MR detectability of posterior pituitary high signal and direction of frequency encoding gradient.

The reported rate of detection of the posterior pituitary high signal (PPHS) in T1-weighted MR images has varied. The purpose of this study was to clarify the influence of the direction of the chemical shift on the detectability of the PPHS. Fifty-three subjects with a normal pituitary gland (n = 41) or an empty sella (n = 12) were studied with sagittal T1-weighted spin-echo imaging using two or three different frequency encoding gradient (FEG) directions: caudocephalad (FEG: CH), cephalocaudad (FEG: HC), and anteroposterior (FEG: AP). The PPHS was detected and clearly separated from the high signal of the fatty marrow of the dorsum sellae in 54% of the normal pituitary gland and 25% of the empty sella cases with FEG: CH, and in none of the cases (n = 5) with FEG: HC. The chemical shift of the fatty marrow in the dorsum sellae tended to overshadow the PPHS when FEG: CH and HC were used. In contrast, when FEG: AP was used, the PPHS was clearly separated from the dorsum sella marrow fat in all cases. Frequency encoding gradient: AP represents the optimal setting for evaluating the posterior pituitary gland.