Visualization of thalamic nuclei on high resolution, multi-averaged T1 and T2 maps acquired at 1.5 T.

The ability to differentiate noninvasively between the primary nuclear divisions of the thalamus has immediate clinical applicability for surgical planning and guidance of functional stereotactic procedures. Comparison of prior qualitative magnetic resonance imaging (MRI) studies carried out at field strengths of 1.5 and 4 Tesla have revealed contrast within the thalamus that varies with field strength, suggesting possible differences in the inherent T1 and T2 relaxation times of the constituent nuclei. We investigate this hypothesis through acquisition of high-resolution, multi-averaged deep-brain T1 and T2 maps of a healthy volunteer. Fourteen nuclei were identified using their center-of-mass coordinates (in Talairach space) and average T1 and T2 values obtained from regions of interest placed within each. Results from this analysis revealed significant differences in T1 and T2 between the nuclei with a T1 range from 700 to 1,400 ms and a T2 range from 89 to 122 ms, allowing visual discrimination between the major nuclei groups. Furthermore, the high-resolution images showed distinct borders of T1 and T2 hypointensity surrounding each nucleus, revealing structure not reported previously. These results confirm our hypothesis and demonstrate the potential high-resolution quantitative imaging for nucleus visualization and surgical planning.