ABSTRACT
Nuclear spins and their interaction with the electromagnetic field form the basis of nuclear magnetic resonance (NMR). Based on NMR, magnetic resonance imaging (MRI) is one of the two most powerful clinical imaging modalities. To perform MRI, the targeted nuclear spins need to be placed in a strong magnetic field to become polarized. The polarization is proportional to the magnetic field strength in conventional MRI, as is the signal-to-noise-ratio (SNR). The ever-increasing demand on high SNR drives magnetic field strengths of MRI scanners ever higher. Presently, the standard high field strength is 1.5 T (1 tesla [T] = 10
gauss [G]), and a new trend in this new century is redefining the standard to 3 T. Needless to say, the higher the field strength, the more expensive the MRI scanner. Currently, a 3-T MRI scanner costs at least $1 million more than a 1.5-T scanner. Moreover, high field strengths make scanners bulky and aggravate problems such as magnetic susceptibility artifacts and lengthening of the spin-lattice relaxation time.
