ABSTRACT
In MRI, in addition to the large static magnetic eld generated by the main MR system coil, which is on the order of 1.5-3 T, low-intensity transient magnetic eld gradients are present that are generated by the gradient coils-these transient magnetic elds are on the order of 40-80 mT/m and result in a range of resonance frequencies that can be traced back to individual tissue points. Specically, to create a 2D image of a tissue slab, phase-encoding and frequency-encoding gradients (orthogonal to one another) are applied on the imaging slice before signal detection. is results in the protons in a small voxel, to resonate at a unique frequency and to have a unique phase, permitting tracing back of the NMR signal to a specic tissue location.
