How do we do ƒMRI?
• We ask the patient to lie in the MRI scanner while we collect a series of MR scans.
• First we collect anatomical scans to visualize the particular sulci and gyri (cracks and bumps) of the patient's brain.
• We next ask the patient to perform certain motor tasks, such as touching her fingers to her thumb successively, or simply moving her wrist.
• While the patient is doing this task, we collect a series of Echo-planar images, time-locked to each of these specific tasks.
• Next we ask the patient to perform a series of memory and language tasks which we use to determine the exact location in her brain where language reception and production takes place.
• Once again we collect a series of Echo-planar images at the precise time the patient is hearing sentences or thinking about specific definitions of words.
• Since ƒMRI images degrade with patient motion, and since the brain is "in motion" whenever someone swallows, or when someone speaks in an animated way, we are careful to ask patients to lie still. As nearly forty percent of the blood pumped by the heart goes directly to the brain, the brain pulses and beats in synchrony with the heart. Therefore, precise timing and co-registration of images, both spatially and temporally, is important for high accuracy.
• We use a series of mathematical algorithms to cancel the effects of this motion.
• We then treat the series of images in a statistical fashion, normally performing linear or parametric based mapping statistic.
• We construct brain maps (images) based on the results of the statistical analyses. Since there is a large number of images (in excess of 1000 images per session) and since many important regions of these images are compared, the number of comparisons can reach into the hundreds of thousands. Great care and great precision are the hallmark of this approach.
It is important to recognize that no two brains are alike. For this reason, ƒMRI is rapidly becoming the technology of choice for many functional brain activation studies in humans. Since it is non-invasive, it is acceptable for repeated use with adult and child (13y +) volunteers. It is very selectively available. It has shown to date, better spatial and temporal resolution than other systems based on some of the same hemodynamic phenomena, such as PET scans. Compared to PET scanning, or MEG scanning, ƒMRI is far less costly to use and to maintain. By its nature, it is safe.
ƒMRI will be used as a substitute, a non-invasive replacement procedure, for two highly invasive procedures: intraoperative brain mapping surgery, and the Wada test. The Wada is a test for localizing language laterality. Compared to either of these invasive procedures, ƒMRI is less costly, is less risky to the patient, and produces higher quality patient outcomes. ƒMRI generates higher specificity for physicians' decisions.
Who will use ƒMRI? In the very near future, ƒMRI will allow better prediction of surgical outcome for epilepsy, tumor, and ultimately, for stroke patients. Centers that support these clinical services will need to provide ƒMRI.
ƒMRI is difficult to use properly because it is complicated, relies on highly trained personnel, advanced equipment, sophisticated statistical image analyses, accurate reconstruction, registration transmission and storage of images.
MTC provides expertise in solving all these problems.