fMRI — Functional MRI (Brain Mapping)

MRI imaging has come a tremendous way since its incorporation into mainstream medicine in the early 1980’s. Traditional “MRI imaging” provides us with very accurate static anatomical pictures. One of the most exciting developments in MRI over the last 10 years is what is called “Functional Imaging.” Functional MRI in its most broad definition generally implies obtaining physiologic information about different parts of the brain. Functional MRI invokes many different thoughts/capabilities to those of us in medicine. However, a straightforward way to think about it is as follows; Traditional “MRI imaging” provides us with very accurate static anatomical pictures. Functional MRI takes the anatomic template or map obtained with traditional MRI imaging, and adds on additional dimensions. There are now a number functional techniques that do a variety of different tasks, such as measuring regional blood flow over time, or perhaps tell us something about the biochemistry of tissue such as a tumor in a specified location in the brain. These types of “Functional MRI” will be addressed elsewhere on this website. For this discussion, “Functional MRI” will be defined more specifically. In reality, the term “Functional MRI” has been incorporated into the neuroradiologists’ daily vocabulary with a more specific meaning. In our day to day medical practices, when physicians speak to each other about getting a “Functional MRI”, we are talking about a technique called “BOLD Activation”, which stands for “Blood Oxygen Level Dependent” tissue contrast techniques. This technique uses the fact that when a region of the brain is activated, there is increased blood flow in this area as well as increased use of oxygen.

Functional MRI allows us to take a patient through a set of tasks or stimulus, (finger tapping, audio, visual, smell), and then see which part of the brain is activated.

Bold Activation for tumor mapping: By having the patient perform simple focused tasks such as tapping the left index finger, showing the patient a picture of an object and having them state the name of the object, we can selectively detect subtle changes in blood flow in the part of the brain that is used. This is leading to many exciting new applications. The most common application is planning for brain surgery. It tells the neurosurgeon where the motor cortex is related to the tumor, or where parts of the speech center are. The study may result in the surgeon taking the tumor out from one approach versus another. It may also tell the surgeon that he/she can or can’t take the entire tumor out depending on the important brain structures that may or may not be next to the tumor.

Finding the relationship between action and brain activity is complicated by the fact that the brain is always engaged in multiple cognitive processes unrelated to the task to which the subject is directing his attention. Furthermore, fMRI provides only an indirect indication of cognitive function, as blood flow in the brain is also modulated by external factors such as heart rate and breathing.