fMRI stands for functional Magnetic Resonance Imaging
The term “functional” indicates that this type of MRI is concerned with brain function during a specific experimental time period, as opposed to the static MRI most often used to diagnose brain (and other tissue) pathology. “Magnetic Resonance” refers to the fact that MRI scanners use a magnetic field to align the hydrogen atoms in brain tissue before exciting them with radio waves, causing the atoms to spin. Computers measure this spin and use the information to create an image reflecting variations in tissue density. Hence the name Magnetic Resonance Imaging. The image to the left is a sagittal (parallel to the midline) MRI scan of the head.
More specifically, fMRI measures something called the Blood Oxygenation Level Dependent, or BOLD, signal. Regions of the brain that are active during a particular task require more oxygen than those regions not directly involved in the task, and this oxygen is delivered via hemoglobin by an increase in blood flow in the activated area. Oxygenated blood (oxyhemoglobin) and deoxygenated blood (deoxyhemoglobin) have different concentrations of hydrogen (the element that is manipulated by the MRI magnet) and therefore different magnetic properties, which can be read and translated into a computerized image. Based on BOLD signal researchers can determine which parts of the brain are most active during different cognitive or perceptual tasks. They can also compare BOLD signal under different experimental conditions to explore how different tasks or contexts engage different, or sometimes the same, parts of the brain. The procedure is totally noninvasive and uses the same MRI scanner utilized in hospital settings. Our studies are conducted at Temple University Hospital in the Radiology Department. The image above and to the right is an axial (parallel to the chin and crown) fMRI scan showing activation in the occipital lobes. Rather than depicting a series of static cross-sections, fMRI scans reveal dynamic shifts in blood flow over a specific time period.
The fMRI magnet is shaped like a large doughnut. Participants undergoing fMRI recline on the scanner bed as it passes inside the “doughnut”. Because this requires the participant to remain still inside a very small space (the roof of the scanner is typically about 6 inches from a participant’s nose), some people find the experience claustrophobic and may become distressed, though most people are able to relax after a short acclimation period. If you participate in a study it is important that you remain totally still while you’re inside the scanner since the equipment is highly sensitive to movement and movement can distort the image. In some instances additional foam padding will be placed around the sides of your head to ensure that it remains motionless. During the procedure the magnet will make some loud knocking or banging noises, which are totally normal and should not cause you to become nervous. In an effort to make you more comfortable and to facilitate communication between you and the imaging staff, you will be fitted with a set of headphones that will block out some of the noise and allow researchers to speak to you. You will also have access to a microphone through which you can speak to the staff during breaks, and a “squeeze ball”, which you can squeeze at any time during the session to get the attention of staff, especially if you feel you need to exit the scanner. You always have the option to leave the scanner before the experiment is complete, but this usually means that any data collected during your session will not be used.
- Space in the scanner is tight. If you tend to have a claustrophobic response to small spaces it is not recommended that you participate in fMRI research.
- If you have back problems or cannot remain in a reclined position for up to 90 minutes it is not recommended that you participate in one of our studies.
- Since the scanner is comprised of a large magnet it is necessary for you to remove any metal in or on your body. This includes all jewelry, belts, watches, and other less obvious items, like nicotine patches. You should tell the research staff if you have any tattoos, as some pigments contain iron oxide, which is not compatible with the scanner. You cannot participate in an fMRI study if you have a pacemaker, aneurysm clip, artificial joint, or any other surgical implant comprised of metal.
- Since scanning sessions must be booked well in advance and the cost of running a single participant is typically about $1000, we ask that you schedule your appointment carefully and allow us as much notice as possible if you must cancel for some reason.
- There are no known long-term physical risks associated with fMRI studies.
- As a precaution, however, you cannot participate if you are pregnant.
- Female research participants will be asked to undergo a pregnancy test to confirm that they are not pregnant.
- There are other labs that are doing fMRI – in utero!