What is fMRI?
fMRI stands for functional magnetic resonance imaging. In order to understand how it works, it is first necessary to understand conventional magnetic resonance imaging, or MRI. MRI is a technique for producing astonishingly detailed images of the brain or other bodily structures (see Fig 1). These images demonstrate the anatomy of the subject’s brain at high resolution, and are used in virtually all modern hospitals to diagnose a wide variety of brain disorders, including brain tumors, multiple sclerosis, and stroke. MRI scanning uses a very strong magnet and radio waves to produce these spectacular images. The subject lies on a table, with his head surrounded by a large magnet. The magnet causes some of the atoms (or, more precisely, particles inside the atoms, called protons) inside the patient’s head to align with the magnetic field. A pulse of radio waves is then directed at the patient’s head and some of it is absorbed by the protons, knocking them out of alignment. The protons, h
FMRI is a device used by doctors or other medical personnel to map brain activity. It stands for functional magnetic resonance imaging. The f at the beginning of fMRI is not capitalized unless at the beginning of a sentence. An fMRI machine is a big, bed-sized, expensive piece of medical equipment that generates high magnetic fields. For this reason, people with pacemakers are warned not to go near fMRI machines. Patients must remove metallic objects before entering the machine. To enter the machine, a patient lies on a horizontal stretcher-like platform which slides into a cylindrical cavity. The patient is scanned magnetically from all sides and a real-time image is created, which is submitted to doctors for further analysis. An fMRI machine works using the principle of magnetic resonance. The practice was formerly known as magnetic resonance tomography (MRT) or nuclear magnetic resonance (NMR). Magnetic resonance works as follows. It has been known for over 100 years that blood flow
back to article fMRI stands for functional magnetic resonance imaging. In order to understand how it works, it is first necessary to understand conventional magnetic resonance imaging, or MRI. MRI is a technique for producing astonishingly detailed images of the brain or other bodily structures. These images are used in virtually all modern hospitals to diagnose a wide variety of brain disorders, including brain tumors, multiple sclerosis, and stroke. MRI scanning uses a very strong magnet and radio waves to produce these spectacular images. The subject lies on a table, with his head surrounded by a large magnet. The magnet causes some of the atoms (or, more precisely, particles inside the atoms, called protons) inside the patient’s head to align with the magnetic field. A pulse of radio waves is then directed at the patient’s head and some of it is absorbed by the protons, knocking them out of alignment. The protons, however, gradually realign themselves, emitting radio waves as they
Functional MRI is based on the increase in blood flow to the local vasculature that accompanies neural activity in the brain. This results in a corresponding local reduction in deoxyhemoglobin because the increase in blood flow occurs without an increase of similar magnitude in oxygen extraction (Roy and Sherrington, 1890; Plum, Posner & Troy, 1968; Posner, Plum & Poznak, 1969; Fox and Raichle, 1985). Since deoxyhemoglobin is paramagnetic, it alters the T2* weighted magnetic resonance image signal (Ogawa, et al, 1990a and b, 1992, 1993; Belliveau, et al, 1990, 1991; Turner, et al, 1991; Tank, et al, 1992). Thus, deoxyhemoglobin is sometimes referred to as an endogenous contrast enhancing agent, and serves as the source of the signal for fMRI. Using an appropriate imaging sequence, human cortical functions can be observed without the use of exogenous contrast enhancing agents on a clinical strength (1.5 T) scanner (Bandettini, et al, 1992, 1993; Kwong, et al, 1992; and Turner, et al, 19
