Magnetic Resonance Imaging or MRI

This is an advanced and specialised field of radiography and medical imaging. The equipment used is very precise, sensitive and at the forefront of clinical technology. MRI is not only used in the clinical setting, it is increasingly playing a role in many research investigations.

Magnetic Resonance Imaging (MRI) utilises the principle of Nuclear Magnetic Resonance (NMR) as a foundation to produce highly detailed images of the human body.

The patient is firstly placed within a magnetic field created by a powerful magnet. The hydrogen atoms in the human body (we are made up of H2O) then align themselves with a North and South orientation within this magnetic field - that is, they behave like tiny bar magnets. Using a transmitting device, the radiographer transmits a radiofrequency (RF) pulse. This causes the hydrogen atoms to alter the direction of their orientation.
The transmitting RF pulse is switched off and the hydrogen atoms begin to return to the alignment they acquired when they were first placed in the magnetic field. As this re-alignment occurs they emit an RF signal which is detected by a receiving device or antenna.
From this received signal, sophisticated electronic and computer equipment is used to determine the intensity of this signal and the exact location from where this signal originated.
From this viewpoint, the computer performs advanced image reconstruction calculations and produces an image that can be viewed, hard and/or soft copied and interpreted for any diagnosis. The images can be acquired in a variety of planes, commonly, sagittal, axial and coronal (also oblique planes can be performed) - while the patient is lying still in the same position.

ref.:    http://www.med.monash.edu.au/radiography