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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

The Process of Magnetic Resonance Imaging  

Tissues, made up of cells, contain hydrogen (marked here as \/ in any direction) as a part of several substances.

 

A strong magnetic field causes a property of hydrogen to line up leading to the formation of a magnetic field inside the tissue.

 

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.

 

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.

 

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.