ARTIFACTS IN T1P-WEIGHTED IMAGING

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This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. Magnetic resonance (MR) tissue contrast depends on differences in tissue relaxation times T1 and T2, diffusion weighting, magnetization transfer (MT) or perfusion effects to distinguish healthy and diseased tissues. In addition to these conventional contrast techniques, a powerful method to create tissue contrast is the spinlattice relaxation time in the rotating frame (T1rho). Ideally, to achieve maximum T1q-weighted contrast, the spin locking amplitude should coincide with the corresponding with the frequency of the physical process involved, although, in practice, possible spin lock amplitudes are compromised by B0 field gradient artifacts and the high specific absorption rate (SAR) of radiation delivered to tissues. Rotary echoes or adiabatic excitation combined with a high amplitude spin lock remove artifacts from gradients in the B1 and B0 field, however, increasing the RF field to reduce artifacts and decreasing the RF field to reduce SAR is a vice, limiting the acceptable spin lock amplitude on 1.5 and 3 T clinical scanners to 400600 Hz to obtain a T1rho-weighted image. Also, as scanners continue to increase in field strength to 7 T, there may be no range over which the RF field amplitude is acceptable. A technique to widen the acceptable spin lock range is necessary, particularly in the low-frequency regime where useful clinical contrast is generated by the scalar coupling between 1H and 17O in studies of brain metabolism or static dipoledipole or 1H exchange dynamics in human cartilage.