Magnetic Resonance
Imaging
Magnetic resonance imaging is
a safe and powerful technique to visualise the brain.
Unlike older methods such as PET scanning, it does
not involve radioactive compounds and results can
be collected in a matter of milliseconds.
Hydrogen is the key to MRI in the body. Present in
every cell in our bodies, in blood, fats and proteins,
hydrogen particles possess a quality called spin which
means they can be aligned by the strong magnetic fields
of the scanner. Following alignment, radio wave pulses
given at a certain frequency deflect the aligned atoms,
resulting in the emission of a signal. This signal
provides information about the tissues scanned. It
is used to create detailed images of the brain. |
Magnetic Resonance Image of the Brain |
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Tissues, made up of cells, contain
hydrogen (marked here as \/ in any direction)
as a part of several substances.
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A strong magnetic field causes a property
of hydrogen to line up leading to the formation
of a magnetic field inside the tissue.
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A short pulse of radio waves at a specific
frequency deflects the hydrogen particles. The
magnetic field is now in a different direction.
This new magnetic field is detected as a signal
by the scanner.
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When the pulse is switched off, the hydrogen
particles again align with the applied magnetic
field.
As the particles realign, the magnetic field
changes direction until it is back to this earlier
alignment. The time taken for the particles
to return is related to a figure, called here
T1. T1 depends on the environment of the particles
and is different for every substance.
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The signal, given off when the particles
returned to their earlier alignment is also
different for every substance. This information
and T1 are used by the scanner to create an
MR image of the brain.
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