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Uncoiling MRI technology.

The key advantage of magnetic resonance imaging is that it allows researchers to see inside living tissues, providing detailed pictures of internal structures without using invasive procedures. An array of specialized techniques allows scientists to visualize blood flow, water and tissue movement, the presence and concentration of various organic molecules, and more.

The core of an MRI machine is made up of coils of wire. Electricity is passed though the wire to create a magnetic field, which aligns the spins of hydrogen protons in water, which is abundant in people and most other life.

A coil, fit specifically for the body part to be imaged, transmits pulses of radiofrequency waves (similar to those used in cellphones and TV and radio broadcasting), causing some of the hydrogen protons to absorb the energy and temporarily change their spins. When the pulse is turned off, the hydrogen protons return to their prior state and give off a detectable energy signal that the coils identify and send to the MRI computer. During imaging, additional small gradient magnetic fields are used to encode this signal with spatial location. A map of the internal tissues can be reconstructed from the signal since protons in different tissues return to equilibrium at different rates.

One of the main techniques investigators use to visualize neural activity in the brain is functional magnetic resonance imaging (fMRI). The technique uses the MRI machine to generate images of brain activity as people perform experimental tasks.

The most common fMRI method detects changes in blood flow when activated areas of the brain are recharged by fresh blood that is rich in oxygen and glucose. Oxygen-rich blood has different magnetic properties than oxygen-poor blood, and these differences in the "blood oxygen-level-dependent" (BOLD) signal can be measured and mapped to provide a picture of brain activity. The resulting images are huge and require complex processing and statistical analyses to extract meaningful data--the work of computing resources connected to the MRI machine.

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Publication:Human Ecology
Geographic Code:1USA
Date:Sep 22, 2013
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