John Gore
Throughout the history of MR imaging there has been a continuous evolution to ever higher magnetic field strengths, catalyzed by the expectation that higher fields provide higher quality images. Since the early 1980s, clinical MRI has moved from 0.15 T through 1.5T to 3T, and each transition has provided increased sensitivity and spatial resolution for detecting pathologic changes in tissues. There are currently approximately 50 7T scanners installed in medical centers around the world, and although there are still several technical challenges to meeting their full potential, it is clear they offer special opportunities for imaging brain structure at high resolution. Moreover, higher fields are more sensitive to some specific contrast mechanisms, such as the presence of microscopic susceptibility variations within tissues that may arise from iron-containing proteins or from microvasculature.
Our study illustrates these capabilities well and shows how higher field images may be able to differentiate subnuclei in midbrain structures and identify critical changes implicated in various neurologic disorders. Characterizing the anatomic architecture of the substantia nigra (SN) in particular has important clinical implications, especially in the diagnosis of Parkinson disease (PD), in which there is a known loss of dopimanergic neurons and an increase in iron deposition. Previous studies have shown T2-weighted hyperintense signal intensity within the SN and changes in the dimensions of critical structures as PD progresses, but in general, anatomic images of the midbrain have suffered from inadequate spatial resolution and contrast to be definitive. The region-based segmentation algorithm used in the present study provides a means of quantifying the dimensions and distance between various midbrain brain structures, especially when the spatial-resolution is optimized. These