Research into functional magnetic resonance imaging (fMRI) as a non-invasive method of understanding the complex relationship between the structure and function of the brain began in the 1990s. Current research programs in tandem with advances in techniques and increased magnet field strength of MR systems hold promise for development of robust clinical applications.
While some clinical departments use fMRI for pre-surgical brain mapping to guide neurosurgical procedures, the approval of three new CPT billing codes that became effective on the first day of 2007 promises to propel use of these scans into a wider array of clinical applications. Meanwhile, major research centers continue to develop new methods designed to improve specificity in data produced by these specialized scans.
Inside the research
Truman R. Brown, director of MR research and professor of radiology at the Columbia University Medical Center in New York explains that the primary thrust of their “bread and butter” studies focuses on a wide variety of psychological experiments to determine which portions of the brain are activated when the subject performs specific tasks.
Functional MRI experiments usually involve looking at single event trials. The subject is shown a stimulus or asked to perform a task, and then the response is measured via analysis of hemodynamic shifts in the brain through analysis of BOLD (Blood Oxygen Level Dependent) signals. In some instances, response time is longer, and sometimes shorter.
A new direction in their research efforts involves using simultaneous measurements from EEG (electroencephalograms) and fMRI. This combination enables measuring neurotemporal events in a millisecond time scale, with spatial resolution provided by fMRI images. “We are able to tell from the EEG whether there is a difference in the electrical signals from the brain when the response is longer. If that is the case, then we can see differences in the fMRI to try to understand where those variations come from, and we are very excited about the possibilities of doing this,” Brown concludes.
He anticipates that while currently these combined scans provide additional basic understanding of the brain’s function, his clinical colleagues are hopeful that this combined technique may prove valuable in studying psychiatric illnesses.
This center has been involved in studying Alzheimer’s disease and other forms of dementia, although they have not begun using the combined EEG/fMRI approach at this point. Preliminary results suggest that there may be different blood flow distributions in individuals with Alzheimer’s as opposed to those who do not exhibit symptoms.
The department of biomedical engineering at Columbia installed a Philips Medical Systems Achieva 3.0 Tesla MR system in July 2006. Brown explains that with the higher field strength, the signal is bigger, and they are able to push the signal to noise limits more effectively, in less time.
One of Brown’s research interests that benefits from the use of a higher field strength magnet is the ability to study metabolites rather than only studying water protons. “In principle, you can observe the metabolites that are present in much lower concentrations than water, like 1000 times less. As we get to higher and higher field strengths, our ability to measure neurotransmitters in the brain — our ability to see what is happening and changing on a minute by minute basis in the brain — I believe will give us greater insights, and this is an area where higher field strength will be invaluable.”
Finally, this group has been using Arterial Spin Labeling (ASL) in their research by applying radiofrequency fields with the gradients. They utilize spins in blood flow up the carotids and magnetically label them by inverting the magnetization, which then slowly reverts to its initial state. By making the signal negative and then positive, they can determine how much blood flowed into the tissue. This provides similar information to those studies where contrast agents are employed, but does not require such an injection.
Brown concludes, “I mention ASL, which has the potential to be better on the 3T because of the relaxation times on T1, so that inverted blood, say in the carotid, will ‘remember’ that for a longer period of time.”
Gary H. Glover, PhD, professor of radiology and director of radiological sciences at Stanford University School of Medicine in California describes his experience in cognitive neuroscience