Magnetic Resonance Imaging

From The Science of Spectroscopy

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1 What is MRI?
2 fMRI
3 Superconducting magnet
4 External links:

What is MRI?

Introduced in the early 1980's, MRI has been called one of the greatest medical achievements since the development of x-ray imaging techniques. MRI stands for Magnetic Resonance Imaging, which is fundamentally the same as Nuclear Magnetic Resonance (NMR), the analysis technique widely used in chemical analysis. The primary advantage of MRI is that it is a non-invasive technique and unlike CT scans it does not use X-rays which may pose the risk of radiation injury. Like proton NMR, MRI allows three-dimensional images of the soft tissue in the brain, eyes and spinal column to be produced by applying radio-frequency (RF) waves to water molecules present in soft tissue, which line up in an applied magnetic field.

The image above shows nuclear spins of atoms in water molecules aligned with an applied magnetic field (note: the molecules themselves may not necessarily align with the field; this image shows them as aligned for visual simplicity)

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fMRI

fMRI or functional Magnetic Resonance Imaging is a new technique which employs MRI to measure the hemodynamic response (changes in blood oxygenation and flow) that correlates to neural activity in regions of the brain. Because of its ability to give researchers quantitative information about how the brain responds to stimuli, fMRI is emerging as a strong complement to the self-reporting of thought and emotional response by research subjects. Martin Paulus, a neuroscience researcher at the University of California, San Diego is using fMRI to study the potential for clinically important predictions in medicine.

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Superconducting magnet

Side view of an MRI magnet

The magnets used in MRI instruments have a bore, or central opening, large enough for a human body on an examination table to fit within the magnet. MRI magnets typically have a field strength of between 0.5 to 4.7 Tesla. While in the magnetic field, the subject under examination can be irradiated with RF from multiple angles to produce a three dimensional "illustration." MRI can also be used to image blood vessels and provide insight into the chemical components of selected tissues.

The anomaly in this brain MRI scan is shown in red

The three dimensional image above shows a human brain and surrounding blood vessels. Different colors in the image represent the signals from water molcules in each region. A mass at top, colored in red, has a different signal than the other two, indicating a foreign mass that does not match brain or blood vessel tissue. An MRI image like the one above, which clearly shows the size and shape of an irregularity, can provide invaluable help to physician diagnosing a patient condition.

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