April 25, 2009 10:21pm CST
A powerful magnet is used to provide a static uniform magnetic feild. Different types of magnet are used including superconducting , resistive and permanent magnets offering feild strength betweeen 0.15 to 2 tesla. Small gradient coils are used to superimpose an additional feild. Thes coils are used to vary the feild strength locally to provide spatial localisation.The number of times the radiofrequency pulse and the gradient feild are turned on and off is equal to the acquisition matrix multiplied by the number of excitations.