fMRI (Functional Magnetic Resonance Imaging) is a widely-used noninvasive method for characterizing central nervous system function. But how does fMRI differ from MRI? While fMRI scans use the same basic principles as MRI scans, an MRI generates images of the anatomical structure, whereas an fMRI image reveals metabolic function. Thus, MRI scans can reveal abnormalities such as tumors (particularly when combined with “perfusion,” the introduction of a contrasting agent), while fMRI scans are images of the metabolic activity within these anatomic structures.
MR imaging was originated in 1971 by a chemist named Paul C. Lauterbur who developed a mechanism to encode spatial information into a nuclear magnetic resonance (NMR) signal using magnetic field gradients. Lauterbur was the first to realize that a gradient magnetic field would allow observers to acquire two-dimensional images of an object, which could then be stacked to create a three-dimensional view.
In fMRI studies, participants are placed into an MRI scanner via a “bore” shaped like a giant donut. The magnetic resonance generated during the fMRI allows researchers to correlate the functional brain activity that occurs relative to any number of physiological signals, such as ECG, EMG, EEG, EDA, PPG, and NICO (Noninvasive Cardiac Output). In other words, the portions of the brain activated by changes to these functions can be clearly observed in an fMRI study.
Acquiring these body signals while operating in the MRI environment is a delicate dance. Components that are not “MR Safe” must be isolated from the MRI chamber, and specific cabling and filtering is necessary to preserve the quality and clarity of the signals acquired from participants in the chamber. The static magnetic fields generated by the MRI are measured in units of “Tesla” or “T.” One Tesla corresponds to 10,000 Gauss—for comparison, the earth’s magnetic field is 0.5 Gauss or a mere 0.00005 Tesla. Modern MRI machines are typically rated 3T or 7T, with 7T offering a higher resolution image.
Components used inside the MRI chamber must be “MR Safe,” meaning they must be non-metallic, non-magnetic, and non-conducting. MR Safe components (such as the electrodes attached to the participant) are referred to as “radiotranslucent.” During an fMRI recording, it is important to not coil or twist leads, simply run parallel to the subject and the bore, up to the point of subject attachment, where the leads make a right angle to be attached to the point of interest. Furthermore, as an additional safety precaution, any conductive leads placed across a subject should be thermally insulated from bare skin (via clothing or towel).
The amplifiers used for acquiring physiological signals inside the MRI chamber contain specialized filters for optimizing the signal quality, such as those employed by BIOPAC’s MRI Smart Amplifiers. The amplifiers and MP160 System are placed in the control room and connected to the MRI chamber via special cable and filter sets through a “patch panel,” or shielded interface between the MRI control room and the MRI chamber. The amplifiers and other ferrous components are always physically isolated from the MRI chamber.
For an in-depth look at how fMRI works in concert with BIOPAC components, we invite you to view this free on-demand webinar, “Data Collection in the fMRI Environment.”
BIOPAC offers a wide array of wired and wireless equipment that can be used in your research. To find more information on solutions for recording and analyzing signals such as ECG, heart rate, respiration, and more using any platforms mentioned in this blog post, you can visit the individual application pages on the BIOPAC website.
Photo by Jen Theodore on Unsplash
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