Soft tissue contrast in MRI depends largely on tissue-specific differences in relaxation times, which are determined by chemical composition, chemical structure, and water content of the tissue. Variations in these parameters can cause substantial changes in relaxation times and in turn, between tissues. These parameters are very powerful factors in determining relaxation times, and their influence has given significant insight into the molecular nature of contrast. However, tissues with only small differences in their relaxation times may be ineffective for, contrast and hence visualization. The dependencies of longitudinal relaxation times T1 and spin-spin relaxation time T2 on resonance frequency have also been widely used to improve the ability of MRI as a clinical diagnostic tool. Since biological tissues contain immobile macromolecules, the dynamics of these molecules can be characterized much better by relaxation parameters at low fields. In addition, the presence of macromolecules in the biological tissues leads to more significant contrast at low static magnetic field since the relative differences in T1 between tissues become larger. However, the signal to noise at low field strength is small, leading to difficulties in applying the applications of these techniques in clinical MRI. New techniques are thus needed to improve soft tissue contrast at high field strength. One effective method is the use of spin-lattice relaxation time in rotating frame which is characterized by relaxation time constant T1p. We have successfully implemented this pulse sequence on 1.9T and studied the T1p-dispersion in mouse-brain. The main purpose of this work is to investigate intrinsic T1r dispersion in brain tissue at 2 Tesla. To this end, we have implemented a T1r imaging pulse sequence on a GE scanner. The data obtained from the mouse indicates that the mouse brain exhibits T1r dispersion only at higher spin lock frequencies.
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