a clinical setting, and data modeling is complicated, he said.

Only a few MEG centers exist worldwide, and they tend to be research centers that are not bound to hospitals. The fMRI technique, meanwhile, is highly robust and simple to perform. As a result, fMRI is becoming the primary modality for investigating brain function, he said.

Although anatomical landmarks can help to identify the gyri in the brain that govern motor function, morphological imaging is difficult because there are only a few reliable landmarks. Functional imaging therefore is a valuable adjunct.

Presurgical blood oxygen-level dependent fMRI mapping of primary motor cortex somatotopy in patient with left parietal glioma. (Provided by C. Stippich)

One of the clinical indications for fMRI is to help clinicians select the safest treatment approach for removing a brain tumor. An fMRI study can assess the risk for operative damage to any nearby critical functional system.

Another possible indication is to determine the extent of surgery, or how much tumor should be removed. This indication is still under investigation, and it may take three to five years of prospective controlled trials using standardized protocols to amass the necessary data, Stippich said.

Functional MRI gives researchers a chance to evaluate plasticity within the brain. Plasticity reflects the ways in which a change in the structure of the brain at the level of the synapse translates into a change in neuronal networks and sensory and motor functions, said Dr. Alberto Bizzi of Milan's Istituto Nazionale Neurologico Carlo Besta.

By measuring acute alterations in the segregation of neuronal functions and connectivity within the brain, fMRI is being used experimentally to assess brain function associated with a focal brain lesion, the process of reconnecting parallel neural processing networks during recovery, and the reorganization of motor and language networks following rehabilitation.